Power supply design considerations for maintaining a minimum sustaining current in a vortex water wall high-pressure argon arc lamp

Abstract

Vortex water wall high-pressure argon arc lamps are used to generate intense light and are capable of operating at radiative efficiencies greater than 50%. These lamps are being considered for use in a pulsed DC mode of operation in the next generation of rapid thermal processing applications. The results of a series of experiments have shown that the breakdown to arc transition consists of a prethermionic electrode emission phase and a prethermal ionization phase. The large dynamic voltage and current range between the breakdown phase and the arc phase necessitates the use of three different power circuit topologies. A high-voltage ignition circuit is connected in series with an arc-sustaining power source. The series connection ensures that the arc-sustaining power supply is isolated from the high-voltage ignition circuit. The arc-sustaining current source power source consists of a step-down hysteresis-current-controlled DC/DC converter cascaded with a constant off-time output-voltage-controlled step-up DC/DC converter. The current-controlled converter supplies the minimum arc-sustaining current, whereas the step-up converter provides the minimum post-ignition prethermal ionization voltage. The inclusion of a shorting switch allows one to reduce the current ratings of the high-voltage circuit components. Finally, experimental verification of a simplified circuit model of the ignition to arc transition, the circuit operation, a power supply design procedure, and a design example are provided.