1. Milan Majoros, Chris Kovacs, G. Li, Mike Sumption, and E.W. Collings
Measurements of YBCO pancake coils: stability, quench, and NZP at 4.2 K and 10 T – and CORC cable quenching at 77 K/SF
Milan Majoros, Chris Kovacs, G. Li, Mike Sumption, and E.W. Collings
Center for Superconducting and Magnetic Materials, MSE, The Ohio State University
D. Van Der Laan
Advanced Conductor Technologies and University of Colorado
his work was supported by the U.S. Department of Energy, Office of Science, Division of High Energy Physics, under Grant DE-SC

2. Motivation and Outline
YBCO coated conductors are of interest in a number of possible HEP applications, including high field dipole and quadrupole magnets
The temperature distribution, quench, the normal zone propagation, and conductor protection are highly important in these applications.
In the present work we have measured stability, and normal zone propagation in a YBCO pancake coil at 4.2 K in liquid helium bath.
The experiments have been done in applied magnetic fields up to 10 T at transport currents of a certain percentage of the coil critical current.
A small pancake coil with 30 mm ID and 39.3 mm OD and using kapton insulation was measured
Coil winding was instrumented for voltage and temperature measurements, such that both radial and azimuthal quench propagation could be measured. Heat pulses of various powers and durations were generated to measure quench and NZP.
This work was performed on a “dry” winding; these results are baselines for comparisons of several different epoxy and insulation winding modes

3. Quench and Thermal Diffusion Measurement Progression
Roebel Cable Current sharing 77 K
CORC cable current sharing 77 K
Roebel Cable quench 77 K
CORC cable quench 77 K
Small, strand wound pancake coil
77 K thermal diffusion, quench
6. Small, strand wound pancake coil
4 K thermal diffusion, quench
7. Roebel cable quench 4 K, T
8. CORC cable quench 4 K, T
Superconductor Science and Technology, v28 n5 ( ): , also IEEE Trans. Appl. Supercond. 24 (2014)
Work in progress
Paper in final stages (data this pres)
Supercond. Sci. and Tech. 23 (2010)
This presentation
Future work

4. Former and Probe

5. Coil Winding

6. Voltage Tap and thermocouple layout
Voltage Tap -- Red Thermocouple -- yellow

7. Room Temperature resistance measurements to test insulation
Resistance along the coil winding.
Resistance of the whole winding of the coil = mΩ

8. I-V test at 10 T, 4 K
Coil I–V curve, measured between voltage taps V1d and Vd (which span the whole coil winding)
In applied magnetic field of 10 T in LHe bath
First quench = 160 A, so some degradation
Apparently some conductor motion

9. Response - 10 T and Icoil = 100 A, heat pulse of 0.05 A/5 seconds
Voltage -- No NZ observed. Voltage taps V1a – V1b are positioned above the heater
Temperature -- No NZ observed. Thermocouple T1b is positioned on the heater.

10. Response - 10 T and Icoil = 100 A, heat pulse of 0.1 A/5 seconds
Voltage -- No NZ observed. Voltage taps V1a – V1b are positioned above the heater
Temperature -- No NZ observed. Thermocouple T1b is positioned on the heater.

11. Quenches are degrading Ic – so we go to lower fields to observe full quench

12. Response - 0 T and Icoil = 60 A, heat pulse of 0.28 A/10 seconds
T -- Non propagating NZ observed just above the heater with maximum temperature of 81.7 K
Voltage -- NZ observed just above the heater, MQE= 33 J.

13. Quench Measurements on CORC cable – 77 K and self field

14. Response –heater =1 A/5 s (210 J) and 200 s (8400 J), I/Ic = 0.318
NZ with recovery (shrinking NZ): Icable = 100 A, Icable/<Ic> = 0.318, Iheater = 1.00 A/5 s, Deposited energy = 210 J/25mm2
NZ with recovery (shrinking NZ): Icable = 100 A, Icable/<Ic> = , Iheater = 1.00 A/200 s, Deposited energy = 8400 J/25 mm2.

15. Response – heater =0.55 A/5 s (63.5 and 63.86 J), I/Ic = 0.476
NZ with recovery: Icable = 150 A, Icable/<Ic> = , Iheater = 0.55 A/5 s, Deposited energy = J/25mm2
NZ no recovery: Icable = 150 A, Icable/<Ic> = , Iheater = 0.56 A/5 s, Deposited energy = J/25mm2

16. Response – heater =0.41 A/5 s (35.6 and 36 J), I/Ic = 0.635
NZ with recovery (shrinking NZ): Icable = 200 A, Icable/<Ic> = 0.635, Iheater = A/5 s, Deposited energy = 35.6 J/25mm2.
NZ with no recovery (expanding NZ): Icable = 200 A, Icable/<Ic> = 0.635, Iheater = A/5 s, Deposited energy = 36.0 J/25mm2.

17. Phase diagram of Normal zones
Icable/<Ic >
Max. deposited energy - no NZ (J/25mm2)
Min. deposited energy - shrinking NZ (J/25mm2)
Max. deposited energy - shrinking NZ (J/25mm2)
Min. deposited energy – expanding NZ (J/25mm2)
0.3176
40.656
42.525
>
0.4764
35.301
37.044
63.525
65.856
0.6350
35.646
35.820
35.993
Includes regimes of :
-no normal zone
-Runaway normal zone
-Stationary-thermal equilibrium normal zones-STE

18. Discussion I This is a generic characteristic of YBCO coils and cables
Similar STE (Stationary Thermal Equilibrium) normal zones were seen in our modelling of YBCO 50 T solenoids
Similar STE were seen in our experiment with YBCO small solenoid coils at 77 K – we could quench one side of the coil – and the other side could be still superconducting – and this would be an equilibrium state
This is a generic characteristic of YBCO coils and cables

19. Discussion II
Quench in HTSC, while having the same physics as LTSC, appears differently two reasons
The time scale of the quench process, for LTSC much smaller that typical measurement time scales (but see work by Bordini) is very much expanded for HTSC because of much larger heat capacities and temperature margins.
-For HTSC, we can see the quench develop, because of the time and temperature resolution
This makes two classes of quench – slow and fast.
The fast is where energy deposition is high enough to generate an MPZ “instantly”
The slow is where power is lower, but we slowly approach MPZ length
In this latter case the max temperature is higher!
In such a case, what does it mean to say MQE ? Is it the energy needed to take the strand to Normal – or the energy to generate a self sustaining quench.
If the latter – we need a name for the energy to take to a normal state -- MQN

20. Discussion III
2. In some cases, there will be a possibility for temperature equilibrium between the hot zone and the coolant – because Tc >> Tbath In such cases, a Stationary Thermal Equilibrium zone will form (STE)

21. Conclusions
We have made winding machine, small YBCO pancake holder, and probe for quench measurements for small YBCO coil quench measurements at 4 K, 10 T
Next steps are using various epoxies and insulations
Testing of thermal conductivity and quench progression
We have measured quench in CORC cables at 77 K
Both efforts are part of a larger strategy for YBCO cable and coil quench studies
We have observed Stationary Thermal Equilibrium normal zones in YBCO cables and coils, and propose the name STE
We also observe systematic effects, and distinguish between fast and slow quenches in YBCO, and propose a term for an energy sufficient to cause a recoverable quench, leaving MQE for a full and non-recoverable quench