International Linear Collider
Encyclopedia
The International Linear Collider (ILC) is a proposed linear particle accelerator
. It is planned to have a collision energy
of 500 GeV
initially, and, if approved after the project has published its Technical Design Report, planned for 2012, could be completed in the late 2010s. A later upgrade to 1000 GeV (1 TeV) is possible. The host country for the accelerator has not yet been chosen. Studies for a competing project called CLIC
the Compact Linear Collider are also underway. It potentially has significantly higher energies (3 to 5 TeV) in a shorter-length machine than the ILC. Research for CLIC
is in progress to demonstrate the feasibility of some of the technologies in the year 2010 to allow a decision to fund the project afterwards. It seems unlikely that both CLIC
and ILC machines will be built.
The ILC would collide electron
s with positron
s. It will be between 30 km and 50 km (19–31 mi.) long, more than 10 times as long as the 50 GeV Stanford Linear Accelerator, the longest existing linear particle accelerator. The proposal was previously known by various names in different regions; see below.
s along a straight path. Circular accelerators, such as the Tevatron
, the LEP, and the Large Hadron Collider
(LHC), use circular paths. Circular geometry has significant advantages at energies up to and including tens of GeV
: With a circular design, particle
s can be effectively accelerated over longer distances. Also, only a fraction of the particles brought onto a collision course actually collide. In a linear accelerator, the remaining particles are lost; in a ring accelerator, they keep circulating and are available for future collisions. The disadvantage of circular accelerators is that particles moving along bent paths will necessarily emit electromagnetic radiation known as synchrotron radiation
. Energy loss through synchrotron radiation is inversely proportional to the fourth power of the mass of the particles in question. That is why it makes sense to build circular accelerators for heavy particles—hadron colliders such as the LHC for proton
s or, alternatively, for lead
nuclei
. An electron-positron collider of the same size would never be able to achieve the same collision energies. In fact, energies at the LEP
, which used to occupy the tunnel now given over to the LHC, were limited to 209GeV by energy loss via synchrotron radiation.
Even if the effective collision energy at the LHC will be higher than the ILC collision energy (14,000 GeV
for the LHC vs. ~500 GeV for the ILC), measurements could be made more accurately at the ILC. Collisions between electrons and positrons are much simpler to analyze than collisions in which the energy is distributed among the constituent quark
s, antiquarks and gluon
s of baryon
ic particles. As such, one of the roles of the ILC would be making precision measurements of the properties of particles discovered at the LHC.
will be detected by experiments at the proposed ILC. In addition, particles and interactions described by the Standard Model are expected to be discovered and measured. At the ILC physicists hope to be able to:
To achieve these goals, new generation particle detectors are necessary.
technology for the accelerator. After this decision the three existing linear collider projects – the Next Linear Collider (NLC), the Global Linear Collider (GLC) and Teraelectronvolt Energy Superconducting Linear Accelerator (TESLA) – joined their efforts into one single project (the ILC). Physicists are now working on the detailed design of the accelerator. Steps ahead include obtaining funding for the accelerator, and choosing a site. In August 2007, the Reference Design Report for the ILC was released.
In March 2005, the International Committee for Future Accelerators (ICFA) announced the appointment of Dr. Barry Barish as the Director of the Global Design Effort
. Barry Barish was director of the LIGO
Laboratory at Caltech from 1997 to 2005.
light pulses to eject electrons from a photocathode
, a technique allowing for up to 80% of the electrons to be polarized; the electrons then will be accelerated to 5 GeV in a 250-meter linac stage. Synchrotron radiation from high energy electrons will produce electron-positron pairs on a titanium-alloy target, with as much as 60% polarization; the positrons from these collisions will be collected and accelerated to 5 GeV in a separate linac.
To compact the 5 GeV electron and positron bunches to a sufficiently small size to be usefully collided, they will circulate for 0.3 seconds in a pair of damping rings, 7 km in circumference, in which they will be reduced in size to a few mm in length and less than 100 μm
diameter.
From the damping rings the particle bunches will be sent to the superconducting radio frequency
main linacs, each 12 km long, where they will be accelerated to 250 GeV. At this energy each beam will have an average power of about 10 megawatts
. Five bunch trains will be produced and accelerated per second.
