Characteriza*on of coated conductors in the ultra- high field regime.

Transcription

1 Characteriza*on of coated conductors in the ultra- high field regime. D. Abraimov 1, F. F. Balakirev 2, and D.C. Larbales9er 1 1 ASC, NHMFL, Tallahassee 2 NHMFL Pulsed Field Facility, Los Alamos Na9onal Laboratory SuperPower Inc. 7.5% and 15% Zr doped tapes produced for CORC applica9on were used for I c measurements 1. Mo*va*on 2. Prepara*on ultra narrow bridges Plan 3. Setup for measuring for ultra fast I- V measurements in pulsed magne*c fields 4. Tes*ng bridges: I c (T, SF) and R(T,B) 5. Measuring V(I,B,T) curves in pulsed fields up to 65T 6. Calcula*on of I c from V(I,B) dependencies 7. Summary 8. Future plans This work was supported in part by the U.S. Na9onal Science Founda9on under Grant No. DMR and the State of Florida.

2 Mo*va*on ReBCO superconductors become a choice material for developing all superconduc*ng magnets capable genera*ng ultra- high fields due to very high cri*cal current densi*es in the presence of magne*c fields and high irreversibility fields Therefore, it is important to develop instrumenta*on suitable for tes*ng I c, J c, f p of ReBCO conductors in such regime Recent progress in introducing high concentra*on ar*ficial pinning centers (APC) in ReBCO conductors makes them op*mized for low- temperature high- field applica*ons The understanding performance of APC at ultra- high fields is fascina*ng vortex dynamics problem and important applica*on task For now pulsed magnets is the only available choice for genera*ng fields above 45T

3 Tapes from different manufacturers have different slope α I c ~ B α Manufacturer Material α at BIIc α at 18 o SuperPower ReBCO SuNAM ReBCO 0.6; ; 0.68 SuperOx ReBCO 0.54; ; 0.59 Fujikura ReBCO 0.641; AMSC ReBCO 0.74 Bruker ReBCO Transport I c (B,4K) were measured by D. Abraimov, A. Fransis, M. Santos, and J. Jaroszynski

4 Comparison J c from different ReBCO samples (0.9um 2um thick) J c (B,4.2K), MA/cm 2 Transport Ic(B,4K) were measured by D. Abraimov, Aixia Xu, J. Jaroszynski 10 1 Uni Houston 15% Zr; 0.9 µm ReBCO Bruker T190D-C SN1; 2 µm ReBCO Bruker T190D-C SN2; 2 µm ReBCO SP215; 7.5% Zr; (2X50 µm Cu); ~1.55 µm ReBCO Uni Houston 7.5% Zr; 0.9 µm ReBCO SP 15% Zr; 1.52 µm ReBCO; W=4mm (2x5µm Cu) SP26; 840 um bridge; 7.5% Zr; 1um ReBCO Uni Houston data taken from : <<Strongly enhanced vortex pinning in a broad temperature and magne*c field range of Zr- added MOCVD coated conductors>> Aixia Xu, et al B, T Mo*va*on

5 Can we trust extrapola*ons? J c (B,4.2K), MA/cm 2 Transport Ic(B,4K) were measured by D. Abraimov, Aixia Xu, J. Jaroszynski Uni Houston 15% Zr; 0.9 µm ReBCO Bruker T190D-C SN1; 2 µm ReBCO Bruker T190D-C SN2; 2 µm ReBCO SP215; 7.5% Zr; (2X50 µm Cu); ~1.55 µm ReBCO Uni Houston 7.5% Zr; 0.9 µm ReBCO SP 15% Zr; 1.52 µm ReBCO; W=4mm (2x5µm Cu) SP26; 840 um bridge; 7.5% Zr; 1um ReBCO Uni Houston data taken from : <<Strongly enhanced vortex pinning in a broad temperature and magne*c field range of Zr- added MOCVD coated conductors>> Aixia Xu, et al B, T Mo*va*on

