Phosphorescence

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Phosphorescence

 

Phosphorescent bird figure

 

Phosphorescent, europium-doped, strontium silicate-aluminate oxide powder under visible light, fluorescing/phosphorescing under long-wave UV light, and persistently phosphorescing in total darkness

Phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluorescence, a phosphorescent material does not immediately reemit the radiation it absorbs. Instead, a phosphorescent material absorbs some of the radiation energy and reemits it for a much longer time after the radiation source is removed.

In a general sense, there is no distinct boundary between the emission times of fluorescence and phosphorescence (i.e.: if a substance glows under a black light it is generally considered fluorescent, and if it glows in the dark it is often simply called phosphorescent). In a modern, scientific sense, the phenomena can usually be classified by the three different mechanisms that produce the light, and the typical timescales during which those mechanisms emit light. Whereas fluorescent materials stop emitting light within nanoseconds (billionths of a second) after the excitation radiation is removed, phosphorescent materials may continue to emit an afterglow ranging from a few microseconds to many hours after the excitation is removed.

There are two separate mechanisms that may produce phosphorescence, called triplet phosphorescence (or simply phosphorescence) and persistent phosphorescence (or persistent luminescence). Triplet phosphorescence occurs when an atom absorbs a high-energy photon, and the energy becomes locked in the spin multiplicity of the electrons, generally changing from a fluorescent "singlet state" to a slower emitting "triplet state". The slower timescales of the reemission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur relatively slowly in certain materials, absorbed radiation is reemitted at a lower intensity, ranging from a few microseconds to as much as one second after the excitation is removed.

On the other hand, persistent phosphorescence occurs when a high-energy photon is absorbed by an atom and its electron becomes trapped in a defect in the lattice of the crystalline or amorphous material. A defect such as a missing atom (vacancy defect) can trap an electron like a pitfall, storing that electron's energy until released by a random spike of thermal (vibrational) energy. Such a substance will then emit light of gradually decreasing intensity, ranging from a few seconds to up to several hours after the original excitation.

Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers, paint and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room.

The study of phosphorescent materials led to the discovery of radioactive decay.

Etymology

The term phosphorescence comes from the ancient Greek word φῶς (phos), meaning "light", and the Greek suffix -φόρος (-phoros), meaning "to bear", combined with the Latin suffix -escentem, meaning "becoming of", "having a tendency towards", or "with the essence of". Thus, phosphorescence literally means "having a tendency to bear light". It was first recorded in 1766.

The term phosphor had been used since the Middle Ages to describe minerals that glowed in the dark. One of the most famous, but not the first, was Bolognian phosphor. Around 1604, Vincenzo Casciarolo discovered a "lapis solaris" near Bologna, Italy. Once heated in an oxygen-rich furnace, it thereafter absorbed sunlight and glowed in the dark. In 1677, Hennig Brand isolated a new element that glowed due to a chemiluminescent reaction when exposed to air, and named it "phosphorus".

In contrast, the term luminescence (from the Latin lumen for "light"), was coined by Eilhardt Wiedemann in 1888 as a term to refer to "light without heat", while "fluorescence" by Sir George Stokes in 1852, when he noticed that, when exposing a solution of quinine sulfate to light refracted through a prism, the solution glowed when exposed to the mysterious invisible-light (now known to be UV light) beyond the violet end of the spectrum. Stokes formed the term from a combination of fluorspar and opalescence (preferring to use a mineral instead of a solution), albeit it was later discovered that fluorspar glows due to phosphorescence.

There was much confusion between the meanings of these terms throughout the late nineteenth to mid-twentieth centuries. Whereas the term "fluorescence" tended to refer to luminescence that ceased immediately (by human-eye standards) when removed from excitation, "phosphorescence" referred to virtually any substance that glowed for appreciable periods in darkness, sometimes to include even chemiluminescence (which occasionally produced substantial amounts of heat). Only after the 1950s and 1960s did advances in quantum electronics, spectroscopy, and lasers provide a measure to distinguish between the various processes that emit the light, although in common speech the distinctions are still often rather vague.

Introduction

Jablonski diagram of an energy scheme used to explain the difference between fluorescence and phosphorescence. The excitation of molecule A to its singlet excited state (¹A*) may, after a short time between absorption and emission (fluorescence lifetime), return immediately to ground state, giving off a photon via fluorescence (decay time). However, sustained excitation is followed by intersystem crossing to the triplet state (³A) that relaxes to the ground state by phosphorescence with much longer decay times.

In simple terms, phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in some cases the mechanism used for glow-in-the-dark materials which are "charged" by exposure to light. Unlike the relatively swift reactions in fluorescence, such as those seen in laser mediums like the common ruby, phosphorescent materials "store" absorbed energy for a longer time, as the processes required to reemit energy occur less often. However, timescale is still only a general distinction, as there are slow-emitting fluorescent materials, for example uranyl salts, and, likewise, some phosphorescent materials like zinc sulfide (in violet) are very fast. Scientifically, the phenomena are classified by the different mechanisms that produce the light, as materials that phosphoresce may be suitable for some purposes such as lighting, but may be completely unsuitable for others that require fluorescence, like lasers. Further blurring the lines, a substance may emit light by one, two, or all three mechanisms depending on the material and excitation conditions.

When the stored energy becomes locked in by the spin of the atomic electrons, a triplet state can occur, slowing the emission of light, sometimes by several orders of magnitude. Because the atoms usually begin in a singlet state of spin, favoring fluorescence, these types of phosphors typically produce both types of emission during illumination, and then a dimmer afterglow of strictly phosphorescent light typically lasting less than a second after the illumination is switched off.

Conversely, when the stored energy is due to persistent phosphorescence, an entirely different process occurs without a fluorescence precursor. When electrons become trapped within a defect in the atomic or molecular lattice, light is prevented from reemitting until the electron can escape. To escape, the electron needs a boost of thermal energy to help spring it out of the trap and back into orbit around the atom. Only then can the atom emit a photon. Thus, persistent phosphorescence is highly dependent on the temperature of the material.

Triplet phosphorescence

After an electron absorbs a photon of high energy, it may undergo vibrational relaxations and intersystem crossing to another spin state. Again the system relaxes vibrationally in the new spin state and eventually emits light by phosphorescence.

Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, in the order of 10 nanoseconds. Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of different (usually higher) spin multiplicity (see term symbol), usually a triplet state. As a result, the excited electron can become trapped in the triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet decay-times in the order of milliseconds.

Common examples include the phosphor coatings used in fluorescent lamps, where phosphorescence on the order of milliseconds or longer is useful for filling in the "off-time" between AC current cycles, helping to reduce "flicker". Phosphors with faster decay times are used in applications like the pixels excited by free electrons (cathodoluminescence) in cathode-ray tube television-sets, which are slow enough to allow the formation of a picture as the electron beam scans the screen, but fast enough to prevent the frames from blurring together. Even substances commonly associated with fluorescence may in fact be prone to phosphorescence, such as the liquid dyes found in highlighter pens, which is a common problem in liquid dye lasers. The onset of phosphorescence in this case can sometimes be reduced or delayed significantly by the use of triplet-quenching agents.

Equation

$${\displaystyle S_0+h\nu \to S_1\to T_1\to S_0+h{\nu }^{\mathrm{\prime }}}$$

where S is a singlet and T a triplet whose subscripts denote states (0 is the ground state, and 1 the excited state). Transitions can also occur to higher energy levels, but the first excited state is denoted for simplicity.

Persistent phosphorescence

Main article: Persistent luminescence

 

An extremely intense pulse of short-wave UV light in a flashtube produced this blue persistent-phosphorescence in the amorphous, fused silica envelope, lasting as long as 20 minutes after the 3.5 microsecond flash.

 

An electron microscope reveals vacancy defects in a crystalline lattice of molybdenum disulfide. The missing sulfur atoms leave dangling bonds between the molybdenum atoms, creating a trap in the empty spaces.

Solid materials typically come in two main types: crystalline and amorphous. In either case, a lattice or network of atoms and molecules form. In crystals, the lattice is a very neat, uniform assembly. However, nearly all crystals have defects in the stacking sequence of these molecules and atoms. A vacancy defect, where an atom is simply missing from its place, leaving an empty "hole", is one type of defect. Sometimes atoms can move from place to place within the lattice, creating Schottky defects or Frenkel defects. Other defects can occur from impurities in the lattice. For example, when a normal atom is substituted by a different atom of much larger or smaller size, a substitutional defect occurs, while an interstitial defect occurs when a much smaller atom gets trapped in the "interstices", or the spaces between atoms. In contrast, amorphous materials have no "long-range order" (beyond the space of a few atoms in any direction), thus by definition are filled with defects.

