Electron cross-field transport in a miniaturized cylindrical Hall thruster

Abstract

Conventional annular Hall thrusters become inefficient when scaled to low power. Cylindrical Hall thrusters, which have lower surface-to-volume ratio, are more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall thrusters. The present paper gives a review of the experimental and numerical investigations of electron crossfield transport in the 2.6 cm miniaturized cylindrical Hall thruster (100 W power level). We show that, in order to explain the discharge current observed for the typical operating conditions, the electron anomalous collision frequency ν B has to be on the order of the Bohm value, ν B ≈ω c /16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant. The optimal regimes of thruster operation at low background pressure (below 10-5 Torr) in the vacuum tank appear to be different from those at higher pressure (~10-4 Torr).

Optimization of Cylindrical Hall Thrusters

“…Quiet operation in the lowfrequency range is speculated to be a result of enhanced electron transport in the discharge caused by the high-frequency plasma oscillations. 16,27 Although the amplitude of oscillations was relatively lower for the 2.6 cm thruster, the discharge at low propellant flow rates is not as quiet as it was found to be in the large CHT. The characteristic peak of oscillations is at frequencies of about 50 to 60 kHz.…”

“…1). [14][15][16] To maintain ionizing collisions, the anode (gas inlet) is placed in the short annular part of the channel. Note that in Ref.…”

“…4a). 16 In the absence of an axial potential, the electrons would simply mirror out of the region of high magnetic field. The axial potential that accelerates ions outwards now also plays an important role in trapping electrons within the thruster.…”

“…The plasma measurements revealed the plasma density peak at the axis of the cylindrical channel. 25 (a) Monte-Carlo simulations 16,26 suggest that the density peak appears due to ambipolar trapping of slow ions.…”

Cathode effects in cylindrical Hall thrusters

“…The cylindrical Hall thruster (CHT) concept features a reduced surface-to-volume ratio in comparison to conventional annular Hall thrusters [3][4][5], making it potentially more attractive for miniaturization. Other features include quiet operation [3,4,6], high ionization efficiency [3,4,7], and a magnetic topology which may reduce channel erosion [5]. These features lead to efficiencies at low power comparable to the state-of-the-art annular Hall thrusters of commensurate size [6].…”