Detector 6 anneal 2012

Detector 6 had no notable issue since the 2012 anneal until the noise/livetime problem occurred in 2014 Jan.

On 2014 Jan 3, Hugh Hudson noticed that the attenuator system has been in state 3 for a few days. It turned out that, in Detector 6 (both front and rear), livetime was decreasing rapidly and preamp-reset and FAST LLD were also rapidly increasing (See also Tohban_Report_2014-01-08). Then, over the next few days, several adjustments were made to D6 high voltage and FAST threshold (both front and rear) as described below.

• 2014 Jan 04: As a first step, D6 HV was lowered by 8 steps down to about 3800 V.

   14-004-06:54:40 /ihvdac detector=6, voltage=198

• 2014 Jan 05: The livetime kept decreasing rapidly and so the D6 HV was lowered again by another 20 steps down to 2671 V.

   14-005-08:14:37 /ihvdac detector=6, voltage=148   (2868 V)
   14-005-08:16:00 /ihvdac detector=6, voltage=138   (2671 V)

• 2014 Jan 06: Previous commandings led to >90% livetime but the FAST LLD was still somewhat high compared to that of D1. Because lowering HV further could result in faster degradation of the detector and also because David Smith reported that the HV changes worsened the spectroscopy (See his email on Jan 5), it was decided not to lower HV anymore. Instead, the front fast threshold was raised from 0x22 (~ 8 keV) to 0x50 (~ 20 keV).

   14-006-08:03:32 /idpudumptabl dibtbl6
   14-006-08:03:57 /idputable6 frontfastdac
   14-006-08:04:08 /idpuload value=0x50

• 2014 Jan 08: The livetime has now reached ~98% and the FAST LLD reached its nominal level. However, it was noticed that the rear segment also had the same noise/livetime problem. Thus, rear fast threshold was raised from 0x45 (? keV) to 0x60 (? keV).

   14-008-07:35:20 /idputable6 rearfastdac
   14-008-07:35:40 /idpuload value=0x55
   14-008-07:36:03 /idputable6 rearfastdac
   14-008-07:36:56 /idpuload value=0x60

• 2014 Jan 08: In the meantime, it was decided to bring back the HV as much as possible to avoid further degradation of the detector. Over the course of 2 passes, the HV was raised by 30 steps up to 3259 V.

   14-008-07:37:49 /ihvdac detector=6, voltage=148
   14-008-07:39:15 /ihvdac detector=6, voltage=158 (3063 V)
   14-008-09:15:22 /ihvdac detector=6, voltage=168 (3259 V)

• 2014 Jan 08: Because noise level seemed to have increased during the HV commandings, front fast threshold was briefly raised from 0x50 to 0x64 then back to 0x50.

   14-008-09:18:13 /idputable6 frontfastdac
   14-008-09:18:39 /idpuload value=0x64
   14-008-09:24:57 /idputable6 frontfastdac
   14-008-09:25:28 /idpuload value=0x50

• 2014 Jan 28: The D6 front fast LLD threshold was raised from 0x50 to 0x60 at 22:13 UTC.

• 2014 Jan 29: The D6 front fast LLD threshold was raised from 0x60 to 0x70 at 22:11 UTC.

• 2014 Feb 5: The D6 front slow LLD threshold was raised from 0x0C to 0x1A (~6 keV) at 20:27 UTC.

• 05-Mar-2014: D6 front fast LLD was raised 0x70 to 0x80 at 2014/058 19:25 UTC. In D6 rear fast valids, no commanding was done to this segments, but the rear fast valids have risen to to ~1,000 --> 5,000 counts over the week, which is now comparable to D9r fast rates. Their lifetime is still at 98%.

• 2014 Mar 10: D6 front fast threshold was raised from 0x80 to 0x90 at 2014-070-03:00 UTC due to rapidly decreased livetime (down to 10% at the time of the commanding). The livetime immediately recovered to ~80%.