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Message ID: 31     Entry time: 01 Feb 2017, 17:42
Author: Jan Grünert 
Location: General 
Severity: Problem 
Subject: XGM resistor issue - analysis progress 

This is the current (w5) progress at DESY concerning the analysis of the serious XGM resistor issue (summary; a detailed report by DESY is available):

  • The new “pulser test” was verified at an operational XGMD at FLASH. The test method is (unfortuately) OK. This means that the test results with issues from last week on all our XGMs are REAL.
  • 25% of all resistors in XBPMs affected, 0% of resistors in HAMPs affected, no capacitors affected.
  • Since no HAMP resistors are damaged, damage by environmental conditions (venting, humidity etc.) can be excluded. The main differences to the affected resistors are the HV-conditioning and the experienced HV-values of the resistors (typically XBPM resisotors are tested up to 12kV, HAMP resistors each see much lower voltages).
  • An XGMD chamber at FLASH was tested-to-destruction-of-resistor by applying a large differential voltage (>3kV) between neighboring electrodes, e.g. on mesh_e and FC_e. These resistors (Caddock MS220) have a nominal voltage breakthrough rating of ~500V but never had issues. They are used in all our XGMs.
  • New, other resistors (Ohmite MOX-1N-13) with higher voltage breakthrough rating of 10kV were procured and arrived tuesday
  • The new resistors were built into the tested-to-destruction XGMD at FLASH, unit is now pumping, will be retested with applying pulsed HV (on both Caddoc and Ohmite resistors) when at suitable pressure.

Further plan (w5end + w6) concerning the XGM resistor issue:

  • If the new resistors survive the test, then next monday the XGM01 at HERA-S will be opened, the tested-defect resistors will be checked and replaced with the new resistors.
  • If all tests on XGM01 are then ok including an acceptable RGA, all other XGMs (XBPM chambers) will be opened and resistors exchanged. Even ok-tested resitors would be exchanged to avoid future unexpected failures. HAMP chamber resistors will not be exchanged (large number >20 of resistors, no failures).
  • If the RGA is not acceptable, the resistor Ohmite MOX-1N-16 is another alternative, but has increased delivery time.
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