Space charge saturated sheath regime and electron temperature saturation in Hall thrusters

Abstract

Secondary electron emission in Hall thrusters is predicted to lead to space charge saturated wall sheaths resulting in enhanced power losses in the thruster channel.Analysis of experimentally obtained electron-wall collision frequency suggests that the electron temperature saturation, which occurs at high discharge voltages, appears to be caused by a decrease of the Joule heating rather than by the enhancement of the electron energy loss at the walls due to a strong secondary electron emission.2

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA-457Mv2 Hall Thruster

“…This similarity in shape is unexpected since these profiles are expected to be influenced by the length and position of the acceleration zone, which should change with operating condition. 17,19 However, these results are consistent with the similarity in radial profiles seen in Fig. 11, since the axial and radial profiles are connected via the magnetic field topology which shapes isothermal lines.…”

“…It has been well-established from previous measurements that the electron temperature increases fairly linearly with local plasma potential in Hall thrusters, with typical reported values of 0.07 -0.16 eV/V of potential. 16,17,19 However, the data in this study show that the average value in the near-field plume of the NASA-457Mv2 is 0.52 and 0.46 eV/V at 300 V and 400 V, respectively. An elevated value of 0.24 eV/V was also found for the NASA-300M at 500 V and 20 kW.…”

“…One explanation is that electron heating is more effective in the near-field plume and drops within the channel due to additional energy losses associated with the channel walls. 19 However, due to the limited data set and the fact that only ~10% of the acceleration zone was captured, additional data taken internal to the channel is required to fully understand the relationship between electron temperature and plasma potential in the NASA-457Mv2. Assuming that the maximum electron temperature is approximately 10% of the discharge voltage, 15 at 0.06 D T,m from the exit plane the temperature has reached: 72% of its maximum at 300 V, 30 kW; 52% of its maximum at 400 V, 30 kW; 50% of its maximum at 500 V, 30 kW; and 51% of its maximum at 500 V, 50 kW.…”

Propagator integral method for plasma physics kinetic equations with practical applications

“…The modelisation of this interaction is usually established by models that may not capture all microscopic processes involved, specially in Weakly Ionized Plasmas (WIP) for which the inclusion of a dense heavy cold neutral species hinders the development of models [137][138][139]. Our research group is interested in the use of these probes to analyse the plasma generated in our low temperature laboratory [99,100,152], making this topic of main interest.…”

“…The I-V curves of collecting probes provide information about parameters such as the local plasma potential, the electron or ion temperatures and the charged species density [131][132][133]. These probes are widely used for the diagnostics of fully [134][135][136] and weakly ionized plasmas [137][138][139]. Theoretically, the operation of Langmuir probes does not depend on the shape of the signal used to bias the probe.…”