Speaker
Description
No-insulation (NI) high-temperature superconducting (HTS) coils offer improved thermal stability and self-protection compared to conventional insulated coils. Despite these advantages, quenches can still occur. The inherent current-sharing property of NI coils allows for coil design with potential recovery after a quench, provided the current redistribution is well characterized.
To enable quantitative measurement of current redistribution during quench and recovery, we developed and tested multi-channel PCB-based antenna arrays on a dry-wound, 130-turn single-layer NI-HTS pancake coil with a 25 mm inner diameter. Two antenna geometries were explored: (1) four wedge-shaped pick-up coils for angular resolution and (2) six concentric rings for radial resolution. The angular configuration demonstrated homogeneous current distribution in the azimuthal direction during quench events. The concentric ring antennas enabled identification of the quench initiation point and its radial propagation, but were ultimately limited by sensitivity to positioning and ambient noise, restricting their use for precise, quantitative profiling.
To overcome these limitations, we propose a new gradiometric antenna design composed of concentric anti-series pick-up coils optimized for mapping radial distribution of azimuthal current. This configuration yields an inductance matrix with a condition number below 4, supporting robust signal inversion. Each gradiometer is highly sensitive to the coil region directly beneath it, while exhibiting significantly reduced cross-talk from adjacent regions. The anti-series design also enhances immunity to external electromagnetic interference.
Although this geometry results in reduced signal strength due to partial magnetic field cancellation, signal quality can be recovered via amplification or by transitioning from PCB fabrication to wound pick-up coils to increase turn density. This sensing approach provides a non-intrusive path toward high-fidelity, spatially resolved measurements, enabling validation of numerical models and deeper understanding of current redistribution in NI-HTS planar coil architectures.
