Dilution Refrigeration
3He-4He DilutionThe CryostatDetails of the CryostatPicturesFridge Links

Details of the Cryostat

The process begins with a dilution of 3He gas and 4He gas being pumped past the "Pot," in which liquid 4He is maintained at around 1 Kelvin. There, heat exchangers allow heat to pass from the mixture to the Pot, effectively cooling the mixture.

After this, the mixture flows through a Condenser and an Impedance, after which the mixture is in liquid form.

Next, the 3He - 4He dilution flows past the Still, maintained at around 600 milliKelvin (0.6 K). Once again, through heat exchangers, the mixture transfers its heat to the Still and is cooled further. A heater is attached to the Still, but this will come into play later.

The mixture flows past the "Cold Plate," through which more heat is transferred from the mixture, until it ends up in the "Mixing Chamber."

Inside the Mixing Chamber the 3He - 4He mixture seperates into two phases, the 3He rich phase and 4He rich phase.

The 4He rich phase is pumped on, sending mostly 3He up past the Cold Plate (where it gains heat from the incoming 3He - 4He mixture) and into the Still. Note that the 4He rich phase always has a little bit of 3He in it no matter how cold the mixing chamber gets. This fact is one of the most important parts of this process.

Inside the Still the 4He rich phase is heated by the heater. 3He is distilled from the mixture and pumped out of the Still in gas form. The 3He gas is then pumped back to the beginning where it mixes with incoming 3He gas and 4He gas and starts back at the beginning. Eventually, the 4He and 3He sources are closed off and pretty much only 3He is circulating through the main part of the cryostat.