1. Microboone Cryostat Mike Zuckerbrot Fermilab

2. Basic Overview of Microboone  Microboone’s 2 Phases of Operation  Phase 1 operations ran from about December 2013 – June 2014  The Phase 1 system contained all major equipment except for the Cryostat/TPC and the Argon condensers  The Argon Buffer Dewar stood in place of the Cryostat during Phase 1  Installation is currently underway for Phase 2 system Fermilab - Microboone Cryostat2

3. Basic Cryostat Overview  BNL played large part in cryostat and TPC design and procurement  Vendor given specifications for leak tightness and cleanliness as well as basic vessel specifications  ASME U-Stamped Pressure Vessel  30 psig – full vacuum  35,125 gal total volume  Will operate with ~33,700 gal LAr or ~4.1% ullage  7/16” thick shell, 150” ID, ~40’ long, reinforcing outer ribs  ASME F&D welded heads  Shipped in temporary steel saddles, 4 pick-points Fermilab - Microboone Cryostat3

4. Basic Cryostat Overview  3D Model and Nozzles (not all shown)  Liquid inlet top of downstream end, liquid outlet bottom of upstream end o Liquid outlet presents additional ODH risk  Liquid return line has small internal phase separator  Gas recirculation lines have long internal sparger pipes Fermilab - Microboone Cryostat4

5. Basic Cryostat Overview  Delivered to Fermi by vendor  Head cut off by vendor  TPC built at Fermi and inserted into vessel  Cleaned before/after TPC insertion  Head welded back on by vendor  Leak tested by Fermi after welding  Transported to LArTF and lowered in through removable roof Fermilab - Microboone Cryostat5

6. Components and Instruments  Redundant level and pressure instrumentation  2 probes and differential pressure measurement for level  Absolute and gauge pressure transmitters  Will operate at 18 psia with about 33,700 gals of LAr  Pneumatic fail closed shutoff valves on all major ports  Especially important on ports below liquid level, minimizes amount of piping which if ruptured would not be able to be isolated  Dielectric isolation of piping and instruments  Dielectric flange gaskets/kits and welded ceramic breaks  Dielectric flange gaskets found to have cold leaks in 35t, not recommended for jacketed piping  2 internal purity monitors and ports to send boil off to gas analyzers for contamination measurements  Multiple RTDs near interior shell and on TPC Fermilab - Microboone Cryostat6

7. Components and Instruments  Dual 4x6 relief valves and safety switchover system  3000 Watts of heater power spread on bottom of external shell with RTDs for monitoring temperature  May be used to increase outgassing/filtering during initial recirculation  Help to control temperature gradients if they develop during cooldown or filling  Chimney purge system for feedthroughs  Small bellows pump for constant purge  Vapor gets recondensed and filtered  Automated system to raise/lower level Fermilab - Microboone Cryostat7

8. Design Considerations  Insulation  2 lb/cf spray on Polyurethane foam, sprayed on in layers, mesh after first couple layers to secure  Originally specified as a jacketed vessel  Foaming is cheaper, potentially safer (no risk of vacuum failure)  Higher heat load, but still within project parameters  Spray on foam with a mastic vapor barrier is far more effective than the foam block type insulation Fermilab - Microboone Cryostat8

9. Design Considerations  Vessel Support  High density Polyurethane foam saddles  SS saddles and hanging sling design considered  Foam saddles give more overhead clearance, simpler and cheaper than SS saddles, and less heat leak  Saddles sit on 2 flat metal plates, epoxied to top plate  Cryostat gets epoxied to saddles  Upstream plates welded together  Downstream plates greased to slide  Allows vessel to thermally contract Fermilab - Microboone Cryostat9

10. Design Considerations  Vessel Heads  Cryostat has welded heads  Vessel specification included the requirement that the endcap be able to be cut and rewelded, R-Stamped  Flanged head was considered  Head does not realistically have to be removed multiple times, flange isn’t necessary  Concerns over leak tightness of the seal on the large head  External Pumps and Condensers  External pumps based on LAPD system, easier for routine maintenance and general access  External condensers with filtering always recommended for ultra high purity systems  Internal condenser adds contamination to the liquid by raining the higher- contamination ullage gas into the liquid  Both pumps successfully ran during phase 1, no operational experience with Microboone specific condensers Fermilab - Microboone Cryostat10

