Comment Re:Curious... (Score 4, Informative) 338
Oh, and 1.9K temperature is used because it has a margin of safety for liquid helium (which has 4K boiling point).
1.9 K is below the so-called "lambda point" of helium, which stands at 2.2 K. That point corresponds to a transition to the superfluid state. This may help with heat dissipation in this setup.