Study on Anomalous Electron Diffusion in the Hall Effect Thruster

Abstract

Over the last two decades, numerous experimental and numerical efforts have examined physical phenomena in plasma discharge devices. The physical mechanisms that govern the anomalous electron diffusion from the cathode to the anode in the Hall Effect Thruster (HET) are not fully understood. This work used 1-D numerical method to improve our understanding and gain insight into the effect of the anomalous electron diffusion in the HET. To this end, numerical solutions are compared with various experimental HET performance measurements and the effects of anomalous electron diffusion are analyzed. The relationships between the anomalous electron diffusion and important parameters of the HET are also studied quantitatively. The work identifies the cathode mass flow rate fraction, radial magnetic field distribution, and discharge voltage as significant factors that affect anomalous electron diffusion. Additionally, the study demonstrates a computational process to determine the radial magnetic field distribution required to achieve specific thruster performance goals.

Atmospheric propellant fed Hall thruster discharges: 0D-hybrid model and experimental results

“…Even if β 0 is lower than the suggested value of 3 for Xe discharges [27], excitation losses are actually larger for atmospheric propellant as the cost coefficient multiplies for higher energy processes (such as N 2 dissociative ionization, requiring an energy of about 26.7 eV as opposed to Xe single ionization energy of 12.1 eV). On the other hand, the anomalous transport coefficient calibrates to α B,0 = 1/126, which is consistent with the α B = 1/100 to α B = 1/160 historically used for Hall thruster Xe discharges [41]. Figure 9 shows the calibrated model solution for 20 ms duration at a reference inlet mass flow rate ṁN 2 ,in = 3.36 mg s −1 , ṁO 2 ,in = 2.64 mg s −1 and discharge voltage V D = 300 V. The thruster ignition transient features a sharp peak in plasma density, followed by damped oscillations reaching steady-state in less than 3 ms.…”

“…The impact on performance is positive: as in calibrated condition the flow is far from being completely ionized, a larger trigger velocity improves flow ionization and increases both thrust, discharge power and anodic efficiency. As discussed in [41], the optimum value of anomalous electron transport is the minimum one ensuring complete flow ionization. Larger electron trigger velocities would only increase the discharge power with negligible impact on thrust, thus negatively affecting the anodic efficiency.…”