High-Current Density Performance of a Magnetically Shielded Hall Thruster

The performance of a magnetically shielded Hall thruster operating on xenon and krypton is characterized at discharge current densities up to 10 times greater than its nominal level. A thrust stand and far-field probe suite are employed to evaluate operation at 300 V discharge voltage and discharge currents from 15 to 125 A (xenon) and from 15 to 150 A (krypton). The thrust, specific impulse, and anode efficiency at the highest currents are found to be $1650\pm 30\mathrm{mN}$, $2309\pm 56\mathrm{s}$, and $52.8\pm 2.0\%$ respectively for xenon, and $1839\pm 18\mathrm{mN}$, $2567\pm 48\mathrm{s}$, and $55.0\pm 1.6\%$ for krypton. The thrust density at the highest conditions are shown to be six (xenon) and eight (krypton) times higher than the lowest current condition. A maximum in anode efficiency as a function of discharge current is observed for both gases. This is attributed to a trade between mass utilization, which increases to unity with current, and beam utilization, which gradually decreases with current. The dependence of these efficiency modes on current is discussed in the context of a series of first-principles scaling laws. The observation that efficiency only moderately decreases with current density is examined in the context of high-power electric propulsion development.