Minimal Acquisition Time Polarized Neutron Imaging of Current Induced Magnetic Fields in Superconducting Multifilamentary YBCO Tape

Anders C. Wulff; Cedric Holme Qvistgaard; Luise Theil Kuhn; Mette Bybjerg Brock; Morten Sales; S{\o}ren Schmidt; Takenao Shinohara

REVIEW 3 major objections 6 minor 10 references

Minimal Acquisition Time Polarized Neutron Imaging of Current Induced Magnetic Fields in Superconducting Multifilamentary YBCO Tape

T0 review · 3 major / 6 minor · reviewed 2026-08-12 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read This paper demonstrates that a single low-acquisition-time polarization measurement can characterize internal magnetic fields and currents in a superconducting tape.

desk verdict A solid proof-of-principle for single-projection polarized neutron imaging of superconducting tapes; the damage maps are convincing, but the headline 5.4 A/filament screening current is a fitted number whose uncertainty is not under control. read the letter →

arxiv 2411.16473 v1 pith:24OCBT3H submitted 2024-11-25 cond-mat.mtrl-sci

Cedric Holme Qvistgaard , Luise Theil Kuhn , Morten Sales , Takenao Shinohara , Anders C. Wulff , Mette Bybjerg Brock , S{o}ren Schmidt This is my paper · ORCID

classification cond-mat.mtrl-sci

keywords polarizedneutronimagingsuperconductingtapeYBCOtrappedmagneticfieldscreeningcurrenttime-of-flightnon-destructiveinspectionforwardsimulation

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper argues that polarized neutron imaging, even when reduced to a single polarization component and a single projection angle, can act as a fast magnetic probe of current-carrying superconductors. Using a field-cooled multifilamentary YBCO tape with both a trapped magnetic field and a 1 A transport current, the authors show that internal damage appears as clear reductions in the polarization signal, and that time-of-flight data yield quantitative integrated field strengths. By simulating the experiment with a critical-state current model and comparing simulated and measured polarization, they estimate the screening current per filament at roughly 5.4 A. The practical payoff is a short-acquisition imaging route that probes internal magnetic structure without surface smearing and without the long measurement times of full 3D tomography.

What carries the argument

The argument runs on the Larmor precession relation $\theta = \gamma t B$, which for a neutron of wavelength $\lambda$ becomes a linear wavelength dependence of the polarization angle with slope proportional to $\int B\,ds$. The measurement pipeline is: record spin-up and spin-down radiographs at a pulsed source, form $P=(\uparrow-\downarrow)/(\uparrow+\downarrow)$, normalize by the open beam, bin by wavelength, fit $\theta = a\lambda$, and extract the integrated field from the slope. For the current estimate, the authors assume a critical-state model of current flow in the superconductor, represent each filament's screening current as expanding rooftop-shaped square loops, compute the resulting magnetic field, and forward-simulate an idealized polarized neutron experiment with a Gaussian blur matched to the measured 0.96 mm blur. Matching the simulated maximum XY-polarization to the measured value (0.56) gives the $5.4\,\mathrm{A}$ per-filament estimate.

What would settle it

Measure a pristine multifilamentary YBCO tape with a known critical current using single-projection time-of-flight polarized neutron imaging, then compare the simulated screening-current estimate with the critical current obtained from transport or magnetization measurements; alternatively, perform a full 3D polarization tomography on the same damaged sample and check whether the integrated fields and inferred currents agree with the single-projection values.

Watch

Extended reading notes

Core claim

The central claim is that single-projection polarized neutron radiography of one spin component, combined with wavelength-resolved time-of-flight analysis, is sufficient to locate internal damage and quantify magnetic fields inside a superconductor carrying both a trapped field and a transport current. In the measured YBCO tape, the transport-current field and the trapped field produce opposite polarization signals, making them separable in a single radiograph. Fitting the wavelength dependence of the polarization angle gives integrated field strengths: $-2.11\,\mu\mathrm{T}\cdot\mathrm{m}$ for the trapped field and $1.26\,\mu\mathrm{T}\cdot\mathrm{m}$ for the transport current, after background correction. Simulating the trapped field with rooftop current loops in a critical-state model and matching the peak polarization to the measured value yields an estimated $5.4\,\mathrm{A}$ screening current per filament, far below the nominal $50\,\mathrm{A}$ capacity, which the authors interpret as evidence that damage has degraded the whole tape, not just the visibly reduced regions.

