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

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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

  • 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?

  • 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)


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


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


Cryostat

  • Probe placed in center of cryostat

  • Surrounding reservoirs filled with Liquid Nitrogen


Getting Started

  • Equipment on Hand

    • Janis Cryostat

    • Lakeshore Temperature Controller

  • Equipment Needed

    • Keithley Sourcemeter

    • Keithley Nanovoltmeter


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.


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


Program Front Panel


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


Resistance vs. Temperature


Plots of Temperature and Voltage


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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