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Angela Adams and Kenneth Purcell Advisor: Dr. Doug Harper Solid State Laboratory

Development of an Automated System to Measure Critical Temperature of High Temperature Superconductors. Angela Adams and Kenneth Purcell Advisor: Dr. Doug Harper Solid State Laboratory Western Kentucky University. Definitions.

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Angela Adams and Kenneth Purcell Advisor: Dr. Doug Harper Solid State Laboratory

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  1. Development of an Automated System to Measure Critical Temperature of High Temperature Superconductors Angela Adams and Kenneth Purcell Advisor: Dr. Doug Harper Solid State Laboratory Western Kentucky University

  2. Definitions • Superconductor -- conducts electricity with no resistance below a certain temperature • Critical Temperature (Tc)-- temperature at which resistivity goes to zero Courtesy of ORNL

  3. Why Investigate Superconductors? • There is still no all encompassing theory to explain superconductor behavior. • BCS Theory describes standard superconductors • No Theory explains HTS • New superconducting materials are still being found. (MgB2) • The record critical temperature continues to increase with new discoveries. (current max = 138K)

  4. Four-Point Measurement Known current applied through two outermost wires Voltage drop measured between two innermost wires Resistance calculated using Ohm’s Law: Making Resistance Measurements

  5. Probe • Sample is attached to bottom of probe • Four wires are connected to the sample for the resistance measurement • Temperature is measured by a semiconductor

  6. Cryostat • Probe placed in center of cryostat • Surrounding reservoirs filled with Liquid Nitrogen

  7. Getting Started • Equipment on Hand • Janis Cryostat • Lakeshore Temperature Controller • Equipment Needed • Keithley Sourcemeter • Keithley Nanovoltmeter

  8. Need for Automated System • Three parameters must be observed at one time. • For good resolution of the resistance change, data must be collected approximately every 500 ms. • Large amounts of data will be collected and stored for each run.

  9. Program Initialization Window • All inputs are entered in initialization phase. • Resistance or resistivity can be calculated. • Either temperature or current can be varied for each run

  10. Program Front Panel

  11. Preliminary Tests Sample -- YBCO, Tc = 93K • Test 1 • Taken with sample in Cryostat • Realized solder joints failed at 140K. • Test 2 • Taken with sample submerged in liquid nitrogen • Realized method of voltage data acquisition is too noisy

  12. Resistance vs. Temperature

  13. Plots of Temperature and Voltage

  14. Future Work • Improve solder joints in order to make measurements at liquid nitrogen temperatures. • Reduce noise by: • Using a filter • Implementing the Current Reversing Technique • Add desired features. • Begin investigation of HTS samples.

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