When a defect occurs, depending on the type and material, it can create a hole, or a "trap". For example, a missing oxygen atom from a zinc oxide compound creates a hole in the lattice, surrounded by unbound zinc-atoms. This creates a net force or attraction that can be measured in electron-volts. When a high-energy photon strikes one of the zinc atoms, its electron absorbs the photon and is thrown out into a higher orbit. The electron may then enter the trap and be held in place (out of its normal orbit) by the attraction. To trigger the release of the energy, a random spike in thermal energy is needed of sufficient magnitude to boost the electron out of the trap and back into its normal orbit. Once in orbit, the electron's energy can drop back to normal (ground state) resulting in the release of a photon.

The release of energy in this way is a completely random process, governed mostly by the average temperature of the material versus the "depth" of the trap, or how many electron-volts it exerts. A trap that has a depth of 2.0 electron-volts would require a great amount of thermal energy (very high temperatures) to overcome the attraction, while at a depth of 0.1 electron-volts very little heat (very cold temperatures) are needed for the trap to even hold an electron. Higher temperatures may cause the faster release of energy, resulting in a brighter yet short-lived emission, while lower temperatures may produce dimmer but longer-lasting glows. Temperatures that are too hot or cold, depending on the substance, may not allow the accumulation or release of energy at all. The ideal depth of trap for persistent phosphorescence at room temperature is typically between 0.6 and 0.7 electron-volts. If the phosphorescent quantum yield is high, that is, if the substance has a large number of traps of the correct depth, these substances will release significant amounts of light over long time scales, creating so-called "glow in the dark" materials.

Persistent phosphorescence is the mechanism of most anything commonly referred to as glow in the dark. Typical uses include toys, frisbees and balls, safety signs, paints and markings, make-ups, art and décor, and a variety of other uses.

Chemiluminescence

Main article: Chemiluminescence

Some examples of glow-in-the-dark materials do not glow by phosphorescence. For example, glow sticks glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemiluminescence, an excited state is created via a chemical reaction. The light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will then transfer to a dye molecule, also known as a sensitizer or fluorophor, and subsequently fluoresce back to the ground state.

Materials

Main article: Phosphor

Common pigments used in phosphorescent materials include zinc sulfide and strontium aluminate. Use of zinc sulfide for safety related products dates back to the 1930s.

The development of strontium aluminate pigments in 1993 was spurred on by the need to find a substitute for glow-in-the-dark materials with high luminance and long phosphorescence, especially those that used promethium. This led to the discovery by Yasumitsu Aoki (Nemoto & Co.) of materials with luminance approximately 10 times greater than zinc sulfide and phosphorescence approximately 10 times longer. This has relegated most zinc sulfide based products to the novelty category. Strontium aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage.

• 

  Zinc sulfide (left) and strontium aluminate (right), in visible light, in darkness, and after 4 minutes in the dark.

• 

  Calcium sulfide (left) and metal-earth silicate (right) phosphoresce in red and blue respectively.

Since both phosphorescence (transition from T₁ to S₀) and the generation of T₁ from an excited singlet state (e.g., S₁) via intersystem crossing (ISC) are spin-forbidden processes, most organic materials exhibit insignificant phosphorescence as they mostly fail to populate the excited triplet state, and, even if T₁ is formed, phosphorescence is most frequently outcompeted by non-radiative pathways. One strategy to enhance the ISC and phosphorescence is the incorporation of heavy atoms, which increase spin-orbit coupling (SOC). Additionally, the SOC (and therefore the ISC) can be promoted by coupling n-π* and π-π* transitions with different angular momenta, also known as Mostafa El-Sayed's rule. Such transitions are typically exhibited by carbonyl or triazine derivatives, and most organic room-temperature phosphorescent (ORTP) materials incorporate such moieties. In turn, to inhibit competitive non-radiative deactivation pathways, including vibrational relaxation and oxygen quenching and triplet-triplet annihilations, organic phosphors have to be embedded in rigid matrices such as polymers, and molecular solids (crystals, covalent organic frameworks, and others).

Uses

Phosphorescent elements of a wrist watch that had been exposed to bright light: clock face with twelve dots as well as minute and hour hand

In 1974 Becky Schroeder was given a US patent for her invention of the "Glow Sheet" which used phosphorescent lines under writing paper to help people write in low-light conditions.

Glow in the dark material is added to the plastic blend used in injection molds to make some disc golf discs, which allow the game to be played at night.

Often clock faces of watches are painted with phosphorencent colours. Therefore, they can be used in absolute dark environments for several hours after having been exposed to bright light.

A common use of phosphorescence is decoration. Stars made of glow-in-the-dark plastic are placed on walls, ceilings, or hanging from strings make a room look like the night sky. Other objects like figurines, cups, posters, lamp fixtures, toys and bracelet beads may also glow. Using blacklights makes these things glow brightly, common at raves, bedrooms, theme parks, and festivals.

Anemometer

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Anemometer

 

A hemispherical-cup anemometer of the type invented in 1846 by John Thomas Romney Robinson.

In meteorology, an anemometer (from Ancient Greek άνεμος (ánemos) 'wind', and μέτρον (métron) 'measure') is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti (1404–1472) in 1450.

History

The anemometer has changed little since its development in the 15th century. Alberti is said to have invented it around 1450. In the ensuing centuries numerous others, including Robert Hooke (1635–1703), developed their own versions, with some mistakenly credited as its inventor. In 1846, John Thomas Romney Robinson (1792–1882) improved the design by using four hemispherical cups and mechanical wheels. In 1926, Canadian meteorologist John Patterson (1872–1956) developed a three-cup anemometer, which was improved by Brevoort and Joiner in 1935. In 1991, Derek Weston added the ability to measure wind direction. In 1994, Andreas Pflitsch developed the sonic anemometer.

Velocity anemometers

Cup anemometers

Cup anemometer animation

A simple type of anemometer was invented in 1845 by Rev Dr John Thomas Romney Robinson of Armagh Observatory. It consisted of four hemispherical cups on horizontal arms mounted on a vertical shaft. The air flow past the cups in any horizontal direction turned the shaft at a rate roughly proportional to the wind's speed. Therefore, counting the shaft's revolutions over a set time interval produced a value proportional to the average wind speed for a wide range of speeds. This type of instrument is also called a rotational anemometer.

With a four-cup anemometer, the wind always has the hollow of one cup presented to it, and is blowing on the back of the opposing cup. Since a hollow hemisphere has a drag coefficient of .38 on the spherical side and 1.42 on the hollow side, more force is generated on the cup that presenting its hollow side to the wind. Because of this asymmetrical force, torque is generated on the anemometer's axis, causing it to spin.

Theoretically, the anemometer's speed of rotation should be proportional to the wind speed because the force produced on an object is proportional to the speed of the gas or fluid flowing past it. However, in practice, other factors influence the rotational speed, including turbulence produced by the apparatus, increasing drag in opposition to the torque produced by the cups and support arms, and friction on the mount point. When Robinson first designed his anemometer, he asserted that the cups moved one-third of the speed of the wind, unaffected by cup size or arm length. This was apparently confirmed by some early independent experiments, but it was incorrect. Instead, the ratio of the speed of the wind and that of the cups, the anemometer factor, depends on the dimensions of the cups and arms, and can have a value between two and a little over three. Once the error was discovered, all previous experiment involving anemometers had to be repeated.

The three-cup anemometer developed by Canadian John Patterson in 1926, and subsequent cup improvements by Brevoort & Joiner of the United States in 1935, led to a cupwheel design with a nearly linear response and an error of less than 3% up to 60 mph (97 km/h). Patterson found that each cup produced maximum torque when it was at 45° to the wind flow. The three-cup anemometer also had a more constant torque and responded more quickly to gusts than the four-cup anemometer.

The three-cup anemometer was further modified by Australian Dr. Derek Weston in 1991 to also measure wind direction. He added a tag to one cup, causing the cupwheel speed to increase and decrease as the tag moved alternately with and against the wind. Wind direction is calculated from these cyclical changes in speed, while wind speed is determined from the average cupwheel speed.

Three-cup anemometers are currently the industry standard for wind resource assessment studies and practice.

Vane anemometers

One of the other forms of mechanical velocity anemometer is the vane anemometer. It may be described as a windmill or a propeller anemometer. Unlike the Robinson anemometer, whose axis of rotation is vertical, the vane anemometer must have its axis parallel to the direction of the wind and is therefore horizontal. Furthermore, since the wind varies in direction and the axis has to follow its changes, a wind vane or some other contrivance to fulfill the same purpose must be employed.

A vane anemometer thus combines a propeller and a tail on the same axis to obtain accurate and precise wind speed and direction measurements from the same instrument. The speed of the fan is measured by a rev counter and converted to a windspeed by an electronic chip. Hence, volumetric flow rate may be calculated if the cross-sectional area is known.

In cases where the direction of the air motion is always the same, as in ventilating shafts of mines and buildings, wind vanes known as air meters are employed, and give satisfactory results.

