Cyclotron

From Wikipedia, the free encyclopedia

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

Lawrence's 60-inch cyclotron, with magnet poles 60 inches (5 feet, 1.5 meters) in diameter, at the University of California Lawrence Radiation Laboratory, Berkeley, in August, 1939, the most powerful accelerator in the world at the time. Glenn T. Seaborg and Edwin M. McMillan (right) used it to discover plutonium, neptunium, and many other transuranic elements and isotopes, for which they received the 1951 Nobel Prize in chemistry. The cyclotron's huge magnet is at left, with the flat accelerating chamber between its poles in the center. The beamline which analyzed the particles is at right.

A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. A cyclotron accelerates charged particles outwards from the center of a flat cylindrical vacuum chamber along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying electric field. Lawrence was awarded the 1939 Nobel Prize in Physics for this invention.

The cyclotron was the first "cyclical" accelerator. In existing electrostatic accelerators of the time, such as the Cockcroft–Walton accelerator and Van de Graaff generator, particles would cross an accelerating electric field only once. Thus, the energy gained by the particles was limited by the maximum electrical potential that could be achieved across the accelerating region. This was in turn limited by electrostatic breakdown to a few million volts. In a cyclotron, by contrast, the particles encounter the accelerating region many times by following a spiral path, so the output energy can be many times the energy gained in a single accelerating step.

Cyclotrons were the most powerful particle accelerator technology until the 1950s, when they were superseded by the synchrotron. Despite no longer being the highest-energy accelerator, they are still widely used to produce particle beams for basic research and nuclear medicine. Close to 1500 cyclotrons are used in nuclear medicine worldwide for the production of medical radionuclides. In addition, cyclotrons can be used for particle therapy, where particle beams are directly applied to patients.

History

Lawrence's 60-inch cyclotron, circa 1939, showing the beam of accelerated ions (likely protons or deuterons) exiting the machine and ionizing the surrounding air causing a blue glow.

 

The magnet yoke for the 37″ cyclotron on display at the Lawrence Hall of Science, Berkeley California.

In late 1928 and early 1929 Hungarian physicist Leo Szilárd filed patent applications in Germany (later abandoned) for the linear accelerator, cyclotron, and betatron. In these applications, Szilárd became the first person to discuss the resonance condition (what is now called the cyclotron frequency) for a circular accelerating apparatus. Several months later, in the early summer of 1929, Ernest Lawrence independently conceived the cyclotron concept after reading a paper by Rolf Widerøe describing a drift tube accelerator. He published a paper in Science in 1930, and patented the device in 1932.

To construct the first such device, Lawrence used large electromagnets recycled from obsolete arc converters provided by the Federal Telegraph Company. He was assisted by a graduate student, M. Stanley Livingston Their first working cyclotron became operational in January 1931. This machine had a radius of 4.5 inches (11 cm), and accelerated protons to an energy up to 80 keV.

At the Radiation Laboratory of the University of California, Berkeley, Lawrence and his collaborators went on to construct a series of cyclotrons which were the most powerful accelerators in the world at the time; a 27 in (69 cm) 4.8 MeV machine (1932), a 37 in (94 cm) 8 MeV machine (1937), and a 60 in (152 cm) 16 MeV machine (1939). Lawrence received the 1939 Nobel Prize in Physics for the invention and development of the cyclotron and for results obtained with it.

The first European cyclotron was constructed in the Soviet Union in the physics department of the Radium Institute in Leningrad, headed by Vitaly Khlopin [ru]. This Leningrad instrument was first proposed in 1932 by George Gamow and Lev Mysovskii [ru] and was installed and became operative by 1937.

Two cyclotrons were built in Nazi Germany. The first was constructed in 1937, in Otto Hahn's laboratory at the Kaiser Wilhelm Institute in Berlin, and was also used by Rudolf Fleischmann. It was the first cyclotron with a Greinacher multiplier to increase the voltage to 2.8 MV and 3 mA current. A second cyclotron was built in Heidelberg under the supervision of Walther Bothe and Wolfgang Gentner, with support from the Heereswaffenamt, and became operative in 1943.

By the late 1930s it had become clear that there was a practical limit on the beam energy that could be achieved with the traditional cyclotron design, due to the effects of special relativity. As particles reach relativistic speeds, their effective mass increases, which causes the resonant frequency for a given magnetic field to change. To address this issue and reach higher beam energies using cyclotrons, two primary approaches were taken, synchrocyclotrons (which hold the magnetic field constant, but increase the accelerating frequency) and isochronous cyclotrons (which hold the accelerating frequency constant, but alter the magnetic field).

Lawrence's team built one of the first synchrocyclotrons in 1946. This 184 in (4.7 m) machine eventually achieved a maximum beam energy of 350 MeV for protons. However, synchrocyclotrons suffer from low beam intensities (< 1 µA), and must be operated in a "pulsed" mode, further decreasing the available total beam. As such, they were quickly overtaken in popularity by isochronous cyclotrons.

The first isochronous cyclotron (other than classified prototypes) was built by F. Heyn and K.T. Khoe in Delft, the Netherlands, in 1956. Early isochronous cyclotrons were limited to energies of ~50 MeV per nucleon, but as manufacturing and design techniques gradually improved, the construction of "spiral-sector" cyclotrons allowed the acceleration and control of more powerful beams. Later developments included the use of more powerful superconducting magnets and the separation of the magnets into discrete sectors, as opposed to a single large magnet.

Principle of operation

Diagram of a cyclotron. The magnet's pole pieces are shown smaller than in reality; they must actually be at least as wide as the accelerating electrodes ("dees") to create a uniform field.

Cyclotron principle

Illustration of a linear accelerator, showing the increasing separation between gaps.

 

Diagram of cyclotron operation from Lawrence's 1934 patent. The "D" shaped electrodes (left) are enclosed in a flat vacuum chamber, which is installed in a narrow gap between the two poles of a large magnet.(right)

 

Vacuum chamber of Lawrence 69 cm (27 in) 1932 cyclotron with cover removed, showing the dees. The 13,000 V RF accelerating potential at about 27 MHz is applied to the dees by the two feedlines visible at top right. The beam emerges from the dees and strikes the target in the chamber at bottom.

In a particle accelerator, charged particles are accelerated by applying an electric field across a gap. The force on the particle is given by the Lorentz force law:

${\displaystyle {\vec {F}}=q{\vec {E}}+q{\vec {v}}\times {\vec {B}}}$

where q is the charge on the particle, E is the electric field, v is the particle velocity, and B is the magnetic field. Consequently, it is not possible to accelerate particles using a static magnetic field, as the magnetic force always acts perpendicularly to the direction of motion.

In practice, the magnitude of a static field which can be applied across a gap is limited by the need to avoid electrostatic breakdown. As such, modern particle accelerators use alternating (radio frequency) electric fields for acceleration. Since an alternating field across a gap only provides an acceleration in the forward direction for a portion of its cycle, particles in RF accelerators travel in bunches, rather than a continuous stream. In a linear particle accelerator, in order for a bunch to "see" a forward voltage every time it crosses a gap, the gaps must be placed further and further apart, in order to compensate for the increasing speed of the particle.