To maintain a sufficient luminosity to produce results in a reasonable time frame after acceleration the bunches will be focused to a few nm
in height and a few hundred nm in width. The focused bunches then will be collided inside one of two large particle detector
s.
in Geneva the tunnel is located deep underground in non-permeable bedrock. This site is considered favorable for a number of practical reasons but due to the LHC
the site is disfavored. At DESY
in Hamburg the tunnel is close to the surface in water saturated soil. Germany leads Europe for scientific funding and is therefore considered reliable in terms of funding. At JINR in Dubna
the tunnel is close to the surface in non-permeable soil. Dubna
has a pre-accelerator complex which could be easily adapted for the needs for the ILC. But all three are more or less well suited for housing a Linear Collider and one has ample choice for a site selection process in Europe.
Outside Europe a number of countries have expressed interest. Japan presently receives a large amount of funding for the neutrino activities, such as the T2K experiment, so it is disfavored. Although, 20 huge caverns with access tunnels have already been constructed in Japan for hydroelectric power plants (eg the Kannagawa Hydropower Plant
). With the impending closure of the Tevatron
some groups within the USA have expressed interest, with Fermilab
being a favored site because of the facilities and manpower already present. Much of the speculated interest from other countries is hearsay from within the scientific community and very few facts have been published officially. The information presented above is a summary of that contained in the International Workshop on Linear Colliders 2010 (ECFA-CLIC-ILC Joint Meeting) at CERN.
6.75 billion
. From formal project approval, completion of the accelerator complex and detectors is expected to require seven years. The host country would be required to pay $1.8 billion for site-specific costs like digging tunnels and shafts and supplying water and electricity.
U.S. Secretary of Energy Steven Chu
estimates the total cost to be US$25 billion. ILC Director Barish says this is likely to be an overestimate. Other Department of Energy officials have estimated a $20 billion total.
Linear particle accelerator
A linear particle accelerator is a type of particle accelerator that greatly increases the velocity of charged subatomic particles or ions by subjecting the charged particles to a series of oscillating electric potentials along a linear beamline; this method of particle acceleration was invented...
. It is planned to have a collision energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
of 500 GeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
initially, and, if approved after the project has published its Technical Design Report, planned for 2012, could be completed in the late 2010s. A later upgrade to 1000 GeV (1 TeV) is possible. The host country for the accelerator has not yet been chosen. Studies for a competing project called CLIC
Compact Linear Collider
The Compact Linear Collider is a proposed linear particle accelerator under design at CERN. CLIC is separate from the International Linear Collider project, and differs from it using normal conducting cavities to achieve a higher planned energy of several TeV.Currently research is in progress to...
the Compact Linear Collider are also underway. It potentially has significantly higher energies (3 to 5 TeV) in a shorter-length machine than the ILC. Research for CLIC
Compact Linear Collider
The Compact Linear Collider is a proposed linear particle accelerator under design at CERN. CLIC is separate from the International Linear Collider project, and differs from it using normal conducting cavities to achieve a higher planned energy of several TeV.Currently research is in progress to...
is in progress to demonstrate the feasibility of some of the technologies in the year 2010 to allow a decision to fund the project afterwards. It seems unlikely that both CLIC
Compact Linear Collider
The Compact Linear Collider is a proposed linear particle accelerator under design at CERN. CLIC is separate from the International Linear Collider project, and differs from it using normal conducting cavities to achieve a higher planned energy of several TeV.Currently research is in progress to...
and ILC machines will be built.
The ILC would collide electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s with positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
s. It will be between 30 km and 50 km (19–31 mi.) long, more than 10 times as long as the 50 GeV Stanford Linear Accelerator, the longest existing linear particle accelerator. The proposal was previously known by various names in different regions; see below.
