arxiv: 2510.07042 · v2 · submitted 2025-10-08 · ⚛️ physics.ins-det · cond-mat.supr-con· physics.app-ph· physics.plasm-ph

Experimental Results from Early Non-Planar NI-HTS Magnet Prototypes for the Columbia Stellarator eXperiment (CSX)

D. Schmeling , M. Russo , B. T. Gebreamlak , T. J. Kiker , A. R. Skrypek , A. R. Hightower , J. Xue , S. Chen

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S. Sohaib C. Martinez K. F. Richardson L. Filor S. Komatsu L. Liu C. Paz-Soldan

This is my paper

Pith reviewed 2026-05-18 08:57 UTC · model grok-4.3

classification ⚛️ physics.ins-det cond-mat.supr-conphysics.app-phphysics.plasm-ph

keywords non-planar HTS coilsstellarator magnetsReBCO prototypesquench management3D-printed coil framesColumbia Stellarator eXperimenthigh-temperature superconductors

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The pith

Non-planar HTS magnet prototypes for CSX achieve expected fields and validate key manufacturing steps.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports results from a staged series of small prototypes for non-planar high-temperature superconducting coils intended for the Columbia Stellarator eXperiment. These prototypes use 3D-printed sectional aluminum frames and gimballed constant-tension winding to form the complex shapes while protecting the strain-sensitive ReBCO tape. Tests at temperatures from 77 K down to 20 K show that the coils produce the predicted magnetic fields, with parallel development of low-resistance joints and solder potting for quench handling. The work aims to reduce risks in building the full-size coils needed for the 0.5 T target field.

Core claim

The P1 planar prototype confirmed additive manufacturing and baseline winding, the P2 non-planar version reached expected fields at 30-40 K with up to 4.5 kAt, and the P3 design with dual double-pancakes and 200 turns approaches the 70 kAt target at 20 K, together demonstrating feasible manufacturing, cooling, quench mitigation, and diagnostics for non-planar NI-HTS stellarator coils.

What carries the argument

Sectional 3D-printed aluminum coil frames with gimballed constant-tension winding mechanics and solder potting, which manage strain and enable radial current redistribution in non-planar geometries.

If this is right

Additive manufacturing and sectional joining produce functional coil frames for non-planar HTS windings.
Thermal gradients and electrical resistance remain manageable in non-planar geometries down to 20 K.
Solder potting supplies passive quench mitigation via current redistribution.
Sub-microhm lap joints support reliable current transfer in the coil assemblies.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

If the methods scale without new issues, university-scale stellarators could become more practical using compact HTS coils rather than larger conventional systems.
The winding and frame techniques could be adapted for other fusion devices that require non-planar magnet shapes.
Intermediate-scale tests between the current prototypes and full CSX coils would help isolate any size-dependent effects before final construction.

Load-bearing premise

That performance measured in small prototypes at modest currents and temperatures will translate directly to full-size coils at target fields without new strain or thermal issues arising at scale.

What would settle it

A full-size non-planar coil energized to the 0.5 T on-axis target in CSX showing unexpected quenching, excess resistance, or deviation from predicted fields.

Figures

Figures reproduced from arXiv: 2510.07042 by A. R. Hightower, A. R. Skrypek, B. T. Gebreamlak, C. Martinez, C. Paz-Soldan, D. Schmeling, J. Xue, K. F. Richardson, L. Filor, L. Liu, M. Russo, S. Chen, S. Komatsu, S. Sohaib, T. J. Kiker.

**Figure 2.** Figure 2: 77 K tests of elliptical prototype magnet P1, shown immersed in a [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗

**Figure 3.** Figure 3: CAD rendering (top) and photograph (bottom) of the P3 prototype [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗

**Figure 4.** Figure 4: CAD rendering (left) and photograph (right) of the cryogenic test [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗

**Figure 6.** Figure 6: Resistance of P2 measured using voltage taps soldered directly to the [PITH_FULL_IMAGE:figures/full_fig_p004_6.png] view at source ↗

**Figure 5.** Figure 5: Resistance characterization of a 30 mm HTS lap joint measured at 77 K. The slope of the V–I curve indicates a joint resistance of approximately 380 nΩ, with good linearity across the 0–10 A range In addition to tests at 77 K, a setup allowing the testing of joints at 20 K in the cryogenic test-stand is being designed. This setup will allow tests at higher critical currents, and the implementation of additi… view at source ↗

