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Title: In-Situ Cleaning of Metal Photo-Cathodes in rf Guns

Abstract

Metal cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to ''clean'' the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and scanned across the cathode surface. However, since the laser is operated near the damage threshold, it can also damage the cathode and increase the dark current. The QE also degrades over days and must be cleaned regularly. We are searching for a more robust cleaning technique that cleans the entire cathode surface simultaneously. In this paper we describe initial results using multiple techniques such as several keV ion beams, glow discharge cleaning and back bombarding electrons. Results are quantified in terms of the change in QE and dark current.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
896939
Report Number(s):
SLAC-PUB-12206
TRN: US200705%%15
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Presented at 28th International Free Electron Laser Conference (FEL 2006), Berlin, Germany, 27 Aug - 1 Sep 2006
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; PHOTOCATHODES; CLEANING; GLOW DISCHARGES; ION BEAMS; RF SYSTEMS; QUANTUM EFFICIENCY; Accelerators,ACCPHY

Citation Formats

Schmerge, J.F., Castro, J.M., Clendenin, J.E., Colby, E.R., Dowel, D.H., Gierman, S.M., Loos, H., Nalls, M., White, W.E., and /SLAC. In-Situ Cleaning of Metal Photo-Cathodes in rf Guns. United States: N. p., 2007. Web.
Schmerge, J.F., Castro, J.M., Clendenin, J.E., Colby, E.R., Dowel, D.H., Gierman, S.M., Loos, H., Nalls, M., White, W.E., & /SLAC. In-Situ Cleaning of Metal Photo-Cathodes in rf Guns. United States.
Schmerge, J.F., Castro, J.M., Clendenin, J.E., Colby, E.R., Dowel, D.H., Gierman, S.M., Loos, H., Nalls, M., White, W.E., and /SLAC. Wed . "In-Situ Cleaning of Metal Photo-Cathodes in rf Guns". United States. doi:. https://www.osti.gov/servlets/purl/896939.
@article{osti_896939,
title = {In-Situ Cleaning of Metal Photo-Cathodes in rf Guns},
author = {Schmerge, J.F. and Castro, J.M. and Clendenin, J.E. and Colby, E.R. and Dowel, D.H. and Gierman, S.M. and Loos, H. and Nalls, M. and White, W.E. and /SLAC},
abstractNote = {Metal cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to ''clean'' the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and scanned across the cathode surface. However, since the laser is operated near the damage threshold, it can also damage the cathode and increase the dark current. The QE also degrades over days and must be cleaned regularly. We are searching for a more robust cleaning technique that cleans the entire cathode surface simultaneously. In this paper we describe initial results using multiple techniques such as several keV ion beams, glow discharge cleaning and back bombarding electrons. Results are quantified in terms of the change in QE and dark current.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 03 00:00:00 EST 2007},
month = {Wed Jan 03 00:00:00 EST 2007}
}

Conference:
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  • As part of the A0 Photo-injector collaboration at Fermi-lab [1, 2] and the TeSLA collaboration [3], a high bright-ness, low emittance electron source has been developed. In the process, a system was constructed for coating molybde-num cathodes with a layer of c├Žsium telluride (Cs2 Te), a photo-emissive material of high quantum efficiency (QE). The use of Cs2 Te was first investigated at CERN [4] and LANL [5]. The development of the systems for the TeSLA Test Facility Linac and the Fermilab Photo-injector was done in Milano [6]. The system at Fermilab incorporates manipulator arms to transfer a cathode from themore » preparation chamber into a 1.3 GHz photo-electron RF gun while it re-mains in an ultra-high vacuum (UHV) environment, in or-der to avoid the deleterious effects of residual gases on the QE. A first prototype electron gun has been operated with a photo-cathode for several months [1]. This paper describes preliminary results obtained with the first 2 photo-cathodes and the first gun. Some of the desired parameters for the TeSLA Test Fa-cility beam are given in Table 1. The desired characteristics for the photo-cathodes include (i) high QE, (ii) high current density (>500 A/cm{sup 2} ), (iii) long lifetime, and (iv) low field emission. The choice of Cs2 Te is a compromise between long lifetime, rugged metal cathodes with low QE (typi-cally between 10{sup -6} and 10{sup -4} and semiconductor cathodes with high QE (>10%), which generally have a short life-time because of their sensitivity to contamination.« less
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