• Vane anemometers
• 

  Vane style of anemometer

• 

  Helicoid propeller anemometer incorporating a wind vane for orientation

• 

  Hand-held low-speed vane anemometer

• 

  Hand-held digital anemometer or Byram anenometer.

Hot-wire anemometers

Hot-wire sensor

Hot wire anemometers use a fine wire (on the order of several micrometres) electrically heated to some temperature above the ambient. Air flowing past the wire cools the wire. As the electrical resistance of most metals is dependent upon the temperature of the metal (tungsten is a popular choice for hot-wires), a relationship can be obtained between the resistance of the wire and the speed of the air. In most cases, they cannot be used to measure the direction of the airflow, unless coupled with a wind vane.

Several ways of implementing this exist, and hot-wire devices can be further classified as CCA (constant current anemometer), CVA (constant voltage anemometer) and CTA (constant-temperature anemometer). The voltage output from these anemometers is thus the result of some sort of circuit within the device trying to maintain the specific variable (current, voltage or temperature) constant, following Ohm's law.

Additionally, PWM (pulse-width modulation) anemometers are also used, wherein the velocity is inferred by the time length of a repeating pulse of current that brings the wire up to a specified resistance and then stops until a threshold "floor" is reached, at which time the pulse is sent again.

Hot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest.

An industrial version of the fine-wire anemometer is the thermal flow meter, which follows the same concept, but uses two pins or strings to monitor the variation in temperature. The strings contain fine wires, but encasing the wires makes them much more durable and capable of accurately measuring air, gas, and emissions flow in pipes, ducts, and stacks. Industrial applications often contain dirt that will damage the classic hot-wire anemometer.

Drawing of a laser anemometer. The laser light is emitted (1) through the front lens (6) of the anemometer and is backscattered off the air molecules (7). The backscattered radiation (dots) re-enters the device and is reflected and directed into a detector (12).

Laser Doppler anemometers

In laser Doppler velocimetry, laser Doppler anemometers use a beam of light from a laser that is divided into two beams, with one propagated out of the anemometer. Particulates (or deliberately introduced seed material) flowing along with air molecules near where the beam exits reflect, or backscatter, the light back into a detector, where it is measured relative to the original laser beam. When the particles are in great motion, they produce a Doppler shift for measuring wind speed in the laser light, which is used to calculate the speed of the particles, and therefore the air around the anemometer.

Fixed mounted 2D ultrasonic anemometer with 3 paths.
Central spike keeps birds away.

Ultrasonic anemometers

3D ultrasonic anemometer

Ultrasonic anemometers, first developed in the 1950s, use ultrasonic sound waves to measure wind velocity. They measure wind speed based on the time of flight of sonic pulses between pairs of transducers. Measurements from pairs of transducers can be combined to yield a measurement of velocity in 1-, 2-, or 3-dimensional flow. The spatial resolution is given by the path length between transducers, which is typically 10 to 20 cm. Ultrasonic anemometers can take measurements with very fine temporal resolution, 20 Hz or better, which makes them well suited for turbulence measurements. The lack of moving parts makes them appropriate for long-term use in exposed automated weather stations and weather buoys where the accuracy and reliability of traditional cup-and-vane anemometers are adversely affected by salty air or dust. Their main disadvantage is the distortion of the air flow by the structure supporting the transducers, which requires a correction based upon wind tunnel measurements to minimize the effect. An international standard for this process, ISO 16622 Meteorology—Ultrasonic anemometers/thermometers—Acceptance test methods for mean wind measurements is in general circulation. Another disadvantage is lower accuracy due to precipitation, where rain drops may vary the speed of sound.

Since the speed of sound varies with temperature, and is virtually stable with pressure change, ultrasonic anemometers are also used as thermometers.

Two-dimensional (wind speed and wind direction) sonic anemometers are used in applications such as weather stations, ship navigation, aviation, weather buoys and wind turbines. Monitoring wind turbines usually requires a refresh rate of wind speed measurements of 3 Hz, easily achieved by sonic anemometers. Three-dimensional sonic anemometers are widely used to measure gas emissions and ecosystem fluxes using the eddy covariance method when used with fast-response infrared gas analyzers or laser-based analyzers.

Two-dimensional wind sensors are of two types:

• Two ultrasounds paths: These sensors have four arms. The disadvantage of this type of sensor is that when the wind comes in the direction of an ultrasound path, the arms disturb the airflow, reducing the accuracy of the resulting measurement.
• Three ultrasounds paths: These sensors have three arms. They give one path redundancy of the measurement which improves the sensor accuracy and reduces aerodynamic turbulence.

Acoustic resonance anemometers

Acoustic resonance anemometer

Acoustic resonance anemometers are a more recent variant of sonic anemometer. The technology was invented by Savvas Kapartis and patented in 1999. Whereas conventional sonic anemometers rely on time of flight measurement, acoustic resonance sensors use resonating acoustic (ultrasonic) waves within a small purpose-built cavity in order to perform their measurement.

Acoustic resonance principle

Built into the cavity is an array of ultrasonic transducers, which are used to create the separate standing-wave patterns at ultrasonic frequencies. As wind passes through the cavity, a change in the wave's property occurs (phase shift). By measuring the amount of phase shift in the received signals by each transducer, and then by mathematically processing the data, the sensor is able to provide an accurate horizontal measurement of wind speed and direction.

Because acoustic resonance technology enables measurement within a small cavity, the sensors tend to be typically smaller in size than other ultrasonic sensors. The small size of acoustic resonance anemometers makes them physically strong and easy to heat, and therefore resistant to icing. This combination of features means that they achieve high levels of data availability and are well suited to wind turbine control and to other uses that require small robust sensors such as battlefield meteorology. One issue with this sensor type is measurement accuracy when compared to a calibrated mechanical sensor. For many end uses, this weakness is compensated for by the sensor's longevity and the fact that it does not require recalibration once installed.

Ping-pong ball anemometers

A common anemometer for basic use is constructed from a ping-pong ball attached to a string. When the wind blows horizontally, it presses on and moves the ball; because ping-pong balls are very lightweight, they move easily in light winds. Measuring the angle between the string-ball apparatus and the vertical gives an estimate of the wind speed.

This type of anemometer is mostly used for middle-school level instruction, which most students make on their own, but a similar device was also flown on the Phoenix Mars Lander.

Pressure anemometers

Britannia Yacht Club clubhouse tour, burgee, and wind gauge on roof

The first designs of anemometers that measure the pressure were divided into plate and tube classes.

Plate anemometers

These are the first modern anemometers. They consist of a flat plate suspended from the top so that the wind deflects the plate. In 1450, the Italian art architect Leon Battista Alberti invented the first mechanical anemometer; in 1664 it was re-invented by Robert Hooke (who is often mistakenly considered the inventor of the first anemometer). Later versions of this form consisted of a flat plate, either square or circular, which is kept normal to the wind by a wind vane. The pressure of the wind on its face is balanced by a spring. The compression of the spring determines the actual force which the wind is exerting on the plate, and this is either read off on a suitable gauge, or on a recorder. Instruments of this kind do not respond to light winds, are inaccurate for high wind readings, and are slow at responding to variable winds. Plate anemometers have been used to trigger high wind alarms on bridges.

Tube anemometers

Tube anemometer invented by William Henry Dines. The movable part (right) is mounted on the fixed part (left).

 

Instruments at Mount Washington Observatory. The pitot tube static anemometer is on the right.

 

The pointed head is the pitot port. The small holes are connected to the static port.

James Lind's anemometer of 1775 consisted of a vertically mounted glass U tube containing a liquid manometer (pressure gauge), with one end bent out in a horizontal direction to face the wind flow and the other vertical end capped. Though the Lind was not the first it was the most practical and best known anemometer of this type. If the wind blows into the mouth of a tube it causes an increase of pressure on one side of the manometer. The wind over the open end of a vertical tube causes little change in pressure on the other side of the manometer. The resulting elevation difference in the two legs of the U tube is an indication of the wind speed. However, an accurate measurement requires that the wind speed be directly into the open end of the tube; small departures from the true direction of the wind causes large variations in the reading.

The successful metal pressure tube anemometer of William Henry Dines in 1892 utilized the same pressure difference between the open mouth of a straight tube facing the wind and a ring of small holes in a vertical tube which is closed at the upper end. Both are mounted at the same height. The pressure differences on which the action depends are very small, and special means are required to register them. The recorder consists of a float in a sealed chamber partially filled with water. The pipe from the straight tube is connected to the top of the sealed chamber and the pipe from the small tubes is directed into the bottom inside the float. Since the pressure difference determines the vertical position of the float this is a measure of the wind speed.

