Field emission is one of the main factors that can limit the performance of superconducting radio frequency cavities. To reduce possible field emission in the Linac Coherent Light Source II (LCLS-II), we are developing plasma processing for 1.3 GHz nine-cell cavities. The ultimate goal of plasma processing will be to apply the technique in situ in the cryomodules in order to mitigate hydrocarbon-related field emission without disassembling them. Herein is presented the first systematic study of plasma processing applied to LCLS-II superconducting radio frequency cavities. Having developed a new method of plasma ignition for LCLS-II cavities, we applied plasma processing to 1.3 GHz cavities starting with a clean nitrogen doped cavity and proceeding with studying natural field emission and artificially contaminated cavities. All the cavities were cold tested before and after plasma cleaning in order to compare their performances. It was proved that this technique successfully removes carbon-based contamination from the cavity iris and that it is able to eliminate field emission in a naturally field emitting cavity. The effect of plasma processing on cavities exposed to vacuum failures was also investigated, showing positive results in some cases. This work shows how successful plasma processing is in removing hydrocarbon related contamination from the cavity surface without affecting the high Q-factors and quench fields characteristic of nitrogen doped cavities.

中文翻译：

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SLAC直线加速器相干光源II超导RF腔中通过原位等离子体处理减轻场发射的研究

场发射是可能限制超导射频腔性能的主要因素之一。为了减少直线加速器相干光源II（LCLS-II）中可能的场发射，我们正在开发针对1.3 GHz九腔腔的等离子体处理。等离子处理的最终目标将是原位应用该技术为了减轻与烃类相关的场发射而无需拆开它们，它们在低温模块中的作用。本文介绍了对应用于LCLS-II超导射频腔的等离子体处理的首次系统研究。为LCLS-II型腔开发了一种新的等离子点火方法，我们从干净的掺氮腔开始，对1.3 GHz腔进行了等离子体处理，然后研究了自然场发射和人工污染的腔。为了比较它们的性能，在等离子清洁之前和之后对所有腔体进行了冷测试。事实证明，该技术成功地从腔虹膜中去除了碳基污染物，并且能够消除自然场发射腔中的场发射。还研究了等离子体处理对暴露于真空失效的腔体的影响，在某些情况下显示出积极的结果。这项工作显示了成功的等离子体处理如何从型腔表面去除烃类相关污染物，而又不影响氮掺杂型腔的高Q因子和淬火场特性。