GTS meeting 9 14 16

• Cathode Prep Chamber
  • Mamun and Yan successfully demonstrated that the heat-puck engagement mechanism works.
  • A spring with 5 leaves was made by the machine shop. Mamun found out that the height of the bend was too much, so he 'flattened' it bit, making the puck easier to insert and remove.
  • Measured force to disengage puck: about 3 lbs.
  • Also found that the length of the leaves has to be shorter, Mamun had to add a second 'hose clamp'
  • Testing under vacuum, found that several heat-cool cycles kept the puck engaged, but after removal form vacuum springs seemed to be more stiff. Mammon thinks it is because the test temp was as high as 300C, which we do not need. Usual photocathode activation is 150-200 C.
  • Mamun is setting up for a temperature calibration using a TC in vacuum.

• HV Gun chamber
  • Did a test fit for the NEGs using the rails and the perforated plate, see picture below.
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  • The gap between the NEG and the perforated plate is about 1 cm.
  • The rails have been tack welded to the chamber
  • Next is assembling the NEG package inside the gun.

• Magnetized beam
  • Magnet fully installed
  • Water and electrical connections done

• Some thoughts about the reasons for "QE drops and associated cathode damage spots while running 1 mA DC, 300keV beam"
  • Why we were not able to run > 1 mA in the GTS while Russel and Riad could run 20 mA in the Test Cave?
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  • This is Carlos' ERL09 presentation about similar observations while running high current in the FEL gun: Media:FEL-Photocathode-'arcing'-ERL09.pdf
  • And this is a link to the GTSLOG with data from July 14th 2016 run
  • This Cornell paper shows that ion trapping effects are likely inducing gun (HVPS) trips: Media:Cornell-gun-trip-ion-trapping.pdf
  • Bruce Dunham's talk on high current cathode damage
  • And Russell's paper on the CsK2Sb BNL cathode high current run
• Really good suggestions by Joe and Matt:
  • Bias the anode negative: use it as an ion clearing electrode
  • 'Existing BPMS CANNOT BE USED ion clearing electrodes because they are 'trip-line' that is they are shorted to ground
  • Use the RGA during high current runs to study the gas species during the current/vacuum bursts associated with photocathode arcing events