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HQ01e-3 magnetic measurements

HQ01e-3 magnetic measurements. The third HQ01e test 4.4 K, December 2012, LBNL, 10-layer PCB probes from J. DiMarco at FNAL Magnetic measurement plan reduced significantly due to the extraction issue Plateau current ≤ 7 kA (41% I ss ) Magnet study and instrumentation improvement

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HQ01e-3 magnetic measurements

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  1. HQ01e-3 magnetic measurements • The third HQ01e test • 4.4 K, December 2012, LBNL, 10-layer PCB probes from J. DiMarco at FNAL • Magnetic measurement plan reduced significantly due to the extraction issue • Plateau current ≤ 7 kA (41% Iss) • Magnet study and instrumentation improvement • Multipole fluctuation and the cause • Synchronized acquisition of imbalance trigger, magnet current, and rotating probe signals • Persistent current effect and impact of the pre-cycle • Stair-step measurement up to 7 kA • Pre-cycles with different reset currents • Z-scan at 5 kA • Improved instrumentation • Measurement uncertainty reduced with 10-layer PCB probes • Rotation speed doubled from 0.5 Hz to 1 Hz HQ01e-3 mag. meas. update

  2. Multipole fluctuations • HQ01e-1 (LBNL): observed and correlated to magnet current fluctuation (4.4 K) • HQ01e-2 (CERN): confirmed and correlated to the flux jump • but less pronounced at 1.9 K • Hypothesis: combination of flux-jumps, power supply response, eddy-current effect: Low cable Rc Multipole fluctuation and decay Imbalance event (e.g., flux jump) Current fluctuation b6 Transfer function HQ01e-3, 13 A/s, 4.4 K HQ01e-3, 13 A/s, 4.4 K HQ01e-3 mag. meas. update

  3. HQ01e-3 multipole fluctuation study • Synchronized acquisition of coil voltage imbalance triggers, probe voltage and magnet current • b6 of each rotation color coded by the number of recorded imbalance triggers* *The absolute number of triggers depends on the threshold. Here it is used as a qualitative indicator of the ‘magnitude’ of the event (amplitude, duration, changing rate will be checked) • Clear correlation betweenmultipole fluctuations and imbalance events HQ01e-3 mag. meas. update

  4. Case study: b6 jump after reaching 7kA plateau C A B • A b6 jump was observed soon after reaching 7 kA, preceded by 52 imbalance events • Detailed correlation with imbalances and magnet currents at 3 points (A, B, C) follows HQ01e-3 mag. meas. update

  5. Rotations A and C (before/after imbalance events) A: before the imbalance occurs C: after the imbalance occurs • Probe signal • Imb. trigger • Mag. current • Magnet coil voltage HQ01e-3 mag. meas. update

  6. Rotation B (during imbalance event) • Coil imbalance voltage and transient current change observed (-30 A/s for ~ 70 ms, 10 A/s for 350 ms) and appeared synchronized • Probe voltage spike recorded (b6 jump appeared afterwards) • Cored cable in HQ02 raises Rc; expecting less pronounced multipole fluctuations at 4.4 K • To be checked: Flux jump DAQ system did not record the current change HQ01e-3 mag. meas. update

  7. Persistent current effect study • Study started to understand the effect for LARP magnets and expectation for QXF • Experimental database • Field quality measurement • TQ, LQ and HQ • Strand magnetization measurement • 54/61, 108/127 strands from HQ01 measured at 4.4 K and 1.9 K • 192/217 RRP strand being measured (QXF) • HQ02 and PIT strands next • Currently participated by BNL, LBL and OSU; more labs welcome for cross-check • Computational tool development and validation • Opera, Roxie and in-house code • Validation with well-understood NbTi data (LHC magnet data useful) • LARP magnet data • Fine current steps implemented in HQ01e-3 test for model validation HQ01e-3 mag. meas. update

  8. HQ01e-3 stair-step data for model validation • Measurement with fine steps • 100 mm probe at the straight section • Ramp rate: pre-cycle 50 A/s, 13 A/s between steps • 400 A steps below 2 kA, 1 kA steps above, 300 s pause at each step • Encouraging output from preliminary comparison with Opera calculation • Two conductor types used in HQ01e to be incorporated in the model HQ01e-3 mag. meas. update

  9. Effect of reset current on b6 at injection • Measurement • 100 mm probe rotated at the straight section • Ramp rate 13 A/s with Imax = 5 kA • Continuous ramping (no pause at the injection) • Reset current: 100, 300, 500, 700 A • b6 at the injection can be tuned by varying the reset current • b6 ~ 0 if reset at 430 A (decay not considered) • Mainly the contributionfrom persistent current is changed • No significant impact on the peak b6 which appears after the injection (-50 to -30 units) HQ01e-3 mag. meas. update

  10. 10-layer PCB probe for HQ01e-3 measurements • Developed by J. DiMarco at FNAL for higher resolution • Measurement variation improved significantly (from 2 units to 0.11 units, gain of ~ 17). Resolution improved by a factor of 3 (from 0.3 units to 0.1 units) at warm condition • +15 A, 0.5 Hz rotation speed • 100 mm long probe • Detailed study with FNAL ongoing. Given limited probe radius (1/3 magnet radius), multi-layer PCB ( 10 layers) is necessary. Large-bore anti-cryostat most desirable • Similar probes will be applied for HQ02 measurements HQ01e-3 mag. meas. update

  11. Summary and next steps • HQ01e-3 field quality measurement limited but very useful • Studied multipole fluctuation • Obtained more data for persistent-current effect study • Measured effect of the reset current • Characterized rotating probes • Useful for HQ02 measurement • Probes, new measurement needs • Compare to HQ02 behavior • HQ02 magnetic measurement preparation • Expectation based on existing HQ and LQ study • Measurement goal/plan • Hardware preparation HQ01e-3 mag. meas. update

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