A cyclotron, by contrast, uses a magnetic field to bend the particle trajectories into a spiral, thus allowing the same gap to be used many times to accelerate a single bunch. As the bunch spirals outward, the increasing distance between transits of the gap is exactly balanced by the increase in speed, so a bunch will reach the gap at the same point in the RF cycle every time.

The frequency at which a particle will orbit in a perpendicular magnetic field is known as the cyclotron frequency, and depends, in the non-relativistic case, solely on the charge and mass of the particle, and the strength of the magnetic field:

${\displaystyle f={\frac {qB}{2\pi m}}}$

where f is the (linear) frequency, q is the charge of the particle, B is the magnitude of the magnetic field that is perpendicular to the plane in which the particle is travelling, and m is the particle mass. The property that the frequency is independent of particle velocity is what allows a single, fixed gap to be used to accelerate a particle travelling in a spiral.

Particle energy

Each time a particle crosses the accelerating gap in a cyclotron, it is given an accelerating force by the electric field across the gap, and the total particle energy gain can be calculated by multiplying the increase per crossing by the number of times the particle crosses the gap.

However, given the typically high number of revolutions, it is usually simpler to estimate the energy by combining the equation for frequency in circular motion:

${\displaystyle f={\frac {v}{2\pi R}}}$

with the cyclotron frequency equation to yield:

${\displaystyle v={\frac {qBR}{m}}}$

The kinetic energy for particles with velocity v is therefore given by:

${\displaystyle E={\frac {1}{2}}mv^{2}={\frac {q^{2}B^{2}R^{2}}{2m}}}$

where R is the radius at which the energy is to be determined. The limit on the beam energy which can be produced by a given cyclotron thus depends on the maximum radius which can be reached by the magnetic field and the accelerating structures, and on the maximum strength of the magnetic field which can be achieved.

K-factor

In the nonrelativistic approximation, the maximum kinetic energy per atomic mass for a given cyclotron is given by:

${\displaystyle {\frac {T}{A}}={\frac {(eBr_{\max })^{2}}{2m_{a}}}\left({\frac {Q}{A}}\right)^{2}=K\left({\frac {Q}{A}}\right)^{2}}$

where ${\displaystyle e}$ is the elementary charge, ${\displaystyle B}$ is the strength of the magnet, ${\displaystyle r_{\max }}$ is the maximum radius of the beam, ${\displaystyle m_{a}}$ is an atomic mass unit, ${\displaystyle Q}$ is the charge of the beam particles, and ${\displaystyle A}$ is the atomic mass of the beam particles. The value of K

${\displaystyle K={\frac {(eBr_{\max })^{2}}{2m_{a}}}}$

is known as the "K-factor", and is used to characterize the maximum beam energy of a cyclotron. It represents the theoretical maximum energy of protons (with Q and A equal to 1) accelerated in a given machine.

Relativistic considerations

In the non-relativistic approximation, the cyclotron frequency does not depend upon the particle's speed or the radius of the particle's orbit. As the beam spirals outward, the rotation frequency stays constant, and the beam continues to accelerate as it travels a greater distance in the same time period.

In contrast to this approximation, as particles approach the speed of light, the cyclotron frequency decreases due to the change in relativistic mass. This change is proportional to the particle's Lorentz factor.

The relativistic mass can be written as:

${\displaystyle m={\frac {m_{0}}{\sqrt {1-\left({\frac {v}{c}}\right)^{2}}}}={\frac {m_{0}}{\sqrt {1-\beta ^{2}}}}=\gamma {m_{0}},}$

where:

• ${\displaystyle m_{0}}$ is the particle rest mass,
• ${\displaystyle \beta ={\frac {v}{c}}}$ is the relative velocity, and
• ${\displaystyle \gamma ={\frac {1}{\sqrt {1-\beta ^{2}}}}={\frac {1}{\sqrt {1-\left({\frac {v}{c}}\right)^{2}}}}}$ is the Lorentz factor.

Substituting this into the equations for cyclotron frequency and angular frequency gives:

${\displaystyle {\begin{aligned}f&={\frac {qB}{2\pi \gamma m_{0}}}\\[6pt]\omega &={\frac {qB}{\gamma m_{0}}}\end{aligned}}}$

The gyroradius for a particle moving in a static magnetic field is then given by:

${\displaystyle r={\frac {\gamma \beta m_{0}c}{qB}}}$

Approaches to relativistic cyclotrons

Synchrocyclotron

Main article: Synchrocyclotron

Since ${\displaystyle \gamma }$ increases as the particle reaches relativistic velocities, acceleration of relativistic particles therefore requires modification of the cyclotron to ensure the particle crosses the gap at the same point in the RF cycle. If the frequency of the accelerating electric field is varied while the magnetic field is held constant, this leads to the synchrocyclotron. 

${\displaystyle f(r)={\frac {qB}{2\pi \gamma (r)m_{0}}}}$

Here the frequency is a function of particle radius, and is adjusted to balance the relativistic change of particle velocity (incorporated into ${\displaystyle \gamma }$) with radius.

Isochronous cyclotron

If instead the magnetic field is varied with radius while the frequency of the accelerating field is held constant, this leads to the isochronous cyclotron.

${\displaystyle f={\frac {qB(r)}{2\pi \gamma (r)m_{0}}}}$

Here the magnetic field B is a function of radius, chosen to maintain a constant frequency f as ${\displaystyle \gamma }$ increases.

Isochronous cyclotrons are capable of producing much greater beam current than synchrocyclotrons, but require precisely shaped variations in the magnetic field strength to provide a focusing effect and keep the particles captured in their spiral trajectory. For this reason, an isochronous cyclotron is also called an "AVF (azimuthal varying field) cyclotron". This solution for focusing the particle beam was proposed by L. H. Thomas in 1938. Almost all modern cyclotrons use azimuthally-varying fields.

Fixed-field alternating gradient accelerator

Main article: Fixed-field alternating gradient accelerator

An approach which combines static magnetic fields (as in the synchrocyclotron) and alternating gradient focusing (as in a synchrotron) is the fixed-field alternating gradient accelerator (FFA). In an isochronous cyclotron, the magnetic field is shaped by using precisely machined steel magnet poles. This variation provides a focusing effect as the particles cross the edges of the poles. In an FFA, separate magnets with alternating directions are used to focus the beam using the principle of strong focusing. The field of the focusing and bending magnets in an FFA is not varied over time, so the beam chamber must still be wide enough to accommodate a changing beam radius within the field of the focusing magnets as the beam accelerates.

Classifications

A French cyclotron, produced in Zurich, Switzerland in 1937. The vacuum chamber containing the dees (at left) has been removed from the magnet (red, at right)

Cyclotron types

There are a number of basic types of cyclotron:

Classical cyclotron

The earliest and simplest cyclotron. Classical cyclotrons have uniform magnetic fields and a constant accelerating frequency. They are limited to nonrelativistic particle velocities (the output energy small compared to the particle's rest energy), and have no active focusing to keep the beam aligned in the plane of acceleration.

