Thermal measurements of TPG and Diamond I. Bonad, R. Bates and F. McEwan

Apparatus Plastic insulation supports Sample Aluminium thermal shield 1 Shield heater Pt100_5 H2OH2O Water cooled Heater wires Pt100_6 Sample heater Anchor Heat sink Pt100 wires Vacuum tank

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 : -40 o C 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 Pocofoam under test Thermal shield Cooling block PT100 with Manganin wire

Reduction of parasitics Cold Block Heater Sample length P=0 P1 T0T0 ΔT1ΔT1 ΔT2ΔT2

Analysis method Impossible to remove all parasitic heat paths, p, to the sample For zero intentional power have ΔT 1 Apply power P –Keep central temperature constant T 0 As long as ΔT 2 is not much larger than ΔT 1 then parasitic effects cancel

Results TPG Conductivity increases with falling temperature Conductivity of 1900 W/mK at -30 o C 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