Presentation is loading. Please wait.

Presentation is loading. Please wait.

PULSE-TUBE PRECOOLED AND HYPERFINE-FIELD-ENHANCED NUCLEAR REFRIGERATION WITH NOISE THERMOMETRY Aya Shibahara, Microkelvin Workshop 2013 JRA1 Task 2 JRA4.

Similar presentations


Presentation on theme: "PULSE-TUBE PRECOOLED AND HYPERFINE-FIELD-ENHANCED NUCLEAR REFRIGERATION WITH NOISE THERMOMETRY Aya Shibahara, Microkelvin Workshop 2013 JRA1 Task 2 JRA4."— Presentation transcript:

1 PULSE-TUBE PRECOOLED AND HYPERFINE-FIELD-ENHANCED NUCLEAR REFRIGERATION WITH NOISE THERMOMETRY Aya Shibahara, Microkelvin Workshop 2013 JRA1 Task 2 JRA4 Task 3a

2 Nanoscience community for fast turnaround µK measurements. Oxford Instruments for industrial/commercial reasons Us for testing noise thermometry Staying below 1mK on a cryogen-free fridge

3 InK: Implementing the new Kelvin  To resolve the long-standing discrepancy between the PLTS 2000 measurements through low uncertainty primary thermometry.

4 Praseodymium Nickel-5: PrNi 5  Hyperfine enhanced paramagnet  Contains rare earth ion Pr 3+, spin 5/2  At low temperatures, the 4f electrons have an electronic singlet non-magnetic ground state.  External magnetic field mixes higher non-singlet states into the ground state, inducing an electronic magnetic moment.  This generates a hyperfine field B int at the Pr nucleus, which is enhanced compared to the externally applied field B.  K = B int /B = 11.2  B enhanced by (1+K), l n enhanced by (1+K) 2

5 Entropy curves

6 Comparison of PrNi 5 with Copper  Large entropy reduction possible  Less eddy-current heating  Less than 1 mol required  Only a maximum of 20% entropy reduction possible  High conductivity  mol used PrNi 5 Copper  Spontaneous ferromagnetic nuclear ordering T = 400 µK  Internal field 65 mT  Spontaneous antiferromagnetic nuclear ordering T = 50 nK  Internal field 0.36 mT

7 The Oxford Instruments Triton 200 Commercial cryogen free dilution fridge Decoupled pulse tube cooler first and second stages from the refrigerator plates

8 Brass MC shield and Still shield Dry 8 T magnet mounted at the second pulse tube stage 3K plate Schematic of shields and magnet on Triton 200

9 The Nuclear stage  128 g of PrNi 5 (0.3 mol)  Nine rods, 6 mm Ø × 50 mm long  99.99% Cadmium solder to 1 mm Ø Cu wires  One wire per rod to upper plate  Eight wires per rod to lower plate  From Jeevak Parpia, Cornell  Aluminium heat switch supplied by Richard Haley, Lancaster.  Noise thermometer heat sunk to lower plate with 37 × 0.7 mm Ø annealed Cu wires

10 Current sensing Noise thermometer Noise sensor: 0.24 m Ω copper foil resistor Heat sinking ground Annealed copper holder Heat sinking copper washer Heat sinking Nb foil  Single calibration at 4.2 K  Simple to install  Compact Nb screw terminals

11 Current sensing Noise thermometer  C636 G24 XXL SQUID from PTB  Input coil L i = 1.8 µH

12 Noise spectra at various temperatures

13 Here we present the performance of the PrNi 5 nuclear stage on the Triton 200 Results

14 Typical demag procedure  Pump on vacuum can overnight  With magnet, base temperature of DU reached in 48 hours  Precool field limited to 6.2 T (90 A)  Due to stray field at aluminium heat switch  But high enough field for significant entropy reduction  Precool duration 24 h for 20 mK  Typically h weekend precool for 19 mK  Corresponds to 80% entropy reduction  Demagnetisation from 6.2 T to 0 T in 6 hours  In steps from 90 A to 0 A with rates from 0.5 A/min to 0.03 A/min

15 How long does it stay cold?  Base temp of 600 µK reached in zero field  20 nW heat leak: 16 hours below 1 mK  5 nW heat leak: over 24 hours below 1 mK  Increased hold time for 210 mT

16 Heat capacity of PrNi 5 Kubota et al. Phys. Rev. Lett. 45, 22 (1980)

17 Thermometer performance on a wet nuclear demag fridge  Traditional copper nuclear stage on a wet system  Noise thermometer of the same design, base T = 190 µK

18 Fast PtW noise thermometer T N = 130 µK

19 Precision of Fast noise thermometer  R = 1.29 Ω  Dilution fridge  1% precision in 100 ms

20 Conclusions  A bolt-on PrNi 5 nuclear demag stage for a pulse-tube pre- cooled system was shown to cool to 600 µK and remain below 1 mK for over 24 hours, with a heat leak of 5 nW.  The use of a current sensing dc SQUID noise thermometer allowed the direct measurement of these sub-mK temperatures.  A precool in a field of ~6.2 T and a starting temperature of ~20 mK with a 6 hour demag is feasible.  Compact and easy to use  Cryogen-free sub-mK platforms seem to be a realistic prospect, dramatically improving the accessibility of ultra-low temperatures

21 Thank you to all our collaborators and funding bodies! And thank you for listening! arXiv:

22 Heat leak measurements


Download ppt "PULSE-TUBE PRECOOLED AND HYPERFINE-FIELD-ENHANCED NUCLEAR REFRIGERATION WITH NOISE THERMOMETRY Aya Shibahara, Microkelvin Workshop 2013 JRA1 Task 2 JRA4."

Similar presentations


Ads by Google