Cryogenics Progression

[swagXDragonSlayer46YT]

Summary

Describes processes of lowering temperature, in order of warmest to coldest. Some of the following methods may only work on some materials with certain properties that allow it to be cooled further.

Heat Exchangers

Similarly to how hotter blast furnace coils increase efficiency, the efficiency of heat exchangers can be increased by using more thermally conductive blocks in the center. Possible materials, from worst to best, include:

• Copper
• Cubic Boron Nitride
• Diamond
• Boron Arsenide

Source: https://en.wikipedia.org/wiki/List_of_thermal_conductivities

Liquefaction of gases (down to 4 Kelvin)

Involves pressurizing, depressurizing, and heat exchanging to cool gases. Already Implemented.

Dilution Cooling (down to 1 mK)

The process used:

"In the mixing chamber, two phases of the 3He–4He mixture, the concentrated phase (practically 100% 3He) and the dilute phase (about 6.6% 3He and 93.4% 4He), are in equilibrium and separated by a phase boundary. Inside the chamber, the 3He is diluted as it flows from the concentrated phase through the phase boundary into the dilute phase. The heat necessary for the dilution is the useful cooling power of the refrigerator, as the process of moving the 3He through the phase boundary is endothermic and removes heat from the mixing chamber environment. The 3He then leaves the mixing chamber in the dilute phase. On the dilute side and in the still the 3He flows through superfluid 4He which is at rest. The 3He is driven through the dilute channel by a pressure gradient just like any other viscous fluid.[5] On its way up, the cold, dilute 3He cools the downward flowing concentrated 3He via the heat exchangers and enters the still. The pressure in the still is kept low (about 10 Pa) by the pumps at room temperature. The vapor in the still is practically pure 3He, which has a much higher partial pressure than 4He at 500–700 mK. Heat is supplied to the still to maintain a steady flow of 3He. The pumps compress the 3He to a pressure of a few hundred millibar and feed it back into the cryostat, completing the cycle."

Materials required:

• Liquified nitrogen and liquified helium to provide the cooling at the beginning of the process
• Vacuum systems
• Heat shields

Magnetic Refrigeration (down to 1 uK)

Step 1: A magnetic field is applied to a magnetocaloric substance, causing the material to lose its heat capacity.
Step 2: The substance is cooled with a dilution refrigerator while it has a low heat capacity.
Step 3: The magnetic field is disabled, causing the material to regain heat capacity while it is still very cold. This causes the material to become even colder, reaching temperatures on the scale of microkelvins.
Step 4: Cooled metals can probably be used to cool other substances that are not magnetic.

Diagram:

Materials required:

• Superconducting magnets to create the magnetic fields
• Only certain materials can be cooled. The main one is Gd5(Si2Ge2)

Bose Einstein Condensates

BECs are produced in a magneto optical trap, rather than just using a canning machine. These methods seem to only work on small gaseous clouds of the following isotopes:

Li-7, Na-23, K-39, K-41, Rb-85, Rb-87, Cs-133, Cr-52, Ca-40, Sr-84, Sr-86, Sr-88, Yb-174, Dy-164, Er-168

Main process:

• Small amount of isotope will have to be turned into a gaseous cloud

Components involved in magneto optical trap:

• Superconducting magnets to create the magnetic fields
• 3 sets of lasers to slow atoms down in 3 dimensions
• Vacuum of below 10 uPa

After the lasers and magnetic fields cool the gas cloud, the second phase (evaporative cooling) begins, which also happens inside the magneto optical trap. The process evaporates the atoms with the highest velocity, leaving behind atoms that have a lower velocity and therefore lower temperature. This process is also done using lasers.

Source: https://en.wikipedia.org/wiki/Magneto-optical_trap
Other source: https://en.wikipedia.org/wiki/Evaporative_cooling_(atomic_physics)