The great advantage of the tube anemometer lies in the fact that the exposed part can be mounted on a high pole, and requires no oiling or attention for years; and the registering part can be placed in any convenient position. Two connecting tubes are required. It might appear at first sight as though one connection would serve, but the differences in pressure on which these instruments depend are so minute, that the pressure of the air in the room where the recording part is placed has to be considered. Thus if the instrument depends on the pressure or suction effect alone, and this pressure or suction is measured against the air pressure in an ordinary room, in which the doors and windows are carefully closed and a newspaper is then burnt up the chimney, an effect may be produced equal to a wind of 10 mi/h (16 km/h); and the opening of a window in rough weather, or the opening of a door, may entirely alter the registration.

While the Dines anemometer had an error of only 1% at 10 mph (16 km/h), it did not respond very well to low winds due to the poor response of the flat plate vane required to turn the head into the wind. In 1918 an aerodynamic vane with eight times the torque of the flat plate overcame this problem.

Pitot tube static anemometers

Modern tube anemometers use the same principle as in the Dines anemometer but using a different design. The implementation uses a pitot-static tube which is a pitot tube with two ports, pitot and static, that is normally used in measuring the airspeed of aircraft. The pitot port measures the dynamic pressure of the open mouth of a tube with pointed head facing wind, and the static port measures the static pressure from small holes along the side on that tube. The pitot tube is connected to a tail so that it always makes the tube's head to face the wind. Additionally, the tube is heated to prevent rime ice formation on the tube. There are two lines from the tube down to the devices to measure the difference in pressure of the two lines. The measurement devices can be manometers, pressure transducers, or analog chart recorders.

Effect of density on measurements

In the tube anemometer the dynamic pressure is actually being measured, although the scale is usually graduated as a velocity scale. If the actual air density differs from the calibration value, due to differing temperature, elevation or barometric pressure, a correction is required to obtain the actual wind speed. Approximately 1.5% (1.6% above 6,000 feet) should be added to the velocity recorded by a tube anemometer for each 1000 ft (5% for each kilometer) above sea-level.

Effect of icing

At airports, it is essential to have accurate wind data under all conditions, including freezing precipitation. Anemometry is also required in monitoring and controlling the operation of wind turbines, which in cold environments are prone to in-cloud icing. Icing alters the aerodynamics of an anemometer and may entirely block it from operating. Therefore, anemometers used in these applications must be internally heated. Both cup anemometers and sonic anemometers are presently available with heated versions.

Instrument location

In order for wind speeds to be comparable from location to location, the effect of the terrain needs to be considered, especially in regard to height. Other considerations are the presence of trees, and both natural canyons and artificial canyons (urban buildings). The standard anemometer height in open rural terrain is 10 meters.

Foundry

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Foundry

 

From Fra Burmeister og Wain's Iron Foundry, by Peder Severin Krøyer, 1885.

 

A Foundryman, pictured by Daniel A. Wehrschmidt in 1899.

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

Foundries are one of the largest contributors to the manufacturing recycling movement, melting and recasting millions of tons of scrap metal every year to create new durable goods. Moreover, many foundries use sand in their molding process. These foundries often use, recondition, and reuse sand, which is another form of recycling.

Process

Main article: Casting (metalworking)

In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Melting

Melting metal in a crucible for casting

 

A metal die casting robot in an industrial foundry

Melting is performed in a furnace. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. External scrap is material from other forming processes such as punching, forging, or machining. Internal scrap consists of gates, risers, defective castings, and other extraneous metal oddments produced within the facility.

The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Refining is done to remove harmful gases and elements from the molten metal to avoid casting defects. Material is added during the melting process to bring the final chemistry within a specific range specified by industry and/or internal standards. Certain fluxes may be used to separate the metal from slag and/or dross and degassers are used to remove dissolved gas from metals that readily dissolve in gasses. During the tap, final chemistry adjustments are made.

Furnace

Several specialised furnaces are used to heat the metal. Furnaces are refractory-lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces. Furnace choice is dependent on the alloy system quantities produced. For ferrous materials EAFs, cupolas, and induction furnaces are commonly used. Reverberatory and crucible furnaces are common for producing aluminium, bronze, and brass castings.

Furnace design is a complex process, and the design can be optimized based on multiple factors. Furnaces in foundries can be any size, ranging from small ones used to melt precious metals to furnaces weighing several tons, designed to melt hundreds of pounds of scrap at one time. They are designed according to the type of metals that are to be melted. Furnaces must also be designed based on the fuel being used to produce the desired temperature. For low temperature melting point alloys, such as zinc or tin, melting furnaces may reach around 500 °C (932 °F). Electricity, propane, or natural gas are usually used to achieve these temperatures. For high melting point alloys such as steel or nickel-based alloys, the furnace must be designed for temperatures over 1,600 °C (2,910 °F). The fuel used to reach these high temperatures can be electricity (as employed in electric arc furnaces) or coke. The majority of foundries specialize in a particular metal and have furnaces dedicated to these metals. For example, an iron foundry (for cast iron) may use a cupola, induction furnace, or EAF, while a steel foundry will use an EAF or induction furnace. Bronze or brass foundries use crucible furnaces or induction furnaces. Most aluminium foundries use either electric resistance or gas heated crucible furnaces or reverberatory furnaces.

Degassing

See also: Hydrogen gas porosity

Degassing is a process that may be required to reduce the amount of hydrogen present in a batch of molten metal. Gases can form in metal castings in one of two ways:

1. by physical entrapment during the casting process or
2. by chemical reaction in the cast material.

Hydrogen is a common contaminant for most cast metals. It forms as a result of material reactions or from water vapor or machine lubricants. If the hydrogen concentration in the melt is too high, the resulting casting will be porous; the hydrogen will exit the molten solution, leaving minuscule air pockets, as the metal cools and solidifies. Porosity often seriously deteriorates the mechanical properties of the metal.

An efficient way of removing hydrogen from the melt is to bubble a dry, insoluble gas through the melt by purging or agitation. When the bubbles go up in the melt, they catch the dissolved hydrogen and bring it to the surface. Chlorine, nitrogen, helium and argon are often used to degas non-ferrous metals. Carbon monoxide is typically used for iron and steel.

There are various types of equipment that can measure the presence of hydrogen. Alternatively, the presence of hydrogen can be measured by determining the density of a metal sample.

In cases where porosity still remains present after the degassing process, porosity sealing can be accomplished through a process called metal impregnating.

Mold making

Diagrams of two pattern types

A diagram of draft on a pattern

In the casting process, a pattern is made in the shape of the desired part. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Cores are used to create hollow areas in the mold that would otherwise be impossible to achieve. Where the cope and drag separates is called the parting line.

When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. This is called draft. The opposite of draft is an undercut where there is part of the pattern under the mold material, making it impossible to remove the pattern without damaging the mold.

The pattern is made of wax, wood, plastic, or metal. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting, and complexity of the casting. These mold processes include:

• Sand casting — Green or resin bonded sand mold.
• Lost-foam casting — Polystyrene pattern with a mixture of ceramic and sand mold.
• Investment casting — Wax or similar sacrificial pattern with a ceramic mold.
• Ceramic mold casting — Plaster mold.
• V-process casting — Vacuum with thermoformed plastic to form sand molds. No moisture, clay or resin required.
• Die casting — Metal mold.
• Billet (ingot) casting — Simple mold for producing ingots of metal, normally for use in other foundries.
• Loam molding – a built up mold used for casting large objects, such as cannon, steam engine cylinders, and bells.

Pouring

Bronze poured from a crucible into a mold, using the lost-wax casting process

In a foundry, molten metal is poured into molds. Pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas. Many modern foundries use robots or automatic pouring machines to pour molten metal. Traditionally, molds were poured by hand using ladles.

Shakeout

The solidified metal component is then removed from its mold. Where the mold is sand based, this can be done by shaking or tumbling. This frees the casting from the sand, which is still attached to the metal runners and gates — which are the channels through which the molten metal traveled to reach the component itself.

Degating

Degating is the removal of the heads, runners, gates, and risers from the casting. Runners, gates, and risers may be removed using cutting torches, bandsaws, or ceramic cutoff blades. For some metal types, and with some gating system designs, the sprue, runners, and gates can be removed by breaking them away from the casting with a sledge hammer or specially designed knockout machinery. Risers must usually be removed using a cutting method (see above) but some newer methods of riser removal use knockoff machinery with special designs incorporated into the riser neck geometry that allow the riser to break off at the right place.

The gating system required to produce castings in a mold yields leftover metal — including heads, risers, and sprue (sometimes collectively called sprue) — that can exceed 50% of the metal required to pour a full mold. Since this metal must be remelted as salvage, the yield of a particular gating configuration becomes an important economic consideration when designing various gating schemes, to minimize the cost of excess sprue, and thus overall melting costs.

