Tomislav and John Chow tested the spare bias supply located in the rack of the electrical services room. This is a FUG HCN 1400 M-60000, serial 11590-01-01, PO TR131986 but when it was installed online we found it could not go above about 40kV. It was replaced but not tested until now. Tomislav says:

"We started testing the FuG this morning, in manual mode it is possible to reach 60 kV, 59.75 according to the display and with the load we have 1.6 mA. From the DC HV point of view, at least in manual mode no problem.

When we looked at the HV through a 1000:1 voltage divider in the oscilloscope there is a situation, the coupling in graphs 4 and 5, attached, is AC, and it was taken at 55 kV. The 200 mV scale represents 200 V because of the divider. There is a strong noise of 200 Vpp at 55 kV, it can be interpreted as ripple of 0.36%, we usually ask in FuGs 10^-5 or 0.001%. Also there are random peaks of 1 V in the divider (1000V in the output) that indicate a possible failure of the PWM circuit that generates the high voltage.

Because of issues like these Friedhelm replaced the old ITW power supply, these instabilities caused problems in the experiments, so I am not sure if it is necessary to continue testing this PS. We can only do a remote test that I do not expect to give different results from what we have now, maybe we will find an issue and it does not go beyond 40 kV, and we can check long term stability, the DC value should remain very constant for at least 8 hrs."