Difference between revisions of "GTS meeting 7 25 16"

Revision as of 11:03, 25 July 2016

1 mA semi-stable running for nearly 7 hours: [1]
- At 300kV, with anode bias at +1500 V, and
- Better beam focusing and centering in the viewers, rather than on the solenoids.
- We think is the latter that made the greatest contribution to high current beam
- Even so, we still see sudden "photocathode-anode arcing" that reduces the QE on the illuminated area, but only slightly

By moving a hand-held magnet around the gun chamber, "something changed" and now there is field emission starting at around 230kV.
- This induced several gun HV trips (on current) while attempting to operate at 300kV.
- We tried Kr processing at no avail. We are then operating at 225kV.

The QE scanner is operational!
- The key to make it work was to bias the gun at -1kV, using the Glassman HVPS, and the anode grounded through the Keithley pico-ammeter that reads in EPICS. YEs, for this we need to lock the GTS enclosure in Run mode.
- The following scan was taken after doing Kr processing. This is why the QE in the un-damaged area is smaller than 2.5%.

@@ Line 14: / Line 14: @@
 * The QE scanner is operational!
+** The key to make it work was to bias the gun at -1kV, using the Glassman HVPS, and the anode grounded through the Keithley pico-ammeter that reads in EPICS. YEs, for this we need to lock the GTS enclosure in Run mode.
 ** The following scan was taken after doing Kr processing. This is why the QE in the un-damaged area is smaller than 2.5%.
 ** [[File:Comparison between QE map and damaged cathode picture.jpg]]
+* The masked cathode was installed:
+** [[File:Picture of masked photocathode.png]]