11. Design Considerations  Initial Purification  The Microboone cryostat is initially purified using the piston purge method  Method has been repeated and verified to be successful in other experiments (LAPD, 35t, etc…)  Was also repeated in Microboone phase 1 operations with the Argon Buffer Dewar, bringing the vessel down to low ppm levels (1-2 ppm) for O2, H2O, and N2 starting from being filled with air o Multiple bottom-to-top volume changes using high purity gas o From air to < 0.5 ppm O2 and H2O, < 2 ppm N2 o Obtained Microboone’s 3 ms (<100 ppt O2 equiv.) electron drift lifetime requirement  Cryostat rated for vacuum as well as a fail safe purification method, stemming from a time when there was uncertainty of how well the piston purge method would scale upward  Before the slow cooldown process, gas will be recirculated using the cooldown compressor through a large capacity molecular sieve to remove as much water as possible Fermilab - Microboone Cryostat11

12. Final Comments  Final Comments  30 psig – full vacuum rating increases amount of material and overall cost, not necessary for piston purged vessels o Also increases amount of cooling power required for initial cooldown  Having the vessel fabricated with the main shutoff valves, including actuators and supports, welded on by the vendor would have been beneficial  Tighter specifications on nozzle tolerances o Straightness, roundness, minimum inner diameter Fermilab - Microboone Cryostat12

13. Microboone Cryogenic System Mike Zuckerbrot Fermilab

14. Presentation Outline  Overview of Microboone  Phase 1 and Phase 2 System  Phase 1 System Design and Operation  Purification System Components  Additional Components for Phase 1  Operational Experience and Data  Phase 2 - Cryostat Cooldown System  Basic Concepts and Major Components  Phase 2 - Purification System  Additions to Phase 1 System  Design of Major Components Fermilab - Microboone Cryostat14

15. Overview of Microboone  Microboone Phase 1 System  Operated from late December 2013 – early June 2014  Contained several of the major components to be used in the phase 2 purification system  No Cryostat or detector, Argon Buffer Dewar stood in place  LAr pumps, filters, 11k gal Nitrogen dewar, regeneration system, gas analyzers, inline purity monitor  Additional components used in the Phase 1 system include the Argon Buffer Dewar and the High Voltage Cryostat Fermilab - Microboone Cryostat15

16. Overview of Microboone  Microboone Phase 2 System  Installation is currently underway for the Phase 2 system  Additional major cryogenic components include o Cryostat o Argon Condensers o Complete Liquid Nitrogen system including large Phase Separator o Cryostat Cooldown system including compressor, heat exchanger, molecular sieve Fermilab - Microboone Cryostat16

17. Microboone Phase 1 System  Late additional to overall plan, designed and implemented in a short time span  Conceptually implemented to test and operate the major cryogenic components of the purification system  LAr pumps, filters, N2 dewar, regeneration system, gas analyzers  High Voltage Cryostat and repurposed inline purity monitor added later for R&D purposes  11k gal Argon Buffer Dewar in lieu of the Cryostat  Internal liquid Nitrogen powered Argon condenser  Filled with leftover LAr from D0 as well as LAr supplied by 35t once their run had been completed Fermilab - Microboone Cryostat17

18. Microboone Phase 1 System  Gas Analyzers  H20 o Vaisala dew point meter – gross measurement o HALO – 0-20 ppm, res. to <2ppb  O2 o DF310 – 0-5000 ppm o DF560 – 0-20 ppm, res. to <1ppb  N2 o LDETEK – 0-100 ppm, <1ppm Fermilab - Microboone Cryostat18

19. Microboone Phase 1 System  Argon Buffer Dewar  Internal Argon condenser, LN2 coolant supplied from neighboring dewar  Initially purified using piston purge method o ~15 bottom-to-top volume changes of HP Argon gas o From air to < 0.5 ppm O2 and H2O, < 2 ppm N2 o Likely didn’t require that many volume changes, was purged over a weekend  Cooled by flowing Argon gas with condenser active until ~100 gallons of LAr was present in the dewar  Initial fill with ~1,000 gals of leftover D0 LAr o 0.2 ppm H2O, 0.55 ppm O2, 2.5 ppm N2  Filled with 2 more 2,000 gal tanker loads from 35t o 140 and 430 ppb H2O, 9 and 11 ppb O2, 9 and 19 ppm N2 Fermilab - Microboone Cryostat19

20. Microboone Phase 1 System  LAr Pumps – Overview  Same pump as used in LAPD  Vacuum jacketed, flanged top with c- seal  100 mesh strainers on suction, flex hoses on suction and discharge  2 pumps in parallel, both ran separately for ~2000 and ~1000 hours during phase 1  Bearing change required about every 5000 hours  Flanged internals and overhead lifting system for easy removal and maintenance Fermilab - Microboone Cryostat20

