FINE GRAIN AND LARGE GRAIN NIOBIUM CAVITY PROTOTYPING FOR A PROTON LINAC

A superconducting cavity has been designed and prototyped for acceleration of particles travelling at 81% the speed of light (β = 0.81). The application of interest is an 8 GeV proton linac proposed as an upgrade to the Fermilab accelerator complex, although the cavity would also be suitable for other ion accelerators. The cell shape is similar to that of the 805 MHz high-beta cavity developed for the Spallation Neutron Source Linac, but the resonant frequency is 1.3 GHz and the beam tube diameter matches that of the 1.3 GHz cavity for the TeSLA Test Facility. Four single-cell prototypes have been fabricated and tested before and after post-purification. Two of the cavities were formed from standard high purity fine grain niobium sheet; the other two were fabricated from large grain niobium, following up on the work at Jefferson Lab to investigate the potential of large grain material for cost savings and/or improved RF performance. Two 7-cell cavity prototypes (one fine grain, one large grain) have also been fabricated. The single-cell results are presented in this paper, and the status of the prototyping effort is reported.