Difference between revisions of "GTS meeting 7 25 16"
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(Created page with "* 1 mA semi-stable running for nearly 7 hours: [https://logbooks.jlab.org/entry/3412699] ** At 300kV, with anode bias at +1500 V, and ** Better beam focusing and centering in...") |
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* The cathode is amazingly robust! | * The cathode is amazingly robust! | ||
| − | ** [[File: | + | ** [[File:Slide10.jpg]] |
| + | |||
| + | * 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%. | ||
| + | ** [[File:Comparison between QE map and damaged cathode picture.jpg]] | ||
| + | |||
| + | * The masked cathode was installed: | ||
| + | ** [[File:Picture of masked photocathode.png]] | ||
| + | ** We got beam, with a ring! | ||
| + | ** QE is very low. | ||
| + | ** This cathode is being heat cleaned and will be activated again. Mamun has a better scheme for masking the alkalies. | ||
| + | ** [[File:Masked cathode compilation picture-QE-beam.png]] | ||
Latest revision as of 14:26, 26 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
- The cathode is amazingly robust!
- 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%.
- The masked cathode was installed:
- We got beam, with a ring!
- QE is very low.
- This cathode is being heat cleaned and will be activated again. Mamun has a better scheme for masking the alkalies.
