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S-FRS magnet tests in B180 - Impedance Spectroscopy

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      Transfer-Function Measurements for Superconducting Magnets: goals and motivation
      Speakers: Vasyl Drozd (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE)), Vasyl Drozd
      MeetingNotes.docx
      MeetingNotes.pdf
      VasylDrozd_TransferFunction_19Jun2026.pdf
      VasylDrozd_TransferFunction_19Jun2026.pptx

      Minutes of Meeting

      Topic: Complex Impedance Spectroscopy for Super-FRS magnets
      Date: 19 June 2026

      H. Bajas, M. Buzzio, M. Bednarek, V. Drozd, C. Petrone. G. Riddone, K. Sugita, A. Verweij

      Objective

      The meeting reviewed plans for frequency-domain transfer-function measurements of superconducting magnets. The goal of this activity is to perform complex impedance characterization, measuring the frequency-dependent electrical response of the Super-FRS magnets, to characterize impedance, resonances, and AC-loss-related effects, while comparing results with CERN experience to validate measurement methods and improve diagnostic capabilities.

      Motivation

      Transfer-function measurements are expected to provide characteristic fingerprints of individual magnets by applying AC excitation and recording both complex impedance magnitude and phase response over frequency.

      Potentially detectable effects include:

      • Inter-filamentary and eddy currents
      • Current redistribution caused by inter-turn shorts
      • Parasitic capacitances and resistive paths
      • Non-linear behaviour and resonance phenomena
      • Long-term drift and reproducibility changes

      The measurements could help identify anomalous magnets, monitor changes over time, and support diagnostics relevant to quench protection and beam-performance studies.

      Experimental Approach

      Instrumentation

      Several measurement configurations were discussed:

      • LCR-meter-based measurements (currently using approximately 1 V AC excitation) operating Z/θ mode
        • Common ground configuration not acceptable.  Isolated grounding required and validated.
        • Measurements through VTAPs and/or current leads
      • Amplifier and shunt-based setup similar to CERN setups
      • Simultaneous acquisition of magnetic signals using fluxmeters or field pickups

      Participants emphasized the importance of measuring the magnetic response together with the electrical transfer function.

      Validation through CERN setup Comparison

      A key topic was the comparison of measurements with CERN experience and equipment.

      Proposed actions include:

      • Obtaining expert feedback on methodology
      • Borrowing or reproducing CERN measurement hardware where possible

      ·       Performing comparable measurements on warm and cold magnets with two measurement systems for comparison and verification.

      Comparisons between warm, cold, pre-installation, post-transport, and post-powering measurements could help determine whether installation or operation introduces measurable changes.

      Participants also recommended acquiring magnetic-field signals during frequency scans to evaluate field-ripple sensitivity, potentially down to the nanotesla level, and to correlate electrical and magnetic transfer characteristics.

      Detection Sensitivity

      - Potential sensitivity to inter-turn shorts.
      - Difference between healthy and damaged coils may be only 1–2%.
      - Need to demonstrate sufficient measurement precision, repeatability and reproducibility.
      - Key question: are we certain that measurement uncertainty is below the observed variation?

      Modeling

      Equivalent-circuit models are being used to reproduce measured responses. Elements of the equivalent scheme include:

      • Inductances
      • Parasitic coil-to-ground capacitance
      • Parasitic coil turn-to-turn capacitance
      • Parallel resistive paths
      • Diode-like or non-linear elements
      • Eddy current coupling, etc.

      Model includes inductive behaviour, eddy currents and inter-turn short scenarios. Sharp feature observed in measurements is not yet reproduced by the model.

      Preliminary room-temperature measurements show partial agreement with simulations. Model parameters such as capacitance and parallel resistance significantly influence resonance frequency and peak sharpness.

      - Melvin’s PhD thesis about LHC dipole complex electrical model. One could profit from the modelling work done that time on LHC magnets.

      Practical Considerations

      Measurement Strategy

      1. Warm measurements for rapid testing and methodology validation.
      2. Cold and on-site measurements once suitable resources and scheduling become available.
      3. Dedicated tests on a single coil recommended.
      4. Kei reported the existence of damaged coils at Elytt that could be used for measurement to check if there is a difference.

      Constraints

      ·       CERN availability is limited and possible cooperative measurements need to be agreed in advance, specifically the comparative measurements between LCR-based measurements and the CERN system.

      • Connector compatibility and access constraints must be addressed.
      • The choice between automated connection systems and manual connections remains open.
      • It is important to demonstrate that the measurement uncertainty, repeatability, and reproducibility limits are strictly below the 1–2% variations observed between healthy and defective coils.

      Prioritization

      Rather than immediately pursuing detailed modelling of every unit, it was suggested to measure a representative sample (up to approximately 20 magnets) to determine baseline and outliers. Detailed analysis can then be focused to interpret anomalous cases.

      Open Questions

      • Final scheduling and resource availability
      • Connector and cabling configuration
      • Baseline measurements on individual conductors versus complete loops
      • Interpretation of the observed single dominant resonance

      Conclusions

      The participants agreed that the transfer-function measurement program is technically valuable and should proceed.

      The recommended path forward is:

      • Conduct initial warm measurements to establish reproducibility and validate the setup.
      • Follow with cold and in-situ comparative measurements when scheduling permits.
      • Include simultaneous magnetic-field measurements whenever possible.
      • Focus first on screening a sample population of magnets to identify outliers before undertaking extensive modeling efforts.
      • Demonstrate that measurement repeatability limits are significantly smaller than the differences distinguishing healthy and defective coils.

      Action List

      ·       Plan comparative measurements using the CERN setup and the LCR-based setup.

      Vasyl, Mateusz

      ·       Prepare cables and a connector adapter for testing with the CERN setup.

      Vasyl

      ·      In parallel, continue research measurements using the LCR setup.

      Anthony , Vasyl

      ·       Modeling and parameter scans for the interpretation of experimental results.

      Anthony, Vasyl

      ·       Finalize the measurement system for systematic measurements

      Should be discussed at the next meeting

       

       

      It has been agreed to share supporting documents and a concise summary through Indico to facilitate coordination and follow-up activities: https://indico.cern.ch/event/1701006/ .

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      Discussion