COPPER PLASMA SPRAYED NIOBIUM CAVITIES

A R&D program concerning new fabrication techniques of SRF cavities has started in a close collaboration between the three french laboratories. The technique is based on copper plasma sprayed onto thin wall niobium cavities. The ultimate goal is to produce 1.3 GHz hydroformed ( or deep drawed and EB welded) multicell niobium cavities stiffened by the copper layer. A first series of 3 GHz cavities were fabricated by deep drawing and EB welding using RRR=4O niobium sheets of 0.5 mm thickness. The cavities were heat treated at 1200 "C with Ti gettering before Cu plasma spraying in the industry. In this paper we present the results of the first two cavities tested at 1.8 K before and after copper plasma spraying. 60 fixed thermometers were used to investigate anomalous RF losses around the equator region. The low field Qo are in the range 1.5 10'-4.5 10' @I .8 K and both cavities are limited by quench (E~? ranging from 13.5 MV/m to 16.5 MV/m) . The quench fields measured before and after Cu plasma spraying are the same (cavity #4), or slightly decreased (cavity #5). The temperature maps have shown an identical quench location before and after Cu plasma spraying. In a separate experiment we have measured the global thermal resistance of the cavity wall (niobium-copper) and the results showed an increase of 16 to 34% when the plasma sprayed copper layer is added.