Wensheng Huang’s research while affiliated with Glenn Falls Hospital and other places

During a laser-induced fluorescence test of a 12.5 kW magnetically shielded Hall thruster, ion characteristics in the discharge channel and near the poles were measured as the background pressure and electrical configuration were varied. The acceleration zone of the thruster moved upstream by 2 and 10% of the channel length when the background pressure was raised to 1.8 times and seven times the lowest achievable pressure, respectively. Examination of the characteristics of the ions near the pole covers suggested that as the background pressure decreased, the pole covers might be experiencing more erosion. When operating at a discharge voltage of 300 V, the acceleration zone was observed to be at the same location for all electrical configurations. When operating at a discharge voltage of 600 V, the acceleration zone was observed to move 3% of the channel length upstream when the thruster body was floated instead of tied to the cathode or grounded to the facility. Characteristics of the ions bombarding the pole covers did not vary across the tested electrical configurations. This observation combined with thruster body voltage measurements suggested that varying the electrical configuration only affected the thruster body sheath voltage and did not affect the plasma potential beyond the sheath.

This paper presents the design and performance of the UAH-78AM, a low-power small Hall effect thruster. The goal of this work is to assess the feasibility of using low-cost 3D printing to create functioning Hall thrusters, and study how 3D printing can expand the design space. The thruster features a 3D printed discharge channel with embedded propellant distributor. Multiple materials were tested including ABS, ULTEM, and glazed ceramic. Thrust measurements were obtained at the NASA Glenn Research Center. Measured thrust ranged from 17.2–30.4 mN over a discharge power of 280 W to 520 W with an anode ISP range of 870–1450 s. The thruster has a similar performance range to conventional thrusters at the same power levels. However, the polymer ABS and ULTEM materials have low temperature limits which made sustained operation difficult.

View Video Presentation: https://doi.org/10.2514/6.2021-3432.vid During development testing of the 12.5-kW Advanced Electric Propulsion System engineering unit Hall thruster, which is magnetically shielded, a laser-induced fluorescence test was performed. During this test, a third medium-energy ion population was found near the inner front pole cover in addition to two low-energy counter-streaming ion populations that were found in previous testing. This newly found ion population matched in characteristics with the single population found near the outer front pole cover. The measured characteristics of the medium-energy ions matched the behavior expected of them if they were energized by a plasma wave with magnetized electrons, such as a lower hybrid wave. Comparison of the data from this test to prior tests showed that this engineering thruster had very similar ion characteristics as the precursor laboratory thruster. The acceleration zone was found to move upstream with increasing background pressure, decreasing anode flow rate, and increasing magnetic field strength. For the low-energy ions, the energy of the ions arriving at the inner pole did not vary noticeably with background pressure but did increase with increasing magnetic field strength and decreasing anode flow rate. For the medium-energy ions, the energy of the ions increased with decreasing background pressure, decreasing anode flow rate, and increasing magnetic field strength. Testing at different cathode flow fraction showed that the energy of the low-energy ions from the cathode decreased with increasing cathode flow.

The plasma plume properties of a three-channel 100-kW-class nested Hall thruster were measured on xenon propellant for total powers up to 80 kW. The thruster was throttled through all seven available channel combinations for conditions spanning 300 to 500 V discharge voltage and three discharge current densities. A plasma diagnostics array, which included a Wien filter spectrometer, a retarding potential analyzer, and a planar Langmuir probe, was placed in the far-field plume of the thruster and used to measure the beam ion charge state, the ion energy distribution function, and the local plasma potential. These data were used to calculate thruster phenomenological efficiencies. These efficiencies are compared across the discharge voltage and channel combination, and they are compared to similar results from the NASA-300M single-channel high-power Hall thruster. An estimate of cross-channel ingestion, which is a phenomenon in the nested configuration that may improve thruster efficiency and that will be present in space, is calculated, and the results for mass utilization efficiency are corrected for this effect. These plasma diagnostic results are discussed in the context of the state of the art, as well as in that of the viability and potential benefits of the nested channel thruster configuration.

