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Johnson Noise Thermometry
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  1. Johnson Noise Thermometry GSECARS

  2. 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

  3. 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)

  4. High P tests results Varying R only (bench) In situ Varying T mainly 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.

  5. “Bench test”: varying R only Bench tests (varying R only) show no significant change in slope over time

  6. Cell assembly (TEL 10 mm) PC USB cable BN guide sleeve WC anvil Spectrometer Fiber cable Steel spacer Alternative approach: Pyrometry Optical window: Single crystal moissanite

  7. Constant intensity light source test: source direction effects Const. current light source Anvil with hole Moissanite window o. fiber Ocean Optics spectrometer

  8. z y x Directional effects Z scan Y scan X scan Light source Thru 0.1 mm pinhole Window crystal 4 mm dia., 6 mm long anvil Conclusion: Dominant signals from center of the window tip. Pyrometry feasible in MA cell

  9. Bench-top W-lamp test I (λ, T) = C1ε(λ,T)λ-5 /[exp(C2/λT)-1] 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 K To be compared with 2000 K given by manufacturer

  10. 6.60 mm Crushable alumina 6.00 mm Pyrophyllite (Soft-Fired) 5.00 mm 4.70 4.00 mm Graphite Pressure marker (MgO+Au, 10:1 by vol) BN Al2O3 with double bore (0.8 mm dia.) & Thermocouple 7.00 mm BN window (2.5 mmØ) 0.80 mm 1.00 1.00 14.00 mm SiC lens (Single Cryst.) T.C. 6.50 mm MgO 4.00 mm TEL 10 mm, ver. 2 ( cell assembly for pyrometry calibration) BN guide sleeve (OD: 1.5 mm, ID: 0.4mm) WC anvil 1.5 mm Optical fiber Cell assembly

  11. Tungsten lamp calibration before applying pressure Upper DIA guide block Moissanite window crystal anvil Lower DIA guide block

  12. 1523 K 1173 K 973 K 1323 K Examples of grey body (abs) fit– 1 ms data collection

  13. 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 - w plot, where ω(λ) = C2/λ. And the slope of the line is -1/T. I (λ, T) = F(l) C1ε(λ, T)λ-5 /exp(-C2/λT) I (λ, T0) =F(l) C1ε(λ, T0)λ-5 /exp(C2/λT0) J (λ, T) = -(1/T)ω(λ)+ln[ε(λ,T)/ε(λ, T0)] = ln[I(l,T)/I(l,T0)] - (1/T0) ω(l) Relative T determination

  14. “J-function” fit, relative to 1523K 973 K 1173 K 1323 K 1573 K

  15. Comparison of T measurements Noise level too high at 1 ms Pressures: 0.2 to 0.5 GPa

  16. Difference plot thermal drift recognized in power-temp relation

  17. 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