18" Photogun ala GTS

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  • 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 was installed 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 front face was replaced with a flat (non-focusing) 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 downstream endplate.
    • This is the vacuum chamber that is being used for the CEBAF gun chamber with R30 insulator+spherical electrode to be installed in March 2023 in the tunnel.
    • This chamber IS NEG coated. See
    • The electrode and anode are the same as CEBAF 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 document the process to accomplish this task, and include links to the history of this vacuum chamber, background, and status as of October 4 2022.
    • The models following the links represent the gun with 18" KJ Lesker NEG coated chamber + white R30 insulator spherical electrode, CEBAF style anode with 6 cm anode-cathode gap AND 2 degree titled anode for beam kick correction.
    • The plan is to install this gun in UITF in November 2022. Demonstrate 200 keV beam without field emission, demonstrate beam kick has been corrected by anode tilt, and install in CEBAF in March 2023.
  • Iso view distance from z=0 to anode spider US plane is 200 mm.png
  • Cross section elevation distance from z=0 to anode spider US plane is 200 mm.png
  • Tilted anode elevation model.png