MICE hydrogen review Summary of system hardware

System function To provide 22 litres of liquid hydrogen for use as a muon absorber within a superconducting solenoid magnet Hydrogen is stored as gas and liquefied using an in-situ closed-cycle cryocooler System operation is remote and (mostly) automatic

Safety philosophy System is safe against two simultaneous failures – Keeping separation of hydrogen and oxygen – Avoiding ignition sources where explosive atmospheres could form Passive safety – Fail open/close valves where appropriate – Redundancy in pressure relief circuits Adherence to codes and regulations – DSEAR – IEC61508 – PED (97/23/EC) – Local SHE codes Operational procedures – Expert operators only – Monitor-only interaction with control system

System overview Hydride bed stores hydrogen gas Gas panel manages gas movement AFC hydrogen turret liquefies hydrogen Control system with dedicated PLC operates system autonomously Ventilation system mitigates any hydrogen leaks

General layout Gas panel inc hydride bed Charging station Ventilation fans Absorber Focus Coil Transfer line Vacuum pumps

Charging station Cabinet to house two hydrogen bottles – Ventilated via ductwork to plenum (see later) – Includes regulator and various hand valves – Incorporates a transparent hatch for access to valves – Pipework for R&D tests was a single continuous piece of ¼” stainless tube with VCR fittings inside the cabinet and gas panel – Protective guards were included where appropriate

Hydride bed Manufactured by Treibacher in m 3 gas max capacity in 0.25 m 3 vessel – At room temperature, pressure is < 30 bar Absorption/evolution controlled by glycol heater-chiller unit – Temperature range of -15°C – 65°C

Gas panel Instrumentation, pneumatic valves and relief components – all ATEX rated intrinsically safe Ventilated, sealed cabinet Pipework welded or VCR fittings

Ventilation systems - fans Ventilation of gas panel and charging station – Mitigates against any minor hydrogen leaks from demountable fittings etc – Filtered air inlet on gas panel – Bifurcated fans on roof powered via a UPS, sized for three systems 11,000 m 3 /hr flow – only 3,600 m 3 /hr required to limit time of persistence to 60s – Polypropylene ducting with blast panel Ventilation of pump enclosure – Ventilates zoned pump enclosure as pumps exhaust hydrogen during empty and purge sequences – Also keeps pumps cool – Similar set up to gas panel ventilation system

Ventilation system - ducting Plastic-welded polypropylene ducting – Plenum distributes ventilation to three gas panel locations and charging station – Incorporates non-return dampers and a gate valve for the charging station duct – Also provides a conduit for the vent line while inside the MICE Hall

Transfer line Gas panel to AFC – 2off welded 1” stainless pipes with VCR fittings – Jacketed by a welded 4” stainless pipe, flushed through with nitrogen gas – Rigid construction – accommodated by flexible connections within the gas panel Charging cabinet to gas panel – Single piece of ¼” stainless pipe with VCR fittings

Absorber Focus Coil Cryogenic turret integrated into Focus Coil magnet module – Single Cryomech PT415 coldhead, heater regulated – Thermal syphon circuit – Separate LN 2 pre-cool / He jacket circuit Absorber vessel with thin beam windows – Vessel machined from a 5000-series aluminium billet – Windows similarly machined from 6061 aluminium billet – Indium seals on absorber windows – O-ring seals on safety windows

Test cryostat Analogous cryogenic system to the AFC – Equivalent absorber was a thick-walled vessel without thin beam windows – Incorporates a radiation shield, so was able to achieve LHe temperatures

Other infrastructure Pump enclosure – Two oil-sealed, rotary vane pumps (one for purging, one to back turbo pump) – All electrical services ATEX rated Gas bottle pack platform – Space for 4 bottle packs Compressed air services – Originate in ISIS, separate isolation valve and regulator for LH2 system Hydride bed heater-chiller – Uses a closed glycol circuit to exchange heat with hydride bed

How it works?

GAS PANEL TEST CRYOSTAT / AFC BOTTLE PLATFORM VENTILATION FANS VENT LINES PUMP ENCLOSURE CHARGING CABINET RELIEF CIRCUIT VACUUM RELIEF CIRCUIT BUFFER TANK HYDRIDE BED

Bed charging

Purging

Hydrogen fill

Hydrogen empty

Emergency vent

R&D programme 6 weeks in mid-2012 of operation with 24/7 supervision – First-time charge of hydride bed – 3 hydrogen fill/empty cycles 1 st – Hydrogen freezing due to improperly implemented heater control loop 2 nd – Fill sequence completed with interruption 3 rd – Fill sequence completed – Purge and application of argon blanket to bed Outcomes – Heater-chiller not powerful enough to reduce temperature of hydride bed quickly enough to absorb hydrogen in the event of an emergency absorber empty – 1500 litres of hydrogen lost from each cycle due to remnant pressure in the buffer tank – Bed pressure unknown due to gauge being downstream of regulator, meaning bed control is open loop