Heat treating

A tank hull undergoing heat treatment

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case-hardening, precipitation strengthening, tempering, and quenching. Although the term "heat treatment" applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Surface cleaning

After degating and heat treating, sand or other molding media may remain adhered to the casting. To remove any mold remnants, the surface is cleaned using a blasting process. This means a granular media will be propelled against the surface of the casting to mechanically knock away the adhering sand. The media may be blown with compressed air, or may be hurled using a shot wheel. The cleaning media strikes the casting surface at high velocity to dislodge the mold remnants (for example, sand, slag) from the casting surface. Numerous materials may be used to clean cast surfaces, including steel, iron, other metal alloys, aluminium oxides, glass beads, walnut shells, baking powder, and many others. The blasting media is selected to develop the color and reflectance of the cast surface. Terms used to describe this process include cleaning, bead blasting, and sand blasting. Shot peening may be used to further work-harden and finish the surface.

Finishing

Modern foundry (circa 2000)

The final step in the process of casting usually involves grinding, sanding, or machining the component in order to achieve the desired dimensional accuracies, physical shape, and surface finish.

Removing the remaining gate material, called a gate stub, is usually done using a grinder or sander. These processes are used because their material removal rates are slow enough to control the amount of material being removed. These steps are done prior to any final machining.

After grinding, any surfaces that require tight dimensional control are machined. Many castings are machined in CNC milling centers. The reason for this is that these processes have better dimensional capability and repeatability than many casting processes. However, it is not uncommon today for castings to be used without machining.

A few foundries provide other services before shipping cast products to their customers. It is common to paint castings to prevent corrosion and improve visual appeal. Some foundries assemble castings into complete machines or sub-assemblies. Other foundries weld multiple castings or wrought metals together to form a finished product.

More and more, finishing processes are being performed by robotic machines, which eliminate the need for a human to physically grind or break parting lines, gating material, or feeders. Machines can reduce risk of injury to workers and lower costs for consumables — while also increasing productivity. They also limit the potential for human error and increase repeatability in the quality of grinding.

CIA Tibetan program

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/CIA_Tibetan_program

Central Intelligence Agency (CIA)

The CIA Tibetan program was a nearly two decades long anti-Chinese covert operation focused on Tibet which consisted of "political action, propaganda, paramilitary and intelligence operations" based on U.S. government arrangements made with brothers of the 14th Dalai Lama, who was not initially aware of them. The goal of the program was "to keep the political concept of an autonomous Tibet alive within Tibet and among several foreign nations".

Although it was formally assigned to the CIA, it was nevertheless closely coordinated with several other U.S. government agencies such as the Department of State and the Department of Defense.

Previous operations had aimed to strengthen various isolated Tibetan resistance groups, which eventually led to the creation of a paramilitary force on the Nepalese border consisting of approximately 2,000 men. By February 1964, the projected annual cost for all CIA Tibetan operations had exceeded US$1.7 million.

The program ended after President Nixon visited China to establish closer relations in 1972. The Dalai Lama criticized this decision, saying it proved wholeheartedly that the US never did it to help the people of Tibet.

Overview

Gyalo Thondup, the second-eldest brother of the 14th Dalai Lama, was a "top asset" of the CIA

In the fields of political action and propaganda, the CIA's Tibetan program was aimed at lessening the influence, capabilities, and territorial scope of the Government of China. Particularly, the United States feared communist involvement in the region. A 1957 report on logistical issues indicated increasing trepidation that the Chinese would escalate their communist presence in Tibet. The spread of communism in the international community was a huge concern for the United States. The CIA considered China's interest in Tibet to be a threat for multiple reasons. A 1950 memorandum noted that some of the reasons stemmed from a notion of bolstered sovereignty and a motivation to forge "a bulwark against possible invasion by western powers via India." However, they also believed that China would "use [Tibet as] a base for attacks against India and the Middle East in the third world war." Therefore, intelligence officials declared action as a preventative measure should their worst-case scenario (WWIII) unfold.

The approval and subsequent endorsement of the program was carried out by the Special Group of the United States National Security Council. The program consisted of several clandestine operations bearing the following code names:

• ST CIRCUS—Cover name for the training of Tibetan guerillas on the island of Saipan, and at Camp Hale in Colorado
• ST BARNUM—Cover name for the airlifting of CIA agents, military supplies, and support equipment into Tibet.
• ST BAILEY—Cover name for a classified propaganda campaign

Chinese-Indian relations also played an important role in framing the CIA's operations. Due to Tibet's geographic location between the two countries, it was strategically important. The CIA released numerous reports assessing relations. The CIA monitored the relations between China and India in various ways, including media such as newspapers and radio broadcasts that reported on the changing relations between India and China. In October 1954, for example, a report was filed by CIA analysts concerning Indian Prime Minister Pt. Jawaharlal Nehru's visit to China. It assessed what the two countries might or might not agree to from a diplomatic standpoint. Following the month-long Sino-Indian War of 1962, the CIA developed a close relationship with Indian foreign intelligence services in both training and supplying agents in Tibet.

The CIA worked to strengthen the Tibetans against the Chinese communist efforts. To do so, the United States planned to issue asylum to the Dalai Lama and his supporters. Some resistance fighters took their own lives when captured by the Chinese to avoid torture. The Tibetan resistance was promised weaponry and resources from the West to continue their resistance against the Chinese. Knowing resistance was unlikely to succeed the resistance accepted Chinese annexation.

History

The Chinese army launched an invasion on the Tibetan capital of Lhasa, codenamed Operation Chamdo, in October 1950, thus solidifying the origin of the tension between China and Tibet. With this tension came Tibetan resistance towards China and the United States' interest in helping them fight the Chinese communist forces. In a memorandum from July 1958, the CIA described the growing resistance to the Chinese in Tibet. The memo noted, "During the past two and one half years, resistance has hardened and grown despite Chinese countermeasures that include military force as well as partial withdrawal of Chinese cadres and postponement of 'reforms' and other programs leading toward socialization"  In the early 1950s, the CIA inserted paramilitary teams from the Special Activities Division (SAD) to train and lead Tibetan resistance fighters against the People's Liberation Army of China. The Tibetans were willing to fight the Chinese, as they shared the CIA's interests in stymieing the influence of communism from China on Tibet. The Tibetan people started to form anti-Chinese protests under the influence of the Dalai Lama. However, the government of Tibet did not encourage such anti-Chinese protest. The reasons behind the Tibetan people's motivation for the coup was because they perceived the Communist party, especially the Chinese, to be a threat to their religion: Buddhism the religion of Tibet is a form of Buddhism known as Vajrayana. The most significant facet obstructing Chinese Communists from successfully infiltrating Tibet was its strong societal structure. The Ganden Phodrang led by the Gelugpa sect of Tibetan Buddhism was the governing political authority in addition to being the most powerful philosophical school. Tibetan polity was known as a theocracy. Monasteries historically tried to create peace and understanding between the people who gave them the power of mass ideological guidance.

Gyalo Thondup, the Dalai Lama's brother, was exiled to India and initiated contact with the Americans. Gyalo reached out to the Americans who were intrigued with the opportunity to create a ‘running sore for the reds,’ as a part of its global anti-communist campaign. These contacts made by the Dalai's brother eventually led to a more than 2 decade long campaign against the Chinese government supported by the CIA. His American contacts enabled Tibetans to go over first to Saipan and then to the U.S. for training. They were trained for 5 months on combat maneuvers. These teams selected and then trained Tibetan soldiers in the Rocky Mountains of the United States; as well as at Camp Hale in Colorado. The SAD teams then advised and led these commandos against the Chinese, both from Nepal and India. In addition, SAD Paramilitary Officers were responsible for the Dalai Lama's clandestine escape to India, narrowly escaping capture by the Chinese government. The Dalai Lama had also gotten very ill during the journey and almost did not make it to India.

1951

On May 23, 1951, Tibet and China signed the Sino-Tibetan agreement, allowing China to station troops in Tibet as well handle its international affairs. In exchange, the Chinese would not alter or affect the current government in Tibet, nor affect the status and authority of the Dalai Lama and Panchen Lama. In October 1951, 12,000 troops from the PLA entered Tibet. Initially, China wanted to send 45,000 troops, but Tibet refused the request, threatening to send the Dalai Lama to India if their refusal was not respected. However, the Tibetans were convinced the Chinese forces in Tibet were not capable of pressing the issue at the time. The composition of the 12,000 soldiers that were sent included 10,000 infantrymen, an animal transport battalion, a battalion of army engineers, and approximately 50 technicians who specialized in the areas of geology, surveying, telecommunications, cultural, propaganda, and party affairs. Additionally, violence directed toward the Tibetan people originated from Beijing. According to an archive document from the National Security Archive at the George Washington University, "Beijing has pursued...suppressing violent protests, arresting scores of ethnic Tibetans in the Qinghai province, which borders Tibet, sentencing one to prison for 13 years, and renewing accusations that the Dalai Lama is encouraging anti-Beijing actions."

