Error Field Characterization and Correction on MUSE Permanent Magnet Stellarator*

MUSE is an optimized quasi-axisymmetric stellarator [1]. It is constructed from planar TF coils, permanent magnets, and additively manufactured support structures in less than 12 months [2].

Electron beam mapping[3] of flux surfaces has been conducted to measure the magnetic topology. Good nested flux surfaces have been confirmed at multiple toroidal field (TF) coil currents. Close agreement of the flux surfaces shapes with flux surfaces from VMEC and FIELDLINES at the corresponding TF value has been demonstrated. The $\iota$ profile has been measured and compared to our model by observing low order resonant structures at different TF values, including cross-field drift effects.  By measuring the width of the 1:5 island, the $b_{1,5}$ error field is calculated to be $6\times10^{-5}$ times the background field. Error field correction through alignement adjustments have been conducted to reduce both 5:1 and 4:1 resonant error field components.

[1] T. Qian, et al, Nucl. Fusion 62 084001 (2022)

[2] T. Qian, et al, Design and Construction of the MUSE Permanent Magnet Stellarator,  Journal of Plasma Physics. 2023;89(5):955890502

[3] S. A. Lazerson, et al, Nucl. Fusion 56 106005 (2016)