A New Superconducting Heavy Ion Accelerating Structure Using Chemically Polished Lead Surfaces

A new heavy ion accelerating structure has been developed which together with a parallel development in chemical polishing techniques makes possible very high accelerating fields for a wide range of particle velocities using inexpensive and easily handled materials. This "Split Ring" accelerating structure has a peak magnetic field approximately one third that of other inductively loaded accelerating structures (less than 10OG at 1MV/m accelerating field) and a peak electric field less than 6 times the effective accelerating field. In addition, a chemical polishing technique appropriate for use on electroplated lead surfaces has been developed which greatly reduces the electric field emission of electrons from the surface. Surface fields greater than 25MV/m have been obtained in superconducting resonators with polished lead surfaces with no detectable loss due to field emission. Using these techniques, we have achieved an accelerating field greater than 4 MV/m in a superconducting structure and have begun long term tests. Preliminary results indicate no surface degradation at high fields (> 3MV/m) for relatively long times (14 hours).