Synchrocyclotron

The synchrocyclotron extended the energy of the cyclotron into the relativistic regime by decreasing the frequency of the accelerating field as the orbit of the particles increased to keep it synchronized with the particle revolution frequency. Because this requires pulsed operation, the integrated total beam current was low compared to the classical cyclotron. In terms of beam energy, these were the most powerful accelerators during the 1950s, before the development of the synchrotron.

Isochronous cyclotron (isocyclotron)

These cyclotrons extend output energy into the relativistic regime by altering the magnetic field to compensate for the change in cyclotron frequency as the particles reached relativistic speed. They use shaped magnet pole pieces to create a nonuniform magnetic field stronger in peripheral regions. Most modern cyclotrons are of this type. The pole pieces can also be shaped to cause the beam to keep the particles focused in the acceleration plane as the orbit. This is known as "sector focusing" or "azimuthally-varying field focusing", and uses the principle of alternating-gradient focusing.

Separated sector cyclotron

Separated sector cyclotrons are machines in which the magnet is in separate sections, separated by gaps without field.

Superconducting cyclotron

"Superconducting" in the cyclotron context refers to the type of magnet used to bend the particle orbits into a spiral. Superconducting magnets can produce substantially higher fields in the same area than normal conducting magnets, allowing for more compact, powerful machines. The first superconducting cyclotron was the K500 at the Michigan State University, which came online in 1981.

Beam types

The particles for cyclotron beams are produced in ion sources of various types.

Proton beams

The simplest type of cyclotron beam, proton beams are typically created by ionizing hydrogen gas.

H⁻ beams

Accelerating negative hydrogen ions simplifies extracting the beam from the machine. At the radius corresponding to the desired beam energy, a metal foil is used to strip the electrons from the H⁻ ions, transforming them into positively charged H⁺ ions. The change in polarity causes the beam to be deflected in the opposite direction by the magnetic field, allowing the beam to be transported out of the machine.

Heavy ion beams

Beams of particles heavier than hydrogen are referred to as heavy ion beams, and can range from deuterium nuclei (one proton and one neutron) up to uranium nuclei. The increase in energy required to accelerate heavier particles is balanced by stripping more electrons from the atom to increase the electric charge of the particles, thus increasing acceleration efficiency.

Target types

To make use of the cyclotron beam, it must be directed to a target.

Internal targets

The simplest way to strike a target with a cyclotron beam is to insert it directly into the path of the beam in the cyclotron. Internal targets have the disadvantage that they must be compact enough to fit within the cyclotron beam chamber, making them impractical for many medical and research uses.

External targets

While extracting a beam from a cyclotron to impinge on an external target is more complicated than using an internal target, it allows for greater control of the placement and focus of the beam, and much more flexibility in the types of targets to which the beam can be directed.

Usage

A modern cyclotron used for radiation therapy. The magnet is painted yellow.

Basic research

For several decades, cyclotrons were the best source of high-energy beams for nuclear physics experiments. With the advent of strong focusing synchrotrons, cyclotrons were supplanted as the accelerators capable of producing the highest energies. However, due to their compactness, and therefore lower expense compared to high energy synchrotrons, cyclotrons are still used to create beams for research where the primary consideration is not achieving the maximum possible energy. Cyclotron based nuclear physics experiments are used to measure basic properties of isotopes (particularly short lived radioactive isotopes) including half life, mass, interaction cross sections, and decay schemes.

Medical uses

Radioisotope production

Cyclotron beams can be used to bombard other atoms to produce short-lived isotopes with a variety of medical uses, including medical imaging and radiotherapy. Positron and gamma emitting isotopes, such as fluorine-18, carbon-11, and technetium-99m are used for PET and SPECT imaging. While cyclotron produced radioisotopes are widely used for diagnostic purposes, therapeutic uses are still largely in development. Proposed isotopes include astatine-211, palladium-103, rhenium-186, and bromine-77, among others.

Beam therapy

Beams from cyclotrons can be used in particle therapy to treat cancer. Ion beams from cyclotrons can be used, as in proton therapy, to penetrate the body and kill tumors by radiation damage, while minimizing damage to healthy tissue along their path. As of 2020, there were approximately 80 facilities worldwide for radiotherapy using beams of protons and heavy ions, consisting of a mixture of cyclotrons and synchrotrons. Cyclotrons are primarily used for proton beams, while synchrotrons are used to produce heavier ions.

Advantages and limitations

M. Stanley Livingston and Ernest O. Lawrence (right) in front of Lawrence's 69 cm (27 in) cyclotron at the Lawrence Radiation Laboratory. The curving metal frame is the magnet's core, the large cylindrical boxes contain the coils of wire that generate the magnetic field. The vacuum chamber containing the "dee" electrodes is in the center between the magnet's poles.

The most obvious advantage of a cyclotron over a linear accelerator is that because the same accelerating gap is used many times, it is both more space efficient and more cost efficient; particles can be brought to higher energies in less space, and with less equipment. The compactness of the cyclotron reduces other costs as well, such as foundations, radiation shielding, and the enclosing building. Cyclotrons have a single electrical driver, which saves both equipment and power costs. Furthermore, cyclotrons are able to produce a continuous beam of particles at the target, so the average power passed from a particle beam into a target is relatively high compared to the pulsed beam of a synchrotron.

However, as discussed above, a constant frequency acceleration method is only possible when the accelerated particles are approximately obeying Newton's laws of motion. If the particles become fast enough that relativistic effects become important, the beam becomes out of phase with the oscillating electric field, and cannot receive any additional acceleration. The classical cyclotron (constant field and frequency) is therefore only capable of accelerating particles up to a few percent of the speed of light. Synchro-, isochronous, and other types of cyclotrons can overcome this limitation, with the tradeoff of increased complexity and cost.

An additional limitation of cyclotrons is due to space charge effects – the mutual repulsion of the particles in the beam. As the amount of particles (beam current) in a cyclotron beam is increased, the effects of electrostatic repulsion grow stronger until they disrupt the orbits of neighboring particles. This puts a functional limit on the beam intensity, or the number of particles which can be accelerated at one time, as distinct from their energy.

Notable examples

Name	Country	Date	Energy	Beam	Diameter	In use?	Comments
Lawrence 4.5-inch Cyclotron	United States	1931	80 keV	Protons	4.5 inches (0.11 m)	No	First working cyclotron
Lawrence 184-inch Cyclotron	United States	1946	380 MeV	Alpha particles, deuterium, protons	184 inches (4.7 m)	No	First synchrocyclotron
TU Delft Isochronous Cyclotron	Netherlands	1958	12 MeV	Protons	0.36 m	No	First isochronous cyclotron
PSI Ring Cyclotron	Switzerland	1974	592 MeV	Protons	15 m	Yes	Highest beam intensity of any cyclotron
TRIUMF 520 MeV	Canada	1976	520 MeV	H−	56 feet (17 m)	Yes	Largest normal conductivity cyclotron
Michigan State University K500	United States	1982	500 MeV/u	Heavy Ion	52 inches (1.3 m)	No	First superconducting cyclotron
RIKEN Superconducting Ring Cyclotron	Japan	2006	400 MeV/u	Heavy Ion	18.4 m	Yes	K-value of 2600 is highest ever achieved

Related technologies

The spiraling of electrons in a cylindrical vacuum chamber within a transverse magnetic field is also employed in the magnetron, a device for producing high frequency radio waves (microwaves). In the magnetron, electrons are bent into a circular path by a magnetic field, and their motion is used to excite resonant cavities, producing electromagnetic radiation.

