Study on the physicalmechanism of a plasma thruster with wide range of thrust

摘要

Summary form only given. Considerable progress has been made in recent years in the study of the Earth's gravitational field by observing the motion of satellites in low altitude orbits. However, such observations are hampered by the aerodynamic drag caused by the residual atmosphere, which modifies the orbits of these satellites in an unpredictable way. In order to overcome this problem, an on-board propulsion system with wide range of thrust is needed which will exactly balance the drag experienced by the spacecraft while measurements are being made. A cusped magnetic field topology is used everywhere to create a dense plasma, such as magnetic confinement fusion, magnetron sputtering, etc. Recently, the cusped magnetic field wa s proposed to be used in electric propulsion. By ejecting ions away from the discharge channel with high velocity to produce thrust, the total propellant mass can be greatly reduced. While the cusped field topology is used to keep high energy ions away from channel walls and mitigate erosion. Thus its lifet ime will be longer compared with some other type of electric propulsion devices. Recently, the cusped field thruster has be en paid much attentions by many organizations, such as Thales Research Institute's HEMPT, MIT's DCFT and Stanford University's CCFT. It is shown that the cusped field plasma thruster is a possible candidate for this task. It has a propellant utilization efficiency of 80 to 90%, a specific impulse of over 3000 sec and, most significantly, can be throttled under computer control from b elow 1 mN to more than 30 mN. A series of experiments has been done in this paper to study t he effect of thruster structure and magnetic field on physical mechanism of the thruster with wide thrust range. Combined with two dimensional Particle in Cell simulated results, it can be found that the main path of electrons before entering the discharge channel is along the magnetic line that intersect with the exit of hollow cathode. El- ctrons are impeded at the last cusp until been conducted to towards anode by collision with heavy particles. After that, there will be two obvious branche s including the central leak path directly to anode without effective confinement and good ionization, and another path move along the magnetic field lines to the upstream cusp to form effective confinement and high ionization rate. The central le ak path increase the plasma stability of the thruster. While the cusped field magnetic field reduce the plasma interaction with the wall, which intends the thrust range.