Equilibrium of a quasi-symmetric simple coil stellarator

Equilibrium studies for a quasi-symmetric stellarator are made, using the DESC code [1], based on the concept of the Columbia Neutral Torus (CNT), being currently repurposed as the Columbia Stellarator eXperiment (CSX). The coil configuration tested in this work, consisting in two circular vertical coils, and two interlinked coils, starts from that proposed in [2]. The physical parameters used as input were the rotational transform ι(r) as a function of r, The toroidal magnetic flux Ψ on axis, the number of periods NFP, and an initial equilibrium supposition given the major radius R_o a minor radius a. Once the equilibrium defined by the coil configuration is defined, an optimization is made for quasi-symmetry (QS). In these preliminary results, a triple product metric as defined in [3] is used as a local error indicator, which is evaluated without resorting to Boozer coordinates.

[1] Dudt D. W. and Kolemen E., DESC: A stellarator equilibrium solver, Physics of Plasmas 27, 102513 (2020).

[2] Yu G., Feng Z , Jiang P. and Fu G., Existence of an optimized stellarator with simple

coils, Journal of Plasma Physics 88, 905880306 (2022).

[3] Dudt D. W., Conlin R., Panici D. and Kolemen E., The DESC stellarator code

suite Part 3: Quasi-symmetry optimization, Journal of Plasma Physics 89 955890201(2023).