VACUUM PROBLEMS IN PARTICLE ACCELERATORS DUE TO INTERACTION OF SYNCHROTRON RADIATION, ELECTRONS AND IONS WITH SURFACES

In high energy particle accelerators where bunches of electrons, positrons and protons are accelerated to energies in the GeV range, and in the near future up to many TeV for protons in the LHC and SSC projects, the pressure requirements are typically in the 10(-10) torr range. However, in operation, the walls of the vacuum system are subjected to bombardment by electrons, ions and/or photons which desorb tightly bound gas and results in large pressure increases detrimental to the operation of the accelerator. Another complication is that the vacuum chamber may be at a temperature of about 10 K. Cryopumping surfaces which are initially beneficial finally turn out to introduce several liabilities-for example, only a few monolayers of cryopumped H-2 already has a vapour pressure at 10 K well in excess of 10(-6) torr. These and other effects will be described in detail along with the methods used to deal with them.