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.

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