New higher-order-mode damping scheme for L-band superconducting cavities using a radial transmission line

For energy recovery linacs, excellent damping of higher-order modes (HOMs) in superconducting cavities is required for preventing beam breakup. As a promising method for this purpose, we propose to damp the HOMs using a radial transmission line attached to the sides of the cavity. The HOM powers are dissipated in RF absorbers while an accelerating field is rejected with a choke filter. An initial design of this radial-line HOM damper was carried out with simulations. Then, we measured the damping of HOMs by means of this method using a model cavity of the TESLA type. Investigations on a single-cell cavity showed a promising performance of HOM damping.