A memo distributed by the CIA on November 20 detailed that the Chinese military, as of October 10, 1951, had arrested over 200 Tibetan people (29 women) for refusing to sell supplies along with desecrating a monastery (Gatza Monastery) in search of weapons. The Chinese military utilized various propaganda to establish a campaign of pacification to suppress growing resentment held by the Tibetan people over Chinese subjugation.

In December, the CIA distributed a report regarding the activities of PLA troops in Tibet. The report contained details regarding new troop activity in Tibet, troop movement, and the PLA's plan to construct a highway connecting Tibet and China. In addition to the information mentioned above, the report outlined China's plan to relocate the Panchen Lama back into Tibet, create military ties between China and Tibet, and build military training facilities within Tibet by March 1952.

1952

The State Department received communication from Thondup in May that revealed an assortment of information concerning the situation in Tibet. The CIA used the line of communication with Thondup to cultivate a credible source of intelligence on the ground and administer possible operations moving forward. Thondup described mounting Tibetan hostility toward the occupying Chinese Communist forces and the recent armed conflict in Lhasa between Tibetan demonstrators and Chinese Communist military police. From the intelligence, the CIA learned of the 10,000-15,000 Chinese troops stationed in Tibet. A dire food shortage also exacerbated tensions as Tibetans found it increasingly difficult provide food for the people. Furthermore, the communication with Thondup revealed the workings of covert actions from Tibetans who refused to follow the Dalai Lama's acceptance of Chinese Communist occupation. The CIA and the State Department both expressed optimism with the circumstances in Tibet and Lhasa, believing that they could maneuver accordingly.

In September 1952, a CIA intelligence report noted the difficulty in continuing to support the Tibetan resistance when the Chinese Communist government and the massive People's Liberation Army (PLA) fully occupied the country. As a result of this Chinese domination over the Tibetans, direct diplomatic relations between Tibet and India ceased. A daily Hindi newspaper reported that this move had ended 16 years of direct contact between the governments of India and Tibet. India was able to have direct communications until that point because China's authority in Tibet was still limited. In the final paragraph of the article, the newspaper writes, "The Chinese occupation of Tibet a year ago has changed this relationship. The cause was inevitable, and India had no choice but to accept this arrangement because the Chinese Communists now have complete control of the foreign affairs of Tibet". Previously, India had provided a link for United States' support to the Tibetan resistance. Later that year (December 1952), the CIA produced an Information Report (Classification: Secret) containing two items in the subject line: 1) Anti-Communist Activities, Tibet, and 2) Chinese Communist Activities, Tibet. The document shows that the agency was closely scrutinizing both Tibetan and Chinese groups and individuals at the time, as well as any other obtained intelligence. The report defines the anti-Communist Tibetan People's Party and identified geographic areas where the Party's support was strongest. A 36-year old leader, Lhopto Rimpochhe was named as the leader of the "warrior monks." The document goes on to report on intelligence regarding a petition sent to the Chinese authorities in Lhasa by Ragashar Shape, Tibetan Defense Minister, that went ignored. The Shape petition included the following points: the Dalai Lama should continue to rule unchallenged; monastery estates should not be confiscated; Tibetans should thank the Chinese for liberation but kindly ask them to leave and, in return, the Tibetan people would never ask for military assistance from the Chinese; and persuading the Chinese to "please buy the [Tibetan] wool." The document then proceeded to provide intelligence on various undesired actions taken by the Chinese including forcing the Dalai Lama to give a speech the threat of death, kidnapping over 200 children for the purpose of retraining them (one was even beheaded as a warning to the others not to cry and complain), and the installation of a puppet governor at Kham. Next, the document listed nine names of Tibetans acting as informers against the Chinese. Lastly, Chinese forces in Tibet were addressed—numbers of troops, names, and leadership transition information.

1953

By February 1953, the Chinese government was attempting a military build-up in Tibet. Airfields could specifically be an advantage as Tibet could then be used as a refueling station between China and India allowing for China to fly extended combat missions over India and target its northern cities. Additionally, as the highest geographical point, Tibet could maintain an aerial advantage over the region. A CIA information report dated July 31, 1953, reveals the CIA was closely monitoring Chinese projects in Tibet. The report notes that earlier that year Chinese soldiers "attempted to build airfields at Lhasa," the capital of the Tibet Autonomous Region, and Gartok, now called Gharyarsa. However, the Dalai Lama disapproved of the project, and the soldiers ceased construction of the airfields. In May 1953, over 1,000 Chinese soldiers marched to the Chumbi Valley with five field artillery pieces. These soldiers increased Chinese presence in Tibet to approximately 20,000 soldiers—all mainly stationed in Chumbi Valley, Bartok, Rudog, and north of Lhasa. In October 1953, the Chinese government placed travel restrictions in Tibet, resulting in a substantial westwardly diversion the wool trade. Concurrently, the Chinese were using Tibetan labor to create new roadways that would be controlled by the Chinese, which resulted in the Chinese controlling nearly all travel within Tibet. In December 1953 China communicated to the Indian Ambassador their position on Tibet; the Chinese gave nine demands to the Indian Ambassador. Their demands included that they do not tolerate any further Indian interest in Tibet and that no objection must be made by India to Chinese construction of fortifications in Tibet near the Indian and Nepalese borders. Another of the demands stated that India must have a strong policy to abolish illegal activities of foreign agents working on the Indian side of the border.

1954

In April 1954, after four months of negotiating, India and China agreed to the Sino-Indian Treaty. This treaty discussed how China would not allow the continuum of interest in Tibet by India. The Indian borders were to be equal between Tibet and border people. India was to devise a robust policy targeting illegal activities in the border areas. Civilians and soldiers were to be left alone when crossing the border into Nepal. Finally, India was not allowed to support any person that may question the sensitive issue of Tibet to the United Nations (UN). China allowed India to retain their three trade agencies in Tibet in exchange for three trade agencies for China in India while also allowing India to maintain three trade posts in Tibet at Yatung, Gyantse, and Gartok. In exchange, India was to allow China to keep three trade posts in New Delhi, Calcutta and Kalimpong. The borders were opened for those who wished to visit religious shrines, but China ordered India to withdraw armed forces. China also ordered India to hand over postal, telegraph, and telephone facilities it had been operating in Tibet. A group of Kazakhs were invited to the Tibetan capital of Lhasa to discuss the political status of the group. The trade between Tibet and China started really strong. China positively influenced the Tibetan economy by introducing silver dollars to Tibet. The products were generally unloaded in Tibet by plane, and from there they were taken on a camel caravan. Tibetans typically utilized camels during cold weather. However, horses, mules, and donkeys were also used to transport products in fair weather.

1955–1957

In 1955, a group of local Tibetan leaders secretly plotted an armed uprising, and rebellion broke out in 1956, with the rebels besieging several Chinese government agencies, killing hundreds of Chinese government staff, and killing many Han Chinese people. In May 1957, a rebel organization and rebel fighting force were established and began exterminating communist officials, discombobulating communication lines, and bombarding institutions and Chinese army troops deployed in the region. This coincides (chronologically) with the creation of the Preparatory Committee for the Tibet Autonomous Region, an organization created to help the Chinese undermine the religious and political systems of Tibet. The Chinese bombed an ancient monastery in February 1956, killing thousands of monks and ordinary citizens. The Tibetans knew that they could not fight off the Chinese on their own so they called in help from an outside source. It was in the shared interest of both Tibet and the United States to limit the power of the Chinese within Tibet's borders. Americans thought that this would be a great opportunity to prevent the spread of Communism throughout Southeast Asia. Starting in 1956, the CIA initiated a large scale clandestine operation against the communist Chinese. During December 1956, the Dalai Lama had left Tibet to attend a Buddhist celebration in India.

A briefing for the DCI from 1959 mentions that "as far back as 1956, we began to receive reports indicating the spread of Tibetan revolt against Chinese communists through areas inhabited by Khamba tribes in eastern Tibet." By May 1957, a rebel organization with its own fighting force was established with the support of the CIA. This was the first time that many Tibetans had seen a white man in person. They subsequently received training for the next five months. Some of the things that they learned while training included the use of modern weaponry, guerrilla tactics, espionage, codes, and operation of hand-cranked radio transmitter/receivers. Tibetans took this training very seriously and can be quoted stating that they "lived to kill Chinese." Because they viewed Chinese as a direct threat to their religion, they viewed animal life as more sacred than the life of the Chinese communists against whom they rebelled. In late 1958, in a Spartan-like setting nestled 10,000 feet above sea level in the Rocky Mountains of Colorado, the CIA trained more Tibetans at Camp Hale with a total of 259 Tibetans trained over five years in tactics representative of guerrilla warfare. The CIA established a secret military training camp called Camp Hale, located near Leadville, Colorado, where the Tibetans were trained to sabotage operations against the Communist Chinese. One of the reasons for the location of Camp Hale was its elevation—10,000 feet above sea level. The altitude preference was thought to mimic the terrain and climate of the Himalayas. The camp shut down in 1966, despite the conclusion of program training occurring already in 1961.

