1. 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

2. Thermometry Primary thermometer Secondary 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 K
Based on best thermodynamic data from primary thermometers available up to 1990
Newer measurements suggest the scale should be improved

3. ITS-90 scale deviates from thermodynamic temperature
Adapted from CCT-WG4 report (2008), Fischer et al., Int. J. Thermophys. 32, 12 (2011),
Astrov et al., Metrologia 32, 393 (1995/96) and Gaiser et al., Int. J. Thermophys. 31, 1428 (2010)

4. 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?

5. 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

6. 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

7. 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)

8. 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

9. 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

10. Thermal expansion coefficient αL
Present data is within 1 st. dev. of literature curve at all temperatures measured

11. Conclusions & future directions
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

12. 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 theory and 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” approach towards the solution and attainment of high accuracy in a variety of measurement problems
Attention to detail commensurate 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:

13. Thank you Dr. Patrick Rourke Measurement Science and Standards