Engineering solutions for the electro-polishing of multi-cell superconducting accelerator structures

Abstract

Due to surface treatment with electro-polishing superconducting niobium resonators can potentially reach accelerating gradients well beyond 35 MV/m at a frequency of 1.3 GHz. The anticipated gradient for the 500 GeV version of the TESLA collider is 23.4 MV/m. In view of the extendibility of the collider towards higher energies this technology is therefore of great importance for the TESLA project. In this paper the engineering aspects of the planned electro-polishing facility at DESY are discussed. The facility will allow for the treatment of single cell cavities as well as the standard TESLA 9-cell structure, and also a so-called superstructure that consists of 2 x 9 cells. The issues described cover the acid circulation including cooling requirements, the required current densities resulting in the specifications of the electrical circuit, removal of oxyhydrogen gas, rotating feed-through and the overall mechanical layout. Furthermore, recent tests of critical components are reported.