Novel methods for in situ high-density surface cleaning (scrubbing) of ultrahigh vacuum long narrow tubes to reduce secondary electron yield and outgassing

Electron clouds in existing accelerators limit machine performance through dynamical instabilities and associated vacuum pressure increases. Bare metal vacuum walls have shown to prevent electron cloud formation. Proper scrubbing of stainless steel, copper, or niobium vacuum walls can mitigate the problems of electron clouds and increase accelerator luminosity. Present scrubbing by ion beams and plasmas has resulted in unsatisfactory surface cleaning by not scrubbing all surfaces and poor debris pumping-out due to low-density plasma generation. Novel plasma discharge cleaning techniques and tools are being developed for in-situ scrubbing long, small diameter tubes by generating high-density plasmas to completely affect each exposed surface. One technique involves high plasma density magnetron mole, the other is based microwave plasma injection that generates high-density plasma. High-density plasma scrubbing in the viscous gas flow range can reach all surfaces and pump out all debris effectively.