1. High Gain Mystery of WS(1-5) Solved (Hopefully…) C.Woody HBD Meeting April 13, 2010

2. C.Woody, HBD Group Meeting, 4/13/102 Chain of Events Preamp boards on WS(1-5) trip off around noon on March 16 th. HBD LV control panel indicates cooling air flow fault. Cannot turn preamps back on. Requires access to fix. All readout board temperatures look ok. Get Controlled Access about 1 hour later. HBD HV and all PHENIX magnets are left on. After entering the IR, we find the air flow indicator light to WS(1-5) shows low air flow. Frank Toldo feels all four fans and determines they are running. Adjusts sensor on WS(1-5) ~ 1 mrad. Indicator light immediately comes back on and indicates airflow is OK. John Haggerty cycles power on all 4 LV crates and does a complete feed. All crates come back on and feed works fine. Everything seems ok.

3. C.Woody, HBD Group Meeting, 4/13/103 Chain of Events (cont’d) Starting immediately with the next run taken, the gains on WS(2-5) look high. WS1 looks ok. Check electronics, noise, gas, etc. Everything looks fine. Problem persists for ~ 3 weeks. Get access on April 7 th to fix partial short on WS5. In the process, Bob notices that the back panels of all the WS modules feel warm. Also no hissing sound of airflow as on WN. Frank checks fan again and determines that it is not working (no air flow, yet sensor says it is ok). Fan is changed and airflow is restored. Gains of WS(2-5) return to normal starting with the next series of runs.

4. C.Woody, HBD Group Meeting, 4/13/104 Probable Cause Lack of cooling on WS modules caused local temperature to go up (rear panels were heated, heating gas in the region of the GEMs where all the gas gain takes place), yet overall temperature of the detector (as measured on the bottom near the gas input) hardly changed (see following plot). Higher local T caused local P/T to be lower, increasing the gain for these modules. Effect was worse on WS4 near the top (heat is partially trapped) and least on the bottom. WS5 has more room to vent.

5. C.Woody, HBD Group Meeting, 4/13/105 Why wasn’t this found earlier ? Air flow sensor for WS(1-5) indicated air flow was ok, but it clearly was not (sensor fault ?) Readout board temperatures did not show any large increase (although these are not monitored carefully, or recorded…) We didn’t notice the small increase in overall detector temperature (~ 1 deg) So, it took a while, but it looks like we solved the mystery...

6. C.Woody, HBD Group Meeting, 4/13/106 Temperature Change Around March 16th

7. C.Woody, HBD Group Meeting, 4/13/107 West Module Gains