GTS meeting 1 17 17

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  • After the gun had been conditioned to 340kV in vacuum, we turned on the magnetized beam coil to 200 Amps and ramped the voltage, slowly up to 340kV.
    • Notice how the signal from the the gun ion pump current responds to the the magnet coil current, as expected
    • BUT the ion pump current ALSO responds to the voltage with the magnet ON: UNEXPECTED! Why the voltage affects the gun ion pump current with the magnet on?
    • GTSLOG showing the ion pump current responding to magnet coil and to gun voltage
    • We will isolate the gun ion pump from the magnetic field, and also monitor the bake ion pump. If it is real vacuum activity, both pumps will show the same behavior with gun voltage and magnet coil on.
    • After increasing the gun voltage to 340kV and with the magnet at 200 Amps, the gun tripped off, resulting in field emission.
    • The gun got re-condtioned with Krypton, and now shows 20 CPS of field emission at 325 kV.
    • We need to re-condition the gun at the chosen operating voltage (300kV, 325kV) for each magnet current setting: 100A, 200A, 300A, and 400A.
  • Photocathode Prep Chamber
    • Last week we tried making photocathode. First, we deposited Sb with the mask and we grow uniform Sb film satisfactorily. Afterward we tried to deposit alkali for about 2.5 hours and did not detect any photocurrent during or after the deposition. We did another round of alkali deposition next day to confirm the alkali evaporation and obtained a good defined spot with alakli. However, throughout the process we still did not see any photocurrent. Then we decided to clean off everything and we observed the Sb to get cleaned prior to cleaning the alkali. We expect this to be the other way around, and it happened likely because of presence of too much O2 and H2O in the system to oxidize the alkali and that oxide form just needs higher temperature to evaporate. At this point Mamun thinks we need a bake for the vacuum to improve and reduce the presence of contaminants to make the chemistry happen in favor of us.


  • Beam Line Vacuum
    • Bubba is almost done with the spool piece / bellow / ion precipitator between the two diagnostic crosses.
    • Survey and Alignment crew are working today on aligning the slits and fiducializing them to the cross.
    • We are still waiting on JT to complete the other two spool pieces.
    • We are aiming to have the beam line assembled and surveyed by the end of next week, to start vacuum and bake.
    • Media:Beamline 12-9-16 ISO VIEW.jpg
    • Media:Beamline 12-9-16 SIDE VIEW.jpg
  • Beam line I&C
    • Keith Cole asked for a meeting to define what we need and when
    • We need to complete the viewer limited SCAM mode (point of contact?)
    • We also need a 3 position actuator for each of the two diagnostic crosses. We have now a 2 position actuator. Who provides what? Who does what? Carlos will schedule this meeting for this week.
    • For high current / lifetime we will need to control the insertable Faraday cup, and add Kevin's diagnostic cross. When?