**Figure 7.** Figure 7: Magnetic field measurements taken at 0.2 m radial distance from the coil axis across multiple experimental runs. Data from three separate experiments are compared with Biot–Savart predictions for probe placements at 0.18 m and 0.20 m. Temperatures across the magnet increased as current was supplied, with the HTS-copper interface and other higher- [PITH_FULL_IMAGE:figures/full_fig_p004_7.png] view at source ↗

**Figure 8.** Figure 8: Exponential decay of magnetic field following current shut-off, [PITH_FULL_IMAGE:figures/full_fig_p005_8.png] view at source ↗

**Figure 9.** Figure 9: Voltage decay across the magnet leads following current shut-off. [PITH_FULL_IMAGE:figures/full_fig_p005_9.png] view at source ↗

read the original abstract

The Columbia Stellarator eXperiment (CSX) is an upgrade of the Columbia Non-neutral Torus (CNT) that aims to demonstrate a university-scale, quasi-axisymmetric stellarator using high-temperature superconducting (HTS) technology at an on-axis magnetic field target of 0.5 T. Due to the strain sensitivity of ReBCO (Rare-earth Barium Copper Oxides), adapting it to non-planar stellarator geometries requires new winding, structural, and cooling strategies. We report on the results of a staged prototype program (P1, P2, P3) employing 3D-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, double-pancake) tested additive manufacture, sectional joining and baseline winding, achieving predicted fields at 77 K. P2 (non-planar, 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 4.5 kAt. Design evolution in P3 introduces concave geometry with dual double-pancakes, 200 turns, and approaches the 70 kAt target at 20 K. In parallel, sub-microhm lap joints have been developed. Together, these results de-risk manufacturing, cooling interfaces, quench management, and diagnostics, paving the way for full-size non-planar HTS stellarator coils for CSX.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Small-scale non-planar HTS prototypes hit basic field targets but leave scaling risks for full stellarator coils untested.

read the letter

Colleague, The one or two things to take away: they've run some early tests on non-planar ReBCO prototypes that hit their field targets at low currents, but this doesn't yet clear the path for full-size versions because of untested scale effects. What is new is the use of 3D-printed sectional frames with gimballed constant-tension winding and solder potting specifically for non-planar stellarator coils. The prototypes P1 to P3 progress from planar tests at 77 K to non-planar at lower temps and higher currents, up to approaching 70 kAt in P3. They also show sub-microhm joints. This targeted engineering for university-scale stellarators adds to the HTS magnet literature. They do well by delivering actual measured results from these custom builds, including field production and thermal studies. That's useful data for similar projects. The soft spots are in the extrapolation. As the stress-test notes, P2 only reached 4.5 kAt at 30-40 K in smaller geometry, far from the 70 kAt target. Full coils will face greater forces and thermal issues that these tests don't cover. The de-risking of manufacturing, cooling, quench management, and diagnostics is claimed but rests on small-scale success without detailed scaling work or full data presentation. The abstract's support is limited without error bars or model comparisons. Readers in fusion magnet development or stellarator experiments would find this relevant. It gives practical insights into building these coils. It deserves a serious referee to evaluate the experimental methods and results in detail. I would send it to peer review.

Referee Report

1 major / 2 minor

Summary. The manuscript reports experimental results from a staged prototype program (P1–P3) developing non-planar non-insulated high-temperature superconducting (NI-HTS) magnet coils for the Columbia Stellarator eXperiment (CSX), which targets 0.5 T on-axis field. Using 3D-printed sectional aluminum frames, gimballed constant-tension winding, and solder potting, the prototypes achieved magnetic fields consistent with predictions: P1 (planar) at 77 K, P2 (non-planar) at 30–40 K up to 4.5 kAt with 42 turns, and P3 (concave dual double-pancake, 200 turns) approaching 70 kAt at 20 K. Sub-microhm lap joints were also developed. The authors conclude that these results de-risk manufacturing, cooling interfaces, quench management, and diagnostics for full-size non-planar HTS stellarator coils.