A retarding potential energy analyzer was used to obtain temporally resolved ion energy distribution functions (IEDFs) of a flowing laboratory plasma. The plasma of time varying ion energy was generated at 1 and 20 kHz using a commercial gridded ion source and modulated using a wideband power amplifier. Three plasma energy modulation setpoints were tested, and their IEDFs were reconstructed. This method leverages high-speed, low-noise instrumentation to obtain fast collector current measurements at discrete retarding bias levels, recombining them in the time domain using two data fusion techniques. The first method is an empirical transfer function, which determines the linear ratio of complex coefficients in Fourier space. The second method, shadow manifold interpolation, reconstructs the IEDFs point-by-point by comparing input and output datasets in a multi-dimensional phase space. Reconstructed IEDFs from the two methods are presented and compared. The two analysis methods show very good agreement.

During development testing of a 12.5 kW magnetically shielded Hall thruster, direct evidence of counterstreaming ions eroding the pole covers was found. One stream of ions appears to originate from the discharge channel while the other stream appears to originate from the centrally mounted cathode. Velocity distribution measurement indicates that each stream impacts the poles of the thruster at high oblique angles of incidence. While the average energy of each stream was in the tens of eV, the energy distributions contained high-energy tails that can be a major contributor to erosion. Starting with the physical picture of high oblique angle bombardment, predictions of change in erosion behavior over time are in good agreement with pole cover erosion measurements taken during wear testing. The new evidence points to a need to study these ions that are traditionally considered “low-energy” ions and the role they play in the erosion of the poles of magnetically shielded Hall thrusters.

This work presents a summary of the detailed characterization test of the 12.5 kW Advanced Electric Propulsion System (AEPS) Engineering Test Unit 2 (ETU-2) thruster produced by Aerojet Rocketdyne. This test campaign had two major goals: to assess the risk of design compliance with thruster requirements and provide a comparison to the previously-tested NASA Hall Effect Rocket with Magnet Shielding (HERMeS) Technology Demonstration Units (TDUs) from which the AEPS ETU design was derived. Assessments of ETU-2 performance and stability were conducted for discharge powers of 6.25 to 13.1 kW, magnetic field strengths between 75% and 125% of nominal, cathode flow fractions between 5% and 10%, and nominal and reversed magnetic field polarities. The results from each of these test segments indicate that ETU-2 performance meets or exceeds all the AEPS thruster performance requirements and matches the values and trends previously measured with the HERMeS TDUs. In addition, similar to the HERMeS TDUs, ETU-2 performance showed minimal sensitivity to both electrical and pressure facility effects. Taken together, these results strongly suggest that the AEPS design is successfully replicating the performance of the HERMeS TDUs and has high probability of compliance with the performance requirements as the design progresses to its Critical Design Review.

A Laser-Induced Fluorescence test was performed during risk reduction testing on the HERMeS Hall thruster. This article focuses on the portion of the test to study trends in the ion acceleration characteristics with varying anode mass flow rate, background pressure, and electrical configuration. The acceleration zone of the HERMeS Hall thruster was observed to move upstream as the anode mass flow rate decreased and upstream as the background pressure increased. Examination of the characteristics of the ions near the pole covers suggested the possibility that thruster was no longer magnetically shielded at the extreme conditions of very low anode mass flow rate and high background pressure. The acceleration zone was also observed to move slightly upstream when the thruster body was floated as opposed to cathode-tied and did not move appreciably when the thruster body was grounded to the vacuum facility. Characteristics of the ions bombarding the pole covers did not vary across the tested electrical configurations.

This work presents a summary of the first wear test of the 12.5 kW Advanced Electric Propulsion System (AEPS) Engineering Test Unit 2 (ETU-2) thruster produced by Aerojet Rocketdyne. The ETU-2 Wear Test accumulated approximately 730 hours of operation split between the nominal 600 V/12.5 kW condition and the 300 V/6.25 kW condition previously identified as the worst-case erosion condition. Thruster performance and stability were invariant throughout the wear test for all thruster throttle conditions and shown to be statistically identical to the values previously measured with the Hall Effect Rocket with Magnet Shielding (HERMeS) Technology Demonstration Units (TDUs) from which the AEPS ETU design was derived. Average pole cover erosion rates at both the 600 V and 300 V operating conditions were shown to satisfy the margined AEPS lifetime requirement and largely be in family with the erosion rates measured on the HERMeS TDU thrusters. Taken together, these results strongly suggest that the AEPS design has a high probability of compliance with the performance and lifetime requirements as the design progresses to its Critical Design Review.