Compact Laser Ignition for Vacuum Arc Thrusters

The lifetime of existing Vacuum Arc Thrusters (VATs) is fundamentally limited by their ignition system, motivating the exploration of alternative approaches. This work presents a novel demonstration of a compact laser ignition system based on laser diodes. A pulsed laser driver was developed to generate adjustable pulses. Microsecond laser pulses were focused onto candidate ablation materials biased by a pulse-forming network (PFN), where laser-induced ablation initiated the arc discharge. Experiments demonstrated successful ignition with pyrolytic carbon and graphite. Pyrolytic carbon showed near-instantaneous plasma ignition, suggesting a very low ignition threshold, but poor repeatability as surface modification by the arc discharge prevented further ignitions. Graphite, in contrast, exhibited strong repeatability with example conditions of a 0.65 mm gap, 400 V PFN voltage, and 49 J/cm² over 500 µs at 455 nm. By introducing a nearby flow path, the initial seed arc was elongated and transferred to a secondary material, where the main discharge occurred. This effectively decouples the ignition process from the electrode erosion. These results mark a pivotal step toward the development of VATs fully reliant on laser ignition.