1. Cryomodule Helium Volumes Tom Peterson, Fermilab AWLC14 13 May 2014

2. Introduction Most helium inventory in a long string of TESLA/ILC-style cryomodules is in the helium vessels Most volume is in the 300 mm pipe During a power outage or severe cryogenic plant outage, the cryomodule string itself may act to provide temporary helium storage The following provides a rough estimate of this storage capacity 5/13/14AWLC14, Cryomodules, Peterson2

3. Cryomodule cross section 5/13/14AWLC14, Cryomodules, Peterson3

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6. Cryomodule helium inventory 5/13/14AWLC14, Cryomodules, Peterson6

7. Closed-volume warm-up process Assume valve control is available – Isolation of supply valves to 2 K space – Isolation valve closes on 2 K vapor return Retain insulation vacuum and beam vacuum Static heat load warms helium Process is warm-up of the 2-phase system starting at 2.0 K, 31 mbar 5/13/14AWLC14, Cryomodules, Peterson7

8. Results of first, coarse analysis 5/13/14AWLC14, Cryomodules, Peterson8 XFEL

9. What that table says Warm-up from 31 mbar to 1.5 bar takes 39 hours – Assuming relief valves open at 1.5 bar, venting would begin at approximately 39 hours Result is evaporation of almost all the liquid – Final state is almost pure vapor at 1.5 bar 5/13/14AWLC14, Cryomodules, Peterson9

10. Sources of error, refinements Seems nice, but – Thermal shield also warming up – Need second-order analysis incorporating slowly increasing static heat load Still expect about one day before reaching venting pressure 5/13/14AWLC14, Cryomodules, Peterson10

11. Conclusions This is just an order-of-magnitude analysis Nevertheless, it illustrates the potential of the cryomodule itself as a temporary storage volume during lack of cooling Implementation requires supply and return valves closing to provide closed volume Suggest further analysis and consideration of options – Secondary effect of slow thermal shield warm-up – Actual volumes including distribution system – Real practical venting pressures – Required valves and control for inventory management – Etc.... This is just a quick look. 5/13/14AWLC14, Cryomodules, Peterson11