A study of the electromagnetic fields leakage in TM020 mode HOM-damped cavity

Abstract

Radiofrequency cavities are crucial components in synchrotron light sources, providing beam energy replenishment and accelerating voltage. TM020 mode cavities offer superior performance compared to conventional TM010 cavities, exhibiting a higher quality factor and accelerating gradient. Their unique electromagnetic field distribution enables effective suppression of both higher and lower order modes via strategically placed dampers at the radial magnetic or electric field wave nodes. However, the sensitivity to misalignment is heightened near these nodes, where the magnetic or electric field gradient is maximized. Consequently, even minor deviations in coupling slot or wave node positioning can induce substantial electromagnetic field leakage, limiting the achievable accelerating voltage due to finite damper power handling. We present a novel leakage suppression scheme employing a Sector waveguide for precise control of coupling slot placement and a waveguide-to-coaxial input coupler to minimize azimuthal perturbations, thus stabilizing the field wave node. This approach drastically reduces accelerating field leakage, enabling stable operation of TM020 damped cavities at high accelerating gradients. Simulations of a 500 MHz TM020 cavity demonstrate leakage reduction to below 1% under operational conditions.