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A model to predict the plasma properties inside a thermionic hollow cathode as a function of operational conditions and geometry is presented. The hollow cathode features a lanthanum hexaboride (LaB6) insert, which is capable of emitting current densities as high as 10(5) Am-2 at temperatures of similar to 1900 K, along with a tantalum orifice plate located at the downstream end of the cathode tube. The model self-consistently computes the plasma parameters in both the emitter and orifice regions. A simple semiempirical relation is suggested to evaluate the plasma penetration depth in the cathode interior, which is of primary importance to establish the plasma conditions. The heat transfer mechanisms and the related temperature gradients along the cathode are evaluated with the aid of a dedicated thermal model, which is coupled to the plasma model and accounts for temperature-dependent material properties. A parametric study of the cathode performance was conducted to assess the dependence of the power consumption and operational lifetime on discharge current and mass flow rate, as well as on the geometry. The results are in good agreement with both theoretical and experimental trends found in the literature as well as with experimental data collected by Alta. Further developments will include a deeper investigation into the cathode erosion phenomena, along with a broader comparison with empirical data

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An experimental investigation of a pulsed, quasi-steady, 100-kW-class applied-field magnetoplasmadynamic thruster is discussed. Measurements were obtained with argon propellant for a variety of currents, mass flow rates, and magnetic field strengths in a power range between 20 and 250 kW. Tests were carried out in Alta's IV-10 vacuum facility. With a volume of about 200 m(3), IV-10 allowed for a current-pulse duration up to 1 s as well as for minimization of the environmental interaction with the plume. Although the shot duration was still too short to achieve steady-state thermal conditions, it allows for direct, time-resolved thrust measurements. To this purpose, a new single-axis thrust stand was designed to improve the frequency response of the existing thrust stands commonly employed in high-power devices. A maximum thrust efficiency of 28% was obtained at about 200 kW for an applied magnetic field of 120 mT and a mass flow rate of 60 mg/s. At 100 kW, for the same mass flow rate and magnetic field, a thrust efficiency of 22% and a specific impulse of about 2500 s were achieved. Moreover, during the arc ignition phase, the cathode current attachment was found to be distributed mainly at the external surface of the electrode while a transition from diffuse to hollow cathode behavior was observed after approximately 400 ms from the breakdown

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