Simulation study of influence of exit magnetic separatrix angle on plume divergence control
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Simulation study of influence of exit magnetic separatrix angle on plume divergence control Hui Liu, Xiang Niua , Xin Li, and Daren Yu Lab of Plasma Propulsion, Harbin Institute of Technology (HIT), Mail Box 458, Harbin 150001, P.R. China Received 25 November 2019 / Received in final form 21 March 2020 Published online 1 October 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. Cusped field thruster is a novel electrostatic thruster suitable for space exploration, but with high plume divergence angle. In this article, a 2D Particle-in-cell plus Monte Carlo (PIC-MCC) model is built to study the influence of exit magnetic separatrix angle on controlling plume divergence of cusped field thruster. The electric potential contour line distribution characteristics near exit magnetic separatrix with different angle are obtained and their formation mechanism is explained by magnetic mirror effect and electron pressure term. Simulation results show laying additional magnetic ring at the exit of channel can transfer exit magnetic separatrix towards inward of channel, which can decrease angle between electric potential contour line and central axis and increase ion axial speed. It is mainly due to change of magnetic field line direction and enhancement of magnetic mirror effect. However, simulation results show that ionization intensity in the channel decreases after adopting the plume control method. The plume divergence control method increases the channel length and causes the exit magnetic cusp inside the channel. Therefore the influence of exit magnetic separatrix angle on the characteristics of electron and ion energy deposition distribution on wall is further investigated.
1 Introduction Plasma focus devices can produce high density and high energy electron and ion beam [1,2] and therefore are widely used in many areas including chemical coating [3,4], neutron fusion [5], spectroscopic source [6] and X rays [7]. In electric propulsion, the divergent plasma plume ejected by thrusters can be focused by controlling their magnetic field configurations which is significant to decrease plasma beam impingement on critical satellite hardwares. Nowadays, the plume control of many electric thrusters is widely studied. It is found that there are many factors responsible for the plasma divergence of Hall thruster [8]. The curved magnetic field lines at the exit of channel can cause the defocusing beam. Besides high electron temperature can cause difference between electric potential contour lines and magnetic field lines and therefore the defocusing electric field would form in the channel [9]. Furthermore, the nonuniform distribution of ion production and ion energy in acceleration region can also cause the defocusing beam [10]. Raitses found that design of segmented electrode could contribute to reducing plume divergence angle [11]. Different from Hall thruster, cusped field thruster adopts strong permanent
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