Significance. If the results hold, this work is significant for advancing HTS magnet technology in stellarators. It provides concrete experimental validation of practical solutions to ReBCO strain sensitivity in non-planar geometries through additive manufacturing of frames and specialized winding/potting methods. The thermal gradient studies and quench-related observations in P2 add useful data on cooling interfaces and passive mitigation. The staged prototype approach and joint development offer a replicable path for de-risking complex HTS systems at university scale, with potential to accelerate CSX construction and similar compact fusion experiments.

major comments (1)

[Abstract] Abstract: The central claim that the P1–P3 results de-risk manufacturing, cooling interfaces, quench management, and diagnostics for full-size non-planar HTS coils is not fully supported. P2 reached only 4.5 kAt (versus the 70 kAt target), and the manuscript provides no explicit scaling analysis or discussion of how higher total Lorentz forces, larger thermal gradients across sectional frames, or altered quench propagation in solder-potted windings would be handled at full scale. This extrapolation is load-bearing for the de-risking conclusion.

minor comments (2)

[Abstract] The abstract would be clearer if it reported the precise achieved current, number of turns, and any quantitative deviation from model predictions for each prototype rather than qualitative statements such as 'achieving predicted fields' or 'approaches the 70 kAt target'.
Presentation of thermal and resistance data from P2 would benefit from explicit error bars, measurement uncertainties, and direct tabulated comparisons to finite-element models to allow readers to assess agreement quantitatively.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We are grateful to the referee for their constructive feedback on our manuscript describing the experimental results from the early non-planar NI-HTS magnet prototypes for CSX. The major comment raises a valid point about the support for our de-risking claims in the abstract. We address this below and have made revisions to the manuscript to strengthen the discussion.

read point-by-point responses

Referee: [Abstract] Abstract: The central claim that the P1–P3 results de-risk manufacturing, cooling interfaces, quench management, and diagnostics for full-size non-planar HTS coils is not fully supported. P2 reached only 4.5 kAt (versus the 70 kAt target), and the manuscript provides no explicit scaling analysis or discussion of how higher total Lorentz forces, larger thermal gradients across sectional frames, or altered quench propagation in solder-potted windings would be handled at full scale. This extrapolation is load-bearing for the de-risking conclusion.

Authors: We agree with the referee that the abstract's claim would benefit from additional support. It is correct that P2 was an intermediate step limited to 4.5 kAt, primarily to validate non-planar winding and thermal gradient studies at 30-40 K. However, the program is staged, and P3 has been designed with 200 turns and has approached 70 kAt at 20 K, which is the relevant target for the full-scale coil performance metrics. The de-risking refers to the successful demonstration of 3D-printed sectional frames, gimballed winding, solder potting for quench mitigation, and sub-microhm joints, all of which are directly applicable to full-size coils. Regarding scaling, while the manuscript focuses on experimental results rather than detailed modeling, we acknowledge the absence of an explicit scaling analysis. In the revised version, we will include a brief discussion in the conclusions or a new section outlining how the observed performance scales with current, including considerations for Lorentz forces (which increase quadratically with current) and thermal management, supported by the P3 results and preliminary calculations. This will clarify the path to full-scale implementation without overclaiming. revision: yes

Circularity Check

0 steps flagged

No circularity: direct experimental measurements with no derivations or fitted predictions

full rationale

This is a straightforward experimental report describing construction and testing of physical prototypes P1–P3. Measured fields, temperatures, and joint resistances are reported as direct outcomes of the hardware at the tested currents and temperatures. No equations, parameter fits, or self-citations are invoked to derive or predict the reported results; the de-risking claim is an interpretive summary of the observed performance rather than a mathematical reduction to prior inputs. The paper is therefore self-contained against external benchmarks of prototype testing.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on standard domain knowledge of ReBCO strain sensitivity and cryogenic behavior rather than new postulates or fitted parameters.

axioms (1)

domain assumption ReBCO superconductors require specialized winding and structural strategies due to strain sensitivity in non-planar geometries
Invoked in the abstract to justify the prototype program and new techniques.

pith-pipeline@v0.9.0 · 5911 in / 1214 out tokens · 34146 ms · 2026-05-18T08:57:52.950941+00:00 · methodology

discussion (0)

Reference graph

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