An experimental study of the effect of magnet length on the performance of a multi-cusped field thruster

The multi-cusped field thruster is a novel concept in electric propulsion, which employs alternating permanent polarity magnets to create a periodic magnetic field. As an important factor for the optimal design, the magnet length of a low-power thruster is designed to be changeable. The effects of the ultimate stage length ( L _u) and the middle stage length ( L _m) on the performance characteristics are studied in a series of experiments. The results show that increasing L _u could prolong the axial motion range of the electrons and promote the ionization process. In addition, it can enlarge the relative distance between the ionization and the acceleration regions. Both of these aspects can help improve the thrust and the anode efficiency. With regard to he reverse trend, wefound that the longer L _m leads to a reduction of the thruster's performance for the enhanced ion loss to the wall. Overall this study can provide some optimal design ideas on the magnet length to improve the total performance of the multi-cusped field thruster. (paper)