Ryan W. Conversano

Development and Initial Testing of a Magnetically Shielded Miniature Hall Thruster

The scaling of magnetically shielded Hall thrusters to low power is investigated through the development and fabrication of a 4-cm Hall thruster. During initial testing, the magnetically shielded miniature Hall thruster was operated at 275 V discharge voltage and 325-W discharge power. Inspection of the channel walls after testing suggests that the outer discharge channel wall was successfully shielded from high-energy ion erosion while the inner channel wall showed evidence of weaker shielding, likely due to magnetic circuit saturation. Scanning planar probe measurements taken at two locations downstream of the thruster face provided ion current density profiles. The ion current calculated by integrating these data was 1.04 A with a plume divergence half-angle of 30°. Swept retarding potential analyzer measurements taken 80-cm axially downstream of the thruster measured the most probable ion voltage to be 252 V. The total thruster efficiency was calculated from probe measurements to be 43% (anode efficiency of 59%) corresponding to a thrust of 19 mN at a specific impulse of 1870 s. Discharge channel erosion rates were found to be approximately three orders of magnitude less than unshielded Hall thrusters, suggesting the potential for a significant increase in operational life.

CubeSat Lunar Mission Using a Miniature Ion Thruster

The feasibility of CubeSats utilizing the Miniature Xenon Ion (MiXI) thruster for lunar missions is the focus of this investigation. The successful heritage, simplicity, and low cost of CubeSats make them attractive candidates for scientific missions to the Moon. This investigation presents the first-order design process for developing a lunar mission CubeSat. The results from this process are then applied to a 3U CubeSat equipped with a MiXI thruster and specifically designed to reach the lunar surface from a low Earth orbit. The small, 3cm diameter MiXI thruster utilized is capable of producing 0.1–1.553mN of thrust with a specific impulse of over 3000s and is projected to be capable of generating over

Magnetically Shielded Miniature Hall Thruster: Performance Assessment and Status Update

The magnetically shielded miniature Hall thruster, originally tested at the University of California, Los Angeles, underwent performance validation experiments at the Jet Propulsion Laboratory. The thruster was operated over a range of discharge voltages, from 150 V – 300V, and currents, from 1 A – 2.3 A. It was discovered that the thruster operated in two distinct modes which were dependent on the thruster’s temperature: a “jet” mode and a “diffuse” mode. At the nominal condition of 275 V and 1.2 A in the jet mode, a thrust of approximately 12 – 13 mN was measured by a thrust stand with an anode efficiency of approximately24%. At the same nominal conditions, the diffuse mode showed a thrust of 11 – 12 mN and an anode efficiency of approximately 21%. Characterization of the plume in both operating modes was accomplished using a shielded Faraday probe, a retarding potential analyzer, and an ExB probe. Discharge current oscillations on the order of 2.5 – 4 times the mean current were observed during jet mode operation, while the oscillations in the diffuse mode were on the order of 20% of the mean current. Results from the plume characterization, post-operation discharge channel inspection, and discharge oscillations, combined with the temperature-dependent mode shift, suggest that changes to the magnetic field strength and topology caused by saturation of the thruster’s magnetic circuit may be occurring at elevated operating temperatures.

A dc plasma source for plasma–material interaction experiments

A new device has been constructed for the investigation of interactions between engineered materials and a plasma in regimes relevant to electric propulsion and pulsed power devices. A linear plasma source, consisting of a hollow cathode, cylindrical anode, and axial magnetic field, delivers a 3 cm diameter beam to a biased target 70 cm away. The ion energy impacting the surface is controlled by biasing the sample from 0 to 500 V below the local plasma potential. This paper discusses the major aspects of the plasma source design and presents measurements of the plasma parameters achieved to date on argon and xenon. Experiments show that splitting the gas injection between the hollow cathode and the anode region provides control of the discharge voltage to minimize cathode sputtering while providing ion fluxes to the target in excess of 1021 m−2 s−1. Sputtering rate measurements on a non-textured molybdenum sample show close agreement with those established in the literature.

Performance Analysis of a Low-Power Magnetically Shielded Hall Thruster: Computational Modeling

The applicability of a fully shielding magnetic field topology to a low-power xenon Hall thruster was demonstrated through testing of the MaSMi-60. Although the discharge channel lifetime was signi...

Performance Analysis of a Low-Power Magnetically Shielded Hall Thruster: Experiments

The successful application of a fully shielding magnetic field topology in a low-power Hall thruster is demonstrated through the testing of the MaSMi-60 Hall thruster (an improved variant of the or...

Improved Model of Long-Term Gain Increases in Traveling-Wave Tubes

An improved model to predict the gain increases in traveling-wave tubes (TWTs) during long-term operation is presented. The conventional gain growth model describes the pressure variation in a TWT over its life using an exponential decrease from the initial outgassing level to a constant base pressure. This model often shows an inability to capture the gain change behavior of many tubes during the transition between early life burn-in and long-term operation, leading to a significant underprediction of long-term gain increases. The model is improved here first through the introduction of another pressure-related term associated with desorption of gas from the tubes inner surfaces that exhibits a t-1/2 time dependence. This new pressure dependence is governed by the behavior of a Langmuirian adsorption isotherm. Second, the exponential pressure decay term is separated into two terms associated with early life and long-term operation with different outgassing time constants. The improved model shows a significantly better matching of long-term TWT gain growth data compared to the conventional model. In addition, the improved model predicts a more physical pressure behavior in the TWT with time.