DRY ICE CLEANING FOR SRF APPLICATIONS

Dry ice cleaning using the sublimation-impulse method removes particulate and film contaminations without any residues. The gases involved in this process, i.e. CO 2 and N2, are chemically inert, thus no negative impact on materials like niobium, copper, alumina etc. used in a superconducting (s.c.) accelerator is expected. As high gradients in s.c. cavities require surfaces free of enhanced field emission, the dry-ice cleaning process was applied to a series of intentionally and defined contaminated niobium samples. The cleaning effect was investigated by means of a dc field emission scanning microscope and an optical microscope, comparing the onset fields and number of emitters as well as the number of particles before and after the cleaning process. A drastic reduction of field emission up to fields of 100 MV/m and of residual particles was achieved without any kind of surface damage by the dry ice jet. These first results encourage us to improve and develop the dry ice cleaning technique for s.c. cavities, for water-sensitive components like rf coupler ceramics and for the final treatment of s.c. accelerating structures.