Status of superconducting spoke cavity development

Superconducting (SC) TEM-class spoke cavities are required for proposed cw and pulsed ion linac applications world-wide. Several laboratories and institutions have demonstrated high field performance (Epeak>30 MV/m) in single- and multi-spoke geometries for use with ions over the full mass range and for velocities 0.15 < v/c < 0.8. Recent results show spoke cavities, previously designed for 4 Kelvin operation, now operate with better efficiency at 2 Kelvin, resulting in large part from performance gains due to techniques such as clean assembly and hydrogen degassing. Low Rf losses even for high accelerating fields (corresponding to Epeak ∼ 30 MV/m) required in operations have been achieved. The status of recent spoke cavity activities at several laboratories is presented.