On Sept. 14 2022, a 10kOhm 30W resistor was installed in each target station faraday cage, in line with the HV bias supply. This was an effort to reduce the current draw from the BIAS supply and protect the power supply controls cards which have been repeatedly breaking due to HV sparks (we think). In the end we still broke cards after the installation, so it doesn't seem to have helped. See below for details on the electrical side:

At 30kV, HV currents are around 100-150uA, meaning the voltage drop over the resistor is around 1.5V. When operating at higher voltages, with higher current draw, the voltage across the resistor could be over 2V and we could get into a situation where it would have an effect outside the normal adjustments needed on the mass separator. We made this decision based on the fact that the power supply's setting resolution is on the order of 1 x 10^-4.

When the resistance of the water changes, this affects the current draw from the power supply and this in turn affects the voltage over this resistor. Based on some sample numbers of running times, there is not much variation in the current except from sparks and if there is some issue, like water leaking between HV and ground. During normal running, the voltage change across the resistor should be less than 0.5V during normal operation. This is on the same order as the 8 hour stability of the power supply.