A betatron uses the change in the magnetic field to accelerate electrons in a circular path. While static magnetic fields cannot provide acceleration, as the force always acts perpendicularly to the direction of particle motion, changing fields can be used to induce an electromotive force in the same manner as in a transformer. The betatron was developed in 1940, although the idea had been proposed substantially earlier.

A synchrotron is another type of particle accelerator that uses magnets to bend particles into a circular trajectory. Unlike in a cyclotron, the particle path in a synchrotron has a fixed radius. Particles in a synchrotron pass accelerating stations at increasing frequency as they get faster. To compensate for this frequency increase, both the frequency of the applied accelerating electric field and the magnetic field must be increased in tandem, leading to the "synchro" portion of the name.

In fiction

The United States Department of War famously asked for dailies of the Superman comic strip to be pulled in April 1945 for having Superman bombarded with the radiation from a cyclotron. In 1950, however, in Atom Man vs. Superman, Lex Luthor uses a cyclotron to start an earthquake.

In the 1984 film Ghostbusters, a miniature cyclotron forms part of the proton pack used for catching ghosts.

Toxic waste

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

Valley of the Drums, a toxic waste site in Kentucky, United States, 1980.

 

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Toxic waste is any unwanted material in all forms that can cause harm (e.g. by being inhaled, swallowed, or absorbed through the skin). Many of today's household products such as televisions, computers and phones contain toxic chemicals that can pollute the air and contaminate soil and water. Disposing of such waste is a major public health issue.

Classifying toxic materials

Toxic materials are poisonous byproducts as a result of industries such as manufacturing, farming, construction, automotive, laboratories, and hospitals which may contain heavy metals, radiation, dangerous pathogens, or other toxins. Toxic waste has become more abundant since the industrial revolution, causing serious global issues. Disposing of such waste has become even more critical with the addition of numerous technological advances containing toxic chemical components. Products such as cellular telephones, computers, televisions, and solar panels contain toxic chemicals that can harm the environment if not disposed of properly to prevent the pollution of the air and contamination of soils and water. A material is considered toxic when it causes death or harm by being inhaled, swallowed, or absorbed through the skin.

The waste can contain chemicals, heavy metals, radiation, dangerous pathogens, or other toxins. Even households generate hazardous waste from items such as batteries, used computer equipment, and leftover paints or pesticides. Toxic material can be either human-made and others are naturally occurring in the environment. Not all hazardous substances are considered toxic.

The United Nations Environment Programme (UNEP) has identified 11 key substances that pose a risk to human health:

• Arsenic: used in making electrical circuits, as an ingredient in pesticides, and as a wood preservative. It is classified as a carcinogen.
• Asbestos: is a material that was once used for the insulation of buildings, and some businesses are still using this material to manufacture roofing materials and brakes. Inhalation of asbestos fibers can lead to lung cancer and asbestosis.
• Cadmium: is found in batteries and plastics. It can be inhaled through cigarette smoke, or digested when included as a pigment in food. Exposure leads to lung damage, irritation of the digestive tract, and kidney disease.
• Chromium: is used as brick lining for high-temperature industrial furnaces, as a solid metal used for making steel, and in chrome plating, manufacturing dyes and pigments, wood preserving, and leather tanning. It is known to cause cancer, and prolonged exposure can cause chronic bronchitis and damage lung tissue.
• Clinical wastes: such as syringes and medication bottles can spread pathogens and harmful microorganisms, leading to a variety of illnesses.
• Cyanide: a poison found in some pesticides and rodenticides. In large doses it can lead to paralysis, convulsions, and respiratory distress.
• Lead: is found in batteries, paints, and ammunition. When ingested or inhaled can cause harm to the nervous and reproductive systems, and kidneys.
• Mercury: used for dental fillings and batteries. It is also used in the production of chlorine gas. Exposure can lead to birth defects and kidney and brain damage
• PCBs, or polychlorinated biphenyls, are used in many manufacturing processes, by the utility industry, and in paints and sealants. Damage can occur through exposure, affecting the nervous, reproductive, and immune systems, as well as the liver.
• POPs, persistent organic pollutants. They are found in chemicals and pesticides, and may lead to nervous and reproductive system defects. They can bio-accumulate in the food chain or persist in the environment and be moved great distances through the atmosphere.
• Strong acids and alkalis used in manufacturing and industrial production. They can destroy tissue and cause internal damage to the body.

The most overlooked toxic and hazardous wastes are the household products in everyday homes that are improperly disposed of such as old batteries, pesticides, paint, and car oil. Toxic waste can be reactive, ignitable, and corrosive. In the United States, these wastes are regulated under the Resource Conservation and Recovery Act (RCRA).

• Reactive wastes are those that can cause explosions when heated, mixed with water or compressed. They can release toxic gases into the air. They are unstable even in normal conditions. An example is lithium–sulfur batteries.
• Ignitable wastes have flash points of less than 60 degrees Celsius. They are very combustible and can cause fires. Examples are solvents and waste oils.
• Corrosive wastes are liquids capable of corroding metal containers. These are acids or bases that have pH levels of less than or equal to 2, or greater than or equal to 12.5. An example is battery acid.

With the increase of worldwide technology, there are more substances that are being considered toxic and harmful to human health. Technology growth at this rate is extremely daunting towards civilization and can eventually lead to more harm/negative outcomes. Some of this technology includes cell phones and computers. Such items have been given the name e-waste or EEE, which stands for Electrical and Electronic Equipment. This term is also used for goods such as refrigerators, toys, and washing machines. These items can contain toxic components that can break down into water systems when discarded. The reduction in the cost of these goods has allowed for these items to be distributed globally without thought or consideration to managing the goods once they become ineffective or broken.

In the US, the Environmental Protection Agency (EPA) and state environmental agencies develop and enforce regulations on the storage, treatment and disposal of hazardous waste. The EPA requires that toxic waste be handled with special precautions and be disposed of in designated facilities around the country. Also, many US cities have collection days where household toxic waste is gathered. Some materials that may not be accepted at regular landfills are ammunition, commercially generated waste, explosives/shock sensitive items, hypodermic needles/syringes, medical waste, radioactive materials, and smoke detectors.

Health effects

Toxic wastes often contain carcinogens, and exposure to these by some route, such as leakage or evaporation from the storage, causes cancer to appear at increased frequency in exposed individuals. For example, a cluster of the rare blood cancer polycythemia vera was found around a toxic waste dump site in northeast Pennsylvania in 2008.

The Human & Ecological Risk Assessment Journal conducted a study which focused on the health of individuals living near municipal landfills to see if it would be as harmful as living near hazardous landfills. They conducted a 7-year study that specifically tested for 18 types of cancers to see if the participants had higher rates than those that don't live around landfills. They conducted this study in western Massachusetts within a 1-mile radius of the North Hampton Regional Landfill.

