Plume control of a plasma thruster

Summary form only given. The cusped field thruster represents a new type of electric propulsion device incorporating cusped magnetic field profiles that keep high energy ions away from channel walls and mitigate erosion. Thus its lifetime will be longer compared with so me other type of electric propulsion devices. Recently, the cusped field thruster has been paid much attentions by many organizations, such as Thales Research Institute´s HEMPT, MI T´s DCFT and Stanford University´s CCFT. The cusped field thrusters use strong permanent ring magnets of alternating polarity to form cusped magnetic field. The magnetic cusps trap and reflect energetic electrons within the dis charge channel, leading to the enhancement of the propellant ionization. The strong magnetic field is used to magnetically shield plasma from the thruster wall so as to minimize ion bombardment and corresponding erosion. Meanwhile, electron´s movement towards the anode is strongly impeded due to this magnetic field configuration, which contributes to the formation of a steep electric field gradient for effective ion acceleration. Recent works on cusped field thrusters have shown that they have great difference with traditional Hall thrusters. It i s demonstrated potential advantage in lifetime, but is limited by a highly divergent plume structure, which means the majority of the ion current coalesce into a conical shell with a half angle of more than 40^o. The divergent plume reduces efficiency and increases the possibility of plasma beam impingement on critical satellite hardware, such as solar cells. In order to reduce the divergence angle as much as possible, a n additional small ring magnet with opposite polarity and a pure iron ring are placed at the exit plane. The additional ring magnet is arranged with a polarity repelling the most downstream magnetic field lines to form a flat downstream separatrix. And the purpose of the pure iron is to weaken the magnetic field in plume reg- on. An obvious variation of separatrix and magnetic field magnitude can be achievement by adopting m ethod.