Superconductivity, Cryogenics, and Vacuum Technology for Linear Accelerators*

The conventional, 10 -8 ’ Torr-range, ion-pumped vacuum system of the SLAC 3.2~km linear accelerator is briefly described, along with typical performance data. Since polarized electron sources are of increasing importance to high-energy research, the necessary physical environments for such sources is given, and differential pumping and/or isolation systems capable of maintaining those conditions while protecting both source and accelerator are discussed. The development of microwave superconducting linear accelerators is summarized. Emphasis is on vacuum and materials processing techniques necessary to the maintenance of low surface resistance and high electric and magnetic fields. Problems remaining and prospects for their solution are briefly described, along with details of the physical processes taking place at the vacuum-metal interface. *Work supported by the U. S. Atomic. Energy Commission. . 1. Accelerator Vacuum System The vacuum system for the 3.2~km Stanford Linear Accelerator has been , described in detail elsewhere, 192) so only a brief summary will be given here. The cross-section of the linear accelerator housing and klystron gallery is shown in Fig. 1. The gauges, pumps, and all valves except for in-line valves