LH2 Absorber Design Mary Anne Cummings MICE Safety Review LBL Dec 9, 2003

Hydrogen Absorber Design Principles Muons can focus going through material!  Absorber must handle significant dE/dx loads and maintain uniform density and temperature (huge for muon colliders!)  Multiple scattering must be minimized (high x 0 material in low ) Convection-driven liquid hydrogen absorber  Internal heat exchange, no external hydrogen loop  Need to monitor temperature, pressure and LH2 level Thin window development  Non-standard designs to minimize central thickness  Must be sufficiently strong and have robust structural attachments Location in center of high solenoidal magnetic field  Concerns for quench forces on structural stability  Heat stresses on windows below elastic tolerance Additionally.. RF between LH 2 absorbers to restore forward momentum: The above goals drive the design of the absorber, its support structures, and placement in the cooling cell:

Liquid Hydrogen Safety  For safe operation, have designed with the redundant requirements: 1)LH 2 and O 2 separation 2)The avoidance of any ignition sources in contact with hydrogen.  The four key features of the design with respect to safety are: 1)Window thicknesses specified based on safety factors of ~4 for the absorber and vacuum windows at the pressure. Vacuum windows required to withstand 25 psi outside pressure without buckling. 2)Two layers of shielding between the outside atmosphere and the LH 2 ; the outer surface at room temperature to minimize the freezing of O 2 on the absorber-system windows. 3)Modular components: separate vacuum volumes provided for the RF cavities, magnets, and LH 2 absorbers 4)Hydrogen evacuation systems using valved vents into external buffer tanks. LH2 x z P1P1 P2P2   accelerator P1P1  RF cavity dE/dx x z  accelerator LH2 Multiple scattering RF cavity  +

Accommodating LH2 1.LH 2 -Air flammability limits: 4-75% ; detonation limits 18-59%  conventional seals and vacuum vessels can provide sufficient barriers between them. 2.Sufficient clearance for LH 2 venting into evacuation tanks (21 liters liquid 20K  ~17000 liters at STP) 3.RF: Window provides spark barrier; vacuum between RF and LH 2 vacuum vessel 4.All safety interlocks mechanical – based on expeditious venting of LH 2 into evacuation tank 5.Two barriers at all points, outer barrier is warm, between the LH 2 and atmosphere, to eliminate chance of O 2 “cryopumping” inside of LH 2 vacuum area RAL safe LH 2 operation

Absorber coil system Ambient temperature on vacuum shields and outer channel wall Quench force on windows is small Static forces are decoupled from the LH 2 absorber Heat from quench and static sources are insufficient to cause boil-off Clearance for possible LH 2 rupture into vacuum volume sufficient to prevent cascading window rupture Absorber Vacuum Volume: Magnet bore Large end plate Absorber Window: Vacuum Window: He inlet: Outer wall

Absorber details LH 2 Volume (at 20K) 21 liters Absorber Vacuum volume 265 liters LH 2 liq/gas surface temp. range K LH 2 operating pressure 1.2 bars Allowable pressure range 1.05 – 1.6 bars Helium inlet temperature 14K Absorber Vacuum Volume: “Large end flange” “Magnet bore” Absorber Window: Vacuum Window: He outlet: He inlet: He heat exchange Normal operating parameters: H 2 inlet:

Thin Windows Design Confirming minimum thickness is crucial! Photogrammetry for non-contact, multipoint measurement Compare with FEA analysis Tapered torispherical (1) test data and FEA results agree – confirmed FEA techniques! Inflected (3) is current design – performance predicted by FEA, yet to test bolted option: Thin window and heavy flange of one piece … many options for absorber attachment Progression of window profiles: “tapered torispherical” (1) and “inflected” (2 & 3) If thinnest point not at the center, where?

Solid Absorber Changeover 1)Has none of the shielding requirements for LH 2 operation 2)Ambient and beam heat deposition require no special cooling requirements 3)Can be mounted and secured in existing absorber shell 4)All cryogenic ports sealed can be easily sealed off 5)Can run with vacuum windows if there are contamination concerns 6)Check for stability by slow magnet ramp-up.

Absorber Instrumention 1.All electronics will have to conform to European safety standards w.r.t. flammable gas. 2.Current absorber readouts:  Temperature probes  Pressure gauges  Level sensors 3.Can port through LH2 or vacuum: example: MDC Vacuum Products Corp 4/24/ UPS PC w/16chan ADC FISO Cryo(temp) IRM Barrier(s) network ACNET Sealed Conduit(s) Intrinsically safe signal conditioners and transmitters power Hazard Safe Intrinsically safe Concerns for absorber electronics: Power per channel Feedthroughs Seals Wire+shielding concerns: Two twisted pairs – not grounded, details depend on overall MICE grounding scheme Common mode surges due to magnets Noise/sensitivity issues

Absorber certification Windows certification done separately Instrumentation certification Pressure test absorber and He heat exchanger (1.25 X design pressure) Nitrogen cool-down (cryogenic seal test) Vacuum leak check of absorber and heat exchanger with helium Purge/pressurize absorber with dry nitrogen to 1.3 bar Install MLI around absorber body All absorber repairs done outside of MICE channel

Absorber/coil certification Purge absorber and helium heat exchanger with dry nitrogen gas Instrumentation certification Vacuum leak check the helium pipe connections and the LH2 pipe connection to verify low vacuum leak rate Pressurize absorber body and heat exchange volume with dry nitrogen Purge/pressurize absorber with dry nitrogen to 1.6 bar for seal test Evacuate absorber body for vacuum test. Check seals. Evacuate absorber heat exchange volume, Check of MICE vacuum space Separate pressure tests of absorber, heat exchanger and absorber vacuum volumes Cool-down of absorber body Opening of valve between absorber and hydride bed for hydrogen fill Into MICE:

Experiment certification Window certifications Absorber pre-assembly and testing Absorber/coil assembly, testing and certification Assembly into MICE cooling channel and certification Hydrogen fill LH2 absorber Coil assembly Transverse absorber/coil removal from channel Metal hydride beds with buffer tanks

Exception Situations  Concern based on the potential hazards of LH 2 Fire:  Large range of flammable and detonation limits  Burning velocity at STP: cm/s –Minimum energy for ignition in air: 0.02 mJ Explosion: detonation velocity (STP): km/s Extreme cold – all the usual cryogenic hazards  Hazard analysis based system parameters: Pressure change  Leaks (rupture, seal failure, incorrect cryo. Connections)  Plugs (frozen LH 2 )  Overcooling/Undercooling of LH 2 Temperature change (unanticipated heat deposition) Gas concentration  Safety failsafes based on 2 independent system failures

Off-normal conditions – LH2 absorber 1)RF cavity vacuum or detector vacuum air leak 2)Absorber vacuum window leak 3)Absorber leak 4)Hydrogen freezing 5)Large heat leak to the absorber 6)Loss of refrigeration or loss of electrical power 7)Quench of the focusing solenoid 8)Rupture of the hydrogen window 9)Rupture of both hydrogen and safety windows Exception handling: Expeditious H 2 evacuation (relief valves, pumping) MICE shut-down Hydride bed temperature regulation Most exceptional conditions can be corrected “passively” Off-normal conditions:

Final thoughts  Defined window certification procedure  Design of absorber and coil consistent with redundant H2 safety requirements  Certification and testing procedures defined  Preliminary HAZOP analysis done  Mucool complementary experiment in parallel