1958–1960

In 1958, with the rebellion in Kham ongoing, two of these fighters, Athar and Lhotse, attempted to meet with the Dalai Lama to determine whether he would cooperate with their activities. However, their request for an audience was refused by Lord Chamberlain, Phala Thubten Wonden, who believed such a meeting would be unwise. According to Tsering Shakya, "Phala never told the Dalai Lama or the Kashag of the arrival of Athar and Lhotse. Nor did he inform the Dalai Lama of American willingness to provide aid".

The situation in Tibet by the late 1950s revealed a strategic and economic interest in maneuvering against the Chinese Communists. Providing aid to the Tibetans continued to occur in the reports flowing in and out of the CIA. Several reports documented the economic needs of Tibetans and compared them to the known resources of the Chinese Communists in the Tibetan Army District. Control of the few networks of roads traversing the mountainous terrain granted the Chinese Communists access to the resources they needed to sustain military occupation. This was problematic for the Americans who needed a way to provide any aid to the Tibetan resistance movements. However, the reports weighing the logistics and costs of supplying aid to the Tibetans revealed that American interests were fueled by opposition to the Chinese Communists rather than a support of Tibetan liberation. The report ultimately concluded that the economic effort required to support troops in Tibet would only have a "modest if not almost negligible impact on the economy of Communist China."

In Eastern Tibet, there was a Khamba tribe that was thought to be in active resistance against the Chinese communists. These rebels displayed a sizeable outbreak in March 1959 because they feared that the Chinese were planning to take the Dalai Lama from the country. Since they had feared he risked kidnapping, they decided to protect him by moving him to an area that was located just outside Lhasa. These rebels claimed an "independent kingdom of Tibet" when they decided to resist the Chinese outpost. To try and get the rebels to back down the Chinese attempted to kidnap the Dalai Lama, leading, in turn, to the 1959 Tibetan Uprising in which thousands took to the streets to stop the supposed kidnapping. A 1959 DCI briefing highlights the measures in which citizens took to protect the Dalai Lama. The report says, "Thousands of Tibetan demonstrators then took the Dalai Lama into protective custody in his summer palace just outside Lhasa". Chinese military forces killed tens of thousands of Tibetans along with thousands more fleeing behind the Dalai Lama. During this revolt, supporters were reported to have "knocked out a Chinese outpost manned by 80 soldiers, interrupted communications with Peiping, and plastered walls of Lhasa with posters declaring 'independent kingdom of Tibet.'" The Chinese attempted to make the Dalai Lama stop the uprising, but they could not, which then led to his flight to India. The Dalai's clandestine departure to India started on March 17, 1959, involved him wearing a disguise where he dressed as a soldier and moved with a column of troops to the Indian border. Resistance fighters smuggled him out of the Potala and through rebel-held territory. Two troops who met the Dalai's escort along the way were trained by the CIA and they reached back to their American contacts via radio to secure permission for the Dalai and his troops to enter India. Permission was granted. Prior to his flight to India (due to shots being fired outside the palace), Dalai and the Tibet representative were sending letters back and forth to each other in hopes of avoiding an attack. Dalai continued fighting for independence for Tibet outside India. Finally, with the hope of halting Chinese aggression and demands, India recognized Tibet as part of China.

In 1959, the CIA opened a secret facility to train Tibetan recruits at Camp Hale near Leadville, Colorado

In 1959, the Dalai Lama and approximately 100,000 followers fled to India and Nepal. The rebels continued to attack Chinese government officials, disrupting communication lines, and targeting Chinese troops. Following a mass uprising in Lhasa in 1959 during the celebration of the Tibetan New Year and the ensuing Chinese military response, the Dalai Lama went into exile in India. At this point, the Chinese began changing their policy of working through institutions to build the Communist Party in Tibet. They began to replace the government with Communist-sponsored leaders. By this time the rebels were under constant Chinese attack and losing the remaining ground that they controlled. A declassified DCI briefing of the Senate Foreign Relation Committee offered some further elaboration on the Dalai Lama's position in India. The Dalai Lama remained insistent on wanting to establish a free Tibet which threatened his asylum in India. Prime Minister Nehru vowed to protect the Dalai Lama's right to practice his spirituality but would not condone any anti-communist politics coming from the Dalai Lama. Nehru's main reason for this was that India had previously recognized Tibet as a part of China. The evidence seemed to imply that popular Indian sentiment and reactions to this policy caused Nehru to become more sympathetic toward Tibet, yet unfortunately the rest of this section was redacted from the public record.

From 1959 to 1960, the CIA parachuted four groups of Camp Hale trainees to meet up with the Tibetan resistance. In Autumn of 1959, the CIA parachuted the second group of sixteen men into Chagra Pembar to meet up with the resistance. By January 1960 the CIA parachuted the fourth and last team into Tibet. Along with these air drops, the CIA also provided pallets of lethal aid to the resistance including rifles, mortars, grenades, and machine guns. All the CIA trained Tibetans from Camp Hale left with personal weapons, wireless sets, and a cyanide tablet strapped onto each man's left wrist.

The resistance movement did accomplish the job of bringing great cost and distraction to the Chinese government. CIA estimates in 1959 were that the Chinese had around 60,000 troops in Tibet and needed 256 tons of supplies daily. Due to there only being 3 viable transport routes into Tibet, the CIA also estimated that if they could get the Chinese to double the needed supplies, then the existing infrastructure would not be able to keep up with supply without supplementary airlifts or construction to repair existing routes. The CIA estimated that even with these supplemental airlifts, it would cause substantial disruption in other air services and the Chinese could not expect to supply double its commitments long-term. The Lanzhou-Lhasa highway was the ideal logistical land supply route at 2,148  km long. The CIA took into consideration factors including road construction, width, grades, curves, bottlenecks, and road conditions impacted by weather. The CIA estimated China could support up to 90,000 troops in Tibet for a few months, but only 60,000 for an extended deployment. In order to support 90,000 troops in the region, China would have to use the Lan-chou-Lhasa highway to its capacity and would require around 7,000 supply trucks per month. However, such heavy usage of the road was estimated to cause substantial damage. The CIA also considered how a build-up of Chinese troops would affect the railroads and determined that, although congestion could impose some burden on the supply chain, there would be no significant effect on the lines. However, if one of the lines failed due to a washout or other reason, supplies would have to be trucked into the staging areas, which the CIA determined would be a time-consuming operation. Petroleum usage in Tibet was estimated at 2.7% of China's total availability, with a total usage of around 200,000 tons for the year. The "blue satchel raid" of the Chinese was considered one of the greatest intelligence hauls in the history of the CIA. This raid obtained Chinese government documents that showed them having trouble moving forward with the spread of communism through Tibet. It also gave the CIA good insight into what was going on in China, and for the first time, they possessed authentic Chinese documents that were not forged or given to them by a rogue agent. This changed the focus of the CIA as they informed the Tibetans not to attack the Chinese but rather to gather intelligence on their enemy. Despite these orders from the CIA, yearly raids during the winter months continued on Chinese encampments and harassment of communist outposts, troops and convoys continued.

In 1959, CIA issued assessment documents that highlighted the background, logistical issues, and the international fallout in regard to Tibet. One paper, entitled "Tibet and China (Background Papers)," described the history and geography of Tibet. The CIA assessed that the economy of Tibet had not changed despite eight years of Chinese rule. The agency concluded that rebellions against Chinese communists would continue in Tibet throughout the years, but believed that the rebellions could not damage the hold that China had on Tibet. The CIA believed that the Chinese aggression in Tibet had severely damaged China's standing within Afro-Asian countries. By invading a sovereign nation and forcing the Dalai Lama into exile, China had gone against the image as a neutral peacemaker in the region that they had been cultivating since the Bandung Conference in 1955. In the briefing note, the CIA stated that the governments of neutral Asian countries, notably India and Burma, had encouraged press and popular opposition to Chinese aggression in Tibet. This was despite the fact that the governments did not formally sanction China for their actions. The background paper specified that one of the strongest reaction to China was from Malaya in which the Foreign Minister condemned the action and likened it to Soviet harsh responses in Hungary. Prince Norodom Sihanouk from Cambodia also showed his sympathy to Tibet and "expressing surprise" that Prime Minister Nehru did not take firmer action against Peking. There were protests on China's repression in Tibet as shown in the section of the press in some countries such as Burma, Indonesia, Pakistan, the Philippines, Japan, and the United Arab Republic. Another report, "Logistical Problems of the Tibetan Campaign," studied the strengths, weaknesses, and power of the Chinese military in Tibet. The report concluded that the Chinese military had hundreds of thousands of soldiers at its disposal and had a good supply of aircraft, but identified the supply roads as a major weakness. The documents remained classified until the early 2000s.

