Notes on STAR Cockcroft-Walton bases

[Elton Smith <elton@jlab.org>]

Hi Paul,

Bernhard just returned from Brookhaven for a review of the barrel 
calorimeter for the STAR detector. They have had considerable trouble with 
their Cockcroft-Walton bases, which I list here for future reference. 
One can argue that several of these issues are probably unrelated to the 
Cockcroft-Walton design per se, but still worth evaluating within the 
context of the Hall D design:

1. 15% of their micro-processors died upon turn-on. The manufacturer had
changed the specs for the reset circuit for the production
micro-processors, causing the failure.

2. Discharge between pmt HV and ground casing, fixed by adding insulation 
around pmt.

3. Corrosion inside surface-mounted dip switch with gold contacts. 
Suspicion is that the mylar cover used during the board soldering process 
did not fully protect switch.

4. Gain changes in the pmt were traced to leakage currents developing
through the capacitors in the circuit. The cause of the failures is
thought to be due to mechanical stresses of the (surface-mounted)
capacitors by the spring tension of pmt installation.

Cheers, Elton.

-- 
Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625