Manuel Ramos University of Texas at El Paso, Physics Department Mentors Dr.Justin Schwartz, Dr. Sastry Pamidi, Doan Ngu

1. Calorimetric measurements of AC losses in HTS (BSSCO-2223) tape Manuel Ramos University of Texas at El Paso, Physics Department Mentors Dr.Justin Schwartz, Dr. Sastry Pamidi, Doan Nguyen, Dr. Ulf Trociewitz National High Magnetic Field Laboratory Florida State University

2. Outline • Basic properties of superconductors • What are Transport AC losses? • Method of Measurements AC losses • Electromagnetic • Calorimetric • Details of the calorimetric measurements • Results and Discussion • Proposal to improve the calorimetric measurement • Acknowledgements

3. Properties of superconductors • Zero resistance • Superconductors carry direct electrical current (DC) below Ic with negligible losses • Meissner effect • Superconductors expel magnetic flux from the interior completely (below Hc1) and partially below Hc2

4. Type I and Type II superconductors • Type I superconductors are not useful for applications. • All useful superconductors and all HTS materials are Type II

5. What are AC losses? • Magnetization losses (Hysteresis loss, eddy current loss….) • When HTS experience in an external AC magnetic field => losses • Transport AC losses (self field loss, flux flow loss….) • When HTS carries AC transport current => Losses • Why are AC losses so important? • Without knowing the AC loss values, it is not possible to design cryogenic systems • In majority of the HTS applications in power systems, one of the challenges is to reduce the energy losses when carrying AC currents.

6. Target ac loss values for applications • For comparison, it is useful to consider energy loss when one kiloampere of current traverses one meter (W/kA-m) • Losses in conventional power systems using copper • 17 W / kA-m at 100 A/cm2 • 68 W / kA-m at 400 A/cm2 • In superconductors, the losses are generated at low T. • Many times more power has to be spent to remove the heat from low T.Cooling penalty depends on operating T • At 40 Kelvin, 25 W is needed to remove 1 W •  0.7 W at 40 K = 17 at RT • To be competitive, loss in superconductor at 40 K has to be < 0.1 W/kA-m • At 77 K, ac loss has to be < 0.25 W/kA-m

7. Methods of Measurement • Electromagnetic • Suitable for short samples • To understand magnetization and transport losses separately (to understand the physics) • Calorimetric • Measure total AC losses • Suitable for both short and long samples • To obtain data for designing engineering systems

8. Characteristics of the samples used • Superconductor tape Bismuth 2, Strontium 2, • Calcium 2, Copper 3, and Oxide10 (BSCCO-2223) • Number of Filaments:64 • Length: 80 mm • Width: 4 mm • Thickness: 0.21 mm • Critical Current (Ic): 115 A • For calibration tape • Material: Silver Ag • Length: 80 mm • Width: 4 mm • Thickness: 0.21 mm

9. Ic measurement of the sample BSCCO-2223 Criteria =1 V/cm

10. Details of the experiment In order to calibrate the calorimeter, we pass a known DC current (0 to 5 A) through the silver tape. The T values are plotted against power dissipation to obtain a calibration curve. Then we pass a AC current on the HTS tape up to 60 Amps (using the power amplifiers) and measure the temperature rise. The experiments are repeated for different frequencies of AC current (50 – 500 Hz). The T values of the HTS sample are recorded for each run. Using the calibration curve, the T values are transformed into AC loss values.

11. The calorimeter Styrofoam Box Thermocouple Type E 60 mm HTS tape BSSCO-2223 AC current Silver Tape DC current V

12. What is Calorimetric measurement? The measure of the amount of heat coming from a source. How do we relate the heat to AC loss in our experiment? Heat is proportional to the temperature increments Temperature increments are proportional to the voltage changes Heat is proportional to the voltage changes are constants since the sample remains at 77o K, Liquid Nitrogen (LN2) Note:

13. Details of the experiment • Set up and design of the sample holder, cutting the pure Silver (calibration tape) to identical size as that of the HTS tape (BSSCO- 2223). • Attach the differential thermocouple at the center of each sample, using GE varnish. • Creation of the Styrofoam box (the calorimeter) • Attach the the samples to the current leads on the G10 sample holder

14. Close-up view

15. Temperature rise of Ag tape in LN2

16. Calibration curve of Ag tape in LN2

17. Temperature rise of HTS at different currents (77 K) (500 Hz)

18. Comparison of measured and calculated data

19. Measurements at several frequencies Losses (Joules/cycle/m)

20. Future work We designed a fiber glass (G-10) vacuum chamber in order to do the same experiment, but in vacuum, to improve the sensitivity of the measurements. This project can be continued by the next generation of REU students (2004), and will provide more information about the Physical properties of HTS tapes.

21. Acknowledgements • My special thanks to: • National Science Foundation • The National High Magnetic Field Laboratory • My mentors: Dr. Justin Schwartz and Dr. Sastry Pamidi, Doan Nguyen • Dr. Pat Dixon and Ms. Gina LaFrazza-Hickey • To all the people of the Machine and Electronic shop for their support and advice during this project.