Operation Experience with DC Photoemission Guns at Jefferson Lab

Conference · Sat Oct 01 04:00:00 EDT 2011

DOI:https://doi.org/10.2172/1994947· OSTI ID:1994947

Hernandez-Garcia, Carlos; Hannon, Fay

The JLab IR FEL injector is driven by a DC photoemission electron gun based on GaAs photocathodes. Since the FEL commissioning in 1998, the DC gun has been rebuilt several times for improved performance and/or for repairs. After demonstrating 9 mA CW and over 7000 Coulombs at 350kV for three consecutive years, the gun was rebuilt in 2008 due to a punctured insulator. Since then, the gun has been operating at 325V (lower voltage due to field emission) and has delivered beam at 65 pC bunch charge for VUV FEL operations, and 135pC for IR FEL operations at beam currents up to 4 mA CW. In February 2011, a copy of that gun was tested in the Gun Test Stand with a partially conductive insulator from Wesgo/Morgan to study bulk conductivity as charge drain for preventing insulator puncture by field emission. Close to 300 hours of high voltage testing showed that processing of field emission with partial pressure of Krypton gas is very effective. The gun held 500kV over 8 hours with 1E-4 Torr of Krypton. However, the gun could not hold more than 440kV under vacuum conditions, at which set point the insulator suffered a puncture. Various observations of Kr processing behavior and voltage-induced gas desorption will be presented. Financial support was provided by the Office of Naval Research, the Army Night Vision Laboratory, the Air Force Research Laboratory, the Joint Technology Office, the Commonwealth of Virginia, and by the U.S. DOE Basic Energy Sciences under contract No. DE-AC05-060R23177.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1994947
• Report Number(s): JLAB-FEL-11-1528; DOE/OR/23177-6961
• Country of Publication: United States
• Language: English