[Aaron, Stephen]

Aaron preliminarily estimated the load for the PSOMA experiment to be 40 MJ. The first nitrogen boil off calculation for 40 MJ of cooling energy is a LN2 volume of ~250 L, as follows:

• The heat of vaporization of liquid nitrogen is 199 kJ/kg = .199 MJ/kg
• The density of liquid nitrogen at atmospheric pressure is .806 kg/L
• Volume_LN2 = Cooling_Energy / ( Heat_of_Vaporization / Density_LN2 )

Thoughts on making a better estimate of current QIL Cryostat thermal load, to inform the PSOMA thermal load estimate.

• I think Radhika and Aaron are doing some estimates based on QIL Cryostat cooldown curves, but I'll do some eyeballing below in the meanjtime.
• Collecting cooldown parameters
  • Eyeballing a representative cooldown curve the QIL Cryostat coldhead temp seems to pass from room temp to 60K in about 2 hours.
  • Eyeballing the capacity map from Sumitomo, there seems to be an average power of 70 W for those first 2 hours, then an average power of 35 W (crossover at ~50K) for the remaining duration.
    • We have about a 36 hour conductive cooldown period to reach steadyish state at below 80K.
    • We have about a 24 hour conductive cooldown period to reach 100K (looking at Inner Shield temperature, dominated by coldplate thermal mass)
• 36 hour cooldown to 80K steady state:
  • 2 hours at 70 W and 34 hours at 35 W gives a total cooldown load of 4.8 MJ. We'll make this the current estimate for the QIL Cryostat cooldown, with ongoing load of 0.12 MJ every hour.
  • This would require an LN2 volume of 19.4 L, with ongoing consumption of .48 L/hr.
• 24 hour cooldown to 100K:
  • 2 hours at 70 W and 22 hours at ~40 W (higher average power than above case) gives a total cooldown load of 3.7 MJ. In the case of PSOMA measurements at 123 K, this is roughly the point at which the LN2 would cease to be used and the cryocooler would take over.
  • This would require an LN2 volume of 14.9 L.
• 64 hour period such as a weekend:
  • 2 hours at 70W and 62 hours at 35 W would make a total cooldown load of 8.3 MJ, with those first 2 hours costing about 0.5 MJ (allowing a refill to make a dent in the required capacity.
  • The required LN2 volume to sustain through 64 hours would be 50L, and for reference the largest LN2 volume offered by IRLabs standard is 8 L.