Optical imaging of breakdown in a low-pressure argon discharge

Breakdown is an elementary process in plasma science, but the physics are still only poorly understood, mainly due to its rapid, transient nature. We investigated breakdown in a low-pressure argon discharge experimentally by making time-resolved images of plasma emission with an intensified charge coupled device (ICCD) camera. Several features of the breakdown, such as a light emission region in front of the anode and a light front crossing the discharge gap from anode to cathode were investigated. We also observed a pre-breakdown light flash, which occurred before the main breakdown stage, at the time when the applied voltage was below the static breakdown voltage. Although details remain unclear, this flash of light is thought to originate from surface charges left over from previous discharges. In addition, we measured the time delay of the discharge as a function of afterglow period, known as a memory curve. These measurements indicated that charges produced in a discharge were mainly lost in volume recombination processes in the first 10 µs of the afterglow