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

2 Cathode Production Parameters CsI Source:CsI Source: –INFN group uses “pre-melted” full boats. –Changed to “broken crystal” chunks (ala D. Anderson) Heating:Heating: –System uses heating of vacuum vessel to eventually heat the cathode (60 o C). –Cylinder heated, not Nose. –New procedure: Bake during pump down (heats all including cathode)Bake during pump down (heats all including cathode) Turn off external heat prior to shot.Turn off external heat prior to shot. Cathode remains hot longer…shoot!Cathode remains hot longer…shoot! Vacuum Quality:Vacuum Quality: –Run the residual gas analyzer DURING shot. –If “puff” of contamination seen during boat heat-up…wait. Vacuum Value: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!!!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)Only cylinder region heated (not rectangular nose) Test: Leave pump going for the weekend monitor RGATest: Leave pump going for the weekend monitor RGA BINGO: Overnight Friday water dropped by 3 orders!!BINGO: Overnight Friday water dropped by 3 orders!! Present vacuum is mostly H 2 (8x10 -8 mbar)Present vacuum is mostly H 2 (8x10 -8 mbar) All present shots done PRIOR to complete elimination of water.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:SS: –Old CsI + air exposure (mis-wired of QE device). –Bad. GEM:GEM: –Old CsI/no air exposure. –Bad (local system and Bob). SS:SS: –New CsI, no air, good vacuum (unknown composition). –Good (local only). GEM: (pictures are from here)GEM: (pictures are from here) –New CsI, no air, good vacuum, mostly water. –Good (local and Bob). GEM:GEM: –New CsI, no air, good vacuum, mostly water. –Good (local…send to Bob soon)

5 Latest result Causes for celebration: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! I told you so!

6 Worries about QE are over…now what? How do we MAINTAIN the good QE?How do we MAINTAIN the good QE? Minor transfer box improvements:Minor transfer box improvements: –Presently gravity-driven Ar fill (2” hole). –Replace hole with electrical feedthrough. No cadillac for the glove box:No cadillac for the glove box: –Bids came in $100,000 – $200,000. –Budget $40,000 How to survive w/ lesser quality Glove Box?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: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 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: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).IT STINKS (quite literally). –Latex gloves…overpowering smell when opened. –Butyl or Hypalon material ($200/pair…16 pairs). Re-pressurizing DewarRe-pressurizing Dewar –Special LN 2 dewar uses internal bubbling regulator to maintain head pressure ~150 psi. –One fill lasts ~1 week. –Large Oxysorb canister…excellent gas supply. –ROUGH measurement = 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 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: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:We can redirect some original GB funds to: –Establish high vacuum storage facility. –Upgrade INFN glove box.