HBD Meeting 3/14/06 B. Azmoun BNL Testing and Preparation of HBD Full Scale Prototype for Upcoming Engineering Run Puzzling Behavior of GEM’s To Do List

B. Azmoun, BNL3/14/20062 HBD Prototype GEM Tests: Summary of Previous and New Results

B. Azmoun, BNL3/14/20063 Iteration 1 Source holder configuration: –250uCi source (7mm aperture) mounted on Cu –clad G-10 panel 1.3cm above mesh. –Source holder electrode faces mesh and gets same voltage as upper electrode of top GEM (weak reverse bias field between mesh and source forces conversions back to source holder electrode). –Source mounted in center of panel, above intersection of thin G-10 support structure of mesh, GEM, and spacer. RESULT: –low amplitude ~ 10Hz –Drift field does not change detected rate. Later found short in 3 strips of top GEM—top GEM wasn’t functional –Speculation that low rate and low gain are due to signals form 1 st transfer gap. GEM/Mesh Support structure HV Fe-55

B. Azmoun, BNL3/14/20064 Iteration 2 Replaced top (shorted GEM), otherwise same configuration. RESULT: Irregular Behavior –Normal Gain –Detected Rate ~ 1Hz (+1kV/cm) Compared Results to Standard Triple GEM Set-Up comprised of 10x10cm Segmented CERN foils (the same field configuration was applied) Fe-55 HV NOTE: In reverse bias, the pulse height amplitude drops by several factors in all cases, and a significant number of pulses are at the level of the noise. Also, positive-going-ringing-pulses (from micro- discharges?) are detected at a rate of a fraction of a Hz. Thus, these additional pulses impose large errors on rate measurements at levels below a Hz. Low Rate measurements depend strongly on the threshold applied.

B. Azmoun, BNL3/14/20065 Iteration 3 Source placed in center of 1 quadrant. RESULT: Normal Behavior –Normal Gain –Detected Rate ~ 30Hz (+1kV/cm) Speculation: thin G-10 support structure is imposing space charge that does not affect operation of the GEM when source is placed in the center of 1 quadrant. Fe-55 HV

B. Azmoun, BNL3/14/20066 Iteration 4 Installed source holder with 2 sources, 1 in quadrant, 1 in center. –Removed mesh and 1.5mm spacer  source holder panel- electrode establishes drift field in place of mesh. RESULT: Irregular Behavior –Low Gain –Normal Rate 1kV/cm) –Drift Field has expected impact on rate –Same results for both sources Fe-55 Top GEM has Leakage Current: I =5.0nA, but shows ~100Gohm of impedance. Towards the end of the test the top GEM tripped and developed a 25Mohm short in 1 strip.

B. Azmoun, BNL3/14/20067 Iteration 5 Removed resistor from shorted strip  top GEM Ok. Replaced mesh and spacer; again 2 sources in center and quadrant. RESULT: Normal AND Irregular Behavior –Initially the GEM’s behaved normally, but after a trip, they started to misbahave: Normal amplitude pulses are rate of ~1Hz (+1kV/cm), similar to iter. 2 Upon further inspection, low amplitude pulses are also rate of ~30Hz (+1kV/cm), similar to iter. 4 Same results under both sources. –Top GEM draws 13nA of current –Middle GEM draws 17nA, which falls to 0.1nA in 15min –After Ramping HV up, the GEMs again start to operate in Normally. Two Operating Modes are Apparent (Results resemble those from earlier iterations): –Normal Mode: Larger amplitude (high gain) ~30Hz –Irregular: Large Amplitude ~1Hz & Smaller amplitude ~30Hz HV Fe-55

B. Azmoun, BNL3/14/20068 Iteration 5 Continued… Normal Mode Behavior: –Normal rate of ~30Hz –Drift Field works as expected –Same Results under both sources –At DG ~0kV/cm, the detected rate is ~3Hz  1/10 of the rate at 1kV/cm: must be collecting charge from 150um layer above top GEM –In normal operating mode, low amplitude pulses are also present and exhibit approx. a factor of 10 less gain, with a rate of ~10Hz. (Rate is the +1kV/cm and 0kV/cm). This is consistent with signals from the 1 st transfer gap  confirmation of results in iteration 1.

B. Azmoun, BNL3/14/20069 Conclusions from HBD prototype GEM Studies The behavior of the GEM’s is independent of the location of the source  same results for both sources  no space charge effects. The GEM’s have two distinct operating modes, the cause of which is unknown  most likely related to either the leakage current from the top GEM or the momentary malfunction of the middle GEM We will continue to investigate the behavior of these GEMS within the USB GEM testing vessel  we have to make sure we don’t encounter such irregular behavior during the engineering run.

B. Azmoun, BNL3/14/ TO DO LIST This Week… –Finish Installing Mounts for installation into PHENIX –Test UV Flash Lamp/Install onto vessel –Too late for new PA PCB –Install protective cover/shield over PA’s –Install temperature / pressure gauges –Go to PHENIX IR during next access (wed.) Run cables, discuss/plan details of installation, etc. Next Week: Bring prototype over to USB –Test GEMs in large testing vessel before PC install. –Produce/Install CsI PC –Test GEMs within prototype after PC install. Low rate Fe-55 source in corner of acceptance? Flash Lamp: read off pe current/pulse for relative measure of QE