Muffin-tin cavities at -band for linear accalerator application

A series of 2-cell, π-mode, standing wave accelerator cavities operating at 8.6 GHz has been fabricated from thin (0.5 mm) Nb sheet metal. The cavities are of the rectangular geometry, muffin-tin variety. Of six cavities, four achieved effective accelerating fields greater than 17 MeV/m; the other two reached 11 and 14 MeV/m. The accelerating gradient in the best cavity was 21.8 MeV/m, corresponding to a peak rf magnetic field of 1400 Gauss. Q0values in all cases were greater than 1 × 10⁹. No significant electronic activity was observed in any of these cavities. As a preliminary undertaking, several 1-cell X- band cavities have also been fabricated using the same technology. Similar statistics for accelerating field values were obtained and the peak rf magnetic field achieved in the best 1-cell cavity was 1600 Gauss. A summary of the fabrication and preparation techniques together with test results are presented.