The Spallation Neutron Source project includes a superconducting linac section in the energy range from 192 MeV to 1000 MeV, operating at a frequency of 805 MHz at 2.1 K. For this energy range two types of cavities are needed with geometrical beta - values of beta= 0.61 and beta= 0.81. An aggressive cavity prototyping program is being pursued at Jlab, which calls for fabricating and testing of four beta= 0.61 cavities and two beta= 0.81 cavities. Both types consist of six cells made from high purity niobium and feature one HOM coupler on each beam pipe and a port for a high power coaxial input coupler. Three of the four beta= 0.61 cavities will be used for a cryomodule test in early 2002.

At this time four medium beta cavities and one high beta cavity have been completed at JLab. The first tests on the beta= 0.61 cavity and the beta= 0.81 exceeded the design values for gradient and Q - value: E_acc = 1 0.3 MV/m and Q = 5 x 10⁹ at 2.1K for beta= 0.61 and E_acc = 12.3 MV/m and Q = 5 x 10⁹ at 2.1K for beta= 0.81. One of the medium beta cavities has been equipped with an integrated helium vessel and measurements of the static and dynamic Lorentz force detuning will be done and compared to the "bare" cavities. In addition two single cell cavities have been fabricated, equipped with welded-on HOM couplers. They are being used to evaluate the HOM couplers with respect to multipacting, fundamental mode rejection and HOM damping as far as possible in a single cell. This paper will describe the cavity design with respect to electrical and mechanical features, the fabrication efforts and the results obtained with the different cavities existing at the time of this workshop.

This work was supported by the U.S. DOE Contract No DE-AC05-00-OR22725.

Authors: G. Ciovati, P. Kneisel , J. Brawley, R. Bundy, I. Campisi, K. Davis, K. Macha, D. Machie, J. Mammosser, S. Morgan, R. Sundelin, L. Turlington, K. Wilson, JLab; M. Doleans, S.H. Kim, SNS; D. Barni, C. Pagani, P. Pierini, INFN Milano; K. Matsumoto, R. Mitchell, D. Schrage, LANL; R. Parodi, INFN Genoa; J. Sekutowicz, DESY; P. Ylae-Oijala, Univ. Helsinki

Submitted for 2001 SRF Workshop, KEK, Tsukuba City, Japan, September 6-11, 2001

Updated August 10, 2001

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