Experiments were performed at ASU and the US Navy’s Edgar Beauchamp High Voltage Test Facility (EBHVTF) in Dixon, CA. A chamber was built in which humidity could be controlled. This is schematically illustrated in Figure 2a. Figure 2b is a photograph of the chamber and the general experimental setup. Uniform fields were obtained using Rogowski profile electrodes of 15 cm diameter made of aluminum 6040 alloy. Gap lengths were less than half the plate diameter to ensure uniformity of the electric field in the gap.