The test stand holds up to 63kV, however at voltages over 54kV there are small discharges, rising to a continuous level around 60kV. The best guess right now is that these are coronal discharges coming from the end of the HV duct to the faraday cage. The only way to fix this would be to round out the edges of the duct, or to move the duct farther away. Since I have heard small discharges in other places, we may need to make a variety of modifications. Things that have had no effect:

1. Changing the EZL/EE voltages - break down is happening only between HV bias and ground

2. Cleaning the faraday cage

3. Locating sparks with a thermal camera

4. Conditioning - break down always happens at the same point