RF-Tests on Deflecting Cavities for a Superconductinig Particle Separator

Abstract

A superconducting S-band RF particle separator is under construction which will be used at the CERN 300 GeV proton synchrotron. It is foreseen to separate particles up to at least 30 GeV/c momentum. We give a summary of quality factors-(Q) and peak magnetic field (Hp) measurements on several test-deflectors. A sequence of surface treatments including electropolishing, anodizing and an UHV-annealing around 1850°C allowed us to obtain in a reliable way Q- and Hp-values well above our minimum requirements (5×108 and 310 Oe respectively). The highest values hitherto obtained for the (high-field) Q and Hp are 4.3×109 and 510 Oe corresponding to a mean deflecting field of 3.3 MV/m. The effect of repeated cooling cycles under vacuum and exposure to clean air or methanol was found not to be critical for our range of Q and Hp. The surface resistance depends linearly on an external dcmagnetic field whereas the dependence on the RF field level is much more complicated. With our surface treatment and our deflecting modes multipacting presents no problem. Breakdowns are nearly always caused by magnetic fields. The frequency tuners foreseen are described. Fine and coarse tuning will be done by separated tuners. They have been tested successfully up to Q-values of 109 and peak fields of 390 Oe. Finally a computer program has been written allowing the calculation of multiperiodic deflector modes. An exemple is shown and compared with a π-mode for uniform periodic structures.