6 Different tape architecture for magnet and cable applica*ons In- field transport proper*es at 4K, BIIc orienta*on for SuperPower Inc. 4 mm wide tapes Project SP machine ReBCO thickness, µm Zr doping, % Substrate thickness, µm Cu layer thickness, µm α <I c (15T, 4K)>, A J e (15T,4K), ka/cm 2 32T M x j 183 j 45.5 j 32T M x * 283* 70.4* CORC M x CORC M x CORC M x Slightly lower α values for M3 tapes suggest that those tapes may have smaller Zr doping, than M4 tapes. Tapes with nominal 15% Zr doping have larger α, but not as high, as for tapes produced in Houston Uni. lab. The first two rows are representa*ve M3 and M4 tapes purchased for 32T magnet project. Other rows were tested for CORC project. * Average out of 15 representa*ve tapes j Average out of 12 representa*ve tapes I c ~B α Transport I c (B,4K) were measured by D. Abraimov, A. Francis, M. Santos, and J. Jaroszynski

7 What is shape of pinning force density at higher fields? f pin (B, BIIc, 4.2K), GN/m K, B tape Un i Ho usto n 1 5% Z r; 0.9 µ m R ebco Br uke r T 19 0D- C SN1 ; 2 µm ReBCO Br uke r T 19 0D- C SN2 ; 2 µm ReBCO 1 10 B, T SP % Zr SP21 5; 7.5 % Z r; ( 2X5 0 µ m C u); ~1.55 µ m R ebco Un i Ho usto n 7.5% Zr ; 0. 9 µ m ReBCO SP 15% Zr SP 1 5% Z r; µ m ReBCO ; W= 4m m (2 x5µ m Cu) SP26 ; 8 40 um br idg e; 7.5 % Zr ; 1 um ReBC O Mo*va*on Transport Ic(B,4K) were measured by D. Abraimov, Aixia Xu, J. Jaroszynski

8 Purposes of this experiment 1. Technical: find procedure of measuring I c (B,T,θ) in pulsed field up to 65T for commercially available high J c ReBCO; 2. For magnet applica*on: Transport current property - explore I c limi*ng factors at cri*cal magne*c field orienta*ons near 18 o - 20 o ; Transport current and mechanical property - find experimentally maximum in field shear stress for ReBCO layer in B_ _ tape orienta*on; 3. Physics/Material science and assistance to tape manufacturers: calculate and compare vortex pinning force dependence f p (B, T) for two SuperPower Inc. tapes containing different Zr doping: 7.5% and 15%;

9 Since pulse dura*ons are <0.1 sec., measurements of high I c are a tough technical task. Major problems: 1. High induc*on voltages in the sample, 2. The very limited *meframe to ramp current, detect voltage, compare it with defined threshold, and decide to stop current ramp just above I c.; 3. Possible Joule hea*ng in the sample due to induced eddy currents; 4. Forces on the sample and leads due to magne*c interac*on with the applied field.

10 Sample prepara*on for I c measurements in ultra- high magne*c fields To compare the effect of different BZO pinning concentra*ons we used SuperPower Inc. tapes with 7.5% Zr and 15% Zr doping Tapes with 30 µm, 38 µm, and 50 µm thick substrates and 5 µm thick Cu layer were used Two stage photolithography process was used to paoern 4mm x 4mm samples. We used chemical etching to remove Cu, Ag, and ReBCO To get uniform width and reduce I c all bridges were subsequently trimmed with a focused ion beam (FIB) Ultra- narrow bridges Using NHMFL facili*es we prepared 14 bridges ranging 47µm- 7.7µm in length and 4.8µm 0.49µm in width.

11 Mask paoern Sample prepara*on Sample: 4X4 mm; Bridge: 50 um X 200 um Current pads: 820 um X 830 um Used chemical Used photolithography to paoern etching structures Bridges were trimmed with focused ion beam in SEM

12 Sample prepara*on ReBCO a- axis grains Hastelloy substrate FIB trimmed bridge Buffer For ultra narrow bridges we choose region free from a- axis grains and CuO par*cles SEM image of bridge N13 7.5% Zr doped ReBCO SuperPower I.D. M

