Testing of the SNS Superconducting Cavities and Cryomodules

The superconducting linac for the Spallation Neutron Source is in the process of being commissioned. Eightyone niobium cavities resonating at 805 MHz are being installed in the SNS tunnel in 11 medium beta (. 61) cryomodules each containing 3 cavities and 12 high beta (. 81) cryomodules each with 4 cavities. The niobium cavities and cryomodules were designed and assembled at Jefferson Lab to operate at 2.1 K. The Central Helium Liquefier has been tested to 2.1 K but is routinely operated at 4.2 K. At this temperature, 70 of the 81 cavities have been tested, mostly in open loop at 10 pulses per second and at a full pulse length of 1.3 msec. The results indicate that high gradients can be reached even at 4.2 K (average value of 17.8 MV/m) and that operation of the superconducting linac at that temperature may be possible.