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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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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
Definitions Temperature of High Temperature Superconductors

  • Superconductor -- conducts electricity with no resistance below a certain temperature

  • Critical Temperature (Tc)-- temperature at which resistivity goes to zero

Courtesy of ORNL


Why investigate superconductors
Why Investigate Superconductors? Temperature of High Temperature 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)


Making resistance measurements

Four-Point Measurement Temperature of High Temperature Superconductors

Known current applied through two outermost wires

Voltage drop measured between two innermost wires

Resistance calculated using Ohm’s Law:

Making Resistance Measurements


Probe
Probe Temperature of High Temperature Superconductors

  • Sample is attached to bottom of probe

  • Four wires are connected to the sample for the resistance measurement

  • Temperature is measured by a semiconductor


Cryostat
Cryostat Temperature of High Temperature Superconductors

  • Probe placed in center of cryostat

  • Surrounding reservoirs filled with Liquid Nitrogen


Getting started
Getting Started Temperature of High Temperature Superconductors

  • Equipment on Hand

    • Janis Cryostat

    • Lakeshore Temperature Controller

  • Equipment Needed

    • Keithley Sourcemeter

    • Keithley Nanovoltmeter


Need for automated system
Need for Automated System Temperature of High Temperature Superconductors

  • 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.


Program initialization window
Program Initialization Window Temperature of High Temperature Superconductors

  • All inputs are entered in initialization phase.

  • Resistance or resistivity can be calculated.

  • Either temperature or current can be varied for each run


Program front panel
Program Front Panel Temperature of High Temperature Superconductors


Preliminary tests
Preliminary Tests Temperature of High Temperature Superconductors

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


Resistance vs temperature
Resistance vs. Temperature Temperature of High Temperature Superconductors


Plots of temperature and voltage
Plots of Temperature and Voltage Temperature of High Temperature Superconductors


Future work
Future Work Temperature of High Temperature Superconductors

  • 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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