People encounter these toxins buried in the ground, in stream runoff, in groundwater that supplies drinking water, or in floodwaters, as happened after Hurricane Katrina. Some toxins, such as mercury, persist in the environment and accumulate. As a result of the bioaccumulation of mercury in both freshwater and marine ecosystems, predatory fish are a significant source of mercury in human and animal diets. Toxic Waste." National Geographic. National Geographic, 2010. Web. 26 Apr 2010.

Handling and disposal

Main article: Hazardous Waste Disposal

One of the biggest problems with today's toxic material is how to dispose of it properly. Before the passage of modern environmental laws (in the US, this was in the 1970s), it was legal to dump such wastes into streams, rivers and oceans, or bury it underground in landfills. The US Clean Water Act, enacted in 1972, and RCRA, enacted in 1976, created nationwide programs to regulate the handling and disposal of hazardous wastes.

The agriculture industry uses over 800,000 tons of pesticides worldwide annually that contaminates soils, and eventually infiltrates into groundwater, which can contaminate drinking water supplies. The oceans can be polluted from the stormwater runoff of these chemicals as well. Toxic waste in the form of petroleum oil can either spill into the oceans from pipe leaks or large ships, but it can also enter the oceans from everyday citizens dumping car oil into the rainstorm sewer systems. Disposal is the placement of waste into or on the land. Disposal facilities are usually designed to permanently contain the waste and prevent the release of harmful pollutants to the environment.

The most common hazardous waste disposal practice is placement in a land disposal unit such as a landfill, surface impoundment, waste pile, land treatment unit, or injection well. Land disposal is subject to requirements under EPA's Land Disposal Restrictions Program. Injection wells are regulated under the federal Underground Injection Control program.

Organic wastes can be destroyed by incineration at high temperatures. However, if the waste contains heavy metals or radioactive isotopes, these must be separated and stored, as they cannot be destroyed. The method of storage will seek to immobilize the toxic components of the waste, possibly through storage in sealed containers, inclusion in a stable medium such as glass or a cement mixture, or burial under an impermeable clay cap. Waste transporters and waste facilities may charge fees; consequently, improper methods of disposal may be used to avoid paying these fees. Where the handling of toxic waste is regulated, the improper disposal of toxic waste may be punishable by fines or prison terms. Burial sites for toxic waste and other contaminated brownfield land may eventually be used as greenspace or redeveloped for commercial or industrial use.

History of US toxic waste regulation

The RCRA governs the generation, transportation, treatment, storage, and disposal of hazardous waste. The Toxic Substances Control Act (TSCA), also enacted in 1976, authorizes the EPA to collect information on all new and existing chemical substances, as well as to control any substances that were determined to cause unreasonable risk to public health or the environment. The Superfund law, passed in 1980, created a cleanup program for abandoned or uncontrolled hazardous waste sites.

There has been a long ongoing battle between communities and environmentalists versus governments and corporations about how strictly and how fairly the regulations and laws are written and enforced. That battle began in North Carolina in the late summer of 1979, as EPA's TSCA regulations were being implemented. In North Carolina, PCB-contaminated oil was deliberately dripped along rural Piedmont highways, creating the largest PCB spills in American history and a public health crisis that would have repercussions for generations to come. The PCB-contaminated material was eventually collected and buried in a landfill in Warren County, but citizens' opposition, including large public demonstrations, exposed the dangers of toxic waste, the fallibility of landfills then in use, and EPA regulations allowing landfills to be built on marginal, but politically acceptable sites.

Warren County citizens argued that the toxic waste landfill regulations were based on the fundamental assumption that the EPA's conceptual dry-tomb landfill would contain the toxic waste. This assumption informed the siting of toxic waste landfills and waivers to regulations that were included in EPA's Federal Register. For example, in 1978, the base of a major toxic waste landfill could be no closer than five feet from groundwater, but this regulation and others could be waived. The waiver to the regulation concerning the distance between the base of a toxic waste landfill and groundwater allowed the base to be only a foot above ground water if the owner/operator of the facility could demonstrate to the EPA regional administrator that a leachate collection system could be installed and that there would be no hydraulic connection between the base of the landfill and groundwater. Citizens argued that the waivers to the siting regulations were discriminatory mechanisms facilitating the shift from scientific to political considerations concerning the siting decision and that in the South this would mean a discriminatory proliferation of dangerous waste management facilities in poor black and other minority communities. They also argued that the scientific consensus was that permanent containment could not be assured. As resistance to the siting of the PCB landfill in Warren County continued and studies revealed that EPA dry-tomb landfills were failing, EPA stated in its Federal Register that all landfills would eventually leak and should only be used as a stopgap measure.

Years of research and empirical knowledge of the failures of the Warren County PCB landfill led citizens of Warren County to conclude that the EPA's dry-tomb landfill design and regulations governing the disposal of toxic and hazardous waste were not based on sound science and adequate technology. Warren County's citizens concluded also that North Carolina's 1981 Waste Management Act was scientifically and constitutionally unacceptable because it authorized the siting of toxic, hazardous and nuclear waste facilities prior to public hearings, preempted local authority over the siting of the facilities, and authorized the use of force if needed.

In the aftermath of the Warren County protests, the 1984 Federal Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act focused on waste minimization and phasing out land disposal of hazardous waste as well as corrective action for releases of hazardous materials. Other measures included in the 1984 amendments included increased enforcement authority for EPA, more stringent hazardous waste management standards, and a comprehensive underground storage tank program.

The disposal of toxic waste continues to be a source of conflict in the U.S. Due to the hazards associated with toxic waste handling and disposal, communities often resist the siting of toxic waste landfills and other waste management facilities; however, determining where and how to dispose of waste is a necessary part of economic and environmental policy-making.

The issue of handling toxic waste has become a global problem as international trade has arisen out of the increasing toxic byproducts produced with the transfer of them to less developed countries. In 1995, the United Nations Commission on Human Rights began to notice the illicit dumping of toxic waste and assigned a Special Rapporteur to examine the human rights aspect to this issue (Commission resolution 1995/81). In September 2011, the Human Rights Council decided to strengthen the mandate to include the entire life-cycle of hazardous products from manufacturing to final destination (aka cradle to grave), as opposed to only movement and dumping of hazardous waste. The title of the Special Rapporteur has been changed to the “Special Rapporteur on the implications for human rights of the environmentally sound management and disposal of hazardous substances and wastes."(Human Rights Council 18/11). The Human Rights Council has further extended the scope of its mandates as of September 2012 due to the result of the dangerous implications occurring to persons advocating environmentally sound practices regarding the generation,management, handling, distribution and final disposal of hazardous and toxic materials to include the issue of the protection of the environmental human rights defenders.

Mapping of toxic waste in the United States

TOXMAP was a geographic information system (GIS) from the Division of Specialized Information Services of the United States National Library of Medicine (NLM) that used maps of the United States to help users visually explore data from the United States Environmental Protection Agency's (EPA) Superfund and Toxics Release Inventory programs. The chemical and environmental health information was taken from NLM's Toxicology Data Network (TOXNET) and PubMed, and from other authoritative sources. The database was removed from the internet by the Trump Administration in December 2019.

