11/4/2005OLAV 1 Workshop CERNW. Maan Fast Vacuum Valves at CERN -Introduction to fast valves -History of fast valves in use/used at CERN -LEP fast shutters -Fast valves for LHC? OLAV Workshop 11/04/2005 W. Maan

11/4/2005OLAV 1 Workshop CERNW. Maan Introduction to Fast Valves Fast Acting Valves or Fast Shutters –Safety devices to protect sensitive equipment from: pressure shocks particle or dust contamination heat load on a cold system Detecting element Fast shutter Trigger generator System to protect Fast shutter controller Type AType B Gate Valve

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: ISR ISR Fast Shutter (‘60 & ’70) –Developed by Dr. J. Delfosse –PhD “Protection des anneaux de stockage contre les irruptions d’air”

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: SPS SPS Fast Shutters early eighties: –Circular Aperture 150 mm –Spring actuation –Closing time about 25 ms –Conductance of 1 mbarl/s –Circular Aperture 250 mm –Compressed air on large piston actuation –Closing time about 50 ms –Conductance of 1 mbarl/s SPS Fast Shutters for protection of sensitive equipment like: –Kicker Magnets –Electrostatic Septa –Super Conducting Cavities Machine functionality –No major incidents –Several justified closures linked to small leaks –Adjustment of detection levels needed during machine operation.

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: LEP The first fast valve at CERN late eighties –Mechanical problems –2 valves installed around one LEP experiment –Machine functionality?

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: LEP2 LEP Fast Shutters mid-nineties. EXP Fast Shutter Super conducting cavities Ion pump Arc di/dt P di/dt P di/dt P di/dt P  Protection of the Super conducting cavities: Ultra clean vacuum Cryogenic heat loads & discharge  Functionality during last LEP runs Poor confidence in the reliability of the product Non controlled closures with important consequences

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: LEP2 Functional problems and solutions –Mechanical: Deformation of shutter blade Radiation damages on –Electro-magnetic actuator –Electro-pneumatic distributor –Electrical: Closing of shutter due to power cuts and other perturbations Low radiation resistance of part of the electronics –Solutions: Re-design of shutter blade New shutter controller Replacement of low radiation resistant parts Controller Valve box Fast shutter Radiation zone

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: AD ring Recent installed (1997) Fast Valve in the AD ring –Commercial available system –Aperture 63 mm, ~15 ms overall closing time –Equipped with five detecting elements around the different experiments in the extraction lines (20 to 35 m away from valve, each individual detecting element generates a trigger to close) –Machine functionality after 7 runs: No real incidents Many Fast Valve closures related to pollution of the detection element –To protect: AD baked UHV main ring vacuum system. Septa, Kicker magnets and other delicate equipment.

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valves: LHC? Fast Valves / Shutters for the LHC? –The goal of the fast valves will be to protect the LHC machine from the potential dangers of the LHCb- experiment. –Two independent vacuum systems, separated with 0.25 mm AlMg3 foil (supports only 10 mbar pressure difference) –2 mm thick, ~Ø650 mm, concave exit foil (beam vacuum inside, atm pressure outside)

11/4/2005OLAV 1 Workshop CERNW. Maan CERN Fast Valve : LHC? Closing scenarios LHC Fast Valves Fast Valve Closed Machine Secured Detection and Trigger Generation Start Beam Dump Beam Dump OK Valve chain broken Fast Valve Closing t0t0 t 1A t 2B t 2A t 3A t o = trigger/interlock signal arrives. t 1 = beam dump OK. t 2 = fast valve 1/2 closed. t 3 = fast valve closed, machine secured. A B t 1B Time line Scenario A only valid for LHCb if t 3A < 20 ms Scenario B only valid if: t 1B <t 2B Start Beam Dump Beam Dump OK Valve chain broken Fast Valve Closing Fast Valve Closed Machine Secured Detection and Trigger Generation t 3B

11/4/2005OLAV 1 Workshop CERNW. Maan A fast valve or shutter should never tough the LHC beam: CERN Fast Valves: LHC? –Destruction of fast valve –Quenches of magnets –Important damage to machine electronics in the tunnel –Damage to the detector of the experiment involved –Important radioactivity in this part of the machine SPS beam interaction with fast shutter plate

11/4/2005OLAV 1 Workshop CERNW. Maan Summary Fast Acting Valves/Shutters = Compromise Installing a security element to protect the vacuum system of a high energy accelerator  Installing an element with potential risks to disturb the operation of a high energy accelerator Installation of Fast Acting Valves/Shutters in the LHC is not confirmed Fast, precise and sensitive detection will result in fast closures and security to system But: – High risk of false triggers – Many unnecessary closing of fast shutters – Increase of machine down time