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 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 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 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)

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

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

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: patrick.rourke@nrc-cnrc.gc.ca

Thank you Dr. Patrick Rourke Measurement Science and Standards patrick.rourke@nrc-cnrc.gc.ca www.nrc-cnrc.gc.ca