Superconducting 345 MHz two-spoke cavity for RIA

This paper reports development of a two-cell 345 MHz spoke-loaded superconducting cavity intended for the U.S. RIA Project driver linac. The 3 cm aperture cavity has a useful velocity range 0.3 c < v < 0.6 c. In initial tests at 4 K the prototype cavity operated cw at peak surface electric fields as high as 40 MV/m, and with 20 Watts of rf input power provides 3 MV of effective total accelerating voltage. As constructed, the niobium cavity shell was fully housed in an integral stainless-steel helium vessel using pure copper braze joints at the niobium to stainless-steel transitions.