Load-bearing premise

The 5.4 A per-filament estimate rests on the assumption that the simplified forward model—idealized rooftop current loops, Gaussian blur, no beam divergence, and background subtraction as the only systematic correction—reproduces the true screening-current geometry closely enough; the paper's own check using a 1 A transport current produced simulated integrated fields about 30% lower than measured.

Editorial extensions

If this is right

Internal damage in a superconducting tape can be located from a single radiograph, because the technique probes internal magnetic fields rather than surface structure.
Time-of-flight analysis of a single polarization component provides quantitative integrated field strengths with a short acquisition time, without full tomography.
Screening-current magnitudes cannot be read directly from polarization images; they require a forward model of the current distribution, as the paper demonstrates.
The estimated $5.4\,\mathrm{A}$ per filament, compared with the nominal $50\,\mathrm{A}$, implies that the damage seen in the image affects the current-carrying capability of the entire tape, not just the most visibly degraded areas.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

With a calibration measurement on a pristine sample of known critical current, this single-projection method could develop into a routine quality-control tool for coated-conductor tapes, catching internal damage that surface inspection misses.
The paper's own validation run, where a simulated 1 A transport current gave integrated fields about 30% lower than measured, suggests that refining the forward model to include beam divergence and local critical-current variation would convert that discrepancy into a quantitative uncertainty budget.
The same minimal-acquisition approach could be extended to other current-carrying systems, such as superconducting cables or operating magnets, where full 3D polarization tomography is impractical.

Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Worth a look if you care about polarized neutron imaging or non-destructive inspection of superconducting tapes. The genuinely new part is applying single-projection PNI to a multifilamentary YBCO tape that carries both a trapped field and a transport current. That combination lets the authors see internal damage as regions of reduced trapped field, and the damage pattern correlates with visible scratches. That qualitative result is the strongest part of the paper: it is direct, spatially resolved, and not smeared by surface effects.

The paper also does some things well analytically. The ToF treatment is standard but clean, and the authors are unusually honest about the limits of their forward model. They explicitly say the 5.4 A estimate is derived, not measured, and they report their own validation run where the same simulation method came in about 30% below the measured integrated field for a known 1 A transport current. That transparency is creditworthy.

The soft spot is exactly where the reader and stress-test put it: the 5.4 A per filament figure is obtained by tuning the simulated current until one number—the maximum XY polarization—matches experiment. There is no sensitivity range, no per-filament freedom, and the forward model has several simplifications (Gaussian blur, no beam divergence, Bean thick-slab assumption on a 1.2 micron tape, homogeneous field in a sample that is visibly damaged). Given the authors' own 30% validation discrepancy, the absolute value is not yet supported. The paper does not oversell this as much as it could have, but the conclusion still presents 5.4 A as the estimate rather than as one plausible model-dependent value.

Who is this for? PNI practitioners and people working on coated-conductor quality control. As a demonstration that a fast single-projection measurement can localize damage and give a rough current scale, it succeeds. As a quantitative metrology claim, it needs more work.

My recommendation: send it to peer review. A serious referee should ask for the quantitative claim to be reframed with explicit uncertainty or a sensitivity analysis, but the experimental demonstration and the honest handling of limitations are worth publishing. I would bring it to a reading group, mostly to discuss how much fitting is acceptable before a derived number becomes a fitted parameter.

