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Thermal measurements of TPG and Diamond. I. Bonad, R. Bates and F. McEwan. Apparatus. Vacuum tank. Anchor. Aluminium thermal shield. Heater wires. Shield heater. Pt100 wires. Sample heater. Pt100_5. 3. 1. 2. 4. Sample. Heat sink. Plastic insulation supports. Pt100_6.
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Thermal measurements of TPG and Diamond I. Bonad, R. Bates and F. McEwan
Apparatus Vacuum tank Anchor Aluminium thermal shield Heater wires Shield heater Pt100 wires Sample heater Pt100_5 3 1 2 4 Sample Heat sink Plastic insulation supports Pt100_6 Water cooled H2O
Details of the measurement • Radiation reduction • Radiation shield around the sample • Shield temperature maintained at sample temperature • Additional shield around the whole apparatus • Cool outside of vacuum tank to -15C or sample temperature • Insulation around outside of vacuum tank • Conduction reduction • RTD wire 44SWG Manganin tied to the cooling block • Thermally insulating mounts for apparatus • Convection reduction • Vacuum tank, with vacuum at 1x10-5 mbar • Accuracy • 4 wire temperature sensors and heater with 4-wire supply • Careful calibration of RTDs against each other (temperature differences important)
Measurement details • Sample size • Defined by thermal shield size and vacuum tank • Presently : 10 cm x 1 cm x 0.1 cm • Heater power • Max at present 0.5 W, typically 0.1 and 0.2 W • Easy to manage temperatures in the shield and only small changes in sample temperature • Requires accurate temperature measurements (TPG ΔT = 0.5C) • Cooling • Use anti-freeze based chiller : -40oC minimum temperature • Peltier elements to further reduce temperature • Measurement cross-check • Used Cu (99.999% pure) sample of similar dimensions • Measured conductivity to be 380 compared to 385 W/mK
The experiment • Sample and thermal shield clamped to cold block • Copper tower to clamp PT100 wires to cold block • Heaters on sample and shield removed Cooling block Pocofoam under test PT100 with Manganin wire Thermal shield
Reduction of parasitics Cold Block P=0 Sample length P1 T0 ΔT1 Heater ΔT2
Analysis method • Impossible to remove all parasitic heat paths, p, to the sample • For zero intentional power have ΔT1 • Apply power P • Keep central temperature constant T0 • As long as ΔT2 is not much larger than ΔT1 then parasitic effects cancel
Results TPG • Conductivity increases with falling temperature • Conductivity of 1900 W/mK at -30oC • Bend in TPG does not affect conductivity along sample Error analysis points to 6% error in conductivity
Results Diamond • Little change in conductivity with temperature • Conductivity only about 1000 W/mK
Final slide • Measured conductivity of TPG and Diamond • Diamond only 1000 W/mK • Bend in TPG does not appear to reduce conductivity • Happy to continue with irradiated samples