Application of non-integer- <i>n</i> RMP coil current waveform for ELM control in JA DEMO

Abstract We have studied the resonant magnetic perturbation (RMP) coil concept for edge localized mode (ELM) suppression in JA DEMO, a design concept of a steady-state tokamak demonstration reactor, based on the vacuum magnetic model. We investigate the RMP coil layout and current pattern that are effective for ELM suppression and the coil current required for ELM suppression including the pedestal height dependence. We examine the effect of RMPs on the trigger of magnetohydrodynamic instabilities, divertor footprints, and alpha-particle loss. When the currents of the RMP coils in a toroidal row are determined to match non-integer- n sinusoidal waveforms, compared to the cases using integer- n waveforms, we demonstrate that (a) the coil current required for ELM suppression is reduced, (b) the range of plasma conditions under which ELM can be suppressed is widened, (c) the amplitudes of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>m</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> perturbation fields are smaller than the locked mode scaling, (d) the increase in alpha-particle loss is an acceptable level in terms of the plasma heating deterioration and the divertor heat load, and (e) special localization is not seen in the divertor strike points and lost alpha-particle incident positions. Here, n ( m ) is the toroidal (poloidal) mode number. Utilizing non-integer- n current waveforms is advantageous for ELM control by RMP in DEMO.