Slide 2 Possible Run Conditions TemperatureRelative HumidityAir Pressure Warm (20º C)High (40-45% RH)Room (1 atm) WarmLow (<1% RH)Room (1 atm) WarmLowVacuum Cold (-20º C)LowRoom ColdLowVacuum ColdHighRoom From what I can determine there are 5 safe and one possible non-optimal combinations of RH%, temperature, and air pressure that the modules are operated in at CERN and Liverpool. Stand conditions are not the same (grounding, LV, HV) at either site. The non-optimal combination (Cold, high humidity, atmospheric pressure) was used study the effects of deposition of ice onto the module surface on the noise
Slide 3 Typical Run Conditions TemperatureRelative HumidityAir Pressure Warm (20º C)High (40-45% RH)Room (1 atm) WarmLow (<1% RH)Room (1 atm) WarmLowVacuum Cold (-20º C)LowRoom ColdLowVacuum ColdHighRoom At CERN assembly lab, majority of tests are cold, low RH% (sub-5%), 1 atm. We can not reproduce this condition at Liverpool. This is the only state in which the noise has been seen (note: stand condition in respect to grounding/shielding have changed during these runs). Only the state combination both sites have tested at is cold, low RH%, vacuum. This is state the vac-test is done at Liverpool on all modules and for the test-beam. Neither site has every seen noise in these conditions All laser tests at Liverpool are performed warm, high RH%, room pressure. No noise is seen.
Slide 4 Extreme tests at Liverpool We have undertaken two extreme sets of tests in order to try to reproduce the noise seen at CERN with our two test systems: With NA60, we reduced the RH% rapidly from 45% to <1% in about 1 minute. This will cause typical humidity effect to be the largest – If effect present, expect increasing bias current and localized noise With vac-tank, we cooled to -30º C in 45% RH air. This was to study the effects of deposited ice on the detector surfaces – Not sure what symptoms should be expected Neither test should any unusual noise effects
Slide 5 Extreme humidity tests For an typical humidity effect, dropping the RH% from room to low will cause the greatest noise effect It traps charge in a configuration on the surface of the sensor which causes high fields at the corner of the implant surface On the laser stand, we dropped the RH from ~45% to <1% in ~1 minute on two modules No change in bias current, noise, or pedestal seen I have no idea of a more extreme test which we can do to try to reproduce the effect
Slide 6 Extreme ice tests I Next, cooling cookies frost Finally, cooling outlet frosts The noise seen may be due to an extremely thin layer of ice forming on the sensor/Beetle surface May act as conductive or capacitive connection between sensor strips We sealed vac-tank full of 45% RH air and then cooled to -30º C while taking thermal images Not clear if ice on detector surface First, the cooling inlet frosts (lower reflectivity, lower uncalibrated temp)
Slide 7 Extreme ice tests II Noise measured on 2 modules at 250 V bias Module was left cold over 20 minutes, then run for less than 1 minute No noise effects seen No localized high noise, no noise wings
Slide 8 Conclusions At Liverpool, a series of tests where taken in order to try to reproduce noise effects seen at CERN Targeted humidity/ice effects We were unable to reproduce any of the effects at Liverpool No explanation of the cause of the noise symptoms seen at CERN are completely consistent – Humidity, ice, pick-up, shielding, power, … As the cause of the effects are not understood, we feel it is extremely important to study them We have no idea of how it will evolve, etc. We dont know what will make the problem better/worse