Measuring small currents at DC high voltages without floating meter
I came up with this way of current sensing on the secondary 20:1 step-up transformer ground side with a shielded non-inductive 10mOHm shunt.



Although 1mohm arc current is a major crosstalk issue with &lt;50ps rise time, this output arc discharge to air gap gives 10% of the voltage secondary 10mOhm shunt.  HV diodes and plastic caps with wise RF/HVDC clean construction are essential.  0.3m BIL 200kV x2 in series, ceramic bushings minimum over a teflon sheet baseplate is what I used.  Even with a grounded safety cage, the paint gave off static discharge 5m away and you could feel the hair on your neck rising. Much more risky than 50kV AC due to dust.