Modelling Parallel-Connected, No-Insulation High-Tc Superconducting Magnets

Ratu Mataira; Mark D. Ainslie; Rod Badcock; Chris W. Bumby

doi:10.1109/TASC.2021.3065284

Modelling Parallel-Connected, No-Insulation High-T_cSuperconducting Magnets

Ratu Mataira^*, Mark D. Ainslie, Rod Badcock, Chris W. Bumby

^*Corresponding author for this work

Engineering

Research output: Contribution to journal › Article › peer-review

11 Citations (Scopus)

Abstract

The charging/discharging delays in superconducting coils wound without insulation (NI coils) are a major drawback of the technique. While removing the insulation improves safety margins, the increase in the characteristic time constant τc can make a coil unfit for a particular purpose. It is widely accepted for instance that NI coils will not be used in ac applications where τc ∼ 1/f. To decrease τc of the NI coils, the same length of superconductor can be wound/connected in parallel rather than in series - decreasing the inductance L, and hence the time constant τ c, while maintaining the number of amp-turns IopN. Here we investigate the effect of parallel connecting coils in a magnet using a 2D axially symmetric model which captures all the necessary electromagnetic properties of the HTS NI coils. These properties include: critical current anisotropy Jc(B,θ), turn-to-turn conductivity, as well as winding parallelism. Our modeling results show that the parallel connected magnet experiences magnet-wide shielding current effects. Whilst these shielding currents affect field homogeneity - the model enables this effect to be quantified. Furthermore, shielding currents are not an issue when running NI coils in saturated mode. The modeling work presented here provides a simple initial example of how magnet designers may approach designing, optimizing, and operating high current, HTS NI coils.

Original language	English
Article number	9376303
Journal	IEEE Transactions on Applied Superconductivity
Volume	31
Issue number	5
DOIs	https://doi.org/10.1109/TASC.2021.3065284
Publication status	Published - 11 Mar 2021

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10.1109/TASC.2021.3065284

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title = "Modelling Parallel-Connected, No-Insulation High-Tc Superconducting Magnets",

abstract = "The charging/discharging delays in superconducting coils wound without insulation (NI coils) are a major drawback of the technique. While removing the insulation improves safety margins, the increase in the characteristic time constant τc can make a coil unfit for a particular purpose. It is widely accepted for instance that NI coils will not be used in ac applications where τc ∼ 1/f. To decrease τc of the NI coils, the same length of superconductor can be wound/connected in parallel rather than in series - decreasing the inductance L, and hence the time constant τ c, while maintaining the number of amp-turns IopN. Here we investigate the effect of parallel connecting coils in a magnet using a 2D axially symmetric model which captures all the necessary electromagnetic properties of the HTS NI coils. These properties include: critical current anisotropy Jc(B,θ), turn-to-turn conductivity, as well as winding parallelism. Our modeling results show that the parallel connected magnet experiences magnet-wide shielding current effects. Whilst these shielding currents affect field homogeneity - the model enables this effect to be quantified. Furthermore, shielding currents are not an issue when running NI coils in saturated mode. The modeling work presented here provides a simple initial example of how magnet designers may approach designing, optimizing, and operating high current, HTS NI coils.",

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note = "Funding Information: Manuscript received December 1, 2020; revised February 22, 2021; accepted February 28, 2021. Date of publication March 11, 2021; date of current version April 16, 2021. This work was supported in part by the New Zealand MBIE Endeavour under Contract RTVU1707, and in part by the NZ Royal Society Marsden under Award MFP-VUW1806. The work of M. D. Ainslie was supported by the Engineering and Physical Sciences Research Council (EPSRC) Early Career Fellowship EP/P020313/1. (Corresponding author: Ratu Mataira.) Ratu Mataira, Rod Badcock, and Chris W. Bumby are with the Robinson Research Institute, Victoria University of Wellington, Lower Hutt 5046, New Zealand, and also with the The MacDiarmid Institute of Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6140, New Zealand (e-mail: [email protected]). Funding Information: The Authors would like to acknowledge financial support from New Zealand MBIE Endeavour grant no. RTVU1707, and NZ Royal Society Marsden Grant no. MFP-VUW1806. M.A. acknowledges financial support from an EPSRC Early Career Fellowship EP/P020313/1. All data are provided in full in this paper. Publisher Copyright: {\textcopyright} 2002-2011 IEEE.",

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N2 - The charging/discharging delays in superconducting coils wound without insulation (NI coils) are a major drawback of the technique. While removing the insulation improves safety margins, the increase in the characteristic time constant τc can make a coil unfit for a particular purpose. It is widely accepted for instance that NI coils will not be used in ac applications where τc ∼ 1/f. To decrease τc of the NI coils, the same length of superconductor can be wound/connected in parallel rather than in series - decreasing the inductance L, and hence the time constant τ c, while maintaining the number of amp-turns IopN. Here we investigate the effect of parallel connecting coils in a magnet using a 2D axially symmetric model which captures all the necessary electromagnetic properties of the HTS NI coils. These properties include: critical current anisotropy Jc(B,θ), turn-to-turn conductivity, as well as winding parallelism. Our modeling results show that the parallel connected magnet experiences magnet-wide shielding current effects. Whilst these shielding currents affect field homogeneity - the model enables this effect to be quantified. Furthermore, shielding currents are not an issue when running NI coils in saturated mode. The modeling work presented here provides a simple initial example of how magnet designers may approach designing, optimizing, and operating high current, HTS NI coils.

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Modelling Parallel-Connected, No-Insulation High-T_cSuperconducting Magnets

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