1. Understand real potential of YBCO CC A Xu, J. Jaroszynski, D. Abraimov, Y. Viouchkov, F. Kametani V. Braccini A. Polyanskii D. Larbalestier Motivation: a)to characterize I c ( , B, T) for HTS magnet design - SuperPower Inc b) to understand “macroscopic” defects of the tape, influence of soldering c) to understand pinning mechanisms d) to explore how engineering of YBCO CC could enhance J c ( , B, T) B = 16 T  = 17.5 deg I c  200 A B = 32 T   0 I c  1 kA Do to the strong anisotropy: the most critical point of the magnet is the end of the outer coil This is in contrast to LTS magnets where the center of the magnet is the most critical To follow rapid changes in commercial conductor from SP

2. RESULTS YBCO Critical Current versus Perpendicular Field up to 31 T 14 T This assessment shows up to 40 % differences @ 31 T

3. Critical current @ T=4.2, B=14 T vs. T=77 K, SF SuperPower claims increase of Ic @ 77 K However our measurements clearly show that it does not necessarily enhances I c @ 4.2 K RESULTS But the latest tape seems to be back on good side

4. Magneto-optical visualization reveals defects RESULTS A. Polyanskii How macroscopic defects in substrate, coating copper etc etc influence growth, performance? Is there any correlation? All perfect defects bad perfect

5. High current probe with rotator current leads: YBCO tape in Cu braid survived week of measurements with Ic=80 A @77 K sample platform drive: fishing line (kevlar) strong enough to survive high torque, low temperature currents up to 500 A in 4.2 K angle -10 to 120 deg B up to 31 T diameter: 1.5 in Angular dependence

6. J c is enhanced significantly by second phase addition. Different doping results in different Jc angular dependence Harrington et al., 2009 Supercond. Sci. Technol. 22, 022001 Feldmann et al., HTS peer review 2009, August 4-6, Alexandria VA @ 77 K J c ( , B) dramatically depends on doping Cf. A. Xu et al.  4.9 //ab//c  11 77K/75.5K 1T Angular dependence

7. In contrast to 77 K, at T =4.2 K different YBCO CC have similar J c ( , B) No c-axis maximum Cusp-like ab maximum Narrow channel to reduce current below 500 A ab

8. Effects of BZO doping at low T: steeper B dependence for B  ab However higher Ic for 5 deg off ab plane I c / B ¡ 0 : 5 I c / B ¡ 0 : 7 30

9. I c ( A / 4 mmw i d t h ) B ( T ) B ( T ) B ( T ) B ( T ) 90 deg 30 20 10 5 0 90 deg 30 20 10 5 0 90 deg 30 20 10 5 0 90 deg 30 20 10 5 0 At 20 deg off plane: upto 200 A at 30 T BZO sample: the highest I c at 5 deg off 186 A 16 T The end of the outer coil B = 16 T  = 17.5 deg I= 186 A I c field dependence at different angles

10. BZO doping makes ab-maxima wider ! Very high Jc sample thickness is only 0.9  m J c seems to be thickness independent (when milling) But is it possible to grow thicker to enhance I c ??? ab

11. Samples: degeneration, delamination e.g. SP02 SP04 were very weak Recent samples: strong But sometimes weird I-V curves Due to macroscopic defects?? Bad contact Cu-YBCO?

12. Elevated temperatures: SP02: for quench modeling A. Xu et al.

13. Standard B (SP02) vs temperature

14. Soldering: Ic degeneration vs. temperature, time Time = 10 s Despite off data scatter the trend is clearly seen M. Santos et al.

15. Result so far Main producer’s characteristics: Ic @ 77 K and claim that it increases However our measurements clearly show that it does not necessarily enhances Ic @ 4.2 K @ 77 K J c ( , B) dramatically depends on doping and can be modified In contrast, at T =4.2 K different YBCO CC have similar J c ( , B) However, we found BZO doping as useful tool to tune Jc(  ) at low T -higher Ic SF but steeper I c (B) decay -substantially wider maximum around ab plane J c (  ) Some early samples very weak easy delaminated Many recent samples weird I-V characteristics strongly suggesting current transfer between Cu/Ag/YBCO along the sample However samples are strong do not change during measurements Soldering: above 200 C degeneration starts

16. Plans: Contactless I c measurements by means of magnetization Development/ Automation of I c setup 1.5 kA rotator/ barrel measurements Extensive characterization including microscopy, magnetooptics Samples from different sources (in house PLD, ORNL, AMSC, MetOx)