Hydrogen Control System MJD Courthold TW Bradshaw Y Ivanyushenkov D Baynham

Introduction Control System Overview of control system Prototype flow diagrams & control sequences Pumps and Instrumentation Implementation and hardware

Overview of control system The control system will be based on Labview for the R&D tests. Once the algorithms have been developed they will be incorporated into EPICS (Experimental Physics and Industrial Control System), which is the control system that has been chosen for the MICE experiment. Fortunately Labview possesses “Channel Access” capability, used by all EPICS clients, which will ease the subsequent transition to EPICS. The control system naturally divides into two components: –Hydrogen Absorber Cryostat system –Hydrogen Delivery system

Overview of control system Hydrogen Absorber Cryostat system –The cryostat vacuum will be maintained by means of a turbo-molecular pump and backing-line pump. –Both pumps will be fitted with purging lines, through which Helium gas will be introduced if a partial vacuum failure occurs, or Hydrogen is detected in the pump exhaust line, to dilute any Hydrogen that may have leaked into the pumping system. Hydrogen Delivery system –Normal control of the Hydrogen Delivery system can be sub-divided as follows: Purging the delivery system with Helium; Filling the Hydrogen Absorber with liquid Hydrogen from the Hydride Bed; Controlling the liguid Hydrogen level in the Absorber; Emptying the Hydrogen Absorber and returning the Hydrogen back to the Hydride Bed. –Additionally it will be necessary to charge the Hydride Bed with Hydrogen at the outset, and following any maintenance on the Hydride Bed.

Overview of control system Safety aspects –Throughout operations Hydrogen detectors in the extractor hood, venting line, and exhaust line from the pumps will be monitored. In the event of any Hydrogen being detected, operation of the Hydrogen Delivery system will be terminated, and an attempt will be made to return the Hydrogen to the Hydride Bed. –If the pressure in the system exceeds the design pressure, relief valves and bursting disks will protect the system. In addition, a flow of Helium gas will be maintained through the venting line, thus ensuring that any Hydrogen that gets vented by the relief valves, bursting disks, or the various venting valves will be diluted before being expelled via the extractor hood.

Flow diagrams & control sequences Prototype flow diagrams & control sequences

Helium Purge Sequence VP1 On Close PV1,14,17,18,1 9 Open PV2,3,5,7 Open CV4 100% Close PV19 Open PV18 Open CV4 5% to control flow VG5<1mbar H2 System Purged Purge Sequence No Open PV19 Yes 1bar<PG1<1.3bar AND 1bar<PG2<1.3bar Close PV19 Open PV18 Open CV4 5% to control flow VG5<1mbar No Close PV18, Open PV19, Open CV4 100% Yes 1bar<PG1<1.3bar AND 1bar<PG2<1.3bar Close PV19 Open PV18 Open CV4 5% to control flow VG5<1mbar No Close PV18, Open PV19, Open CV4 100% Yes 1bar<PG1<1.1bar AND 1bar<PG2<1.1bar Yes No Close PV18

Control logic – Fill Sequence Chiller on Set TS1_sp = TS1_initial PV2,3,5,7,14,17,18,19 closed CV4 closed PV1 open VP2 on, PV20 open Cooling System on Set TS2_sp = 15K Start Pressure Control Loop Start Vac Monitor Open PV2,3 Open CV4 TS1<TS1_sp And VG3<1mbar PG1  PG1_sp Close PV2&3 and CV4 Stop Pressure Control Loop Set TS1_sp = TS1_low Open PV5 LS1 > LS1_sp H2 System Ready Increment/Decrement TS1 Empty Sequence VG3<1mbar Vac monitor Pressure Control Yes No Yes NoYes No Fill Sequence

Empty Sequence Open PV7 Close PV2,3,4 Set TS1_sp = TS1_low Set TS2_sp = 20K (to achieve PG2 ~1bar) Set cryocooler to 30K Start Absorber Heater Control Loop (adjust to obtain sensible flow rate) LS1<LS1_low Empty Sequence Yes No Close PV1 PG2<0.1bar AND TS3>100K H2 System Empty Yes No 1bar<PG2<1.3bar Increment/Decrement TS3 Absorber Heater Control Yes No Stop cryocooler Stop Absorber Heater Control Loop TS3>30K Yes No

Pumps and Instrumentation General pump considerations There will be two sets of pumps for the MICE RandD system, one for maintaining the Hydrogen Absorber Cryostat vacuum, and the other for use when purging the Hydrogen Delivery system. Both sets of pumps will be located outside the building, but protected from the weather. The chosen location is close to the ISIS Control Room. However, pumping noise is expected to be no more than ~57db. In addition, the connection to the Absorber Cryostat is expected to be 100mm diameter, with approx’ 15m of pipework between the cryostat and the turbo-molecular pump outside the building. Pirani gauges must not be used in the presence of Hydrogen, so a combination of Penning and capacitance gauges will be utilised. There are no Hydrogen detectors available for use in vacuum systems, so it will be necessary to locate all Hydrogen detectors in the pump exhausts, venting/purging lines, and system hood. Note that the final system will comprise three sets of Hydrogen Absorber Cryostats, each with a turbo-molecular pumping system, but only one pump will be required for the three Hydrogen Delivery systems.

Pumps and Instrumentation Pumping System for the Hydrogen Absorber Cryostat Given the pump location and pipework, a Turbovac 151C turbo-molecular pump, rated at 150 l/sec, has been selected for the Absorber Cryostat, which should achieve a pumping speed of ~8 l/sec, thus taking several hours to pump down the cryostat to 1x10-5 bar. This is regarded as acceptable. Note: The pumping speed will be determined mostly by the pipework, with larger pumps having negligible effect on the pumping speed. A Trivac BCS backing pump, rated at ~16 m3/hr, has also been selected, to ensure a backing-line pressure of < 1x10-1 bar can be maintained. With the potential presence of Hydrogen, the backing pump will need to be purged. Synthetic oil will also be used in the backing pump instead of mineral oil for increased safety. A combination of Penning and capacitance gauges will be required for this pumping system.

Pumps and Instrumentation Pumping System for the Hydrogen Absorber Cryostat (cntd) To avoid the need for an expensive explosion-proof pumping system for the Absorber Cryostat, the turbo-molecular pump and its protection systems will operate as follows: –During normal operation the pumps will be operated with their purging lines closed. –If a minor Hydrogen leak is detected and/or the pressure in either pump exceeds 5x10-3 mbar, both the turbo-molecular and backing pumps will continue operating, but with Helium gas introduced via their purging lines to dilute any Hydrogen present. –If the pressure in the cryostat pumping line rises above 5x10-2 mbar, which could be the result of a major Hydrogen leak, the gate-valve to the pumping system will close, thus avoiding any risk of explosion. –Further rises in pressure in the cryostat pumping line will then be handled by the associated relief valve and bursting disk. Notes: The Trivac BCS backing pump can be run at atmospheric pressure if necessary (with the turbo-pump off). By default the backing pump does not have any fault indications. However, the turbo- pump has both fault indications and associated relays. The turbo-pump can be water or air-cooled, but water-cooling is more convenient. Pirani gauges must not be used where Hydrogen might be present.

Pumps and Instrumentation Pumping System for the Hydrogen Delivery system A pumping system is only required for the Hydrogen Delivery system during the purging sequences, and only needs to be able to achieve a vacuum of 1 mbar. The following pumping system is thus envisaged for the Hydrogen Delivery system: –Trivac D40B rotary pump. –A capacitance gauge will be sufficient for this pumping system.

Implementation and hardware