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Experimental study of non-inductive current in Heliotron J

It is important to control non-inductive current for generation and steady-state operation of highperformance plasmas in toroidal fusion devices. Helical devices allow dynamic control of non-inductive current through a wide variety of magnetic configurations. The reversal of non-inductive current consisting of bootstrap current and electron cyclotron driven current in electron cyclotron heating plasmas has been observed in a specific configuration at low density in Heliotron J device. By analyzing the non-inductive current for normal and reversed magnetic fields, we present experimental evidence for the reversal of bootstrap current. Our experiments and calculations suggest that the reversal is caused by a positive radial electric field of about 10 kV/m. Moreover, we show that the typical electron cyclotron current drive efficiency in Heliotron J plasma is about 1.0 × 10 17 AW −1 m −2 , which is comparable to other helical devices. We have found that the value is about 10 times lower than that of tokamak