# Presentation: 882766

## Nb3Sn Magnet Instability Observations at LBNLAlan Lietzke, Paul Bish, Bill Lau, Sara Mattafirri, Mark Nyman Superconducting Magnet TestingLawrence Berkeley National Laboratory

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Introduction

- Magnet Instabilities:
- Mechanical (wire moves in B-field)
- Diamagnetic (B-field moves thru wire): “Flux-Jump”
- Observations
- Summary of instability observations at LBNL
- Observational challenges
- Examples
- Summary & Conclusions
- Future Plans

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Experimental Goals:Fast-Flux Investigations

- Initial (1996) Goals:
- Identify quench trigger.
- Locate mechanical triggers.
- Differentiate between training and “thermal” quenches.
- Recent Focus:
- Mechanical or flux-jump quench triggers

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Summary: Instability Observations at LBNL

| Date Magnet | Fast-Flux Focus | Primary Observations | DAQ Frustration | Flux-jumps (#/ramp) |
| --- | --- | --- | --- | --- |
| 1996
D19h | Pre-quench transients. | Many events every ramp. | Many PS noise events | n.a. |
| 1997 
D20 | Causes of training quenches. | Good “stick-slip” signatures.
S-slip “training”. | Missed most quench starts. | ~6 (?). |
| 2002 
SM02 | “Mixed-strand” q-prop, training & stability (high Jstrand). | Flux-jump limited performance (40% Iss).
All q-origins near a splice V-tap (??) | High RRR & mixed strand = small, noisy quench signals | ~1000 |
| 2002
RD3c | Stick-slip training |  |  | ~15 |

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Summary: (boot-legged)Instability Observations at LBNL

| Date Magnet | Fast-Flux Focus | Primary Observations | DAQ Frustration | Flux-jumps (#/ramp) |
| --- | --- | --- | --- | --- |
| Jul’03
NMR | High band-width amplifiers. | F-J limited (60% Iss) by RRR = 5 coil. | Blinded DAQ (PS switching noise) | ??? |
| Sep’03
UND | Trigger, noise improvements | F-J limited (40% Iss).
All quenches in one coil, near a splice. |  | ~1000 |
| Oct’03
HD1 | RRP conductor stability | Many flux-jumps!!
S-S training and limit. | Inadequate trigger | 100’s |
| Dec’03
UND-A | Check “good” UND coil alone. | “Good” UND-coil is also F-J limited. |  | Not examined yet |
| Apr’04 SM06 | Check NMR “sisters” | F-J limited (60% Iss) by RRR = 5 coil. | Window trigger failure | 100’s |

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Observational Challenge: PS Noise

- Voltage View:
- PS ripple
- PS switching transients

- dV/dt view:
- PS switching transients

**Flux-jump**

**PS transients and ripple**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Quench Trigger

- Mechanical
- or
- Diamagnetic?

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Fast-Flux Differentiation

- “Stick-slip”:
- Higher frequency.
- Oscillation.

- “Flux-jump”:
- Lower freq.
- Little overshoot, no ringing.

**300V/s, 30mV flux-jump**

**300V/s, 30 mV Stick-slip**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Flux-Jump Variations

- Cascade (sometimes to quench)

- Single:

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## D20 (1997): 1st Four-Layer Nb3Sn

- Geometry:
- Dipole
- Cos-theta
- Four-layer Nb3Sn
- 50 mm clear bore
- L > 1 meter.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## D20 (1997) Training

- Quench:
- 13.5T, but slow training.
- Stick-slip limited (??)

- Fast-Flux:
- Stick-slip... slow “training”
- Flux-jumps??: rare (~ 8/ramp).

**Flux-jumps**

**Stick-slip training**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## D20 (1997) Fast-Flux Signals

- Typical (100’s)
- Stick-slip
- ~40mV, ~500V/s

- Rare (6-8/ramp):
- Flux-jump??
- ~3mV (small), ~25V/s

**Accel**

**Decel**

**Ring**

**Flux-jump??**
**Low-B, no training, no decel., no ring., but repeatable, and little net flux change.**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## D20: Fast Flux Change...

- Summary:
- Trained to its 4.3K Iss. (reluctantly!).
- Many fast-flux changes
- Mostly mechanical.
- Little “memory”.