13 SEM image of bridge N13 W= 577 nm L= 12.4 µm t= 1.5 µm (ReBCO thickness) Thanks to Bob Goddard and Fumetake Kametani we have very negligible stage driv and therefore can make rou*nely bridges about ~0.5µm wide and about 8 µm long

14 SEM image of bridge N10

15 SEM image of bridge N10

16 Probe for measuring in pulsed magnet Heater Sample Cernox Pick- up coil Sapphire holder To prevent overhea*ng and genera*ng forces/torques due magne*za*on currents minimize volumes of conduc*ve materials in sample; To avoid using massive current leads reduce crixcal current values by reducing bridge cross sec*on; To prevent breaking a bridge by Lorentz force choose sample orienta*on in which Lorentz force is directed toward substrate; To avert large Eddy currents in current and voltage leads use twisted pairs with a small pitch. Place connec*ons between probe leads and sample leads away from field center. To avoid voltage and bias current noise fix voltage and current leads to probe;

17 Electronics used for ultrafast I c (B,T) measurements: For data acquisi*on we use RedPitaya development board with o RF input and output: DAC, ADC - Sample rate 125 Msps; o CPU: Dual core ARM Cortex A9 / FPGA: Xilinx Zynq 7010 SoC o Used to generate bias current signal, detect sample voltage and voltage propor*onal to sample current o RedPitaya was programmed in Verilog o Board was connected with PC via TCP protocol (Internet) Current source: Valhalla Scien*fic 2500 Voltage amplifiers: o Home built X100, o Stanford Research SR560 with low noise preamplifier Cryonon 22C temperature controller RedPitaya development board RedPitaya development board in Aluminum box

18 Width and length of FIB trimmed ReBCO bridges 6 SuperPower 15% Zr doped tapes W, µm L, µm

19 Es*ma*on of bias current values by extrapola*on 1000 I c measured in 15T SC magnet rescaled from full width tape to bridge width B perpendicular to tape orientatrion We need to measure currents up to 10 ma ma I c (4K, B), ma BN1 3.3um Ic (ma) BN2 4.8um Ic (ma) BN3 2.1um Ic (ma) BN4 1.9um Ic (ma) BN5 2.48um Ic (ma) BN6 1.21um Ic (ma) BN7 1.2um Ic (ma) BN8 1.44um Ic (ma) BN9 0.76um Ic (ma) BN um Ic (ma) BN um Ic (ma) BN um Ic (ma) BN um Ic (ma) BN um Ic (ma) B, T

20 Expected Lorentz force at 60T for prepared bridges Expected Lorentz force at 60T, mgf Bridge Width, um 2

21 Geometry of FIB trimmed ReBCO bridges from SuperPower tapes and es*mated transport /mechanical proper*es

22 Temperature dependence of self field I c for Bridge N5 100 I c (0T) at <E>=10 µv/cm, ma May 9, 2016 Bridge N5 measured with KE 6220 and KE2182A T, K

23 Example of I- V curve for bridge N10 measured at 84.6 K; SF I- V point measure during ~70 ms. with voltage noise ~25 nv (SD=9nV) Ic up= 4.0 A n up= 18.8

24 R(B,T) measured in pulsed magnet - bridge N5 R, a.u K K 81K 79 K 77K 75T 73 K 71K 69 K 67 K 65 K 63 K 61 K 59 K 57 K o to magne*c field; maximum Lorentz force B, T

25 H irr (T) measured in pulsed magnet - bridge N µ o H irr, T o to magne*c field; maximum Lorentz force T, K

26 H irr (T) for bridges N5 and N T BN10 BN5 µ o H irr, T T BN5 at 33.6 o to magne*c field; BN10 at 41.6 o to magne*c field; maximum Lorentz force orienta*on Temperature, K

27 Example of *me dependencies of magne*c field, bias current and sample voltage for bridge N10 at 52K Current step 200 µa Voltage trace values are calculated by FPGA algorithm at the end of each current pulse as a difference between current on and current off por*ons of the pulse deg. to magne*c field; maximum Lorentz force orienta*on

28 Time dependencies of magne*c field, bias current and sample voltage for bridge N10 at 30K Current step 200 µa We detected one V- I- B point in about 0.33 ms. with voltage noise reaching up to about 2-3 µv. Field values were sampled at rate 2 µs. per point. Dura*on of this process 36 ms deg. to magne*c field; maximum Lorentz force

