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11/4/2005 OLAV 1 Workshop CERN W. 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
11/4/2005 OLAV 1 Workshop CERN W. 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
Triggergenerator
System to protect
Fast shuttercontroller
Type A Type B
Gate Valve
11/4/2005 OLAV 1 Workshop CERN W. 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”
11/4/2005 OLAV 1 Workshop CERN W. 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.
11/4/2005 OLAV 1 Workshop CERN W. Maan
CERN Fast Valves: LEP
The first fast valve at CERN late eighties– Mechanical problems– 2 valves installed around one LEP experiment– Machine functionality?
11/4/2005 OLAV 1 Workshop CERN W. Maan
CERN Fast Valves: LEP2
LEP Fast Shutters mid-nineties.
EXP
Fast ShutterSuper conducting cavities Ion pump
Arc 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
11/4/2005 OLAV 1 Workshop CERN W. 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
ControllerValve box
Fast shutter
Radiation zone
11/4/2005 OLAV 1 Workshop CERN W. 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.
11/4/2005 OLAV 1 Workshop CERN W. 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)
11/4/2005 OLAV 1 Workshop CERN W. Maan
CERN Fast Valve : LHC?
Closing scenarios LHC Fast Valves
Fast ValveClosed
MachineSecured
Detectionand
Trigger Generation
StartBeamDump
BeamDump
OKValvechain
broken
Fast ValveClosing
t0
t1A
t2B
t2A t3A
to= trigger/interlock signal arrives.t1= beam dump OK.t2= fast valve 1/2 closed.t3= fast valve closed, machine secured.
A
B
t1BTime line
Scenario A only valid for LHCb if t3A < 20 msScenario B only valid if: t1B<t2B
StartBeamDump
BeamDump
OK
Valvechain
broken
Fast ValveClosing
Fast ValveClosed
MachineSecured
Detectionand
Trigger Generation
t3B
11/4/2005 OLAV 1 Workshop CERN W. 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
11/4/2005 OLAV 1 Workshop CERN W. 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 systemBut:
– High risk of false triggers– Many unnecessary closing of fast shutters– Increase of machine down time