Referee Report

3 major / 6 minor

Summary. The manuscript reports a polarized neutron imaging (PNI) study of a multifilamentary YBCO tape that contains a trapped magnetic field and carries a 1 A transport current. Using a single polarization component and time-of-flight analysis, the authors identify regions of internal damage from the trapped-field image, extract integrated magnetic field values for three regions of interest, and estimate the per-filament screening current by simulating the experiment with a Bean/rooftop model and tuning the current until the simulated peak polarization matches the measured value, yielding 5.4 A per filament.

Significance. The qualitative result—that single-projection PNI can reveal internal damage in a superconducting tape—is convincing and useful, and the authors are transparent about the assumptions in their forward model and background correction. If the quantitative estimate were robust, the paper would demonstrate a fast screening capability for current-carrying superconductors. However, the headline value of 5.4 A per filament is the result of a one-parameter fit to a single scalar data point, and the model's own validation run shows a roughly 30% discrepancy in integrated field. These issues do not invalidate the qualitative contribution but they do mean the central quantitative claim is not yet supported with the needed uncertainty analysis.

major comments (3)

[III.C] The 5.4 A per-filament screening current is obtained by tuning the simulated current until the simulated maximum XY polarization equals the measured maximum of 0.56. This is a one-parameter fit to a single scalar value. Because the trapped-field image (Fig. 1b) is visibly inhomogeneous, a single uniform current per filament is an effective model parameter rather than a uniquely determined integrated screening current. No sensitivity analysis or uncertainty estimate is provided for 5.4 A, and the spatial inhomogeneity means the fitted value could be consistent with a wide range of true local current distributions. The paper should report a range of plausible currents under different model assumptions and clearly state whether 5.4 A is an upper bound, a mean, or an effective value.
[IV] The validation run for a 1 A transport current produced simulated integrated field strengths about 30% lower than the measured values. Since the same forward model (Gaussian blur, no beam divergence, ideal geometry) is used for the trapped-field simulation, this ~30% discrepancy is a direct indication of model bias that should be propagated into the uncertainty of the inferred 5.4 A value. The authors acknowledge the discrepancy in the discussion but do not correct for it or include it in the uncertainty of the headline estimate. At minimum, the conclusion should state that the true screening current is uncertain by a factor comparable to the validation discrepancy, and the analysis should be repeated with a bias-corrected forward model.
[III.B] The background correction subtracts the background polarization bin-by-bin. However, the precession angle from the combined sample and background fields is the sum of the individual precession angles, while the polarization is a sinusoidal function of that angle (Eqs. (2)-(4)). Subtracting polarization values is therefore not equivalent to removing the background field contribution, even approximately, unless the angles are small and the field directions are known. With a background polarization of about 0.1, this approximation introduces a systematic error in the extracted integrated fields that is not quantified. The authors should either perform the correction at the level of precession angles after accounting for the background field direction, or justify the linearization with a numerical estimate of its effect.

minor comments (6)

[V] In the Conclusion, the phrase 'an approximate value of of 5.4 A' contains a duplicated 'of'; remove the repetition.
[III.A] The notation for the regions of interest is inconsistent: the figure caption uses PTC, PTF, PBG, while the text uses 'PT C', 'PT F', 'PBG'. Unify the subscript formatting.
[III.B] The sign convention of the extracted integrated field values in Table I deserves clarification: the transport-current region gives a negative value and the trapped-field region a positive value, but the text describes the two signals as having opposite orientations relative to the polarization axis. A short statement connecting the sign of the slope to the sign of Bz along the neutron path would prevent confusion.
[I] In Eq. (5), the index i on θi is not defined. Since the equation is used for the XY polarization component later, define i as the incoming polarization direction or remove the subscript.
[II] The text states that spin up/down open-beam measurements for the YY polarization were acquired for 2700 s each, while the sample measurements are for XY polarization. The relationship between this calibration and the sample polarization component should be stated more explicitly.
[III.C] Figure 4 shows the simulated and measured trapped-field images, but the color scale or normalization is not described. Without this information, the claimed 'structural agreement' is difficult for the reader to assess quantitatively.