Future Circular Collider

From Wikipedia, the free encyclopedia

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

 

The future circular colliders considered under the FCC study compared to previous circular colliders.

The Future Circular Collider (FCC) is a proposed post-LHC particle accelerator with an energy significantly above that of previous circular colliders (SPS, Tevatron, LHC). The FCC project examines scenarios for three different types of particle collisions: hadron (proton–proton and heavy ion) collisions in a collider design known as FCC-hh, electron–positron collisions in a collider design known as FCC-ee, and proton–electron collisions in a collider design known as FCC-eh.

In FCC-hh, each beam would have a total energy of 560 MJ. With a centre-of-mass collision energy of 100 TeV (vs 14 TeV at LHC) the total energy value increases to 16.7 GJ. These total energy values exceed the present LHC by nearly a factor of 30.

CERN hosted an FCC study exploring the feasibility of different particle collider scenarios with the aim of significantly increasing the energy and luminosity compared to existing colliders. It aims to complement existing technical designs for linear electron/positron colliders (ILC and CLIC).

The study explores the potential of hadron and lepton circular colliders, performing an analysis of infrastructure and operation concepts and considering the technology research and development programmes that are required to build and operate a future circular collider. A conceptual design report was published in early 2019, in time for the next update of the European Strategy for Particle Physics.

Background

The CERN study was initiated as a direct response to the high-priority recommendation of the updated European Strategy for Particle Physics, published in 2013 which asked that "CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide". The goal was to inform the next Update of the European Strategy for Particle Physics (2019-2020) and the wider physics community for the feasibility of circular colliders complementing previous studies for linear colliders as well as other proposal for particle physics experiments.

The launch of the FCC study was also in line with the recommendations of the United States’ Particle Physics Project Prioritization Panel (P5) and of the International Committee for Future Accelerators (ICFA).

The discovery of the Higgs boson at the LHC, together with the absence so far of any phenomena beyond the Standard Model in collisions at centre of mass energies up to 8 TeV, has triggered an interest in future circular colliders to push the energy and precision frontiers complementing studies for future linear machines. The discovery of a "light" Higgs boson with a mass of 125 GeV revamped the discussion for a circular lepton collider that would allow detailed studies and precise measurement of this new particle. With the study of a new 80–100 km circumference tunnel (see also VLHC), that would fit in the Geneva region, it was realized that a future circular lepton collider could offer collision energies up to 400 GeV (thus allowing for the production of top quarks) at unprecedented luminosities. The design of FCC-ee (formerly known as TLEP (Triple-Large Electron-Positron Collider)) was combining the experience gained by LEP2 and the latest B factories.

Two main limitations to circular-accelerator performance are energy loss due to synchrotron radiation, and the maximum value of magnetic fields that can be obtained in bending magnets to keep the energetic beams in a circular trajectory. Synchrotron radiation is of particular importance in the design and optimization of a circular lepton collider and limits the maximum energy reach that can be reached as the phenomenon depends on the mass of the accelerated particle. To address these issues a sophisticated machine design along with the advancement of technologies like accelerating (RF) cavities and high-field magnets are needed.

Future "intensity and luminosity frontier" lepton colliders like those considered by the FCC study would enable the study with very high precision the properties of the Higgs boson, the W and Z bosons and the top quark, pinning down their interactions with an accuracy at least an order of magnitude better than today. The FCC-ee could collect 10^12 Z bosons, 10^8 W pairs, 10^6 Higgs bosons and 4 x 10^5 top-quark pairs per year. As a second step, an “energy frontier” collider at 100 TeV (FCC-hh) could be a “discovery machine” offering an eightfold increase compared to the current energy reach of the LHC.

The FCC integrated project, combining FCC-ee and FCC-hh, would rely on a shared and cost effective technical and organizational infrastructure, as was the case with LEP followed by LHC. This approach improves by several orders the sensitivity to elusive phenomena at low mass and by an order of magnitude the discovery reach for new particles at the highest masses. This will allow to uniquely map the properties of the Higgs boson and Electroweak sector and broaden the exploration for different Dark Matter candidate particles complementing other approaches with neutrino beams, non-collider experiments and astrophysics experiments.

Motivation

The LHC has greatly advanced our understanding of matter and the Standard Model (SM). The discovery of the Higgs boson completed the particle content of the Standard Model of Particle Physics, the theory that describes the laws governing most of the known Universe. Yet the Standard Model cannot explain several observations, such as:

• evidence for dark matter,
• prevalence of matter over antimatter,
• the neutrino masses.

The LHC has inaugurated a new phase of detailed studies of the properties of the Higgs boson and the way in which it interacts with the other SM particles. Future colliders with a higher energy and collision rate will largely contribute in performing these measurements, deepening our understanding of the Standard Model processes, test its limits and search for possible deviations or new phenomena that could provide hints for new physics.

The Future Circular Collider (FCC) study develops options for potential high-energy frontier circular colliders at CERN for the post-LHC era. Among other things, it plans to look for dark matter particles, which account for approximately 25% of the energy in the observable universe. Though no experiment at colliders can probe the full range of dark matter (DM) masses allowed by astrophysical observations, there is a very broad class of models for weakly interacting massive particles (WIMPs) in the GeV – 10's of TeV mass scale, and which could be in the range of the FCC.

FCC could also lead the progress in precision measurements of Electroweak precision observables (EWPO). The measurements played a key role in the consolidation of the Standard Model and can guide future theoretical developments. Moreover, results from these measurements can inform data from astrophysical/cosmological observations. The improved precision offered by the FCC integrated programme increases the discovery potential for new physics.

Moreover, FCC-hh will enable the continuation of the research programme in ultrarelativistic heavy-ion collisions from RHIC and LHC. The higher energies and luminosities offered by FCC-hh when operating with heavy-ions will open new avenues in the study of the collective properties of quarks and gluons.

The FCC study also foresees an interaction point for electrons with protons (FCC-eh). These deep inelastic scattering measurements will resolve the parton structure with very high accuracy providing a per mille accurate measurement of the strong coupling constant. These results are essential for a programme of precision measurements and will further improve the sensitivity of search for new phenomena particularly at higher masses.

Five percent of the matter and energy Universe is directly observable. The Standard Model of Particle Physics describes it precisely. What about the remaining 95%?

Scope

The FCC study originally put an emphasis on proton-proton (hadron or heavy-ion) high-energy collider that could also house an electron/positron (ee) high-intensity frontier collider as a first step. However after assessing the readiness of the different technologies and the physics motivation the FCC collaboration came up with the so-called FCC integrated programme foreseen as a first step FCC-ee with an operation time of about 10 years at different energy ranges from 90 GeV to 350 GeV, followed by FCC-hh with an operation time of about 15 years.

The FCC collaboration has identified the technological advancements required for reaching the planned energy and intensity and performs technology feasibility assessments for critical elements of future circular colliders (i.e. high-field magnets, superconductors, Radio-frequency cavities cryogenic and vacuum system, power systems, beam screen system, a.o). The project needs to advance these technologies to meet the requirements of a post-LHC machine but also to ensure the large-scale applicability of these technologies that could lead to their further industrialization. The study also provides an analysis of the infrastructure and operation cost that could ensure the efficient and reliable operation of a future large-scale research infrastructure. Strategic R&D has been identified in the CDR over the coming years will concentrate on minimising construction costs and energy consumption, whilst maximising the socio-economic impact with a focus on benefits for industry and training.

