Johnson Noise Thermometry

GSECARS

Overview• 2004:

– 3rd year of Getting’s P, T Calibration Project) – Preparation for JNT migration from UC Boulder to GSECARS, Chicago– Evaluation of electrical noise in 13-ID-D

• 2005: – Development of high P cell at GSECARS, continued bench test at Boulder (varying

R only)– First high P test at Boulder (July), w/o JNT, for TC noise assessment

• 2006:– Jan - First JNT test at high P, discovered JNT circuitry problems, preamp filters

added– Mar – JNT migrated to GSECARS– Nov – Takeshi Sanehira Joined GSECARS working on JNT

• 2007:– Jan – John Labenski (post-doc prospect) visited GSECARS, and worked with crew

to solve ground loop problems– High P JNT tests throughout the year, with inconsistent results

• 2008:– JNT tests continue, results still inconsistent– Preparation for pyrometry using radiospectrometry– Nov – Takeshi to leave GSECARS

Difficulties in high P JNT tests

• Ground loop issues – eliminated floating voltages at microV level

• Electrical noise from equipment – all unnecessary equipment turned off, shielding, grounding

• Power supply – “clean” transformer, power conditioner to eliminate any frequencies other than 60 Hz

• Contamination in cell assembly – no glue, no acetone, all parts fired at 900C for 1 – 2h.

• Numerical filtering to eliminate 60 Hz harmonics in the JNT signal

• Non-white noise at high temperature persists (usually above 300C)

High P tests results

Varying R only(bench)

Wide variation in slope in various runs, cannot be contributed to electrical noise alone.Overall, slopes appear to become shallower with time (Data legends in order of time: 2006 - 2008.

0

0.4

0.8

1.2

1.6

2

0 10000 20000 30000 40000 50000

Sensor RT, ohm K

JNT

out

put

JNT060JNT069_20TJNT069_25TJNT069_25T-2JNT069_35TD0893_20TD0893_30TD0893_40TD0893_30T-2D0893_60TD0894_15TD0894_30TD0903_20TPoly. (JNT060)

In situVarying T mainly

“Bench test”: varying R onlyBench Test All

-2.000

0.000

2.000

4.000

6.000

8.000

10.000

12.000

14.000

16.000

0 50000 100000 150000 200000 250000 300000 350000 400000

RT

JNT

Sig

nal

JNT 058

JNT 060

JNT 076

JNT 077

JNT 078

JNT 079

JNT 080

JNT 081

Bench tests (varying R only) show no significant change in slope over time

Alternative approach: Pyrometry

PC

WC anvil

Fiber cable

BN guide sleeve

Cell assembly (TEL 10 mm)

Spectrometer

Steel spacer

USB cableOptical window:Single crystalmoissanite

Constant intensity light source test: source direction effects

Const. current light source

Moissanitewindow

Anvil with hole

o. fiber

Ocean Opticsspectrometer

Directional effects

0

10000

20000

30000

40000

-0.8 -0.4 0 0.4 0.8 1.2 1.6

Y, mm

Inte

ns

ity

Y scan, Intensity

0

10000

20000

30000

40000

3 3.5 4 4.5 5 5.5

Z, mm

Inte

ns

ity

Z scan, Intensity

0

20000

40000

60000

2 3 4 5 6 7 8 9

X, mm

Inte

ns

ity

X scan, Intensity x

y

z

anvil

Window crystal4 mm dia., 6 mm long

Light sourceThru 0.1 mm pinhole

Y scan Z scan

X scan

Conclusion: Dominant signals from center of the window tip. Pyrometry feasible in MA cell

Bench-top W-lamp test

Tungsten lamp source

Use radiation at 15 Amp as standard, cross check T at 10.48 Amp by radio-spectroscopy ( both points manufacturer calibrated),

Direct fit to the radiation spectrum yields T10.48A = 2085 KTo be compared with 2000 K given by manufacturer

I (λ, T) = C1ε(λ,T)λ-5 /[exp(C2/λT)-1]

Cell assembly

Pyrophyllite (Soft-Fired)

Graphite

Crushable alumina

BN

SiC lens(Single Cryst.)

14.00 mm

6.50 mm

7.00 mm

4.00 mm

TEL 10 mm, ver. ２( cell assembly for pyrometry calibration)

MgO

Al2O3 with double bore (0.8 mm dia.)& Thermocouple

1.00

4.70

0.80 mm

4.00 mm

5.00 mm6.00 mm

6.60 mm

WC anvil

Optical fiber

1.5 mm

BN guide sleeve(OD: 1.5 mm, ID: 0.4mm)

T.C.

BN window (2.5 mmØ)

Pressure marker (MgO+Au, 10:1 by vol)

1.00

Tungsten lamp calibration before applying pressure

anvil

Moissanite window crystal

Lower DIA guide block

Upper DIA guide block

Examples of grey body (abs) fit – 1 ms data collection

1523 K

973 K 1173 K

1323 K

Relative T determination

Assuming that a reference T0 is known, from Wien’s approximation

The ratio of two observations is a straight line give by the J (λ, T) function (Yagi and Susaki, 1992)

in the J - plot, where ω(λ) = C2/λ. And the slope of the line is -1/T.

J (λ, T) = -(1/T)(λ)+ln[ε(λ,T)/ε(λ, T0)] = ln[I(,T)/I(,T0)] - (1/T0) ω()

I (λ, T) = F() C1ε(λ, T)λ-5 /exp(-C2/λT) I (λ, T0) =F) C1ε(λ, T0)λ-5 /exp(C2/λT0)

“J-function” fit, relative to 1523K

973 K 1173 K

1323 K 1573 K

800

1000

1200

1400

1600

800 900 1000 1100 1200 1300 1400 1500 1600

T (T.C.), K

T (

Py

rom

etr

y),

K

T(pyro_J ), up, 1ms

T(pyro_J ), down, 1ms

One to one line

T(pyro_abs), up, 1ms

T(pyro_abs), down, 1ms

Linear (One to one line)

Comparison of T measurements

Pressures: 0.2 to 0.5 GPa

Noise level too high at 1 ms

Difference plot

-600

-500

-400

-300

-200

-100

0

100

800 1000 1200 1400 1600

T (T.C.), K

T(T

C)-

T(p

yro

), K

T(TC)-T(pyro_J), up

T(TC)-T(pyro_J), down,

T(TC)-T(pyro_abs), up

T(TC)-T(pyro_abs), down

thermal drift recognized in power-temp relation

Outlook

• Obtained optical windows (single-crystal diamond) for DIA cells between 12 and 6 mm edge length (P up to ~8 GPa)

• Tests under way for both W/Re and Pt/Rh thermocouples

• One technical paper currently in prep.

• Expect to obtain data up to 8 GPa and ~1800 K by Nov, 2008, results will be out 2009