Circularity Check

1 steps flagged · score 6.0 of 10

The 5.4 A/filament screening-current estimate is a fit parameter tuned to reproduce the measured maximum polarization, not an independent prediction.

fitted input called prediction [Section III.C, 'Simulation of current distribution', paragraph beginning 'Tuning the simulated current strength...']
"Tuning the simulated current strength until the simulated polarization agrees with the background corrected measurements of the exclusively trapped magnetic field, we can retrieve an estimate for the current strength generating the trapped field during the experiment. ... using a total loop current of 5.4 A pr filament, we retrieved a maximum XY-polarization of 0.56, which was equal to the largest experimental value measured."

The headline quantitative result, 5.4 A per filament, is the free parameter of the forward model, adjusted until the simulated maximum XY polarization equals the measured maximum of 0.56. It is therefore not derived from a first-principles prediction or measured independently; it is a best-fit input chosen to reproduce the single most salient data point. The paper's own wording confirms this: 'Tuning the simulated current strength until ... agrees' and 'equal to the largest experimental value measured.' No separate prediction, no sensitivity range, and no per-filament degrees of freedom are given despite visible spatial inhomogeneity.

full rationale

The paper's ToF-based integrated field values (Table I) are legitimate direct measurements derived from the physical relation theta = a*lambda, and the qualitative damage identification is an independent visual observation. However, the central quantitative claim of 5.4 A/filament screening current is obtained by tuning the simulation's current until the simulated maximum polarization matches the measured maximum. This is pattern 2 (fitted input called prediction): the parameter is fitted to the data and then presented as the result. The forward model adds physical content, so the circularity is partial rather than total, but the headline estimate reduces to a one-number best fit with no independent verification and with acknowledged ~30% model underestimation in the analogous transport-current check. Self-citations to [4] and [5] for sample geometry and critical current are external characterizations and are not load-bearing in a circular way. Overall score 6 reflects partial circularity: a central 'prediction' reduces by construction to a fitted parameter.

Assumptions & free parameters 2 free parameters · 5 assumptions · 0 invented entities

The central quantitative claim depends on one fitted parameter (5.4 A per filament), two physical modeling assumptions (Bean and rooftop models), a simplified forward model, and an ad hoc background correction. No fundamentally new entities are introduced.

free parameters (2)

Per-filament screening current I_fil = 5.4 A
Tuned in Section III.C so the simulated maximum XY polarization equals the largest experimental value of 0.56; this is the paper's central quantitative result.
Gaussian blur sigma = 3.4 pixels (0.96 mm)
Chosen in Section III.C to match the estimated experimental blur of 0.96 mm; an input to the forward model that affects the simulated peak and spatial profile.

assumptions (5)

domain assumption Bean critical-state model with full field penetration at 1 T
Section III.C assumes the applied 1 T field exceeds the full-penetration field so critical current flows throughout every filament after the field is removed.
domain assumption Rooftop model represents screening currents as expanding square loops
Section III.C and Figure 3 use this current-path model to compute the trapped field; if the real current distribution differs, the 5.4 A estimate is invalid.
domain assumption Forward model neglects beam fluctuations and divergence, approximated by a Gaussian blur
Stated in Section III.C; the 30% validation discrepancy for a 1 A transport current suggests this simplification is quantitatively imperfect.
ad hoc to paper The homogeneous background polarization is the only systematic error and can be subtracted bin-by-bin
Sections III.B and IV assume the background is a constant systematic error, attributed to Earth's field entering through holes in the mu-metal shield; this correction directly shifts all reported integrated field values.
standard math Weak-field linear precession relation and single-component polarization analysis (Eq. 5)
Eq. 5 assumes small precession cascade effects; standard PNI approximation used in the ToF linear regression.

how reviews work

0 comments

Cite this review

Pith. "Pith review of Minimal Acquisition Time Polarized Neutron Imaging of Current Induced Magnetic Fields in Superconducting Multifilamentary YBCO Tape." pith.science (2026). https://pith.science/paper/24OCBT3H