The CIA Tibetan Task Force continued the operation against Chinese forces alongside the Tibetan guerrilla army for another 15 years, until 1974. This is the same time that the monthly payments made to the Dalai Lama by the United States ceased. The goal was to keep Tibet autonomous both within Tibet and in the international community.

1960–1975

As stated by Palden Wangyal, a veteran guerrilla fighter, the rebels were directly paid by the Americans to attack Chinese government facilities and installations in Tibet:

"Our soldiers attacked Chinese trucks and seized some documents of the Chinese government. After that, the Americans increased our pay scale".

Flag of the Chushi Gangdruk, a prominent Tibetan guerrilla organization backed by the CIA

Some CIA trainees ended up commanding an army of 2,000 resistance fighters dubbed the Chushi Gangdruk, or "Four Rivers, Six Gorges". These fighters were specialized in ambushing Chinese targets from elevated bases in the mountains of Nepal.

Furthermore, the CIA was attempting to assist the Tibetan rebels enhancing their ability to move troops and materials. The CIA conducted studies on how the Tibetan resistance movement could best counter the Chinese Communists. Therefore, the CIA worked with the leaders of the campaign to garner more support for the resistance as well as manage the logistics of the movement of these troops. The CIA examined the difficulty in moving the additional forces necessary to counter the Chinese. This logistical conundrum meant that the CIA was giving recommendations for the capacity and ability of roadways to support the troop movements. Without this logistical support, the Tibetans could not sufficiently counter the Chinese Communists. However, a declassified CIA document from July 1958 outlined the agency's assessment of the possibility that Communists would infiltrate Tibetan society, and completely assimilate all aspects of Tibetan life into the culture of Communist China.

The CIA was aware of China's attempts at enacting cultural assimilation in Tibet and, therefore, they wanted to take measures to counteract that possibility. However, according to the document, the possibility of the "complete integration," of "political, social, and economic" aspects of Tibetan life was not substantial.

Long before the current Chinese occupation, Tibet had a longstanding tradition of independence. The memo cites numerous historical accounts of Chinese attempts at conquering and controlling Tibet, none of which ended in success or the integration of Tibet into Chinese society. The documents also mention the problematic "terrain, climate, and location" of Tibet. Tibet contains protruding mountains, massive plateaus, deep river valleys, and gaping gorges that make communication and military operations extremely arduous. The topography of the region enhanced the isolation felt by large swaths of the population, allowing for guerrilla warfare to thrive and causing "political fragmentation among the Kham," the southeastern region of Tibet. Because most Tibetans are peasants and not monks or nobles, they have experience with the terrain and are often nomads. This nomadic propensity consequently effects how they maintain their independent spirit The Chinese focused substantial resources on keeping roads and supply lines functioning, a difficult task in Tibet's challenging landscape. Other CIA documents reaffirm this notion, by recognizing the enormous cost of resupplying operatives and keeping supply chains moving in the country.

The July 1958 document also cites the structure of Tibetan society as a primary source of trouble for the Chinese. Tibetan society revolves around the Lamaist Church, and its spiritual leader the Dalai Lama. The Dalai Lama was not merely a spiritual guide, but a political and ideological leader. Tibetan monasteries were more than just houses of worship, they were the economic and political centers of Tibetan society, which allowed the clergy to wield considerable power. The clergy was conservative and extremely traditionalistic. This traditionalism meant that any deviation from traditional Tibetan life was strictly opposed. Altogether, the author suggests that the socialization of Tibet may be "prolonged" despite the substantial investments of the Chinese to integrate the area. Tibetan's spirit for independence, the country's fractured and isolated population, the harsh Chinese policies, and the Chinese military occupation all contribute to the problems that the Chinese have had in controlling the country.

The McMahon Line, proposed in 1914 by British colonial administrator Henry McMahon, is the demarcation line between Tibet and the North-east region of India, stretches along the crest ridge of the Himalayas. The Chinese, however, refuse to accept the McMahon Line as the legal boundary. Nevertheless, India remains adamant that it stands. With this disagreement, the Chinese believe that they have grounds for charging Indian troops with the invasion of their territory. Tibet is predominantly composed of rugged terrain, with plateaus, mountains and deep river valleys. However, the land has never been surveyed, and no markers have been placed thus providing room for disagreement.

In 1972, before the seismic head of state meeting between Chairman Mao and President Nixon, the CIA cut off all support to the Tibetan resistance as American foreign policy objectives in China, emblematic of Nixon and Kissinger's drive for an open door policy with China, underwent a rapid transformation. As a result, each of the 1,500 CIA-trained rebels received 10,000 rupees to buy land in India or to open a business instead of fighting the People's Liberation Army of China. Additionally, the White House decided that the training of Tibetan guerrillas by the CIA would have to cease because the risk of damaging Sino-American relations would be too high and costly.

This rebellion was one of the greatest intelligence successes of the Cold War because of the significant amount of Chinese military documents captured by Tibetan fighters and given to the CIA.

The CIA is alleged to have been involved in another failed revolt in October 1987 resulting in unrest and the continuation of Chinese repression until May 1993.

Contemporary Tibet-China relationship

Although the Chinese liberalization program for Tibet occurred decades ago, there is still tension between the two parties, in part, because of the U.S. involvement. In late September 2012, a U.S. Ambassador visited Beijing but also met with Tibetan monks. The Ambassador is Gary Locke, who himself is a third-generation Chinese American. The fact that he met with Tibetan monks displeased China. The tension between Tibet and China has influenced the Chinese to "always protests vehemently whenever U.S. officials meet with the Dalai Lama."

China also faces opposition movements from the Uyghur Muslims in Xinjiang province, an autonomous region of northwest China, as well as the Falun Gong. Inspired by these tensions and domestic schisms, the CIA is thought to look for the right opportunity to destabilize Chinese rule in Tibet.

Many foreign policy officials in Washington continue to view China with a critical eye, aided in their view by CIA assessments which view China as non-cooperative in the war on terror. The CIA charges that China does not stop the flow of arms and men from western China (including Xinjiang) into Afghanistan and Central Asia, bolstering support for Islamic terrorist organizations in the region. This has included the East Turkestan Islamic Movement, which U.S. officials report has enjoyed support from the Taliban.

Modernization has also made it easier for the Chinese to resupply due in part to the construction of the first railway into Tibet occurring between 2001 and 2007. This railway makes for easier movement of troops and equipment.

Costs

A total of 1,735,000 U.S. dollars (equivalent to $16,370,805 in 2022) was devoted to the Tibetan program for FY1964.

The following table illustrates the costs of the CIA's Tibetan program in 1964:

Item	Cost
Tibetan resistance efforts in Nepal	US$500,000
Tibet Houses in New York and Geneva (1/2 year)	US$75,000
Training	US$855,000
Subsidy to the Dalai Lama	US$180,000
Miscellaneous costs	US$125,000

Moreover, the estimate for the Tibetan program underwent an estimated budget cut of $570,000 in 1968 when the United States relinquished all related training programs. The remaining $1,165,000 was allocated to the CIA budget for the program in the fiscal year 1968. However, a considerable degree of uncertainty exists regarding the exact amount approved for the program during this time due to classification issues.

International lobbying

The 14th Dalai Lama was financially supported by the CIA between the late 1950s and the mid-1970s, receiving $180,000 a year. The funds were paid to him personally, although he used most of them for Tibetan government-in-exile activities such as funding foreign offices to lobby for international support.

The Dalai Lama sought asylum in India, but the issues regarding Tibet and China received substantial attention from the press. Many protests erupted in response to the political conflicts between Tibet and China in countries including Burma, Pakistan, and Japan (and many more). Although the Dalai Lama's pleas proved to be less effective with the passing of time, his office in New York did not cease to lobby several U.N. delegations for the Tibetan cause. Also, the Dalai Lama was aided by a former U.S. delegate to the U.N.

Criticism

In his 1991 autobiography Freedom in Exile, the 14th Dalai Lama criticized the CIA for supporting the Tibetan independence movement "not because they (the CIA) cared about Tibetan independence, but as part of their worldwide efforts to destabilize all communist governments".

In 1999, the Dalai Lama suggested that the CIA Tibetan program had been harmful to Tibet because it primarily served American interests, claiming "once the American policy toward China changed, they stopped their help ... The Americans had a different agenda from the Tibetans."

During the Tibetan program's period of activity, some of its largest contributions to the CIA's interests in the region came in the form of keeping the Chinese occupied with resistance, never actually producing a mass uprising establishing independence for Tibet from Beijing. The program also produced a trove of army documents that Tibetan insurgents seized from the Chinese and turned over to the CIA in 1961 in what has been referred to as "one of the greatest intelligence successes of the Cold War".

The CIA faced criticism for breaking promises regarding declassification, including some documentation regarding the support of Tibetan guerilla fighters in the 1950s until the early 1960s.