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Consolidation and Upgrade plans for the LHC Vacuum System

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Consolidation and Upgrade plans for the LHC Vacuum System
Ray Venessfor the Vacuum, Surfaces and Coatings GroupAt CERN
Talk Overview
LHC operation scheduleConsolidation of the vacuum systemFollowing the 2008 incidentFollowing what we have learned from LHC operationRequested by LHC experimentsUpgrade highlightsRequested by the LHC experimentsFor the LHC machineConclusionsAnd subjects for discussion…
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LHC Schedule
LHC operation schedule has changed several times over the last 2 years as we learn how things workAny interventions in the cold arcs require 6 months+ shutdownWe will require 14 months to allow magnets to go to 7TeV/beamLHC is currently working better than expected in many waysThe experiments are keen to fully exploit the ‘discovery potential’ at 3.5TeV/beamShutdown strategyAnnual shutdown for ~2 monthsLong shutdowns for 12+ months every 3 years, starting 2013Goals for the next long shutdownsConsolidation of machine and experimentsCompleting the recovery from the 2008 incident so that the LHC can operate at nominal spec.Making changes based on our experience of LHC operationAdding final machine elements needed for nominal performanceUpgrades to the machine and experimentsFor the machine, the first goal is increased luminosityThe experiments will need re-design to handle the greater event rates and associated radiation and background
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Completing the Consolidation following the 2008 Incident
The LHC was off-line for more than a year following the failure of a superconducting cable splice in 2008CERN reviewed the causes and effects of this incident and is implementing changes to avoid re-occuranceThe main actions concerning the vacuum system involveMajor consolidation of magnet splices, requiring opening of all cold interconnect zonesMitigation of potential secondary damage to the vacuum system
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Damage during 2008 Incident
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A faulty bus-bar in a magnet interconnect failed, leading to an electric arc which dissipated some 275 MJ
This burnt through beam vacuum and cryogenic lines, rapidly releasing ~2 tons of liquid helium into the vacuum enclosure
Conclusion: We need to avoid arcing to beam lines or mitigate damage to sensitive beam vacuum interconnects
Consolidation: Protect the interconnects
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All of the ~1700 beam vacuum interconnects will be fitted with shells made fromUltem(PEI) to prevent arcing and stiffen the module against buckling
Damage during 2008 Incident
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The expanding helium generates forces which lift 30 T magnets off their supports, breaking additional lines
Conclusion: We need to prevent pressure build-up in the insulation vacuum system
Consolidation: Pressure relief on Insulation Vacuum
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~1500 of these DN200 ports will be added to dipoles
120 of these DN160 self-closing ports on stand-alone magnets
~300 DN90 relief valves on the QRL
Damage during 2008 incident
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Thepressurisedhelium enters the beam vacuum, buckling bellows designed for external pressure which are then crushed as the magnets warm-up to room temperature
Conclusion: We need to prevent pressure build-up in the beam vacuum system and strengthen bellows against buckling under internal pressure
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Consolidation: Pressure Relief on Beam Vacuum
A combination of rupture disc, non-return valve and sensor will protect beam vacuum from over-pressure, whilstminimisingcontamination of the sector and permitting easy identification of vented sectors
Damage during 2008 Incident
The pressure wave pulls debris – principally metallic soot and fragments of cryogenic ‘super-insulation’ and distributes it over the whole 2.5 km of continuous cryostat
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Conclusion: We need to prevent debris propagation in the beam vacuum system
Consolidation: Fast Shutters
CERN is currently considering two options
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Modifying existing sector valves to improve their closing speed should protect from incidents in most of the cold arcs where pressure fronts travel at ~35 ms-1
Commercial or existing dedicate fast shutter systems will be needed in the warm sectors where front speeds reach ~1000 ms-1
Other Consolidation for 2013
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Addition of solenoids on critical non NEG-coated segments for electron cloud suppression
Identification and correction of warm bellows modules causing aperture and impedance problems
Consolidation & Upgrades for LHC Experiments
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Completion of critical spares for special LHC experimental vacuum chambers
Re-optimisationof supports for experimental chambers: getting the best out of the detectors
2013 Upgrades: LHC Experiments
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Results from LHC detectors has given feedback for the real positions of vacuum chambers and detectors
Experiments have taken advantage of this to request smaller diameterbeampipes, making space for extra detector layers
Future Upgrades: LHC Machine
High-Luminosity LHC (HL-LHC)Major changes to insertion magnets and vacuum system to increase luminosityNewNbSninsertion magnets, with new vacuum systemModified apertures in experimental areas, so new vacuum chambersDeliver more than 10 times higher luminosity, so more transparent chambers needed: ATLAS request 40m of beryllium…Other longer-term machine options will depend on physics outcomesLHeC: electron-proton collisions by adding a second ring or recycling LINACHE-LHC: Increasing LHC proton-proton collision energy
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Conclusions
The LHC has started-up and is operating better than expectedOperating and shutdown schedules are evolving as we learn how to operate the LHC andoptimiseit for physicsThere is a largeprogrammeof ongoing work to complete the machine and ensure reliable operationThe machine shutdown in 2013 will be extremely busy for our groupWhat we learn from LHC physics will determine the upgrade pathThere are a number of areas where we would appreciate input from the accelerator vacuum communityDamage mitigation following incidents in other labsStored energy in cryogenics and vacuumReliability and operation of fast shuttersComposite UHV chambers
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Consolidation and Upgrade plans for the LHC Vacuum System