@misc{pith2026241116473,
  author       = {Pith},
  title        = {Pith review of: Minimal Acquisition Time Polarized Neutron Imaging of Current Induced Magnetic Fields in Superconducting Multifilamentary YBCO Tape},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/24OCBT3H}},
  note         = {Machine review of arXiv:2411.16473}
}

read the original abstract

In this paper we showcase the strengths of polarized neutron imaging as a magnetic imaging technique through a case study on field-cooled multifilamentary YBCO tape carrying a transport current while containing a trapped magnetic field. The measurements were done at J-PARC's RADEN beamline, measuring a radiograph of a single polarization component, to showcase the analysis potential with minimal acquisition time. Regions of internal damage are easily and accurately identified as the technique probes the internal magnetic field of the sample, thereby avoiding surface-smearing effects. Quantitative measurements of the integrated field strength in various regions are acquired using time-of-flight information. Finally, we estimate the strength of the screening currents in the superconductor during the experiment by simulating an experiment with a model sample and comparing it to the experimental data. With this, we show that polarized neutron imaging is not only a useful tool for investigating magnetic structures but also for investigating samples carrying currents.

Figures

Figures reproduced from arXiv: 2411.16473 by the authors.

**Figure 3.** FIG. 3: Schematic configuration of screening current [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 4.** FIG. 4: Comparison between [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

10 extracted references · 7 canonical work pages

[1]

Kardjilov, I

N. Kardjilov, I. Manke, M. Strobl, A. Hilger, W. Treimer, M. Meissner, T. Krist, and J. Banhart, Three- dimensional imaging of magnetic fields with polarized neutrons, Nature Physics 4, 10.1038/nphys912 (2008)

work page doi:10.1038/nphys912 2008
[2]

Sales, M

M. Sales, M. Strobl, T. Shinohara, A. Tremsin, L. T. Kuhn, W. R. B. Lionheart, N. M. Desai, A. B. Dahl, and S. Schmidt, Three dimensional polarimetric neu- tron tomography of magnetic fields, Scientific Reports 8, 10.1038/s41598-018-20461-7 (2018)

work page doi:10.1038/s41598-018-20461-7 2018
[3]

M. Busi, E. Polatidis, S. Samothrakitis, P. K¨ ohnen, F. Malamud, C. Haase, and M. Strobl, 3d characteri- zation of magnetic phases through neutron polarization contrast tomography, Additive Manufacturing Letters 6, 10.1016/j.addlet.2023.100155 (2023)

arXiv 2023
[4]

A. C. Wulff, A. B. Abrahamsen, and A. R. Insinga, Mul- tifilamentary coated conductors for ultra-high magnetic field applications, Superconductor Science and Technol- ogy 34, 10.1088/1361-6668/abee2b (2021)

work page doi:10.1088/1361-6668/abee2b 2021
[5]

Insinga, M

A. Insinga, M. Solovyov, A. Usoskin, A. Rutt, U. Betz, J. H. Lundeman, A. B. Abrahamsen, J. C. Grivel, F. Gomory, and A. C. Wulff, Lift- factor analysis of multifilamentary coated conductor produced using two level undercut-profile substrates, IEEE Transactions on Applied Superconductivity 29, 10.1109/TASC.2019.2896463 (2019)

work page arXiv 2019
[6]

Shinohara, K

T. Shinohara, K. Hiroi, Y. Su, T. Kai, T. Nakatani, K. Oikawa, M. Segawa, H. Hayashida, J. D. Parker, Y. Matsumoto, S. Zhang, and Y. Kiyanagi, Polarization analysis for magnetic field imaging at raden in j-parc/mlf, Journal of Physics: Conference Series 862, 10.1088/1742- 6596/862/1/012025 (2017)

doi:10.1088/1742- 2017
[7]

