Performance of a Superconducting Accelerator Structure with a Modified Geometry

A 2.4 m long superconducting niobium 1300 MHz disk loaded accelerator structure whose cell geometry was modified to reduce its sensitivity to one-point multipacting was constructed and tested. The structure has a maximum cw energy gradient for electrons of 2.3 MeV/m and an unloaded Q of 9 × 108 at this field, both of which are satisfactory. The structure appears to be less sensitive to one-point multipacting; however, this result is not conclusive because of a small helium leak in the structure. We have also found that structures which undergo large multipactor frequency shifts can be operated successfully in a pulsed-off mode.