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Going straight
04 May 2002
From New Scientist Print Edition.
Eugenie Samuel

A gigantic electron gun resembling a television tube dozens of kilometres long could take particle physics to a new level and spell the end for some of today's circular colliders.

Linear colliders, which accelerate particles in a straight line, fell out of favour several decades ago. The need to reach ever higher energies would have meant building unfeasibly long and expensive accelerators.

So physicists turned to circular accelerators such as the Large Electron Positron (LEP) collider at CERN in Geneva, which has a circumference of 27 kilometres. These can accelerate particles to successively higher energies on each circuit.

But circular accelerators have disadvantages too. Bending a beam of electrons or positrons causes it to emit radiation, and this loss ultimately limits the energy these accelerators can reach.

Now the tide has turned again. Particle physicists are drafting proposals for their next big accelerator, called the Next Linear Collider (NLC), in which beams of electrons and positrons will collide head-on at 500 gigaelectronvolts (5×1011eV).

Chris Adolphsen, an NLC supporter at the Stanford Linear Accelerator (SLAC) in California, told last week's American Physical Society meeting in Albuquerque, New Mexico, that it should be possible to reach this energy over only a few dozen kilometres by increasing the strength of the electric fields used to accelerate particles. This has not been possible in the past because very strong fields tended to rip electrons out of the walls of the machine, causing damaging sparks.

Now researchers at the German Electron-Synchrotron research centre (DESY) in Hamburg have found that by heat treating to drive off impurities, and carefully cleaning the surface of a prototype device's walls, they could safely use fields four times as strong as those reached at SLAC.

From issue 2341 of New Scientist magazine, 04 May 2002, page 8

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