A. S. Tremsin, J. B. McPhate, J. v. Vallerga, O. H. W. Siegmund, J. S. Hull, W. B. Feller, and E. Lehmann, De- tection efficiency, spatial and timing resolution of thermal and cold neutron counting mcp detectors, Nuclear In- struments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 604, 10.1016/j...

work page doi:10.1016/j.nima.2009.01.041 2009
[8]

C. P. Bean, Magnetization of high-field superconductors, Reviews of Modern Physics 36 (1964)

work page 1964

Show all 10 references

[9]

E. H. Brandt, Electric field in superconductors with rectangular cross section, Physical Review B 52, 10.1103/PhysRevB.52.15442 (1995)

1995 doi
[10]

Ortner and L

M. Ortner and L. G. Coliado Bandeira, Magpylib: A free python package for magnetic field computation, Soft- wareX 11, 10.1016/j.softx.2020.100466 (2020)

2020

Pith tools

Reviewed August 12, 2026 · model on record in the stance chip above.

[1] [1]

Kardjilov, I

N. Kardjilov, I. Manke, M. Strobl, A. Hilger, W. Treimer, M. Meissner, T. Krist, and J. Banhart, Three- dimensional imaging of magnetic fields with polarized neutrons, Nature Physics 4, 10.1038/nphys912 (2008)

work page doi:10.1038/nphys912 2008

[2] [2]

Sales, M

M. Sales, M. Strobl, T. Shinohara, A. Tremsin, L. T. Kuhn, W. R. B. Lionheart, N. M. Desai, A. B. Dahl, and S. Schmidt, Three dimensional polarimetric neu- tron tomography of magnetic fields, Scientific Reports 8, 10.1038/s41598-018-20461-7 (2018)

work page doi:10.1038/s41598-018-20461-7 2018

[3] [3]

M. Busi, E. Polatidis, S. Samothrakitis, P. K¨ ohnen, F. Malamud, C. Haase, and M. Strobl, 3d characteri- zation of magnetic phases through neutron polarization contrast tomography, Additive Manufacturing Letters 6, 10.1016/j.addlet.2023.100155 (2023)

arXiv 2023

[4] [4]

A. C. Wulff, A. B. Abrahamsen, and A. R. Insinga, Mul- tifilamentary coated conductors for ultra-high magnetic field applications, Superconductor Science and Technol- ogy 34, 10.1088/1361-6668/abee2b (2021)

work page doi:10.1088/1361-6668/abee2b 2021

[5] [5]

Insinga, M

A. Insinga, M. Solovyov, A. Usoskin, A. Rutt, U. Betz, J. H. Lundeman, A. B. Abrahamsen, J. C. Grivel, F. Gomory, and A. C. Wulff, Lift- factor analysis of multifilamentary coated conductor produced using two level undercut-profile substrates, IEEE Transactions on Applied Superconductivity 29, 10.1109/TASC.2019.2896463 (2019)

work page arXiv 2019

[6] [6]

Shinohara, K

T. Shinohara, K. Hiroi, Y. Su, T. Kai, T. Nakatani, K. Oikawa, M. Segawa, H. Hayashida, J. D. Parker, Y. Matsumoto, S. Zhang, and Y. Kiyanagi, Polarization analysis for magnetic field imaging at raden in j-parc/mlf, Journal of Physics: Conference Series 862, 10.1088/1742- 6596/862/1/012025 (2017)

doi:10.1088/1742- 2017

[7] [7]

A. S. Tremsin, J. B. McPhate, J. v. Vallerga, O. H. W. Siegmund, J. S. Hull, W. B. Feller, and E. Lehmann, De- tection efficiency, spatial and timing resolution of thermal and cold neutron counting mcp detectors, Nuclear In- struments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 604, 10.1016/j...

work page doi:10.1016/j.nima.2009.01.041 2009

[8] [8]

C. P. Bean, Magnetization of high-field superconductors, Reviews of Modern Physics 36 (1964)

work page 1964