Detector 2 anneal 2012

From RHESSI Wiki

• Detector 2 has been unsegmented since the 2012 anneal. The entire detector volume is read out through the front segment electronics, so rates look higher for G2 (and also G4) than for the other detectors.

• Detector 2 is located in a position where it can receive light leak through a valve at the back of the cryostat. This problem occurs when the back of the spacecraft is pointed towards the sunlit earth, so it comes and goes with the orbital precession. Light leak only affects the rear sections of the detector, but since Detector 2 is unsegmented, the excess counts are seen in the front segment readout. Symptoms of this problem are enhanced reset rates and fast LLD rates, and the problem does degrade livetime. (Example) Raising the LLD level can ease the livetime problem, but this will have a negative effect on lower-energy spectroscopy. Light leak can be seen to a lesser extent in detector 3, and very rarely in 5 and 9.

• 2012 Feb 27 02:12: Small isolated spike in G2. No steps taken.

• 2012 March 30 17:53:27 UT: The front fast event threshold for detector 2 was raised by 0x10, from 0x60 to 0x70, to free up livetime (due to light leak problem)

• 2012 18 - 25 April:
  • Front slow threshold from 0x50 -> 0x60
  • Front fast threshold from 0x70 -> 0x80
    • /IDPUDUMPTABL DIBTBL2
    • /IDPUTABLE2 FRONTSLOWDAC  ;Load address 0x25B9
    • /IDPULOAD VALUE=0x60  ;Byte 7, Front Slow threshold
    • /IDPULOAD VALUE=0x80  ;Byte 8, Front Fast threshold

• 2012 August 1: In the past week detector 2 livetime has occasionally been compromised by the light leak problem. No action is being taken, since we do not want to impair low-energy spectroscopy.