Investigation of pre-breakdown phenomena in CO₂

While performing high-voltage pulsed breakdown tests in room temperature pure CO2 at 0.1 MPa, significant voltage dips (up to 20 kV) were observed preceding the breakdown on application of voltages in the range of 40-70 kV. The time duration of these voltage dips can be up to a few hundred nanoseconds, followed by the full breakdown of the gap. Such dips were observed on application of negative polarity impulses to the electrode in a rod-plane configuration at 0.1 MPa. However, the dips were absent at higher pressures. To investigate these pre-breakdown discharges in detail, an experimental setup was developed with necessary diagnostic tools to measure the pre-breakdown current. Optical diagnostics such as a photomultiplier and a (fast) intensified-CCD camera were also used to study the discharge characteristics. In the setup developed to measure the pre-breakdown currents, a commercial fiber optic transmission link is used to isolate the current measurement on the high volage side from ground. However, to power the fiber optic connectors, a novel method called 'power over fiber', was employed. In this study, along with the findings of the pre-breakdown phenomena to qualitatively describe the discharge process in CO2 at various pressures (0.1-0.9 MPa), the technique used to measure the current on the high voltage electrode side is also described.