Evaluation of electropolished stainless steel electrodes for use in DC high voltage photoelectron guns

DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (∼nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-b...

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Bibliographic Details
Published in:Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2015-07, Vol.33 (4)
Main Authors: BastaniNejad, Mahzad, Elmustafa, Abdelmageed A., Forman, Eric, Covert, Steven, Hansknecht, John, Hernandez-Garcia, Carlos, Poelker, Matthew, Das, Lopa, Kelley, Michael, Williams, Phillip
Format: Article
Language:English
Subjects:
ACCELERATORS
COMPARATIVE EVALUATIONS
DIAMONDS
ELECTRIC POTENTIAL
ELECTRON BEAMS
ENGINEERING
FIELD EMISSION
GALLIUM ARSENIDES
PHOTOCATHODES
STAINLESS STEELS
SURFACES
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Summary:DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (∼nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-based photocathode used to produce the electron beams. High-level field emission (>μA) can cause significant damage the photogun. To minimize field emission, stainless steel electrodes are typically diamond-paste polished, a labor-intensive process often yielding field emission performance with a high degree of variability, sample to sample. As an alternative approach and as comparative study, the performance of electrodes electropolished by conventional commercially available methods is presented. Our observations indicate the electropolished electrodes exhibited less field emission upon the initial application of high voltage, but showed less improvement with gas conditioning compared to the diamond-paste polished electrodes. In contrast, the diamond-paste polished electrodes responded favorably to gas conditioning, and ultimately reached higher voltages and field strengths without field emission, compared to electrodes that were only electropolished. The best performing electrode was one that was both diamond-paste polished and electropolished, reaching a field strength of 18.7 MV/m while generating less than 100 pA of field emission. The authors speculate that the combined processes were the most effective at reducing both large and small scale topography. However, surface science evaluation indicates topography cannot be the only relevant parameter when it comes to predicting field emission performance.
ISSN:0734-2101
1520-8559