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 head loads and maintain uniform density and temperature (huge for muon colliders!)  Beam heating must be minimized (high L R 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 LH2 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)LH2 and O2 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 4.0 for the absorber and vacuum windows at maximum allowable working pressure (MAWP). Vacuum windows required to withstand 25 psi outside pressure without buckling. 2)Three layers of shielding between the outside atmosphere and the LH2; the outer surfaces are at room temperature to minimize the freezing of O2 on the absorber-system windows. 3)Separate vacuum volumes provided for the RF cavities, magnets, and LH 2 absorbers. 4)Hydrogen evacuation systems using valved vents into external buffer tanks. xx zz P1P1 P2P2    LH2 accelerator LH2 P1P1  Multiple scattering RF cavity dE/dx  +

Accommodating LH2 1.LH2-Air flammability limits: 4-75% ; detonability limits 18-59%  conventional seals and vacuum vessels can provide sufficient shield between them 2.Sufficient clearance for LH2 venting into evacuation tanks (21 liters liquid  liters at STP) 3.RF & Vacuum windows considered a “hazard/safe” barrier. 4.All safety interlocks mechanical – based on expeditious venting of LH2 5.Two sets of windows, cooling channel containment (with Ar gas seals at all flanges) RAL safe LH2 operation ISIS style safety scheme

Absorber details LH2 Volume (at 20K) 21 liters Absorber Vacuum volume 91 liters LH2 operating temp. 20.8K LH2 operating pressure 1.2 bars Allowable pressure range 1.05 – 1.7 bars Helium inlet temperature 14K Absorber Vacuum Volume: “Dome” “Magnet bore” Absorber Window: Vacuum Window: He outlet: He inlet: He heat exchange

Absorber coil system Ambient temperature on vacuum shields and outer channel wall Quench force on windows is small Static and quench forces are decoupled from the LH2 absorber Heat from quench and static sources are insufficient to cause boil-off Clearance for possible LH2 rupture into vacuum volume sufficient to prevent cascading window rupture

Thin Windows Design Progression of window profiles: “tapered” (1) and “bellows” (2 & 3) If thinnest point not at the center, where? Thin window and heavy flange of one piece … many options for absorber attachment Certification: No closed form relation between pressure and largest stress. Need to accurately confirm: Window manufacture Performance under pressure tests Two radii of curvature may not be concentric - critical to confirm minimum thickness 2 bolted options:

Photogrammetric measurements Strain gages ~ 20 “points” Photogrammetry ~1000 points CMM ~ 30 “points” Non-contact method ~ 1000 pts. measured simultaneously High accuracy for pressure tests and shape measurements Detailed enough data to confirm FEA calculations for extreme performance situations, and to confirm window manufactured as designed Portable system

Solid Absorber Changeover 1)None of the shielding requirments for LH2 2)Ambient and beam heat deposition require no special cooling requirements 3)Can be mounted and secured in existing absorber shell 4)Quench hazard?

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 Basic barrier Wire+shielding concerns: Two twisted pairs – not grounded, details depend on overall MICE grounding scheme Common mode surges due to magnets Noise/sensitivity issues

Experiment certification Windows certification done separately Certification of windows-absorber assembly Establish correct placement of absorber inside coil Pressurization tests of absorber/coil vacuum system Non-LH2 cryogenic test of absorber/coil system and instrumentation Assembly into channel: final purge before hydrogen fill LH2 absorber Coil Tranverse absorber/coil removal from channel

Exception Situations  Concern based on the potential hazards of LH2 Fire:  Large range of flammable and detonable limits  Burning velocity at STP: cm/s – MACC’s time in 200 meter run: 28.5 s = 702 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 LH2)  Overcooling/Undercooling of LH2 Temperature change Gas concentration  Safety failsafes based on 2 independent system failure