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Low-temperature primary thermometry development at NRC. Dr. Patrick M.C. Rourke Measurement Science and Standards (MSS) National Research Council Canada (NRC) CAP Congress, Sudbury, 19 June 2014. Thermometry. Primary thermometer Directly measure “real” thermodynamic temperature T

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low temperature primary thermometry development at nrc

Low-temperature primary thermometry development at NRC

Dr. Patrick M.C. Rourke

Measurement Science and Standards (MSS)

National Research Council Canada (NRC)

CAP Congress, Sudbury, 19 June 2014

thermometry
Thermometry
  • Primary thermometer
    • Directly measure “real” thermodynamic temperature T
    • Complicated, large, difficult to use  not many in existence
  • Secondary thermometer
    • Needs calibration in order to set scale
    • Almost all thermometers are secondary
  • International Temperature Scale of 1990 (ITS-90)
    • Used for secondary thermometer calibrations worldwide between 0.65 K and 1357.77 K
    • Based on best thermodynamic data from primary thermometers available up to 1990
    • Newer measurements suggest the scale should be improved
its 90 scale deviates from thermodynamic temperature
ITS-90 scale deviates from thermodynamic temperature

Adapted from CCT-WG4 report (2008), Fischer et al., Int. J. Thermophys. 32, 12 (2011),

Astrovet al., Metrologia 32, 393 (1995/96) and Gaiseret al., Int. J. Thermophys. 31, 1428 (2010)

refractive index gas thermometry rigt in principal
Refractive index gas thermometry (RIGT) in principal
  • Microwave resonances in a gas-filled conducting cavity
    • Fixed temperature & gas pressure
  • Resonance frequency f gas refractive index n
    • c0: speed of light in vacuum
    • ξ: electromagnetic eigenvalue for microwave resonance
    • a: radius of spherical cavity
    • Thermal expansion coefficient αL and isothermal compressibility κT important
  • Calculate thermodynamic temperature T from n using virial equations
    • Helium gas: quantum mechanics
  • Similarities to other techniques
    • Acoustic gas thermometry (AGT)
    • Dielectric constant gas thermometry (DCGT)
    • Resolve differences between them?
rigt in practice
RIGT in practice
  • Quasi-spherical resonator
    • Controllably lift resonance degeneracy
  • Finite electrical conductivity
    • microwaves penetrate into skin layer
    •  resonances broadened & shifted
  • Eigenvalue corrections
    • Shape effects
    • Disturbances due to waveguides
experimental details
Experimental details
  • Motivation: RIGT to measure T - T90: 5 K – 300 K
    • Initially, characterize resonator in vacuum
    • Microwave resonances  resonator size, shape, conductivity
  • Prototype copper resonator
  • Copper pressure vessel
    • Resistive thermometers (ITS-90) on copper coupling rod
  • Two-stage pulse-tube cryocooler
    • Home-made thermal control system
microwave fitting
Microwave fitting
  • Measure microwave resonances using 2-port Portable Network Analyzer
  • Complex 3-Lozentzian + polynomial background fitting routine
    • Peak frequencies and half-widths
  • Several microwave modes measured
    • Optimized spectral fitting background terms, 1st- & 2nd-order shape corrections, and waveguide corrections
    • Room temperature results agree with those done at NIST May et al., Rev. Sci. Instrum. 75, 3307 (2004)
electrical conductivity
Electrical conductivity
  • Temperature dependence of resonator conductivity (from peak width)
    • Stable, fixed temperatures over entire temperature range
    • Agrees with literature within literature curve’s 15% uncertainty Simon et al., NIST Monograph 177, 1992
    • Free parameter σ(T = 0) ≡ 1/ρ0 set to present experimental data at 5 K
thermal expansion coefficient l
Thermal expansion coefficient αL
  • Experimental data from 3 microwave modes
    • Good consistency
  • Literature curve – no free parameters!
    • Simon et al., NIST Monograph 177, 1992
    • NIST Cryogenic Materials Properties Database (2010 revision)
  • Excellent agreement with literature values over entire temperature range
thermal expansion coefficient l1
Thermal expansion coefficient αL
  • Present data is within 1st. dev. of literature curve at all temperatures measured
conclusions future directions
Conclusions & future directions

Conclusions

  • International Temperature Scale of 1990 deviates from thermodynamic temperature
    • More measurements needed to resolve issues before replacement scale created
    • NRC developing microwave RIGT for Canadian thermodynamic temperature measurement capability
  • Microwave resonances measured in quasi-spherical copper resonator
    • Vacuum, 5 K – 300 K
  • Comparison to literature properties of copper measured with other methods
    • Excellent agreement over wide temperature range
    • Increased confidence in our microwave implementation

Next steps

  • Measure triaxial ellipsoid resonator
    •  Better shape, reduced background effects
  • Gas in resonator
    •  Refractive Index Gas Thermometry
we re looking for a few good physicists do you have what it takes
We’re looking for a few good physicists: do you have what it takes?

THE PROJECT

  • Electrical resistivity and Seebeck voltage of platinum-group metals (and other metals and alloys) – considerable interest to thermometry
    • Solid-state theoryand experimental measurements to understand the temperature dependencies of these properties
    • Electronic band structure, electron-phonon scattering, electron-electron (s-d) scattering, oxidation, recrystallization, and scattering from vacancies and dislocations
  • Suitability of various phase transformations as reference temperatures
    • Typically liquid/solid and solid/liquid transformations of pure elements or eutectics
    • Various metal-carbon eutectics and peritectics are of current interest at high temperatures

KEY SPECIFICATIONS

  • Ph.D. in Physics (experimental solid state / condensed matter physics preferred)
  • Ability to design, construct, and operate experimental equipment with a minimum of technical assistance
  • Innovative “hands on” approachtowards the solution and attainment of high accuracy in a variety of measurement problems
  • Attention to detailcommensurate with the operation of a primary standards facility
  • Ability to work effectively within a small group devoted to the research, development, and dissemination of temperature standards

Get in touch for more information: patrick.rourke@nrc-cnrc.gc.ca

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Thank you

Dr. Patrick Rourke

Measurement Science and Standards

patrick.rourke@nrc-cnrc.gc.ca

www.nrc-cnrc.gc.ca