Comparison with LHC
There are two basic shapes of accelerators. Linear accelerators ("linacs") accelerate elementary particleElementary particle
In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...
s along a straight path. Circular accelerators, such as the Tevatron
Tevatron
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
, the LEP, and the Large Hadron Collider
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
(LHC), use circular paths. Circular geometry has significant advantages at energies up to and including tens of GeV
GEV
GEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
: With a circular design, particle
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
s can be effectively accelerated over longer distances. Also, only a fraction of the particles brought onto a collision course actually collide. In a linear accelerator, the remaining particles are lost; in a ring accelerator, they keep circulating and are available for future collisions. The disadvantage of circular accelerators is that particles moving along bent paths will necessarily emit electromagnetic radiation known as synchrotron radiation
Synchrotron radiation
The electromagnetic radiation emitted when charged particles are accelerated radially is called synchrotron radiation. It is produced in synchrotrons using bending magnets, undulators and/or wigglers...
. Energy loss through synchrotron radiation is inversely proportional to the fourth power of the mass of the particles in question. That is why it makes sense to build circular accelerators for heavy particles—hadron colliders such as the LHC for proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s or, alternatively, for lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
. An electron-positron collider of the same size would never be able to achieve the same collision energies. In fact, energies at the LEP
Large Electron-Positron Collider
The Large Electron–Positron Collider was one of the largest particle accelerators ever constructed.It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP was a circular collider with a circumference of 27 kilometres built in a...
, which used to occupy the tunnel now given over to the LHC, were limited to 209GeV by energy loss via synchrotron radiation.
Even if the effective collision energy at the LHC will be higher than the ILC collision energy (14,000 GeV
GEV
GEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
for the LHC vs. ~500 GeV for the ILC), measurements could be made more accurately at the ILC. Collisions between electrons and positrons are much simpler to analyze than collisions in which the energy is distributed among the constituent quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s, antiquarks and gluon
Gluon
Gluons are elementary particles which act as the exchange particles for the color force between quarks, analogous to the exchange of photons in the electromagnetic force between two charged particles....
s of baryon
Baryon
A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...
ic particles. As such, one of the roles of the ILC would be making precision measurements of the properties of particles discovered at the LHC.
ILC physics and detectors
It is widely expected that effects of physics beyond that described in the current Standard ModelStandard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
will be detected by experiments at the proposed ILC. In addition, particles and interactions described by the Standard Model are expected to be discovered and measured. At the ILC physicists hope to be able to:
- Measure the mass, spin, and interaction strengths of the Higgs bosonHiggs bosonThe Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. Its existence is postulated as a means of resolving inconsistencies in the Standard Model...
- If existing, measure the number, size, and shape of any TeVElectronvoltIn physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
-scale extra dimensions - Investigate the lightest supersymmetricSupersymmetryIn particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners...
particles, possible candidates for dark matterDark matterIn astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
To achieve these goals, new generation particle detectors are necessary.
Merging of regional proposals into a worldwide project
In August 2004, the International Technology Recommendation Panel (ITRP) recommended a superconducting radio frequencySuperconducting Radio Frequency
Superconducting Radio Frequency science and technology involves the application of electrical superconductors to radio frequency devices. The ultra-low electrical resistivity of a superconducting material allows an RF resonator to obtain an extremely high quality factor, Q...
technology for the accelerator. After this decision the three existing linear collider projects – the Next Linear Collider (NLC), the Global Linear Collider (GLC) and Teraelectronvolt Energy Superconducting Linear Accelerator (TESLA) – joined their efforts into one single project (the ILC). Physicists are now working on the detailed design of the accelerator. Steps ahead include obtaining funding for the accelerator, and choosing a site. In August 2007, the Reference Design Report for the ILC was released.
In March 2005, the International Committee for Future Accelerators (ICFA) announced the appointment of Dr. Barry Barish as the Director of the Global Design Effort
Global Design Effort
The Global Design Effort is an international team tasked with designing the International Linear Collider , a particle accelerator to succeed current machines such as the Large Hadron Collider and the Stanford Linear Accelerator...
. Barry Barish was director of the LIGO
LIGO
LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT,...
Laboratory at Caltech from 1997 to 2005.
Design
The electron source for the ILC will use 2-nanosecond laserLaser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
light pulses to eject electrons from a photocathode
Photocathode
A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...
, a technique allowing for up to 80% of the electrons to be polarized; the electrons then will be accelerated to 5 GeV in a 250-meter linac stage. Synchrotron radiation from high energy electrons will produce electron-positron pairs on a titanium-alloy target, with as much as 60% polarization; the positrons from these collisions will be collected and accelerated to 5 GeV in a separate linac.
