Control of non-inductive current in Heliotron J*

Abstract

Non-inductive currents of electron cyclotron heated plasmas have been examined in the helical-axis heliotron device, Heliotron J. The bootstrap and EC currents were separated by comparing experiments with positive and negative magnetic field. The estimated bootstrap current was found to be affected by the magnetic field configuration. It increases with an increase in the bumpy component of the magnetic field spectrum, which agrees well with a neoclassical prediction calculated using the SPBSC code. The EC current driven by oblique launch with respect to the magnetic field strongly depends on the field configuration and the location of the EC power deposition. The EC current is enhanced when the EC power is deposited on the magnetic axis. The maximum EC current is I EC = −4.6 kA and the current drive efficiency is η = n e RI p/P EC = 8.4 × 1016 A W−1 m−2. The flow direction of the EC current depends on the magnetic field ripple structure where the EC power is deposited.

Stabilization of energetic-ion-driven MHD modes by ECCD in Heliotron J

“…These currents can be separated by comparing the experimental results obtained for clockwise and counter-clockwise magnetic fields, since the flow direction of the bootstrap current, which is proportional to BB drift, is reversed by reversing the magnetic field, while that of the EC current associated with the B strength is not The ECCD experiment in Heliotron J showed that the EC driven current strongly depended on the magnetic field configuration [11][12] [13], suggesting that ECCD is determined by the balance between the Fisch-Boozer effect [14] and the Ohkawa effect [15]. We also demonstrated that net zero current state was maintained by cancelling the bootstrap current with ECCD [11]. Experimental research on ECCD has been performed in several helical systems, showing that the ECCD efficiency was found to be similar [16].…”

Simulation Study of ECCD in Helical Plasmas

“…In order to study the ECCD physics, a number of ECCD experiments have been performed in many devices [3]. Especially in Heliotron J, which is the helical-axis heliotron device, EC currents were measured experimentally and ECCD dependence on the magnetic configuration and the density were obtained [4,5]. It was found that the EC current decreased as electron density was increased and that the current changed depending on magnetic configurations.…”

Physics of Heliotron J Confinement

“…ECCD experiments were performed, focusing on the effects of the magnetic field ripple [30,31]. The EC-driven current decreased as power was deposited at the deeper ripple bottom.…”