Jason D. Frieman's research while affiliated with Georgia Institute of Technology and other places

... Due to its high specific impulse, large thrust to power ratio and high reliability, the Hall thruster has become the most frequently used electric thruster in orbit. In recent years, Hall thrusters have been applied to the orbit maneuver missions for satellites and the main propulsion missions for space probes [1,2]. In a Hall thruster, as shown in Figure 1, electrons are confined by a magnetic field to produce ionization. ...

... The second thruster, ETU-2, was used to evaluate thruster performance, stability, thermal, and life characteristics [11,12,20,21,30,38]. Additionally, detailed ion velocity measurements were made via laserinduced fluorescence (LIF) that are used to validate physics-based plasma models of thruster erosion [28,42]. ...

... ETU-1 successfully completed all environmental testing and the facilities and processes were demonstrated to be capable of performing qualification testing. The second thruster, ETU-2, was used to evaluate thruster performance, stability, thermal, and life characteristics [11,12,20,21,30,38]. Additionally, detailed ion velocity measurements were made via laserinduced fluorescence (LIF) that are used to validate physics-based plasma models of thruster erosion [28,42]. ...

... In Ref. [30], a statistics-based methodology was developed and used to derive the AEPS performance specification at the wear test RFCs listed in Table 2. In order to develop a suitably large data set for application of that methodology to the expanded set of RFCs listed in Table 3, a minimum of four performance measurements were acquired at each RFC with measurements spread over several test days and two facility vacuum cycles. ...

... In Section V, we provide a comparison between the closed-form and numerical solutions of a one-dimensional Outer pole cover Inner pole cover With the development of magnetic shielding [12,13], a method that protects the discharge chamber from ion sputtering, the magnetic field lines that graze the channel walls of a Hall thruster are now designed to carry only cold electrons (1-5 eV). Though magnetic shielding has practically eliminated channel erosion as the main life-limiting process in these thrusters, subsequent experiments [14] and numerical simulations [15][16][17] have also revealed minor but measurable erosion along the downstream magnetic pole surfaces facing the plume. It was found that the maximum erosion rates at the downstream face rarely exceed 0.1 mm/kh and, as a result, thin pole covers made of low sputtering materials (like graphite) would be sufficient in protecting the poles in long duration space missions. ...

... Studies on midpower HETs show that elevated facility pressures allow the thruster to ingest the background neutral gas as propellant, thereby augmenting the measured thrust. Recent investigations by Snyder et al. show that SPT-140 thrust measurements increase from 278 mN to almost 300 mN as the facility pressure increased by an order of magnitude at the constant 4.5 kW, 300 V operating condition [82,108]. In addition, elevated facility pressures can also enhance erosion rates of thruster components due to larger populations of charge-exchange (CEX) ions, change plasma properties of the thruster plume, affect discharge oscillations, and vary the location of the acceleration zone in HETs [199][200][201]. ...

... Many high-power GIEs have endured carbon backsputtering effects on grid erosion rate studies [207,211]. The H6MS and HERMeS TDU-1 were the only highpower HETs that have engaged in such investigations [92,209]. Although there is some progress along this front, there is no consensus on the best practices for measuring backsputtered carbon deposition rates, acceptable facility wall lining materials, or facility internal structure geometries to minimize these contamination effects on thruster lifetime assessments. ...

... Nevertheless, the now-about-a-decade-long experience of developing and testing this class of Hall thrusters has casted light, on the one hand, on the enormous cost and time required to mature this new technology to the qualified and flight-ready status. On the other hand, extensive research into the Hall thrusters in the past years have demonstrated the influence of the on-ground vacuum testing facilities on the performance and stability of Hall devices in both magnetically shielded and conventional 'unshielded' configurations [6][7][8][9]. In fact, the testing environment is observed to alter the underlying physical processes, such as the electrons' cross-field mobility and the global discharge dynamics [10][11][12], thus, notably affecting the reliability of the characterization/qualification test results with respect to the operation on orbit. ...

... In order to assess these wearout failure modes and also to prepare for the planned qualification life test of the AEPS qualification thruster, wear tests with durations ranging from as short as 10 h [58] to as long as 3.6 kh [59] have been conducted with the H6MS [60,61], HERMeS [62][63][64], and AEPS ETU-2 [11,38]. HERMeS and AEPS wear testing has focused on quantifying known and potentially unknown erosion modes of the discharge chamber, pole covers, and cathode. ...

... The overall HERMeS design incorporates technologies developed over nearly two decades, including a magnetic shielding topology and graphite pole covers for a design lifetime exceeding 23 kh [6,7]. The HERMeS TDU-3 thruster configuration was largely unchanged from that used during the previous Long Duration Wear Test and is shown in Fig. 1 [8,9]. It is important to note that at the time of testing, TDU-3 had accumulated approximately 4,500 hours of total operation. ...