Scientists and engineers are also working on the detector concepts needed to address the physics questions in each of the scenarios (hh, ee, he). The work programme includes experiment and detector concept studies to allow new physics to be explored. Detector technologies will be based on experiment concepts, the projected collider performances and the physics cases. New technologies have to be developed in diverse fields such as cryogenics, superconductivity, material science, and computer science, including new data processing and data management concepts.

Colliders

The FCC study developed and evaluated three accelerator concepts for its conceptual design report.

FCC-ee (electron/positron)

A lepton collider with centre-of-mass collision energies between 90 and 350 GeV is considered a potential intermediate step towards the realisation of the hadron facility. Clean experimental conditions have given e⁺e⁻ storage rings a strong record both for measuring known particles with the highest precision and for exploring the unknown.

More specifically, high luminosity and improved handling of lepton beams would create the opportunity to measure the properties of the Z, W, Higgs, and top particles, as well as the strong interaction, with increased accuracy.

It can search for new particles coupling to the Higgs and electroweak bosons up to scales of Λ = 7 and 100 TeV. Moreover, measurements of invisible or exotic decays of the Higgs and Z bosons would offer discovery potential for dark matter or heavy neutrinos with masses below 70 GeV. In effect, the FCC-ee could enable profound investigations of electroweak symmetry breaking and open a broad indirect search for new physics over several orders of magnitude in energy or couplings.

Realisation of an intensity-frontier lepton collider, FCC-ee, as a first step requires a preparatory phase of nearly 8 years, followed by the construction phase (all civil and technical infrastructure, machines and detectors including commissioning) lasting 10 years. A duration of 15 years is projected for the subsequent operation of the FCC-ee facility, to complete the currently envisaged physics programme. This makes a total of nearly 35 years for construction and operation of FCC-ee

FCC-hh (proton/proton and ion/ion)

A future energy-frontier hadron collider will be able to discover force carriers of new interactions up to masses of around 30 TeV if they exist. The higher collision energy extends the search range for dark matter particles well beyond the TeV region, while supersymmetric partners of quarks and gluons can be searched for at masses up to 15-20 TeV and the search for a possible substructure inside quarks can be extended down to distance scales of 10⁻²¹ m. Due to the higher energy and collision rate billions of Higgs bosons and trillions of top quarks will be produced, creating new opportunities for the study of rare decays and flavour physics.

A hadron collider will also extend the study of Higgs and gauge boson interactions to energies well above the TeV scale, providing a way to analyse in detail the mechanism underlying the breaking of the electroweak symmetry.

In heavy-ion collisions, the FCC-hh collider allows the exploration of the collective structure of matter at more extreme density and temperature conditions than before.

Finally, FCC-eh adds to the versatility of the research programme offered by this new facility. With the huge energy provided by the 50 TeV proton beam and the potential availability of an electron beam with energy of the order of 60 GeV, new horizons open up for the physics of deep inelastic scattering. The FCC-he collider would be both a high-precision Higgs factory and a powerful microscope that could discover new particles, study quark/gluon interactions, and examine possible further substructure of matter in the world.

In the FCC integrated scenario, the preparatory phase for an energy-frontier hadron collider, FCC-hh, will start in the first half of the FCC-ee operation phase. After the stop of FCC-ee operation, machine removal, limited civil engineering activities and an adaptation of the general technical infrastructure will take place, followed by FCC-hh machine and detector installation and commissioning, taking in total about 10 years. A duration of 25 years is projected for the subsequent operation of the FCC-hh facility, resulting in a total of 35 years for construction and operation of FCC-hh.

The staged implementation provides a time window of 25 – 30 years for R&D on key technologies for FCC-hh. This could allow alternative technologies to be considered e.g. high-temperature superconducting magnets, and should lead to improved parameters and reduced implementation risks, compared to immediate construction after HL-LHC.

High-Energy LHC

A high-energy hadron collider housed in the same tunnel but using new FCC-hh class 16T dipole magnets could extend the current energy frontier by almost a factor 2 (27 TeV collision energy) and delivers an integrated luminosity of at least a factor of 3 larger than the HL-LHC. This machine could offer a first measurement of the Higgs self-coupling and directly produce particles at significant rates at scales up to 12 TeV - almost doubling the HL-LHC discovery reach for new physics. The project reuses the existing LHC underground infrastructure and large parts of the injector chain at CERN.

It is assumed that HE-LHC will accommodate two high-luminosity interaction-points (IPs) 1 and 5, at the locations of the present ATLAS and CMS experiments while it could host two secondary experiments combined with injection as for the present LHC.

The HE-LHC could succeed the HL-LHC directly and provide a research programme of about 20 years beyond the middle of the 21st century.

Technologies

As the development of a next generation particle accelerator requires new technology the FCC study has studied the equipment and machines that are needed for the realization of the project, taking into account the experience from past and present accelerator projects.

The FCC study drives the research in the field of superconducting materials.

The foundations for these advancements are being laid in focused R&D programmes:

• a 16 tesla high-field accelerator magnet and related super-conductor research,
• a 100 MW radiofrequency acceleration system that can efficiently transfer power from the electricity grid to the beams,
• a highly efficient large-scale cryogenics infrastructure to cool down superconducting accelerator components and the accompanying refrigeration systems.

The CERN magnet group produced a 16.2 tesla peak field magnet – nearly twice that produced by the current LHC dipoles - paving the way for future more powerful accelerators.

 

New superconducting radiofrequency (RF) cavities are developed to accelerate particles to higher energies.

Numerous other technologies from various fields (accelerator physics, high-field magnets, cryogenics, vacuum, civil engineering, material science, superconductors, ...) are needed for reliable, sustainable and efficient operation.

Magnet technologies

High-field superconducting magnets are a key enabling technology for a frontier hadron collider. To steer a 50 TeV beam over a 100 km tunnel, 16 tesla dipoles will be necessary, twice the strength of the magnetic field of the LHC.

Evolution of superconducting niobium-titanium magnets for particle accelerator use.

The main objectives of a R&D on 16 T Nb₃Sn dipole magnets for a large particle accelerator are to prove that these types of magnets are feasible in accelerator quality and to ensure an adequate performance at an affordable cost. Therefore the goals are to push the conductor performance beyond present limits, to reduce the required "margin on the load line" with consequent reduction of conductor use and magnet size and the elaboration of an optimized magnet design maximizing performance with respect to cost.

The magnet R&D aims to extend the range of operation of accelerator magnets based on low-temperature superconductors (LTS) up to 16 T and explore the technological challenges inherent to the use of high-temperature superconductors (HTS) for accelerator magnets in the 20 T range.

