Journal
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT
Volume 818, Issue -, Pages 76-81Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.nima.2016.02.049
Keywords
Plasma processing; Uniform plasma-surface interaction; Asymmetric plasma; SRF cavity
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Funding
- Office of High Energy Physics, Office of Science, Department of Energy [DE-SC0007879]
- JSA/DOE [DE-AC05-060R23177]
- U.S. Department of Energy (DOE) [DE-SC0007879] Funding Source: U.S. Department of Energy (DOE)
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An apparatus and a method are described for plasma etching of the inner surface of superconducting radio frequency (SRF) cavities. Accelerator SRF cavities are formed into a variable-diameter cylindrical structure made of bulk niobium, for resonant generation of the particle accelerating field. The etch rate non-uniformity due to depletion of the radicals has been overcome by the simultaneous movement of the gas flow inlet and the inner electrode. An effective shape of the inner electrode to reduce the plasma asymmetry for the coaxial cylindrical rf plasma reactor is determined and implemented in the cavity processing method. The processing was accomplished by moving axially the inner electrode and the gas flow inlet in a step-wise way to establish segmented plasma columns. The test structure was a pillbox cavity made of steel of similar dimension to the standard SRF cavity. This was adopted to experimentally verify the plasma surface reaction on cylindrical structures with variable diameter using the segmented plasma generation approach. The pill box cavity is filled with niobium ring- and disk-type samples and the etch rate of these samples was measured. (C) 2016 Elsevier B.V. All rights reserved.
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