29 Example of V(I,B) curve measured at 30K in pulsed field V µ, e g lta o V B (T) C u rrent, µa

30 Seven V(I,B) curves measured at 30K (maximum B=50T) 12 8 V µ, e g lta o V B (T) C u rrent, µa

31 Time dependencies of magne*c field, bias current and sample voltage for bridge N10 at 10.4K Current step 220 µa Current offset 100µA Couple hundred megabytes of high resolu*on current and voltage traces are recorded by the same apparatus for each 30-65T magnet pulse, allowing careful off- line analysis of current- voltage response. Dura*on of this process 39 ms.

32 Transport I c (B) at 3µV ( 3700 µv/cm) of 15% Zr doped ReBCO oriented at 41.6 o to field measured in pulsed magnet I c (B), µa 1000 T=10.4 K T=30 K; run 1 T=30 K; run This sample survived 19 pulses B max = 5T 65T B, T

33 B, T Transport J c (B) at 3µV ( 3700 µv/cm) of 15% Zr doped ReBCO oriented at 41.6 o to field measured in pulsed magnet 1 J c (B), MA/cm T=30K data fit to I c ~ B α 14.3 T T α= T- 34 T α= T=10.4 K T=30 K; run 1 T=30 K; run

34 Calcula*ng I c defined at standard voltage criterion V o (<E>=1 µv/cm) from data measured at different voltage criterion using n- value V 1 = V c ( I c1 / I c ) n I c = I c1 /exp[ ln( V 1 / V c )/n ]

35 Timescales related to this experiment V- I- B point measured in pulsed mode ~0.332 ms. Current pulse length t current =0.166 ms. (smooth sin(ωt) shaped) Magnet pulse dura*on about 100 ms. db/dt = 2408 T/s, which is about 9 *me larger max. db/dt in AC modern loss setup Inverse aoempt frequency of pinned fluxons usually to is assumed to be of order s. A.Gurevich, et al. PRB (1993) << t current Therefore in spite of fast V- I- B detecxon we could expect observing flux creep regime and therefore power dependence E~J n. V However, exposing sample to high db/dt will lead to high electric fields µv/cm much above E c = 1 µv/cm. Therefore we expect to get flux flow regime. J. Huang, et al., Physica C 184, 371 (1991). I

36 Fixng I c data from V(I,B) curves To calculate I c in experiments with DC field we use several I- V points near region of resis*ve transi*on by fixng data points with dependence V= V c ( I/ I c ) n. During pulsed measurements we measure V(I, B) dependence, therefore fixng is more difficult: V(I,B)= V c ( I/ I c (B) ) n For short periods of *me: B(t) B o + db/dt t I(t)= I o + di/dt t Within small field range I c (B)= I c0 B α Combining above equa*ons together: B(I) B 0 + db/di (I I 0 ) Near pulse peak we may add d 2 B/ di V(I)= V c ( I/ I c0 ( B 0 + db/di (I I 0 )) α ) n Too many fixng parameters

37 Summary We have shown the possibility of detec*ng the I c of high J c ReBCO tapes in ultra- high pulsed fields; However α values ( I c ~ B α ) are unrealis*cally high. Future plans: In future to understand the influence of I- V sampling rate, we plan to correlate J c measured with standard low noise electronics and FPGA- based electronics using a superconduc*ng magnet; To get more V(I,B,T) curves per magnet pulse, we plan to introduce *me- dependent maximum ramping current synchronized with pulse profile B(*me). With more I c points measured, we expect to get smooth pinning force density f p (B,T) dependencies in the ultra- high field region; We plan to correlate J c (B,T) and f p (B,T) measured in ultra- high fields at different orienta*ons with images of pinning defects obtained on the state of the art sub- Angstrom scanning/transmission electron microscope (NHMFL- FSU). Such correla*ons can be used for improving understanding of pinning anisotropy in new coated conductor tapes and, therefore, s*mulate engineering pinning precipitates op*mized for magnet applica*ons.