> If you have a lot of pure helium gas and a really good compressor you can increase the pressure until the boiling point is high enough to exceed the temperature of the gas, so now you have a liquid helium at an insane pressure.
The critical temperature of Helium is 9.35 °R -- above that it will not be a liquid at any pressure. So we have to go through successive phases of compression (which heats it up), cooling via another cryogen (liquid nitrogen initially, then liquid hydrogen in subsequent passes), and expansion (at the right conditions, because of the oddities of the Joule-Thompson effect[0] for elements like Helium), in order to cool it enough to produce a liquid.
The critical temperature of Helium is 9.35 °R -- above that it will not be a liquid at any pressure. So we have to go through successive phases of compression (which heats it up), cooling via another cryogen (liquid nitrogen initially, then liquid hydrogen in subsequent passes), and expansion (at the right conditions, because of the oddities of the Joule-Thompson effect[0] for elements like Helium), in order to cool it enough to produce a liquid.
[0] https://chemistry.stackexchange.com/questions/61517/reason-f...