The Global Linear Collider

The Global Linear Collider is a proposal made by Japanese particle physicists with colleagues from other Asian countries to build a new leptonic collider in Japan. This leptonic collider would be a very important complement to the LHC.

A new kind of linear collider

Usually particle colliders (both leptonic and hadronic) are circular. This allow the particles to be accelerated over many turns and the reduces the required acceleration capability of the collider. Unfortunately electrons produces some radiations when they turn (this radiation is called synchrotron radiation) and thus loose part of there energy. The faster they go, the more energy they loose. There is a point where they loose as much energy as they receive in a turn and thus it is not possible to accelerate them further. To go beyond that energy limit, the collider must be straight. But in a linear (straight) collider, it is not possible to have the electrons passing many times in the same accelerating device, thus the collider must be long enough to reach high energy. To reach the energy required to reach new theories, a length of the order of 30 km is needed! Building such new kind of particle accelerator is not an easy task and many studies need to be done beforehand.

A challenging R\&D program

One of the first Linear particle accelerator has been established in France near Paris on the Orsay University campus in the 1950s. More recently a Linear Collider was built on the Stanford University premises. This collider has shown some of the challenging technical difficulties ahead the construction of the GLC. %http://www.ressac.org/mediath/e1_0.html

Producing electrons and positrons at a high rate

Producing and accelerating electrons is a very well-known task (for example old TV with a cathodic tube contain a small electron accelerator) but the quantities usually produced are very small compared to to amounts needed by the GLC thus it is necessary to develop a new method to produce the electrons and positrons required by the GLC.

Reaching a high acceleration gradient at very high frequency

Once the electrons (and positrons) are produced, they must be accelerated up to almost the speed of light. To reach such speed within the length of the GLC huge accelerating electric fields must be created, but when such fields are created they often produce a spark and an electric discharge. Furthermore these electric fields must be produced at very high frequency (of the order of the Gigahertz). Studies are ongoing to design accelerating structures that can accept such high electric fields at very high frequency without breaking down.

Delivering enough power

The generation of high electric fields at very high frequency requires the delivery of a tremendous amount of electric power within a few hundreds of nanoseconds. This has never been done so far but physicists are actively working on it.

Site studies

The location where the linear collider will be built must also be chosen carefully. It must be close enough from a power plant producing the energy required. As it will be an international research facility, it can not be in a desert far from major roads, cities and airports. But being too close from a major road can also harm the accelerator as the road would generate vibrations that could misalign the various components used. Many possible locations in Japan have been reviewed and 12 are still considered as a potential host candidate. Further studies must be done to choose the best of these 12 candidates.

Facilities

Building a 30~km long tunnel is not an easy task. It can be compared to the longest underwater tunnel built in Japan and Europe. This also requires planning.

Detector

The particles that will be produced by the GLC will be much too small to be seen even with an electronic microscope. Thus, like for the previous accelerators, detecting devices must be built to detect these particles. Although most of the technologies to be used have already been used in the past, a lot of work is required to design the detector that will produce the results interesting particle physicists.

Similar projects

Two other projects similar to the GLC have been proposed, one in Germany known as TESLA (Tev-Energy Superconducting LInear Accelerator) and the other in the United States known as NLC (Next Linear Collider). The NLC uses a technologies very close from the GLC whereas TESLA has chosen a novel approach in particle accelerator design with superconducting cavities. As these projects will be very expensive (of the order of 5 billions Euros), only one of the three project will finally be built.

Schedules

A first choice is expected to take place in 2004 to decide which technology can better answer the needs of the particle physicists. The construction of the Linear collider should start around 2007 and the first collisions are expected to be recorded around 2015.
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Last modified: "Sep 16 2003"
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