Abstract
The effects of neutral particle density on equilibrium of field-reversed configuration (FRC) plasmas sustained by rotating magnetic fields (RMF) were investigated in the FRC Injection Experiment apparatus. Two different gas feeding methods were used to realize different neutral particle density conditions. The experimental results show that a higher current drive efficiency with full penetration of the RMF was achieved in the lower neutral particle density case. On the other hand, the plasma current in a higher neutral particle density case flowed in a narrower region near the geometric axis than in a lower neutral particle density case. The FRC equilibrium with higher neutral particle density resulted in lower current drive efficiency, possibly due to the shorter penetration length of the RMF. No significant ion spin-up was observed in the present conditions.
