1. Mathew C. Wright October 2016
Cryogenic Cooling
Mathew C. Wright
October 2016

2. Cryogenic Operations Overview
11/12/2018

3. Cryogenic Cooldowns Types of Cryogenic Cool Downs:
Using LN2 to cool down Cold Boxes
Using 4K helium to cool down cryo modules
Using LN2 HX to cool helium to cool magnets
Mixing 300K helium with 4K helium
Using Turbines to cool down cold boxes before LN2
Directly injecting LN2 into helium dewars then finishing the cool down with 4K helium

4. Cryogenic Cooldowns Things to be concerned about:
Thermo-mechanical stresses of the components
Especially heat exchangers
Oil or contamination migration
Capacity Limitations of the Equipment
Refrigeration
Helium Recovery / Purification
Gas Management

5. Cryogenic Cooldowns Basic Rule:
Cooling provided by the supply stream must be greater than that absorbed by return stream – rest of the cooling is used to cool down the equipment (HX etc.).
This imbalance across the two streams is created by the bypass flow.

6. More strain = More Stress!
Cryogenic Cooldowns
Concerns:
To reduce thermo-mechanical stresses of the components
Normally Delta T less than 50K
Thermal strain (i.e. contraction rate) is directly proportional to ∆T.
More strain = More Stress!
Cool down rate is less than 1K/min

7. Cryogenic Cooldowns Concerns
To reduce Thermo-mechanical stresses of the components
Delta T less than 50K
Here, ∆T is the temperature difference between the streams at warm end or at the cold end.

8. Cryogenic Cooldowns Concerns
To reduce Thermo-mechanical stresses of the components
Flow through all HX passes should be low, causing the Cooldown to be extremely slow

9. Cryogenic Cooldowns Concerns Contamination migration
Loads / Cryogenic Vessels: Always assumed Dirty. Entire cool down flow is taken to recovery system (via. Vaporizer). This also creates flow imbalance across HX.
Cold Box Adsorbed Beds: Isolated/Bypassed until the process flow reaches the temperature they are meant to operate (i.e. 80K/20K). If possible they should be cooled separately (using same method as 1).

10. Cryogenic Cooldowns Basic Rules Oil or contamination migration
Start Cool Downs of all Cold boxes w/ LN2
Check outlet vent to ensure the LN2 supply valve is only cracked open
Use a bag over the vent pipe and crack open the valve until the bag starts to slowly inflate
Cold box 80K carbon beds are 100K or less before starting turbines to reduce the chance of contamination getting down stream when turbines are started

11. Cryogenic Operations Overview
11/12/2018

12. Cryogenic Cooldowns
CHL1
Direct
LN2
injection

13. Cryogenic Cooldowns
CHL1
Direct
LN2
injection

14. Cryogenic Cooldowns Jlab Style Cryo Module Cool Down
Direct 4K injection

15. Cryogenic Cooldowns
Jlab Style Cryo Module Cool Down

16. Cryogenic Cooldowns Both LINAC’s can be supported by either
CHL1 and CHL2 without having to warm-up any cryo modules
Modules typically have to be warmed up for maintenance on the module

17. Solenoid in Hall D Bore 4m long 2m diameter
Field at the axis ~ 2T at 1350A
Full energy ~ 23 MJ at 1350A
4 coils in 4 separate He baths
Built at SLAC in 1970’s, refurbished at IUCF and Jlab
Total helium reservoirs 3500 liters

18. Cryogenic Operations Overview
11/12/2018

19. Cryogenic Cooldowns
Hall D:
Employing cool-down heat exchangers

20. Cryogenic Cooldowns
Employing cool-down heat exchangers

21. Cryogenic Cooldowns
Hall D:
Employing cool-down heat exchangers

22. Cryogenic Operations Overview
11/12/2018

23. Cryogenic Cooldowns
Hall A:
Employing cool-down heat exchangers

24. Cryogenic Cooldowns Other Cool Down Methods Mixing 300K w/ 4K helium
Uses 4K capacity when LN2 could be used
Flow may need to be limited based on
Size of the Recovery system
Size of the Refrigerator
Warm (300K) start-up of turbines
Concern is that the 80K carbon beds are not cold and that contamination will migrate to the turbines
Cool Down with LN2 directly into the process
Rumors of people using LN2 directly injected into a helium dewar to cool down, then pump out the N2, and continue cooling with helium
Concerned amount contamination
If there are valves back to the helium system, concerned those valves leak and that the helium system has to be shut down to clean it up.

25. Cryogenic Operations Overview
11/12/2018

26. Cryogenic Operations Overview
11/12/2018