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
Feb. 15, 2013
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
Transfer function b6
HQ01e-3, 13 A/s, 4.4 K
HQ01e-3, 13 A/s, 4.4 K
Feb. 15, 2013
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 between multipole fluctuations and imbalance events
Feb. 15, 2013
HQ01e-3 mag. meas. update

4. Case study: b6 jump after reaching 7kA plateau
How about B2 and other low-order harmonics? 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
Feb. 15, 2013
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
Feb. 15, 2013
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
Feb. 15, 2013
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
Feb. 15, 2013
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
Feb. 15, 2013
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 contribution from persistent current is changed
No significant impact on the peak b6 which appears after the injection (-50 to -30 units)
Feb. 15, 2013
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
Feb. 15, 2013
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
Feb. 15, 2013
HQ01e-3 mag. meas. update