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
• 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
2
ITS-90 scale deviates from thermodynamic temperature
4
2
Gas Thermometers
0
Constant Volume
(CVGT)
Kemp 1986
Steur 1986
Astrov rev.
1995/96
T - T90 (mK)
-2
-4
Acoustic
(AGT)
Moldover 1999
Ewing 2000
Benedetto 2004
Pitre 2006
-6
-8
Dielectric Constant
(DCGT)
Gaiser 2008
Gaiser 2010
-10
-12
0
50
100
150
200
250
300
Temperature (K)
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)
3
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?
4
RIGT in practice
45
TM11 mode at 297 K and 5 K, in vacuum
• Quasi-spherical resonator
peak 3 ("z")
f3
• Controllably lift resonance
degeneracy
40
35
6
10 |S21|
30
25
• Finite electrical
conductivity
g3
peak 1 ("y")
f1
• microwaves penetrate into skin
layer
•  resonances broadened &
shifted
20
g1
15
10
peak 2 ("x")
f2
g2
• Eigenvalue corrections
5
0
2.612
• Shape effects
• Disturbances due to waveguides
2.613
2.614
2.615
2.616
2.617
2.618
2.619
Frequency (GHz) at T = 297 K
2.621
2.622
2.623
2.624
2.625
2.626
Frequency (GHz) at T = 5 K
5
2.627
2.628
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
6
Microwave fitting
10
TM11 mode at 297 K, in vacuum
• Measure microwave resonances
using 2-port Portable Network
Analyzer
8
4
2
0
-2
• Complex 3-Lozentzian +
polynomial background fitting
routine
-4
6
10 [Re(S21) or Im(S21)]
6
-6
-8
-10
2.612
2.613
2.614
2.615
2.616
2.617
2.618
2.619
Frequency (GHz)
40
TM11 mode at 5 K, in vacuum
35
• Several microwave modes
measured
6
10 [Re(S21) or Im(S21)]
30
25
20
• Optimized spectral fitting background
terms, 1st- & 2nd-order shape
corrections, and waveguide corrections
15
10
5
0
-5
-10
-15
2.621
2.622
2.623
2.624
2.625
Frequency (GHz)
7
• Peak frequencies and half-widths
2.626
2.627
2.628
• Room temperature results agree with
those done at NIST May et al., Rev. Sci.
Instrum. 75, 3307 (2004)
Electrical conductivity
9
1x10
• Temperature
dependence of
resonator conductivity
(from peak width)
Copper conductivity, TM11 peak 1 half-width
8
9x10
8
Present study
8
OFHC Cu from Simon et al. 1992 /
Hust & Lankford 1984
+/- 15% of Simon et al. 1992 /
Hust & Lankford 1984 curve
8x10
-1
r,CuCu (S·m )
7x10
8
6x10
•
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
8
5x10
8
4x10
8
3x10
8
2x10
8
1x10
0
0
50
100
150
200
Temperature (K)
8
250
300
Thermal expansion coefficient αL
-5
• Experimental data
from 3 microwave
modes
Copper thermal expansion coefficient
1.6x10
-5
1.4x10
• Good consistency
-5
1.2x10
• Literature curve –
no free parameters!
-5
-1
L (K )
1.0x10
• Simon et al., NIST
Monograph 177, 1992
• NIST Cryogenic
Materials Properties
Database (2010
revision)
-6
8.0x10
-6
6.0x10
Present study, TM11 mode
Present study, TE11 mode
Present study, TM12 mode
-6
4.0x10
-6
2.0x10
OFHC Cu from Simon et al. 1992 / NIST CMPD 2010
-7
-1
+/- 1.4 × 10 K standard deviation of Simon et al. 1992
0.0
0
50
100
150
200
Temperature (K)
9
250
300
• Excellent
agreement with
literature values
over entire
temperature range
Thermal expansion coefficient αL
Copper thermal expansion coefficient
with Simon et al. 1992 / NIST CMPD 2010 curve subtracted
-7
-1
L, present study - L, literature(K )
2.0x10
-7
1.0x10
0.0
-7
-1.0x10
Present study, TM11 mode
Present study, TE11 mode
Present study, TM12 mode
-7
-1
+/- 1.4 × 10 K standard deviation of Simon et al. 1992
-7
-2.0x10
0
50
100
150
200
250
300
Temperature (K)
• Present data is within 1 st. dev. of literature curve at all temperatures measured
10
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
11
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
12
Thank you
Dr. Patrick Rourke
Measurement Science and Standards
patrick.rourke@nrc-cnrc.gc.ca
www.nrc-cnrc.gc.ca