Progress on Cathodes

1. Progress on Cathodes Thomas K Hemmick, Richard Hutter, Alberica Toia, Bill Anderson, Jason Kamin

2. Cathode Production Parameters • CsI Source: • INFN group uses “pre-melted” full boats. • Changed to “broken crystal” chunks (ala D. Anderson) • Heating: • System uses heating of vacuum vessel to eventually heat the cathode (60o C). • Cylinder heated, not Nose. • New procedure: • Bake during pump down (heats all including cathode) • Turn off external heat prior to shot. • Cathode remains hot longer…shoot! • Vacuum Quality: • Run the residual gas analyzer DURING shot. • If “puff” of contamination seen during boat heat-up…wait. • Vacuum Value: • 8x10-7 mbar (1 mbar = 0.76 torr) at shot. • After weekend… 8x10-8 mbar!! (NOTE: CsI on walls helps)

3. Residual Gas Analyzer Observations: • The vacuum has been mostly water!!! • Initially a surprise since the cryo pumps water MUCH faster than N2 or O2 (other major components). • Assumption: Walls are a source of water. • Only cylinder region heated (not rectangular nose) • Test: Leave pump going for the weekend monitor RGA • BINGO: Overnight Friday water dropped by 3 orders!! • Present vacuum is mostly H2 (8x10-8 mbar) • All present shots done PRIOR to complete elimination of water. • Good vacuum means little water even when its mostly water. • We can only improve from previous shots. • We KNOW at all times our exact status (driving a Cadillac)

4. Cathode History • SS: • Old CsI + air exposure (mis-wired of QE device). • Bad. • GEM: • Old CsI/no air exposure. • Bad (local system and Bob). • SS: • New CsI, no air, good vacuum (unknown composition). • Good (local only). • GEM: (pictures are from here) • New CsI, no air, good vacuum, mostly water. • Good (local and Bob). • GEM: • New CsI, no air, good vacuum, mostly water. • Good (local…send to Bob soon)

5. Latest result I told you so! • Causes for celebration: • Equally as good as Amos Breskin. • Equal to assumptions for successful GEM. • Reproducible. • Shot onto GEM. • GEM was cleaned and held voltage prior to shot. • Vacuum value and quality have only improved since this result!

6. Worries about QE are over…now what? • How do we MAINTAIN the good QE? • Minor transfer box improvements: • Presently gravity-driven Ar fill (2” hole). • Replace hole with electrical feedthrough. • No cadillac for the glove box: • Bids came in $100,000 – $200,000. • Budget $40,000 • How to survive w/ lesser quality Glove Box? • DUH!!! Vacuum is MUCH better than any Glove Box! • Change procedure to minimize the exposure of cathodes to Glove Box air. • “Upgrade” INFN Glove box to make it good enough.

7. Procedural Modifications: • Old procedure: • New cathodeGB; Cathode rejoins full stack; Gain test in GB; Stack  HBD….repeat… • Multiple openings w/ cathodes already on HBD. • Air Lock…excellent atmosphere ALWAYS required. • New procedure: • New cathodeGB; Cathode rejoins full stack; Gain test in GB; Stack  HIGH VACUUM STORAGE (HVS) • When vacuum storage is full, all GEMSHBD in a single short term operation. • Maybe don’t need airlock? • INFN Box begins to look attractive. • How to implement: • Use fraction of original GB money to make HVS. • Work on INFN Glove Box to make it good enough.

8. INFN Glove Box • IT STINKS (quite literally). • Latex gloves…overpowering smell when opened. • Butyl or Hypalon material ($200/pair…16 pairs). • Re-pressurizing Dewar • Special LN2 dewar uses internal bubbling regulator to maintain head pressure ~150 psi. • One fill lasts ~1 week. • Large Oxysorb canister…excellent gas supply. • ROUGH measurement = 30-40 ppm water after weekend (with latex gloves). • Want to borrow better water/oxygen meters…

9. Summary • The required QE is achieved and almost certainly reproducible. • The QE achievement era is over. • The QE maintenance era begins. • We can lessen requirements on GB by changing procedure: • Use high vacuum storage of GEMS. • Assemble GEMS into HBD as single task. • We can redirect some original GB funds to: • Establish high vacuum storage facility. • Upgrade INFN glove box.