Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

Abstract

Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the nearwall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO 2 . Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations. V C 2014 AIP Publishing LLC. INTRODUCTIONAt present, using Hall-effect thrusters in interplanetary missions and geostationary satellites with affordable propellants can reduce costs and improve economics. Optional propellants include gases of argon, krypton, nitrogen, and nitrogen dioxide. Although the atomic masses of these gases are smaller and the degrees of first ionization are higher than xenon, thereby yielding lower propulsive efficiency, these propellants are more affordable. 1 The Hall-effect thruster is universally applicable in many countries involved in aeronautics and in which giving the krypton-plasma thruster greater research attention. [2][3][4] Although previous studies show that compared with xenon, the thruster efficiency is low with krypton, some studies show that improvements in efficiency can be made in propellant utilization rate, along with other means, which approach the efficiency of xenon. [5][6][7][8]12 Other research shows that thruster performance based on krypton is significantly lower than that on xenon. 6,[9][10][11] With a low utilization rate of krypton, krypton (with a decrease of 37% in atomic mass) relative to xenon under normal conditions, the thrust decreases 20%-30% and the specific impulse decreases 37%. 13 Previous studies have concluded that the main factor of krypton's low efficiency is its low propellant utilization rate. To study the reason for this low efficiency, it is necessary to study the plasma in the thruster's discharge channel. 14 Estimates of classical conduction produced by collisions between electrons and atoms is far less than experimental results; that is, other unusual conduction occurs allowing electrons to cross magnetic field lines. 15 Some researchers believe that this unusual conduction is due to collective oscillation in the plasma of the thruster, which is called Bohm conduction. Bohm conduction is used to explain the reason why the current is greater than that produced solely by collision between electrons and atoms in discharge devices using plasma with a high degree of ionization. The Bohm conduct...

Performance Simulation of a 5 kW hall Thruster

“…At present, the discharge characteristics of the plasma and the performance of a hall thruster are evaluated mainly by conducting high-cost and time-consuming experiments. As research on plasma discharge mechanism becomes in depth and numerical methods improve continuously, simulation plays an increasely important role in understanding the micro physical process of hall thruster (Arkhipov and Bishaev, 2007;Hofer, 2008;Zhang et al, 2011;Zhang et al, 2014). Lentz built a one-dimensional particle-in-cell (PIC) model (Lentz, 1993) and simulated the plasma characteristics and performance of a Japanese hall thruster.…”