Adrian Woodley | Searcharxiv

arXiv2026

Pulse Shaping Increases Efficiency in Pulsed Plasma Accelerators

The performance of a gas-fed pulsed electromagnetic thruster is governed by the ability to deposit electrical energy while propellant is available for acceleration. Current pulsed-power systems require tradeoffs between high-current discharges that produce high exhaust velocities and longer pulses that overlap the energy deposition with more of the gas injection. This limited control restricts the specific impulse and mass utilization of these thrusters. This work introduces programmable pulse shaping as a method to increase control over energy deposition and expand the accessible operating space. We use solid-state integrated power modules to vary the discharge delay, pulse width, peak current, and the shape of the current waveform as propellant is injected. Experiments varying pulse widths from 30 to 500 $\mu$s and peak currents from 3 kA to 16 kA show that short, high-current pulses produce higher exhaust velocities and greater impulse bits than longer, lower-current pulses at comparable discharge energy. The switches also enable multiple discharges of arbitrary positioning and duration during a single gas injection. This micro-burst operation is shown to increase specific impulse in air by 278\% from 840 to 3177 s through improved propellant utilization. This same pulse shaping ability is found to increase thrust efficiency from 0.2\% in single-shot operation to 3.3\% in micro-burst operation while operating with air.

physics.plasm-ph↗

arXiv2025

Magnetohydrodynamic Operating Regimes of Pulsed Plasma Accelerators for Efficient Propellant Utilization

The presence of magnetohydrodynamic (MHD) acceleration modes in pulsed plasma thrusters has been verified using the magnetic extension of Rankine-Hugoniot theory. However, the impact of initial conditions within the accelerator volume on the formation and structure of these modes remains poorly understood. This work develops a regime map to clarify how key initial conditions - such as propellant gas dynamics, pulse energy, and the timing between propellant injection and discharge initiation - govern transitions between two distinct MHD operating modes, a magneto-detonation and magneto-deflagration, along with an unstable transition regime that connects them. To characterize these regimes, a combination of time-of-flight and thrust stand diagnostics was used to assess their properties, scalability, and structure while operating with air. Time-of-flight measurements reveal that reducing the initial downstream propellant mass ($m_{dwn}$) of air from 120 $μ$g to 60 $μ$g shifts the thruster from the magneto-detonation to the magneto-deflagration regime, increasing exhaust velocity ($v_{ex}$) from 20 km/s to 55 km/s. In this regime, the thruster exhibits improved propellant utilization as less mass is injected. At a constant 8 kA of peak current, specific impulse (Isp) increases from ~100-2000 s as $m_{dwn}$ decreases from 70 to 10 $μ$g, corresponding to an increase in utilization efficiency ($η$util) from 5% to 35%. Thrust-to-power ratios, measured using a thrust stand, also improve with peak current in the magneto-deflagration regime, increasing from 4.5 mN/kW to 8 mN/kW and 6.7 mN/kW for injected mass bits of 25 $μ$g and 50 $μ$g, respectively. This work provides critical insights into how the initial conditions in pulsed plasma thrusters dictate the formation of ionization waves, structure of plumes, and the performance of thrusters.

physics.plasm-ph↗