Numerical study on a novel method for the plasma vertical position control using non-axisymmetric coils in JT-60SA

Abstract A numerical investigation explored the feasibility of controlling the plasma vertical position using non-axisymmetric coils in JT-60SA. Non-axisymmetric coils offer an alternative to conventional axisymmetric in-vessel coils, addressing challenges in installation and maintenance, particularly in the context of the Japanese DEMO reactor. However, the main concern with using non-axisymmetric coils is the potential generation of locked modes, and the consumption of control margins for other control actions such as edge localized mode suppression. To address such challenges,, we developed control logic to maximize accessible elongation while simultaneously minimizing coil currents. To assess controllability, we employed a magnetohydrodynamic equilibrium control simulator (MECS) and used vacuum magnetic field analysis. We demonstrated that with the application of non-axisymmetric coils, the plasma elongation was extended from 1.75 which was achieved with superconducting poloidal field (SCPF) coils to 1.95, even in the presence of a minor I p disruption. We also found that an error field correction coil (EFCC) could control during full discharge from ramp-up to ramp-down. The impact of non-axisymmetric magnetic fields on locked modes was evaluated using a three-mode error index ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>TMEI</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), revealing that n = 1 perturbations remained within acceptable limits ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>B</mml:mi> <mml:mrow> <mml:mi>TMEI</mml:mi> </mml:mrow> </mml:msub> <mml:mtext>⩽</mml:mtext> <mml:mn>0.05</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>mT</mml:mi> </mml:mrow> </mml:mrow> </mml:math> ) in most scenarios.