- Conclusion:
- Flux-jumps _NOT_ a problem (at this Jc, Istrand, & RRR).
- Slow stick-slip “training” ~ slow quench training.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM-02 (Feb’02): 1st Magnet “Failure”

- 14 low Cu SC + 7 hi-purity Cu:
- RRR = 250 (7-Cu strands)
- 42% Iss (Istrand = 285A).
- Splice quenching (??, hi-RRR sig.).
- No ramp-rate hump.

- “Fast-Flux” data (finally) examined Aug’03:
- Flux-jump quench onsets.
- Cascade, mirror symmetric.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM-02 (Feb’02): Violent Quench-Start

- Large inductive voltages:
- 10x D20
- Swamped PS transients.
- Swamped resistive growth
- 20m/s ~ 4V/s
- Erratic signals
- No ringing!

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: 11T Racetrack Common-Coil Dipole

- Cost-effective “field-quality” demo:
- Reuse 14.5 Tesla POP outer coils.
- Reuse “19 Tesla” support structure:
- Iron yoke
- Bladder & Key
- Al shell

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Challenges:
Correct large positive sextupole (RD3b outer coils).
Large (a2) quadrupole       (reused yoke).
Large SC-hysteresis       (Nb3Sn)
Smallest measurable bore (max. force on correction coil).

- Correct large positive sextupole (RD3b outer coils).
- Large (a2) quadrupole       (reused yoke).
- Large SC-hysteresis       (Nb3Sn)
- Smallest measurable bore (max. force on correction coil).

- RD3c: Magnetic Design

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: Training Performance

- Slow training:
- Erratic plateau.
- 0.9 Iss.
- Stick-slip.
- Many (repeating) fast-flux events.
- Study platform for FFC events.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: “Stick-Slip” Quench Triggers

- Accel/decel, ringing :
- >2000V/s
- Freq~1/size
- < 1% trigger quenches.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: Fast Flux Changes

- Two Kinds:
- “Flux-Jumps”:
- Slow (10ms)
- I < 50% of Iss
- Polarity ~ dB/dt.
- Every ramp.
- “Stick-Slip”:
- Fast (0.1ms)
- “Training”:
- Yes < 8KA.
- No  > 8KA.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: Multi-Ramp FFC’s

- “Flux Jump”:
- Same # every ramp... reversed polarity during down-ramp.
- “Stick-Slip”: up-ramp  only... “forgets” every ramp > 8kA.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## RD3c: Fast-Flux Summary

- Quench-training stalled:	     10.7 kA (92% Iss).
- Huge  (>2KV/s) stick-slip triggers.
- “Stick-slip training” stalled:
- No “memory” above 8 kA (20% lower).
- Flux-jumps:
- Record number... _did not limit performance_.
- All from higher Deff coil.
- # independent of ramp repetition and direction.
- Fast-flux-change polarity reverses with dI/dt.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## NMR (2003)

- Magnet Performance:
- 7T (60% of Iss)
- No training effect.
- No ramp-rate hump.

- Conductor/splice performance:
- RRR = 5.6
- 0.2 < Rsplice < 0.3 nOhm.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## NMR

- Quench origins:
- Outside of splice.
- All but 1st in SC-12.
- Propagation:
- ~50% into nearby splice in ~1 ms.
- Max. splice temperature after quench: 40K.

- Conclusions:
- Splices: low heating, well cooled, but quenching nearby.

**Splice quench.**

**Quench start**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## UND (2003):1st NbSn Undulator

- 6-0.7mm, high-I strand (~1kA)
- RRR = low (??)
- ~40% Iss (Istrand = 333 A).
- Splice quenching every quench
- After quench-start (no damage)

- Fast-Flux:
- Many flux-jumps
- All quenches had F-J start.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## UND (2003): Quench Augmentation

- Cascade during quenching:
- Increases effective quench speed.
- Reduces peak temperature.

**Small flux-jumps start quench.**

**F-J’s during quench augmentquench rate.**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## HD1: Coil & Mod-B Cross-Section

| Imag (kA) | Bbore (T) |
| --- | --- |
| 9 | 13.82 |
| 10 | 14.04 |
| 11 | 16.26 |
| 12 | 17.46 |
| 13 | 18.65 |

**150MPa **
**Pre-stress Target**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## HD1: Quench Training

- 1st Quench:
- 8.7 kA
- 13.3 T
- 78% of Iss.
- Layer-1
- Return-end spacer
- Cond. Limits:
- 11.3-11.5 kA
- 16.6-16.9 T

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## HD1: Typical Quench Trigger (15.8T)

-  Fast motion:
- 2 kV/s (huge)
-  Delay:
- 0.6 ms
- decaying tremors
-  Resistive growth:
- large surges (multi-turn, or F-J?)

