18" Photogun ala GTS

Synopsis

• The gun high voltage chamber is 18 " diameter compared to CEBAF's 14 " diameter.
• The vacuum chamber accommodates an R30 inverted insulator with spherical electrode and shed.
• There were two vacuum chambers made: one by MDC currently installed in the GTS which produced 300 kV 4 mA un-polarized beam, and 200 kV 28 mA magnetized beam, both with CsKSb cathodes.
  • The GTS gun started in 2016 with a Pierce geometry focusing cathode front end and 6 inch diameter anode 9 cm anode-cathode gap.
  • Later in 2021 the cathode from face was replaced with a flat (non-fusing) en piece, flat anode, and the anode-cathode closed to 5 cm to increase the photocathode gradient from 3 to 8 MV/m [1]
  • The new anode was designed with the aperture shifted y=-1.6 mm to compensate for beam kick, which was effectively demonstrated with beam [2]
• The second 18" diameter vacuum chamber was made by Kurt J. Lesker and has a thicker 'dish' head.
  • This is the vacuum chamber that is being used for the CEBAF gun with to be installed in March 2022 in the tunnel.
  • The electrode and anode are the same as CENAF with Pierce focusing geometry
  • Anode-cathode gap remains unchanged from CEBAF 14" gun at 6 cm
  • The anode has a new fixture tube that allows for 2 deg tilt to compensate for beam kick, more slots for improved vacuum, and 10 kV SHV feedthrough for anode (not tube) biasing.
  • The links below document the process to accomplish the task.
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• 18" high voltage chamber history

• Background and status as of July 1 2021

• Must, Should and Likes

• Tasks

• Drawings

• Electrostatic and beam dynamics simulations

• Update meetings

• Presentations