1. Mike Sumption, M. Majoros, C. Myers, and E.W. Collings
Modelling and Measurement of Magnetization of YBCO CORC and Roebel Cables for Accelerators
Mike Sumption, M. Majoros, C. Myers, 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
This work was supported by the U.S. Department of Energy, Office of Science, Division of High Energy Physics, under Grant DE-SC

2. OSU Magnetization Rigs
Magnetization Measurement Facilities: A number of options are available, some systems better suited to given samples or given test requirements

3. MAG-0: 14 T, 2K-RT PPMS
Quantum Design Physical Property Measuring System (PPMS) equipped with a 14 T superconducting magnet and temperature control from 1.8 K to 400 K, can measure: M-H, AC susceptibility, AC transport, DC transport, Thermal conductivity, Hall effect, Heat capacity. Used to measure Nb3Sn M-H loops and magnetizations, as well as those of Bi:2212 strand

4. MAG-1: 4.2 K, T
Magnetization rig MAG-1, for samples larger than can be measured in the PPMS, but smaller than use for MAG-2. This is a susceptibility rig type magnetometer inside of a 12 T cryocooled magnet. Inside the 3” diameter room temperature bore is a varitemp dewar with a magnetization insert (b) side view, (c) face view. A current of up to 200 A can be applied to samples which are being measured for M-H.
Figure A6.2. Magnetization rig MAG-1, for samples larger than can be measured in the PPMS, but smaller than use for MAG-2. This is a susceptibility rig type magnetometer inside of a 12 T cryocooled magnet. Inside the 3” diameter room temperature bore is a varitemp dewar with a magnetization insert (b) side view, (c) face view. A current of up to 200 A can be applied to samples which are being measured for M-H.

5. MAG-2
Cable Magnetization measuring facility (projected operational Fall 2015);
3 T coil (Cryomagnetics design and made), NbTi wound, 150 amperes, Inductance of 10 milliHenries. Clear bore is 5.5 cm total length cm.
Cryofab dewar and hang-down assembly.
Drawing of coils, homogeneity on-axis is +/- 5% over 15 cm,
radial field homogeneity. a
(d) b c

6. MAG-3
M-H and AC Loss device for 77 K measurements of YBCO, with typical sample shown above (YBCO CORC cable in this case).
External-Field M-H and AC Loss is measured in the applied fields of copper wound solenoids and race-track coils of various sizes.
A system of pick-up coils connected to a digital oscilloscope records the samples' M-H loops
Used in this program for screening and as a comparison/calibration measurement at 77 K

7. Why the focus on Magnetization
Why the focus on Magnetization? – its b3 and its change for accelerator magnets

8. Magnetization Decay Suppression with Zr doping
New YBCO conductor with Zr pinning, University of Houston
Magnetization decay for coated conductors from UoH with (a) : 0% Zr, (b) : 7.5% Zr, (c) : 25%
Measurement with PPMS

9. Measurements on CORC at 77 K

10. Striated measurement results 77 K
Striations do significantly reduce loss
Some factor from striation, some from Ic loss

11. CORC Loss Striated vs non-straited

12. Magnetization – but loss?
For the LHC NbTi dipoles ramping at about 7 mT/s AC loss is only a small contributor to cryogenic load
Could be larger for YBCO cables.
For a YBCO cable carrying a current of 10 kA at 20 T the loss at 7 mT/s is estimated to be 200 mW/m
For an HTS insert of, say, 70 turns the winding dissipation would be 14 W/m -- more than double the LHC ring’s 4.5 K/1.8 K refrigeration capacity
This is a handle-able problem, but not of no interest

13. FEM Modelling Initial approach
Model to start as model of one helix, then moving to multiples
Treat the SC film as distributed
Jc values are representative of 4 K, 0 T

14. Modelling Treatment – Average to composite Volume
Composite, 250 m
SC, 1 m
Substrate, 50 m
Penetration field,
Bp = CJcd
So, only OK if re-normalization is in same dimension as d
M = CJcd
Msc = msc/Vsc= CJcd
Let Je=Jc/ff
Mcomp = Msc/Vcomp = Msc/(Vsc*ff)=mscJcd/ff=mscCJed
So we can treat the current as flowing through the whole composite and get a proper M

15. Magnetization calculation for 1 strand CORC cable 4 K, Bean model

16. Comparison loss shape to model
AC loss of sample R3 at 50 Hz in liquid nitrogen bath (77 K)
FEM model prediction

17. Summary
Various magnetization rigs are in operation and also commissioning
Under construction – 3 T, 4 K AC loss rig capable of 25 cm YBCO cable samples
Magnetization measurement, modelling, and comparison to accelerator targets underway
Drift measurements to look at changes in b3 underway – improvement seen with new superpower Zr doping