Gas cluster ion beam surface treatments for reducing field emission and breakdown of electrodes and SRF cavities

Sub-micron-scale surface roughness and contamination cause field emission that can lead to high-voltage breakdown of electrodes, and these are limiting factors in the development of high gradient RF technology. We are studying various Gas Cluster Ion Beam (GCIB) treatments to smooth, clean, etch and...

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Bibliographic Details
Published in:Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2007-08, Vol.261 (1-2), p.630-633
Main Authors: Swenson, D.R., Wu, A.T., Degenkolb, E., Insepov, Z.
Format: Article
Language:English
Subjects:
BREAKDOWN
CAVITIES
Cluster-surface interactions
CONTAMINATION
ELECTRODES
FIELD EMISSION
Gas cluster ion beam
ION BEAMS
MATERIALS SCIENCE
MICROSCOPES
POLISHING
RF breakdown
ROUGHNESS
STAINLESS STEELS
SUBSTRATES
Superconducting RF cavity
SURFACE TREATMENTS
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Summary:Sub-micron-scale surface roughness and contamination cause field emission that can lead to high-voltage breakdown of electrodes, and these are limiting factors in the development of high gradient RF technology. We are studying various Gas Cluster Ion Beam (GCIB) treatments to smooth, clean, etch and/or chemically alter electrode surfaces to allow higher fields and accelerating gradients, and to reduce the time and cost of conditioning high-voltage electrodes. For this paper, we have processed Nb, stainless steel and Ti electrode materials using beams of Ar, O2, or NF3+O2 clusters with accelerating potentials up to 35kV. Using a scanning field emission microscope (SFEM), we have repeatedly seen a dramatic reduction in the number of field emission sites on Nb coupons treated with GCIB. Smoothing effects on stainless steel and Ti substrates, evaluated using SEM and AFM imaging, show that 200-nm-wide polishing scratch marks are greatly attenuated. A 150-mm diameter GCIB-treated stainless steel electrode has shown virtually no DC field emission current at gradients over 20MV/m.
ISSN:0168-583X
1872-9584
DOI:10.1016/j.nimb.2007.04.277