HBD HV Commissioning

1. HBD HV Commissioning Itzhak Tserruya DC meeting, BNL, February 7, 2006

2. HV commissioning: executive summary • Main HBD activity over the last six weeks. • Progress not as smoothly as it should be or as expected. • Systematic individual GEM conditioning in N2. • Individual GEM conditioning in CF4. • Presently approaching operational HV in groups of modules.

3. Short reminder • The HBD consists of 24 identical detector modules. • Each module is composed of a mesh and 3 GEMs. Size • The top face of the top GEM is covered with a thin layer of CsI. Electron microscope view of a GEM foil Electron field in the GEM holes

4. Resistive Chain Outside HBD =2.2M Inside HBD 28 HV segments in each GEM R2=20M Top GEM =10M Middle GEM Bottom GEM • Normal operation: HV= 3720V VGEM = 500V I = 150A • Dead short in one HV-segment of one GEM: • I increases by 1.56% • active area loss of 0.15 %

5. Status as of Feb. 1, 2007 After completing the conditioning in CF4 • We have found problems in 28 GEMs (out of 72): • 16 top • 7 middle • 5 bottom • Out of them: • 7 have a dead (or almost dead) short and the 10M has been replaced by a 20. • 14 draw high current with non-ohmic behavior. The current ranges from 3 – 25A at about ~500V reflecting a GEM impedance of 0 – 140M. • 3 draw low current (410 and 777nA) at ~500V reflecting a very high GEM impedance (0.6 and 1.3 G). • 4 seem to have multi-strip problems and the 10M has been removed.

6. Status as of Feb. 1, 2007

7. 20 MOhm slope 10 MOhm slope Conditioning in N2 Conditioning in CF4 EN0,1,2

8. GEM test history • All GEMs were subject to the following tests: a) in open air & clean room (WI): • ohmic test before and after framing • 100 V test after soldering the 20M resistors b) Inside test box (WI): • 520 V in CF4 • 480-500V in Ar/CO2 during the single GEM gain mapping. c) Inside glove box (SUNY): • 550 V in pure N2 • ~350 V in Ar/CO2 during the final triple GEM gain mapping. d) After installation and prior of closing the HBD (SUNY): • 100V test and capacitance test

9. Diagnostics • There is no reason to believe that there was something wrong on the GEMs up to installation inside the HBD. • There is no reason to believe in some damaging chemistry between the CF4 and the CsI. We have accumulated experience (integral of several months of operation CF4 & CsI) and we never observed a problem. • The observations are consistent with dust inside the detector and/or some physical damage of the GEMs most likely during the transportation from SUNY to BNL. • Time may help sharpening this diagnostic or we may need to open the detector.

10. Present status • The entire detector is rather stable at 3200 V. • At 3200 V we have clearly seen cosmic signals at the expected rate of 1 count/10 sec per pad in a perfect module (ES3). The rate decreased for those modules that have a current flowing thru the top GEM. • We are attempting to bring a group of 8 modules up to 3500V • We are monitoring stability of the other modules.

11. Feb.1 Feb.6 Stability Monitor the relative difference of the module current wrt to the ideal module current ES3 Example of a good and stable module WN0 Example of an unstable module

12. HBD IN HBD W ~30 % Loss HBD E ~30-40 % Loss Gas monitoring ~1 Week Ago • 30% loss should correspond to 80 ppm of water. However, according to the hygrometer the detector is at app. 12 ppm. Origin of discrepancy not yet understood. • Working assumption: the gas monitoring results are correct. At the present flow of 2lpm we are loosing 25% of the UV photons. • Rob is working on increasing the flow by a factor of two.

13. Other activities • Chi has implemented zero suppression. We shall test it soon. • Good progress in the full fledge Monte Carlo (Maxim, Ilia and Anne) • Takao working on the on-line monitoring. • Rob working on increasing the gas flow through the HBD.