Superconducting radiofrequency cavities

The beams that move in a circular accelerator lose a percentage of their energy due to synchrotron radiation: up to 5% every turn for electrons and positrons, much less for protons and heavy ions. To maintain their energy, a system of radiofrequency cavities constantly provides up to 50 MW to each beam. The FCC study has launched dedicated R&D lines on novel superconducting thin-film coating technology will allow RF cavities to be operated at higher temperature (CERN, Courier, April 2018),^[21][22] thereby lowering the electrical requirement for cryogenics, and reduce the required number of cavities thanks to an increase in the accelerating gradient. An ongoing R&D activity, carried out in close cooperation with the linear collider community, aims at raising the peak efficiency of klystrons from 65% to above 80%. Higher-temperature high-gradient Nb-Cu accelerating cavities and highly-efficient RF power sources could find numerous applications in other fields.

Cryogenics

Liquefaction of gas is a power-intensive operation of cryogenic technology. The future lepton and hadron colliders would make intensive use of low-temperature superconducting devices, operated at 4.5 K and 1.8 K, requiring very large-scale distribution, recovery, and storage of cryogenic fluids.

Improving refrigeration cycle efficiency from 33% to 45% leads to 20% reduced cost and power.

As a result, the cryogenic systems that have to be developed correspond to two to four times the presently deployed systems and require increased availability and maximum energy efficiency. Any further improvements in cryogenics are expected to find wide applications in medical imaging techniques.

The cryogenic beam vacuum system for an energy-frontier hadron collider must absorb an energy of 50 W per meter at cryogenic temperatures. To protect the magnet cold bore from the head load, the vacuum system needs to be resistant against electron cloud effects, highly robust, and stable under superconducting quench conditions.

It should also allow fast feedback in the presence of impedance effects. New composite materials have to be developed to achieve these unique thermo-mechanical and electric properties for collimation systems. Such materials could also be complemented with the ongoing exploration of thin-film NEG coating that is used in the internal surface of the copper vacuum chambers.

Collimation

A 100 TeV hadron collider requires efficient and robust collimators, as 100 kW of hadronic background is expected at the interaction points. Moreover, fast self-adapting control systems with sub-millimeter collimation gaps are necessary to prevent irreversible damage of the machine and manage the 8.3 GJ stored in each beam.

To address these challenges, the FCC study searches for designs that can withstand the large energy loads with acceptable transient deformation and no permanent damage. Novel composites with improved thermo-mechanical and electric properties will be investigated in cooperation with the FP7 HiLumi LHC DS and EuCARD2 programmes.

Timescale

The Large Hadron Collider at CERN with its High Luminosity upgrade is the world’s largest and most powerful particle accelerator and is expected to operate until 2036. A number of different proposals for a post-LHC research infrastructure in particle physics have been launched, including both linear and circular machines.

The FCC study explores scenarios for different circular particle colliders housed in a new 100 km circumference tunnel, building on the tradition of the LEP and LHC, which are both housed in the same 27 km circumference tunnel. A time-frame of 30 years is appropriate for the design and construction of a large accelerator complex and particle detectors.

The experience from the operation of LEP and LHC and the opportunity to test novel technologies in the High Luminosity LHC provide a basis for assessing the feasibility of a post-LHC particle accelerator. In 2018, the FCC collaboration published the four volume Conceptual Design Report (CDR) as input to the next European Strategy for Particle Physics. The four volumes focus on: (a) "Vol. 1 Physics Opportunities"; (b) "Vol. 2 FCC-ee: The lepton collider"; (c) "Vol. 3 FCC-hh: The hadron collider"; and (d) "Vol. 4 The High-Energy LHC".

The significant lead time of approximately twenty years for the design and construction of a large-scale accelerator calls for a coordinated effort.

Organisation

The FCC study, hosted by CERN is an international collaboration of 135 research institutes and universities and 25 industrial partners from all over the world.

The FCC study was launched following a response to the recommendation made in the update of the European Strategy for Particle Physics 2013, adopted by CERN's council. The study is governed by three bodies: the International Collaboration Board (ICB), the International Steering Committee (ISC), and the International Advisory Committee (IAC).

The organization of the FCC Study

The ICB reviews the resource needs of the study and finds matches within the collaboration. It so channels the contributions from the participants of the collaboration aiming at a geographically well-balanced and topically complementary network of contributions. The ISC is the supervisory and main governing body for the execution of the study and acts on behalf of the collaboration.

The ISC is responsible for the proper execution and implementation of the decisions of the ICB, deriving and formulating the strategic scope, individual goals and the work programme of the study. Its work is facilitated by the Coordination Group, the main executive body of the project, which coordinates the individual work packages and performs the day-to-day management of the study.

Finally, the IAC reviews the scientific and technical progress of the study and shall submit scientific and technical recommendations to the International Steering Committee to assist and facilitate major technical decisions.

Criticism

The FCC's proposed particle accelerator has been criticized for costs, with the cost for the energy-frontier hadron collider (FCC-hh) variant of this project projected to be over 20 billion US dollars. Its potential to make new discoveries has also been questioned by physicists. Theoretical physicist Sabine Hossenfelder criticized a relevant promotional video for outlining a wide range of open problems in physics, despite the fact that the accelerator will likely only have the potential to resolve a small part of them. She noted that (as of 2019) there is "no reason that the new physical effects, like particles making up dark matter, must be accessible at the next larger collider".

Response to this criticism came both from the physics community as well as from philosopher and historians of science who emphasized the exploratory potential of any future large-scale collider. A detailed physics discussion is included in the first volume of the FCC Conceptual Design Report. Gian Giudice, Head of CERN's Physics Department wrote a paper on the "Future of High-Energy Colliders" while other commentary came from Jeremy Bernstein, Lisa Randall, James Beacham, Harry Cliff and Tommaso Dorigo among others. In a recent interview theorist for the CERN Courier, Nima Arkani-Hamed described the concrete experimental goal for a post-LHC collider: "While there is absolutely no guarantee we will produce new particles, we will definitely stress test our existing laws in the most extreme environments we have ever probed. Measuring the properties of the Higgs, however, is guaranteed to answer some burning questions. [...] A Higgs factory will decisively answer this question via precision measurements of the coupling of the Higgs to a slew of other particles in a very clean experimental environment." Moreover there has been some philosophical responses to this debate, most notably one from Michela Massimi who emphasised the exploratory potential of future colliders: "High-energy physics beautifully exemplifies a different way of thinking about progress, where progress is measured by ruling out live possibilities, by excluding with high confidence level (95%) certain physically conceivable scenarios and mapping in this way the space of what might be objectively possible in nature. 99.9% of the time this is how physics progresses and in the remaining time someone gets a Nobel Prize for discovering a new particle."

Studies for linear colliders

A high-luminosity upgrade of the LHC [HL-LHC] has been approved to extend its operation lifetime into the mid-2030s. The upgrade will facilitate the detection of rare processes and improve statistical measurements.

The Future Circular Collider study complements previous studies for linear colliders. The Compact Linear Collider (CLIC) was launched in 1985 at CERN. CLIC examines the feasibility of a high-energy (up to 3 TeV), high-luminosity lepton (electron/positron) collider.

The International Linear Collider is a similar to CLIC project, planned to have a collision energy of 500 GeV. It presented its Technical Design Report in 2013. In 2013, the two studies formed an organisational partnership, the Linear Collider Collaboration (LCC) to coordinate and advance the global development work for a linear collider.