1. Setup to look at the HV current on side walls of HPD (diode is isolated from this current path) ?? Cable capacitance HV 1G PC HPD HV gnd diode 10 M B Voltmeter 20 Mohm OR V RBX gnd Scope on 50 ohm

2. HV current to Ground through ~5Mohm Previous measured at CERN

3. Correlation between DC measured current through the side-walls of HPD and Noise (CERN B157)

4. Correlation between AC measured current through the side-walls of HPD and Large noise pulses (Pulse in the HV current is first) (negative so it is opposite from photo current)

5. We can see the small pulses with keithly bias supply Without amplifier we see also large pulses in bursts

6. When getting on an angle small pulses increase but large ones disappear

7. Lifting the HPD window We cut the HV cable We milled of this the plastic and rubber on the top on a lay After that you should heat the Indium Tin seal to 80C We had to poke with a needle to break vacuum before we could lift the Window. What also could be tried is don't pop the window but just heat it ones until the solder is melted and liquid (at that piont the vacuum is not broken ) and then let cooldown and re-measure noise. It could be that there are some variation from HPD to HPD in the seal  ?????