01/07/08I. Ravinovich1 HBD Update Ilia Ravinovich DC Meeting, January 9, 2008

01/07/08I. Ravinovich2 Main activities on the HBD front During last two months HBD crew has been working on resolving the HV instability issue. The activities were divided into several tasks: 1. BNL+SB+WIS people worked at BNL testing triple GEM stacks to find out the origin of the HV instability. 2. Stony Brook people worked at SB tent to improve the cleanliness of the assembly place, namely the glove box, and the CsI evaporator. 3. BNL people worked at SB to establish a cleaning procedure to recuperate non-performing GEMs.

01/07/08I. Ravinovich3 Triple GEM stack tests at BNL (I) We set up a test facility at BNL using Weizmann equipment that has been used for R&D, for test of the final GEMs and that was specially sent to BNL in November. This includes SS vessel test box, HV divider, preamps, CAEN HV PS etc. The goal was to figure out what is wrong, why the GEM stacks DO work in a stable mode (we did several endurance tests) at WIS and why they show HV instability at SB. I also brought with me in November five fresh standard GEMs from the new (2007) production using a different packaging in order to exclude also the possibility that the standard plastic box shipment did some damage.

01/07/08I. Ravinovich4 Triple GEM stack tests at BNL (II) During my last visit to BNL four triple GEM stacks were assembled and tested: 1. Stack # 1, called “Thanksgiving” stack because it was tested during the Thanksgiving holidays. All three electrodes were standard GEMs that I brought with me. The stack went up to a gain of ~5000 without any problem and showed stable operation. 2. Then we had a number of a stupid technical problems like gas system leaks, bad SHV connectors, broken mesh, CAEN HV PS problem etc. That cost us quite some time but finally we fixed them. 3. Stack # 2 (“Hanukah” stack): all three electrodes were again standard GEMs, a mixture of 2006 and 2007 GEM productions. These GEMs were shipped to SB using usual shipment (plastic box with 24 GEMs packed into a wooden box). This stack also reached stable operation at a gain of 5000.

01/07/08I. Ravinovich5 Triple GEM stack tests at BNL (III) 4. Stack # 3: all three electrodes were again standard GEMs that did not pass SB quality control. Pretest in the clean room showed no problem but going up to 400 V in CF 4 one GEM showed a non-ohmic behavior. We washed it with de-ionized water but without success. 5. Stack # 4 (test stack #1): made of a new Gold plated GEM without CsI (top) and two standard GEMs from the “Hanukah” set (middle and bottom). It had at the beginning 2-3 trips but then showed stable operation at a total voltage of 3700 V corresponding to  V=497 V and a measured gain of There were some more trials to test more stacks just before the Christmas holidays but they failed due to bad GEMs that need cleaning. 7. At that time it was decided that we take all successfully tested GEMs to SB, assemble the stacks inside the glove box and try to reproduce the same results that were obtained at BNL.

01/07/08I. Ravinovich6 Triple GEM stack tests at BNL (IV)

01/07/08I. Ravinovich7 Work at SB (I): Glove box 1. In the meantime the conditions in the glove box at SB have improved dramatically: - purchase of vacuum cleaner installed inside the glove box - particle meter installed inside the glove box 2. The particle meter shows a reading of 400 when blowing inside the stainless steel box as compared to 10,000 previously. 3. It was then decided to take to SB the GEMs successfully tested at BNL, to assemble the stacks inside the glove box and try to reproduce the results obtained at BNL.

01/07/08I. Ravinovich8 Work at SB (II): Glove box Two stacks were successfully installed and tested at Stony Brook reproducing the same results as obtained at BNL. The next step is to evaporate CsI on a Gold plated GEM and repeat the gain test. This test is in progress now as we speak.

01/07/08 Work at SB (III): CsI evaporator SB folks investigated the CsI evaporator with the dust meter and found that inside the unit was clean (class 1000) when they had not disturbed it. The evaporation box and the evaporator walls were relatively clean. However, it was possible to wipe the CsI powder off of a number of surfaces, some severe e.g. the PMT shield. The PMT shield is a SS wall. It is closer to the boats and is a “mirror finish” stainless steel. HUGE quantities of CsI dust are removed by a simple swipe of this plate. It was cleaned with DI water.

01/07/0810 Cleaning the GEMs with de-ionized water At SB, there is excellent de-ionized water: typically 18 M  -cm, alarmed below 16 M  -cm Delivered at “faucet pressure” Can be sprayed forcefully like a rambunctious kid with a garden hose:

01/07/0811 Cleaning success rate: 6 for 6! FIX: GEM 218 (was ok up to 350V but drew non-ohmic current higher than that) FIX: Au#206 dead short strip 15 washed once, no change. second wash + dry Ar at 500V, fixed. FIX: Cu#152: dead short, strip9. FIX: Cu#172: two SST (strips shorted together), strips 2&3 and 24&25. FIX: Au#221: two separate dead shorts. this is the gem that is part of "Test Stack 1". (Story follows…) FIX: Au#230: CsI coated GEM with no resistance. SUMMARY: HARD cleaning (forceful spray) works great and every GEM tested so far has recovered. We will continue to clean through everything we presently have.

01/07/0812 Plans Complete the tests at SB: evaporate CsI and demonstrate smooth ramp up and stable operation at a gain of Clean all GEMs before testing as STD procedure. Remove the 4 stacks assembled in the HBD (they reached operating conditions only after many discharges and 2-3 days conditioning) and retest them after washing. Resume stack assembly in the HBD. We will see how much we have achieved by the end of January and then judge whether we have a chance for an in-beam test before the end of run 8.