21. Microboone Phase 1 System  LAr Pumps – Initial Startup  Initial startup was difficult, required piping geometry change and extra instrumentation on the suction line  Eliminated high points on piping, added level probe and automatic vent to eliminate all vapor bubbles, constant bleed  Heat load on foam insulated piping was high, required constant flow of ~0.5 gpm or more to prevent rapid boiling in the lines  Pump must be fully primed to start  If fully primed, expected flow rate differential pressure are steadily established almost instantly  Pump switchover was less challenging, done within a few hours Fermilab - Microboone Cryostat21

22. Microboone Phase 1 System  LAr Pumps – Other Notes  During operations the each pump tripped off once for unrelated reasons  A pump restart is just as involved as an initial startup, requiring a significant amount of time and venting to refill the system with liquid and establish flow before the restart  One trip was caused by unstable Argon Buffer Dewar pressure, when pressure is rapidly dropped the liquid starts to flash and the pump loses prime o Stable pressure was important, may be less of an issue with a larger liquid supply but still important for the experiment  Both pumps leaked into the vacuum jackets while cold, had to continuously run on vacuum pump on the active one o Under investigation, internal plumbing shouldn’t be duplicated until the issue is understood and corrected Fermilab - Microboone Cryostat22

23. Microboone Phase 1 System  Filter Skids  Primarily based on the LAPD filter skids  2 filter skids, each with a molecular and copper sieve vessel  Run one at a time, allows for changeover when saturated so interruption to purification process is minimized  Top-down flow to prevent bed lift, check valve on outlet to prevent backflow  Slotted plate and mesh screens encapsulate filter media  5 micron sintered metal filter vessel on outlet for particulates  Ports to send gas to analyzers after each vessel  9 RTDs in each vessel Fermilab - Microboone Cryostat23

24. Microboone Phase 1 System  Filter Skids  One filter skid used in phase 1 operations  Never fully saturated, started with very clean liquid o Plot on left – 40 ppb O2 down to 0 within a weekend, ~5,000 gals  Attempted to bring second filter online, was difficult due to long, small diameter, return line o Plot on right shows several downward steps in O2 concentration from cooling the skid down o Indications that the flow through the active skid was not well distributed, center media likely saturated, outer media had remaining capacity Fermilab - Microboone Cryostat24

25. Microboone Phase 1 System  Regeneration System  Leased 500 gallon argon dewar and tube trailer with premixed 97.5/2.5% Argon Hydrogen o Flow and ratio of each set by mass flow controllers  Both sieves heated simultaneously with Argon gas to about 200 C o 18-24 hours to heat and regenerate molecular sieve  Slowly bleed in mixture to regenerate copper sieve and throttle down on the Argon gas flow o Must watch carefully for self heating of the copper media o Can be done within 8-12 hours if already hot  Regenerating both sieves simultaneously provides some extra efficiency Fermilab - Microboone Cryostat25

26. Microboone Phase 2 System  Phase 2 system additions  Cryostat and cooldown system  Condensers  LN2 coolant systems  Most of the cryogenic piping in phase 1 and 2 all analyzed for thermal stresses using Ansys FEA  Goal is one full cryostat volume change per day running both pumps in parallel  Purity requirement is < 100 ppt O2 equivalent or 3 ms electron drift lifetime  Was obtained during phase 1, measured with same inline purity monitor present in phase 2  Initial liquid purification may require 5-10 filter switchovers and regenerations Fermilab - Microboone Cryostat26

27. Microboone Phase 2 System  Argon condensers  2 identical condensers, one is a spare or could be used during abnormally high heat load situations like filling  Based on the LAPD design, scaled up for larger system  Heat transfer of boiling LN2, condensing Ar, and two phase pressure drop calculations extremely thorough  2 inner coils for LN2 flow, outer shell for argon gas  Extra coil support and restraints to prevent excessive vibrations from flashing liquid  Foam insulated with 4” of a two part Polyurethane mixture Fermilab - Microboone Cryostat27

28. Microboone Phase 2 System  Cryostat cooldown system  Argon gas diaphragm compressor, positive displacement machine presents additional relief requirements  3 pass plate-fin heat exchanger, requires slow cooldown as well  Large capacity molecular sieve  Will recirculate warm gas to remove as much water as possible before cooldown  Same piping supplies gas for the piston purge  Slow cooldown over 2-3 weeks to about 100K before filling  Slow cooldown rate set by the TPC requirements  Alternative designs should be considered, very expensive and complex system with regards to equipment and design  Sprayer nozzles?  TPC wire frame design? Fermilab - Microboone Cryostat28

29. Final Comments  Final Comments  Regeneration system o In house mixing system far cheaper over time than purchasing premixed gas in tube trailers o Does present additional safety concerns due to flammable gas  Used equipment o Should be cautious when implementing used equipment o Thorough evaluation and testing  Building o Round building is cheaper if it’s a pit o Increases design time, but roundness not as critical as overall size Fermilab - Microboone Cryostat29