He3 Cryostats and He3- He4 Dilution Refrigerators

Report
Wet Fridges
Reference- Matter and Methods at Low Temperatures,
Frank Pobell
Debaleena Nandi
06/12/14
Motivation
Integer and Fractional Quantum Hall Effect
VXY
I
I
VXX
A.D.K. Finck, Ph.D. Thesis
Motivation
Scanning Tunneling Microscope (STM) measurements
Motivation
Cooling nanomechanical resonators to quantum ground states
M. LaHaye, O. Buu, B. Camarota, K. Schwab, Science 304, 74 (2004)
Lets make a decision on the cryogenic liquid
Liquids
Boiling point at 1 atm
Melting point at 1 atm
Liq. N2
77K
63 K
Liq. O2
90K
54K
Liq. Ne
27K
25K
Liq. H2
20K
14K
Liq. He4
4.2K
perpetually liquid !
Liq. He3
3.2K
perpetually liquid !
He-3 and He-4 are our cryogenic liquids of choice, inert and
lowest boiling and melting point
Terrestrial availability of He-4
He-4
• Alpha particle from radioactive decay of Uranium and Thorium
• Half-life of 238U =4.5×109 years;
Half-live of 232Th= 1.4×1010 years;
• Light gas, once released escapes from earth’s atmosphere
• Trapped in few natural gas mines at ~1%
Cooling to T 4.2K
Sample
Liq He4 @ 4.2K
Outer Vacuum jacket
Cooling to T 1.3K
To He4 pump
Sample
Liquid He4
Liq He4 @ 1.3K
Inner Vacuum jacket
Liq He4 @ 4.2K
Outer Vacuum jacket
40% of the liquid He4 has to be evaporated to cool to 1.3K
Cooling to T 0.3K
To He4 pump
To He3 pump
1.3K
Inner
vacuum
jacket
Liquid He4
Sample
Liq He3
@ 0.3K
Liq He4 @ 4.2K
Outer Vacuum jacket
20% of the liquid He3 has to be evaporated to cool to 0.3K
Closed Cycle He3 Fridge T 0.3K
To He4 pump
Charcoal pump with heater
1.3K
Inner
vacuum
jacket
Liquid He4
Sample
Liq He3
@ 0.3K
Liq He4 @ 4.2K
Outer Vacuum jacket
20% of the liquid He3 has to be evaporated to cool to 0.3K
Cooling to T 10mK :
Working principle
Liq He3
∆S1 < ∆S2
Liq He4
Liq. He3 +
Liq. He4
Has to absorb latent
heat of mixing from
the surroundings
Two phase separated liquids,
more ordered state , ∆S1
He3/He4 mixture, more
disordered state, ∆S2
Phase diagram of He3-He4 mixtures
6.6% molar concentration of He3 in He4 even at T  0
Operating principle
Concept
of a dilution fridge
He3 Pump
1.3K
6.6% He3 in
He3-He4
Liq. He3
He3-He4 Dilution Refrigerator
Schematic of a He3-He4 dilution refrigerator
To He3 pump
1.3K
Still
T=600mK
> 90% He3 vapor
<1%
<1% He3
in He3
He3-He4
Heat Exchangers
100% Liq. He3
Mixing Chamber
T=10mK
6.6% He3 in He3-He4
Sample
Still Heat Exchangers
He3-He4 dilution refrigerator
Mixing chamber
100% Liq. He3
6.6% He3 in He3-He4
(Dilute phase)
T=10mK
Heat Exchanger
Still
> 90% He3 vapor
<1%
<1% He3
in He3
He3-He4
IK Pot
1.3K
Dumps
Cooling to T< 1mK
B
B=0T
PrNi5 rods
Adiabatic demagnetization of nuclear magnetic moments
Adiabatic nuclear demagnetization
100% Liq. He3
6.6% He3 in He3-He4
(Dilute phase)
T=10mK
Superconducting Switch
PrNi5 rods
(host the nuclear spins)
B
B=0T
T=1mK
T=
10mK
Sample
Conclusion
• He3 Fridge – Latent Heat of Evaporation
• He3-He4 Dilution Refrigerator- Heat of Solution
Acknowledgements
Jim Eisenstein, Aaron Finck & Johannes Pollanen

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