Design and Uncertainty Analysis of an AC Loss Measuring Instrument for Superconducting Magnets

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper describes  a thorough evaluation of the uncertainty of the measurements of losses in coils used in superconducting magnets. The authors use a Monte carlo analysis to quantify the measurement uncertainty, and the approach is compliant with the guide of uncertainty of measurements from the JCGM. This analysis is then used to evaluate how the uncertainty can be improved by considering a reduction of the main contributions to the total uncertainty.

The paper is well written and answers a need in the metrology of AC losses. The analysis and the results are well described, and the conclusions are supported by the data. I recommend the paper to be published after the authors consider adding precisions on the following points.

1) page 3 and in the conclusion, the authors mention "cutting edge components". What is "cutting edge" in 2025 may not be the case in a few years time. It would be good to add and highlight the specifications that allow some particular components of the data acqusition chain to be considered as "cutting edge" (bandwidth? accuracy ?). 

2) In the whole analysis, is the magnet inductance considered as frequency-independent? If yes, could the authors add justifications why it could be the case, or which restrictions this hypothesis gives to the analysis (no iron or metallic pieces in the vicinity of the magnet ?) If no or if the frequency-dependence is irrelevant, could authors justify why it is the case ?

3) page 5 the mentions crucial voltage taps; could they define which voltage taps are crucial and give examples ?

 

Author Response

Comment 0: The paper describes a thorough evaluation of the uncertainty of the measurements of losses in coils used in superconducting magnets. The authors use a Monte carlo analysis to quantify the measurement uncertainty, and the approach is compliant with the guide of uncertainty of measurements from the JCGM. This analysis is then used to evaluate how the uncertainty can be improved by considering a reduction of the main contributions to the total uncertainty.

The paper is well written and answers a need in the metrology of AC losses. The analysis and the results are well described, and the conclusions are supported by the data. I recommend the paper to be published after the authors consider adding precisions on the following points.

Response 0: The Authors thank the Reviewer for the appreciation of the work and for the comments and suggestions helping to enhance the manuscript.

 

Comment 1: page 3 and in the conclusion, the authors mention "cutting edge components". What is "cutting edge" in 2025 may not be the case in a few years time. It would be good to add and highlight the specifications that allow some particular components of the data acqusition chain to be considered as "cutting edge" (bandwidth? accuracy ?). 

Response 1: To address the comment, the Authors modified the manuscript in different parts to avoid using a time-sensitive adjective like “cutting edge”:

• Line 3: “The instrument improves metrological performance with respect to existing instruments by reaching a target power loss uncertainty in the order of 0.1 W.”
• Line 90: “The novelty resides in the adoption of system components that achieve the required metrological performance, and into a Monte Carlo analysis to investigate measurement uncertainty by design.”
• Line 430: “To this aim, system components were selected to fulfil the metrological requirements.”

Additionally, the Authors highlighted the main specifications that helped meeting the requirements:

• Line 206: “The target uncertainty could be thus achieved especially thanks to the combination of low phase mismatch and high amplitude resolution.”

 

Comment 2: In the whole analysis, is the magnet inductance considered as frequency-independent? If yes, could the authors add justifications why it could be the case, or which restrictions this hypothesis gives to the analysis (no iron or metallic pieces in the vicinity of the magnet ?) If no or if the frequency-dependence is irrelevant, could authors justify why it is the case ?

The Authors thanks the Reviewer for the comment, which allowed to clarify this aspect in Section “4.1 Case study” as:

• Line 311: “For the magnet model, the inductance value is L = 22.5 mH. This was reasonably assumed as frequency-independent and constant given the very low frequency of the current waveform and in accordance with previous works on AC losses [8,38]”

Notably, frequency effects appear not deeply explored in the literature on superconducting magnets, but it was possible to add the ensuing reference to furtherly support the statement:

Kim, J.H.; Kim, C.H.; Iyyani, G.; Kvitkovic, J.; Pamidi, S. Transport AC loss measurements in superconducting coils. IEEE Transactions on Applied Superconductivity 2010, 21, 3269–3272.

 

Comment 3: page 5 the mentions crucial voltage taps; could they define which voltage taps are crucial and give examples?

Response 3: To address the suggestion, the Authors modified the content provided at page 5 as follows:

• Line 199: “Notably, the signals acquired from the voltage taps concern the current leads, so that the magnet can be properly protected from quench events. Moreover, acquiring voltages along the conductor by additional taps will allow the monitoring of the coil itself.”

Reviewer 2 Report

Comments and Suggestions for Authors

Review analysis on manuscript designation instruments-3480995.

The Authors present a comprehensive experimental and numerical study of AC losses and its accurate assessment in ramped superconducting magnets. The experimental setup and approach rely on well developed  instruments architecture with high level of metrological performance - aimed at minimal as possible target power loss uncertainty - tested with a  Monte Carlo analysis. The manuscript is well developed in all aspects and would be very useful for the superconductivity engineering community and can be published in the present form.

 

 

 

 

Author Response

Comment 0: The Authors present a comprehensive experimental and numerical study of AC losses and its accurate assessment in ramped superconducting magnets. The experimental setup and approach rely on well developed  instruments architecture with high level of metrological performance - aimed at minimal as possible target power loss uncertainty - tested with a  Monte Carlo analysis. The manuscript is well developed in all aspects and would be very useful for the superconductivity engineering community and can be published in the present form.

Response 0: The Authors thank the Reviewer for the appreciation of the work.