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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
  • 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?
  • 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

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
  • 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
  • Probe placed in center of cryostat
  • Surrounding reservoirs filled with Liquid Nitrogen
getting started
Getting Started
  • Equipment on Hand
    • Janis Cryostat
    • Lakeshore Temperature Controller
  • Equipment Needed
    • Keithley Sourcemeter
    • Keithley Nanovoltmeter
need for automated system
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
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
preliminary tests
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
future work
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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