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Performance, plume properties, and discharge stability of a 9 cm diameter laboratory model Hall thruster were measured at vacuum chamber background pressures ranging from 1e-6 to 6e-5 Torr. The thruster was operated at constant discharge powers of 300 and 500 W while background pressure was varied from the minimum achievable value to values 10, 20, and 40 times greater than the minimum at each power level. Discharge current oscillation amplitude generally increased with increasing background pressure, and the sensitivity of oscillation amplitude to background pressure increased with increasing applied magnetic field strength. The fundamental frequency of the discharge current oscillations varied with background pressure. Thrust, specific impulse, and efficiency declined as stability degraded, primarily as a result of increased electron cross-field mobility, broadening of the ion energy distribution, and increased multicharged ion production. Ingestion of background neutrals appeared to lengthen the ionization zone and shift it toward the anode. NomenclatureF = thrust α = thrust correction due to multicharged ions β = thrust correction due to off-axis flow J D = discharge current V D = discharge voltage m = ion mass q = elementary charge J n+ = beam ion current in n th charge state (n = 1, 2, 3) g = acceleration due to Earth's gravity at sea level η c = current utilization efficiency η V = voltage utilization efficiency η m = mass utilization efficiency n n = thruster exit plane neutral density m  = total anode flow rate A e = thruster exit plane area k = Boltzmann's constant T n = neutral temperature at thruster exit plane

Absolute partial and total crosssection functions for the electron impact ionization of C60 and C70Absolute photodissociation cross sections of gas phase sodium chloride at room temperature

An investigation of a fully cylindrical Hall thruster was performed using laser induced fluorescence (LIF) to measure ion velocity profiles in the plume. The measurements confirm a previously reported 9% increase in the exhaust energy when the cathode keeper draws an excess current (overrun mode). Furthermore, the velocity directions in the plume remain relatively unchanged for the cusped and direct magnetic field configuration in both overrun and nonoverrun modes. Previously reported plume narrowing in the overrun mode was confirmed and found to be due to the shift of the acceleration and ionization regions toward the anode. The electric field inferred from the LIF measurements allowed calculation of the electron E×B drift. Close to the centerline of the thruster, electrons drift azimuthally with velocity decreasing away from the centerline, thus creating shear. This shear can be a source of plasma instabilities and influence electron transport. Further away from the centerline, electrons drift in the opposite direction with their velocity increasing with increasing radius. In that region, electrons rotate without shear.