To compact the 5 GeV electron and positron bunches to a sufficiently small size to be usefully collided, they will circulate for 0.3 seconds in a pair of damping rings, 7 km in circumference, in which they will be reduced in size to a few mm in length and less than 100 μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
diameter.
From the damping rings the particle bunches will be sent to the superconducting radio frequency
Superconducting Radio Frequency
Superconducting Radio Frequency science and technology involves the application of electrical superconductors to radio frequency devices. The ultra-low electrical resistivity of a superconducting material allows an RF resonator to obtain an extremely high quality factor, Q...
main linacs, each 12 km long, where they will be accelerated to 250 GeV. At this energy each beam will have an average power of about 10 megawatts
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
. Five bunch trains will be produced and accelerated per second.
To maintain a sufficient luminosity to produce results in a reasonable time frame after acceleration the bunches will be focused to a few nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
in height and a few hundred nm in width. The focused bunches then will be collided inside one of two large particle detector
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
s.
Proposed sites
Presently three sites for the International Linear Collider are leading contenders at established High Energy Physics center in Europe. At CERNCERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
in Geneva the tunnel is located deep underground in non-permeable bedrock. This site is considered favorable for a number of practical reasons but due to the LHC
LHC
LHC may refer to:* Large Hadron Collider, a particle accelerator and collider located on the Franco-Swiss border near Geneva, SwitzerlandLHC also may refer to:* La hora Chanante, a Spanish comedy television show...
the site is disfavored. At DESY
DESY
The DESY is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen....
in Hamburg the tunnel is close to the surface in water saturated soil. Germany leads Europe for scientific funding and is therefore considered reliable in terms of funding. At JINR in Dubna
Dubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
the tunnel is close to the surface in non-permeable soil. Dubna
Dubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
has a pre-accelerator complex which could be easily adapted for the needs for the ILC. But all three are more or less well suited for housing a Linear Collider and one has ample choice for a site selection process in Europe.
Outside Europe a number of countries have expressed interest. Japan presently receives a large amount of funding for the neutrino activities, such as the T2K experiment, so it is disfavored. Although, 20 huge caverns with access tunnels have already been constructed in Japan for hydroelectric power plants (eg the Kannagawa Hydropower Plant
Kannagawa Hydropower Plant
The Kannagawa Hydropower Plant is an under construction pumped-storage hydroelectric power plant near Minamiaiki in Nagano Prefecture and Gunma Prefecture, Japan. The power plant utilizes the Minamiaiki River along with an upper and lower reservoir created by two dams, the upper Minamiaiki Dam and...
). With the impending closure of the Tevatron
Tevatron
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
some groups within the USA have expressed interest, with Fermilab
Fermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
being a favored site because of the facilities and manpower already present. Much of the speculated interest from other countries is hearsay from within the scientific community and very few facts have been published officially. The information presented above is a summary of that contained in the International Workshop on Linear Colliders 2010 (ECFA-CLIC-ILC Joint Meeting) at CERN.
Cost and time estimates
The Draft Reference Design Report estimates the cost of building the ILC, excluding R&D, prototyping, land acquisition, underground easement costs, detectors, contingencies, and inflation, at US$United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
6.75 billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
. From formal project approval, completion of the accelerator complex and detectors is expected to require seven years. The host country would be required to pay $1.8 billion for site-specific costs like digging tunnels and shafts and supplying water and electricity.
U.S. Secretary of Energy Steven Chu
Steven Chu
Steven Chu is an American physicist and the 12th United States Secretary of Energy. Chu is known for his research at Bell Labs in cooling and trapping of atoms with laser light, which won him the Nobel Prize in Physics in 1997, along with his scientific colleagues Claude Cohen-Tannoudji and...
estimates the total cost to be US$25 billion. ILC Director Barish says this is likely to be an overestimate. Other Department of Energy officials have estimated a $20 billion total.
External links
- International Linear Collider Website
- ILC NewsLine
- Karl Van Bibber about the NLC
- In symmetry magazine:
- Special issue, August 2005
- "out of the box: designing the ILC", March 2006
- New York Times article
- Science Magazine article
- Scientific American article preview
- 1600 International Linear Collider Article