**Flux-jumps (?) during quench augment quenching rate.**

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

##  Fast motion:
18 mV
 Magnetization decay:
0.6 ms
23 mV
 Rapid resistance growth:
400V/s

- 18 mV
-  Magnetization decay:
- 0.6 ms
- 23 mV
-  Rapid resistance growth:
- 400V/s

- HD1: Typical Quench Trigger (15.8T)

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## HD1: Fast-Flux Summary

- Quench training stalled:	     16 Tesla (~93% Iss).
- Stick-slip “training” stalled?? (not examined yet).
- Flux-jumps:
- 100’s, most ever seen in a large magnet.
- _Did not limit magnet!_

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr’04)

- Set-up:
- Oxford conductor
- Small common-coil
- SC13 & SC14
- Reacted with NMR 11 & 12.
- Lightly loaded.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr’04)

- Observations:
- SC13 flux-jump trigger
- 1/10 had splice quenching.

- Training:
- All in SC13 (0.68 Iss).
- All but 1st in outer layer.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06: T03’s Quench Initiation

- Massive flux-jump trigger:
- 4kV/s.
- 3V, 750us.
- Massive parallel propagation
- 2300V/s.
- ~10 turns.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06: T03’s Flux-Jump Trigger

- Quench-trigger:
- 4 V/ms F-J
- Reverse polarity.
- Precursor:
- Oscillatory
- Reverse polarity.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06: T03’s Flux-Jump Precursor

- Oscillatory
- Reverse polarity.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr ’04) Fast-Flux Comparison

- Experimental Set-up:
- Quenched-start.
- Ramp:
- Up-Down-Up.
- Trigger:
- Vn-m (+5mV)
- Observed:
- Mostly flux-jumps
- 7/400 stick-slip
- 1st up-ramp.
- Max. freq. @:
- 2.5 kA
- 25% of Iss.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr ’04) Fast-Flux Comparison

- Experimental Set-up:
- Quenched-start.
- Ramp:
- Up-Down-Up.
- Trigger:
- Vn-m (+5mV)
- Observed:
- Mostly flux-jumps
- 7/400 stick-slip
- 1st up-ramp.
- Max. freq. @:
- 2.5 kA
- 25% of Iss.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr ’04) Fast-Flux Comparison

- Experimental Set-up:
- Quenched-start.
- Ramp:
- Up-Down-Up.
- Trigger:
- Vn-m (+5mV)
- Observed:
- Mostly flux-jumps
- 7/400 stick-slip
- 1st up-ramp.
- Max. freq. @:
- 2.5 kA
- 25% of Iss.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 (Apr ’04) Fast-Flux Comparison

- Set-up:
- Trigger: +5mV
- Counter reset:
- dI/dt reversal.
- Faster 2nd ramp:
- 2x faster
- Statistics:
- UpRamp-1: 440 cnts
-  Coil-N
- DnRamp-1: 215 cnts
- Coil-M (49%)
- UpRamp-2: 360 cnts
- dI/dt = ~2x
-  Coil-N (82%)

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## SM06 Summary

- Higher bandwidth amplifiers:
- dV/dt extended from 10 kHz to 80 kHz.
- Still have trigger problems.
- Coil “M” limited performance:
- Zero training:  68% Iss.
- Lower RRR (5.2 vs. 7.1)
- Ramp-rate variations:
- “M” flux-jumped less than “N”:
- Fewer flux-jumps at higher speed.
- Larger flux-jumps at higher speed??

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Summary of Observations

- Incremental DAQ Progress:
- Noise suppression.
- Higher bandwidth viewing.
- Triggering improvements.
- Differentiating “mechanical” from “flux-jumps”.
- Flux jumps have become a problem recently:
- 2002: SM02, mixed (Cu/Sc) strand (high Istrand).
- 2003: NMR, SM06: Low RRR.
- 2003: UND, UNDA: High Istrand, Low RRR.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Conclusions

- Flux-jumps are only a problem if they avalanche adjacent elements:
- Observation and localization continues to be a challenge:
- Need a way to manage them (if they can’t be eliminated.

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004

## Future Plans:

- Better FFC-DAQ trigger:
- Quieter PS & environment.
- Better localization
- More channels,
- FFC antennas (coil arrays).

- Superconducting Magnet Group  AFLietzke@lbl.gov

- FNAL 28-30 Apr 2004