ITW has been behaving badly at higher voltages recently, even without protons on. I conditioned it up to 50kV with heaters off in the TCS and it was fine. But when I tried to do the same with heaters on in the station, it was quite sparky and it kept tripping the TGHT/TBHT. I went to 49kV where it was unstable, then lowered to 48kV where it looked fine for 30mins. But even operating at 40kV, it tripped the heaters several times. The TBHT voltage came back lower than before on the last trip, so I am getting worried about it.

I decided to make sure all the electronic spark protection was ok in the faraday cage. There is a resistor/gmov combination across the terminals of each TGHT/TBHT in which Tomislav replaced the gmovs for me because his tester did not work at those low voltages, so we couldnt see if they were broken. The electronics diagram called for 18V gmovs, the replacements are 22V because that's all we have.

We also tested and re-installed the capacitor-gdt-resistor combinations that John installed last year from TGHT/TBHT bubars to HV common. I originally removed them because we couldn't bias a FEBIAD with them on - this still has to be investigated. The measured values are 0.148uF, 90kOhms and a breakdown voltage on the gdt of 410-450V.

Hopefully this prevents sparking the power supplies off.

Sunday, June 16, 2024, 07:03 : power supplies have not tripped off since electronics repair. See data/TM4sparkingbehaviour_June152024.dat for sparking frequency over ~10hrs of protons (5-14uA). >14 sparks during this time (14 captured by PLC when voltage dropped, many more current peaks).