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Progress on CathodesProgress on Cathodes

Thomas K Hemmick, Richard Hutter, Thomas K Hemmick, Richard Hutter, Alberica Toia, Bill Anderson, Alberica Toia, Bill Anderson, Jason KaminJason Kamin

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Cathode Production ParametersCathode Production Parameters• CsI Source:CsI Source:

– INFN group uses “pre-melted” full boats.INFN group uses “pre-melted” full boats.– Changed to “broken crystal” chunks (ala D. Anderson)Changed to “broken crystal” chunks (ala D. Anderson)

• Heating:Heating:– System uses heating of vacuum vessel to eventually heat System uses heating of vacuum vessel to eventually heat

the cathode (60the cathode (60oo C). C).– Cylinder heated, not Nose.Cylinder heated, not Nose.– New procedure: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.Run the residual gas analyzer DURING shot.– If “puff” of contamination seen during boat heat-up…wait.If “puff” of contamination seen during boat heat-up…wait.

• Vacuum Value:Vacuum Value:– 8x108x10-7-7 mbar (1 mbar = 0.76 torr) at shot. mbar (1 mbar = 0.76 torr) at shot.– After weekend… 8x10After weekend… 8x10-8-8 mbar!! (NOTE: CsI on walls helps) mbar!! (NOTE: CsI on walls helps)

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Residual Gas Analyzer Observations: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 Initially a surprise since the cryo pumps water MUCH faster

than N2 or O2 (other major components).than N2 or O2 (other major components).– Assumption: Walls are a source of water.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 HPresent vacuum is mostly H22 (8x10 (8x10-8-8 mbar) mbar)

• All present shots done PRIOR to complete All present shots done PRIOR to complete elimination of water.elimination of water.– Good vacuum means little water even when its mostly Good vacuum means little water even when its mostly

water.water.– We can only improve from previous shots.We can only improve from previous shots.– We KNOW at all times our exact status (driving a Cadillac)We KNOW at all times our exact status (driving a Cadillac)

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Cathode HistoryCathode History• SS:SS:

– Old CsI + air exposure (mis-wired of QE device).Old CsI + air exposure (mis-wired of QE device).– Bad.Bad.

• GEM:GEM:– Old CsI/no air exposure.Old CsI/no air exposure.– Bad (local system and Bob).Bad (local system and Bob).

• SS:SS:– New CsI, no air, good vacuum (unknown composition).New CsI, no air, good vacuum (unknown composition).– Good (local only).Good (local only).

• GEM: (pictures are from here)GEM: (pictures are from here)– New CsI, no air, good vacuum, mostly water.New CsI, no air, good vacuum, mostly water.– Good (local and Bob).Good (local and Bob).

• GEM:GEM:– New CsI, no air, good vacuum, mostly water.New CsI, no air, good vacuum, mostly water.– Good (local…send to Bob soon)Good (local…send to Bob soon)

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Latest resultLatest result

• Causes for Causes for celebration:celebration:– Equally as good as Equally as good as

Amos Breskin.Amos Breskin.– Equal to assumptions Equal to assumptions

for successful GEM.for successful GEM.– Reproducible.Reproducible.– Shot onto GEM.Shot onto GEM.– GEM was cleaned and GEM was cleaned and

held voltage prior to held voltage prior to shot.shot.

– Vacuum value and Vacuum value and quality have only quality have only improved since this improved since this result!result!

I told you so!

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Worries about QE are over…now what?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).Presently gravity-driven Ar fill (2” hole).– Replace hole with electrical feedthrough.Replace hole with electrical feedthrough.

• No cadillac for the glove box:No cadillac for the glove box:– Bids came in $100,000 – $200,000.Bids came in $100,000 – $200,000.– Budget $40,000Budget $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!DUH!!! Vacuum is MUCH better than any Glove Box!– Change procedure to minimize the exposure of cathodes to Change procedure to minimize the exposure of cathodes to

Glove Box air.Glove Box air.– ““Upgrade” INFN Glove box to make it good enough.Upgrade” INFN Glove box to make it good enough.

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Procedural Modifications:Procedural Modifications:

• Old procedure:Old procedure:– New cathodeNew cathodeGB; Cathode rejoins full stack; Gain test in GB; Cathode rejoins full stack; Gain test in

GB; Stack GB; Stack HBD….repeat… HBD….repeat…– Multiple openings w/ cathodes already on HBD.Multiple openings w/ cathodes already on HBD.– Air Lock…excellent atmosphere ALWAYS required.Air Lock…excellent atmosphere ALWAYS required.

• New procedure:New procedure:– New cathodeNew cathodeGB; Cathode rejoins full stack; Gain test in GB; Cathode rejoins full stack; Gain test in

GB; GB; Stack Stack HIGH VACUUM STORAGE (HVS) HIGH VACUUM STORAGE (HVS)– When vacuum storage is full, all GEMSWhen vacuum storage is full, all GEMSHBD in a single HBD in a single

short term operation.short term operation.– Maybe don’t need airlock?Maybe don’t need airlock?– INFN Box begins to look attractive.INFN Box begins to look attractive.

• How to implement:How to implement:– Use fraction of original GB money to make HVS.Use fraction of original GB money to make HVS.– Work on INFN Glove Box to make it good enough.Work on INFN Glove Box to make it good enough.

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INFN Glove BoxINFN Glove Box

• IT STINKS (quite literally).IT STINKS (quite literally).– Latex gloves…Latex gloves…overpoweringoverpowering smell when opened. smell when opened.– Butyl or Hypalon material ($200/pair…16 pairs).Butyl or Hypalon material ($200/pair…16 pairs).

• Re-pressurizing DewarRe-pressurizing Dewar– Special LNSpecial LN22 dewar uses internal bubbling dewar uses internal bubbling

regulator to maintain head pressure ~150 psi.regulator to maintain head pressure ~150 psi.– One fill lasts ~1 week.One fill lasts ~1 week.– Large Oxysorb canister…excellent gas supply.Large Oxysorb canister…excellent gas supply.– ROUGH measurement = 30-40 ppm water after ROUGH measurement = 30-40 ppm water after

weekend (with latex gloves).weekend (with latex gloves).– Want to borrow better water/oxygen meters…Want to borrow better water/oxygen meters…

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SummarySummary

• The required QE is achieved and almost The required QE is achieved and almost certainly reproducible.certainly reproducible.– The QE achievement era is over.The QE achievement era is over.– The QE maintenance era begins.The QE maintenance era begins.

• We can lessen requirements on GB by We can lessen requirements on GB by changing procedure:changing procedure:– Use high vacuum storage of GEMS.Use high vacuum storage of GEMS.– Assemble GEMS into HBD as single task.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.Establish high vacuum storage facility.– Upgrade INFN glove box.Upgrade INFN glove box.