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This article or section contains information about an expected future scientific facility. It is likely to contain information of a speculative nature and the content may change as the facility approaches completion.

The International Linear Collider (ILC) is a proposed linear particle accelerator. It is planned to have a collision energy of 500 GeV initially, and to be completed in the late 2010s.^[1] A later upgrade to 1000 GeV is possible. As of November 2007, the host country of the accelerator has not been chosen.

It will collide electrons with positrons. It will be between 30 km and 40 km 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.

Contents 1 Comparison with LHC 2 ILC physics 3 Merging of regional proposals into a worldwide project 4 Design 5 Cost and time estimates 6 Notes 7 External links

There are two basic shapes of accelerators. Linear accelerators ("linacs"), such as the accelerator in SLAC and the ILC, accelerate the elementary particles along a straight path. Circular accelerators, such as Tevatron, LEP, and Large Hadron Collider (LHC), use a circular orbit. The circular geometry, in which counterrotating particle and antiparticle beams can be accelerated and collide multiple times, is preferred for hadron colliders, but is impractical for electron accelerators at the ILC energy scale, due to synchrotron radiation losses.

The ILC will have a lower energy than the LHC, which is due to be completed earlier, in 2008. The total collision energy of the protons at the LHC will be 14 TeV. However, the effective collision energy at the LHC will be lower than this, since the actual collisions happen between the quarks, antiquarks and gluons which compose the protons. The energy of the protons is shared amongst these particles so each individual collision has a lower energy. Even so, a typical collision at the LHC will still have a higher energy than the ILC collision energy, but measurements can be made more accurately at the ILC since a collision between an electron and a positron is much simpler than a collision between many quarks, antiquarks and gluons. Hence it is anticipated that the ILC will be used to make precision measurements of the properties of particles discovered at the LHC.

Thus the data provided by the LHC and the ILC are complementary.

It is widely expected that effects of physics beyond that described in the current Standard Model will be detected by experiments at the LHC and 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 interactions strengths of the Higgs boson
• If existing, measure the number, size, and shape of any TeV-scale extra dimensions
• Investigate the lightest supersymmetric particles, possible candidates for dark matter

In August 2004, the International Technology Recommendation Panel (ITRP) recommended a superconducting 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. On 8 February 2007 the Draft Reference Design Report for the ILC was released.^[2]

In March of 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 previously head of the ITRP.

The electron source for the ILC will use 2-nanosecond laser 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 0.2 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 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.

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 two large particle detectors.

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$6.65 billion.^{[citation needed]} 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.

1. ^ ILC Design Summary Document. ILC web site (8 February 2007). Retrieved on 2007-02-09. (PDF)
2. ^ ILC Draft Reference Design Report. ILC web site (8 February 2007). Retrieved on 2007-02-09. (PDF)

• International Linear Collider Website
• 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