Evaluation of High Repitition Rate Laser-Guided Discharges at Low Pressure*

Pulsed low temperature plasmas are commonly applied to plasma chemical processing, plasma assisted combustion, and plasma aerodynamic applications. The current study presents the development and characterization of a high repetition rate laser-guided electric discharge system for low pressure flow control applications. In this work, the focusing of a femtosecond laser creates an ionization channel in air at gas pressures ranging from 5 – 60 Torr, producing sufficient ionization to reduce the breakdown threshold and initiate a high-current electric discharge.

For this purpose a custom discharge circuit was designed capable of attaining continuous pulse rates up to 10 kHz with an average power up to 20 W. Simulations in LTSpice were performed to design the circuit and optimize energy delivery and discharge efficiency within the constraints of available equipment. To improve simulation fidelity, an electrical model of the plasma was developed to capture the transient expansion of the ionization channel and its impact on the conductivity and circuit behavior. Experiments were performed and compared with simulations, showing reasonable agreement over the available range of test conditions. Experiments were conducted in stagnant air at frequencies up to 1 kHz with varying discharge voltages up to 2kV and a gap distance between pin electrodes of 5 mm. A measurable reduction in breakdown voltage of 200V – 500V was observed over a range of laser energy from 1 – 4 mJ using 200 ns duration 1030 nm laser pulses.