Question: Can you please explain in detail how the cryogenic system for telescope amplifier cooling works? I was recently at the VLA and noticed boxes outside the yokes that looked like home air-conditioning units, and what looked like cryogenic piping. I’m guessing LHe boiling off to produce cooling gas, all inside a jacket of LN2. If so, is the helium recirculated or just vented? — Dan
Answer: Your guess is correct! The liquid He is recirculated (i.e. it is a closed-cycle refrigerator system). This all allows the VLA receivers to operate near the liquid phase temperature for Helium, or about 4 K.