WEXA08
ODU, Norfolk, Virginia, USA
Grain boundaries (GBs) in polycrystalline Nb cavities do not significantly degrade the SRF performance. However, the situation may change for Nb3Sn in which GBs can partially obstruct current and pin vortices, as it has been established in many previous studies. Such weak-linked GBs can cause a medium-field Q slope and cavity quench triggered by guided penetration of vortices along networks of GBs. Vortices trapped at GBs can also contribute to the residual surface resistance. This talk gives an overview of current-limiting mechanisms of GBs and dissipation of vortices in strongly-coupled GBs under RF field. We present results of extensive numerical simulations of vortices in GBs in polycrystalline bulk and thin films, and contribution of vortices to the RF dissipation. Our simulations revealed Cherenkov instability of Josephson vortices driven by strong RF currents and generation of vortex-antivortex pairs, dynamic transition of vortices into phase slips in thin films, and dynamic interaction of moving vortices with pinning centers. Contributions of these mechanisms to the field dependent surface resistance and reduction of the RF breakdown field is discussed.
