Experimental Results From Early Nonplanar NI-HTS Magnet Prototypes for the Columbia Stellarator eXperiment (CSX)

The Columbia Stellarator eXperiment (CSX) is an upgrade of the Columbia Nonneutral Torus (CNT) that aims to demonstrate a university-scale, quasi-axisymmetric stellarator using high-temperature superconductors (HTS) technology at an on-axis magnetic field target of 0.5 T. Due to the strain sensitivity of rare-earth barium copper oxide (ReBCO), adapting it to nonplanar geometries requires new winding, structural, and cooling strategies. We report on the results of a staged prototype program (P1, P2, and P3) employing 3-D-printed, sectional aluminum coil frames with winding channels, gimballed constant-tension winding mechanics, and solder potting for radial current redistribution and passive quench mitigation. The first prototype, P1 (planar elliptical and double-pancake), was used to test additive manufacture, sectional joining, and baseline winding, achieving predicted fields at 77 K. P2 (nonplanar and higher strain) was wound to 42 turns, energized at 30–40 K to produce expected magnetic fields, and studied thermal gradients and resistance at up to 110 A (4.5 kAt). Design evolution in P3 introduces concave geometry with dual double-pancakes and 200 turns, and has been commissioned at 20 K, with high-field characterization ongoing. In parallel, sub-$\mu \Omega $lap joints have been developed. Together, these results de-risk manufacturing, cooling interfaces, quench management, and diagnostics, paving the way for full-size nonplanar HTS stellarator coils for CSX.