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Joint LHC Machine-Experiments Joint LHC Machine-Experiments Meeting on Experiment Meeting on Experiment
Protection from Beam FailuresProtection from Beam FailuresSummary and action list
D. Macina TS/LEA/INT
LEMIC 91
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Machine protection at the LHC :Machine protection at the LHC :‘organization’‘organization’
• Machine protection activities of the LHC and the SPS are coordinated by the LHC Machine Protection Working Group (MPWG), co-chaired by R. Schmidt & J. Wenninger.
• The MPWG WEB site (only from inside CERN !)http://lhc-mpwg.web.cern.ch/lhc-mpwg/
• The detailed description of the commissioning of the LHC Machine Protection System and the record the test results is the mandate of the Commissioning of the Machine Protection System Sub-Working-Group. It reports to the LHCCWG. Web site:
http://lhccwg.web.cern.ch/lhccwg/MPS/mps.htm• New :
• The MPWG has asked each LHC experiment to provide a contact person (BISU) to interface on machine protection issues between machine and experiments. Antonello Di Mauro (ALICE)Siegfried Wenig (ATLAS)Alick Macpherson (CMS)
Richard Jacobsson (LHCb)Anne-Laure Perrot (LHCf)Mario Deile (TOTEM)
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ProgramProgram
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Safe beamSafe beam
The MPWG has adopted for the LHC a limit for safe beams (nom. emittance) of
1012 protons at 450 GeV ( <~ Cu melting point)1010 protons at 7 TeV (scaled from 450 GeV) - under
discussion!!
Standard procedure: if empty machine => inject pilot bunch (5x109 p) BUT it is technically possible to inject a safe beam into an empty machine (no interlock forbids it)
If safe beams no injection protection required and, in case of circulating beam, absorbers and collimators at relaxed settings/not required. Safe beams are used for the fine tuning of the machine protection elements at each new fill.
Some interlock may/will be masked IF and ONLY IF beam is safe
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Beam cleaningBeam cleaning
The protons that are lost must be intercepted with very high efficiency before they can quench a superconducting magnet : collimation!
Unlike HERA, TEVATRON, RHIC.. the LHC cannot be operated without collimators (except at injection with low intensity).
At the LHC the collimators must define the aperture (primary + secondary) which has an important impact for MP : for most multi-turn failures the beam will hit collimators first !
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Machine Machine ApertureAperture
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450 GeV
7 TeV, * 0.5 m
Vertical axis :Machine aperture in units of beam sigma (), including alignment errors and other tolerances.
Horizontal axis :Longitudinal position on left side of ATLAS (seen from the ring center).Arc
ATLAS
Injection :•Aperture limit is the LHC ARCs (~ 7-8 ).•The triplet magnets in front of ATLAS/CMS are slightly behind the ARC (~ 8-9 ).
Collimators @ ~5-6 !
Collisions, squeeze to * 0.5 m :•Aperture limit is defined by the triplet magnets in front of ATLAS/CMS (~ 8 )..
Collimators @ ~6 !Triplet
Experiments-Machine WS / June 07
End of the squeeze (* < 6 m) bottleneck in the triplets => TCT needs to be closed
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Additional general itemsAdditional general items
Software interlock– The reaction time of this system will be at the level of a few seconds.– The systems rely entirely on the machine technical network,
databases, etc – clearly not as safe as HW systems !– The Injection SIS will complement the Injection Interlock
Systems:• - Active from the beginning.• - Stops injection through the Injection Interlock Systems.• -Receives the experiments injection inhibits, either through our
middleware (preferred) or through DIP.
Post Mortem Analysis– All machine user systems connected to the LHC BIS must provide Post-
Mortem information for diagnostics, even systems that have NOT triggered the dump.
• To resume beam operation after a beam dump, the PM data must be analysed and ‘understood’
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Injection - ExtractionInjection - Extraction Same principle for injection and
extraction: – “kicker” magnets: fast rise time
→ much less than one turn, large (~ mrad) angles
– septa: two(/more) apertures with different magnetic fields
Injection: – Beam 1: IR 2– Beam 2: IR 8
Extraction:– Both beams in IR 6
Injection process and extraction process can lead to single turn beam loss!! =>
– Everything” required for injection/(extraction) plus the LHC ring must have the right value/state
– Dedicated passive protection
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MSI
Q5 Q4 D2MKITransfer line
IP2
Injection overviewInjection overview The injection septum MSI bends the beam into the LHC in the horizontal
plane The injection kicker MKI kicks the beam in the vertical plane onto the LHC
orbit
Possible injection failures: – Wrong current setting in the transfer line magnets + injection septum, fast trip
of power supply, failure of SPS extraction kicker (MKE) during extraction, fast trip of power supply – e.g. downstream of transfer line collimators (protection: current surveillance, fast current monitors, absorbers)
– Injection kicker failures in the LHC => caught by DEDICATED MOVEABLE ABSORBER TDI behind kicker and auxiliary
movable collimators TCLI in the injection regions
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Error settings at injectionError settings at injection Error settings at injection (empty machine) of D1/D2 and
orbit correctors in the LSS may drive in beam in the experimental areas. It affects all experimental insertions.
Not possible to hit directly the detectors if only one failure considered (at least in IR1/IR5)
Ex. MCBXH wrong settings (30-100%) nominal at injection is 5%Ex. MCBXH wrong settings (30-100%) nominal at injection is 5%
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LHC Extraction (IR6)LHC Extraction (IR6)
Q5R
Q4R
Q4L
Q5L
Beam 2
Beam 1
Beam Dump Block
Septum magnet deflecting the extracted beamMSD H-V kicker
for painting the beam
about 700 m
about 500 m
15 kicker magnetsMKD
Clean dump•Synchronisation: the kicker rise time must coincide with the particle free abort gap•Particle free abort gap•Energy Tracking – (required kick strength from the beam energy via magnet currents)
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Possible failures at Possible failures at extractionextraction
Lost synchronisation with the abort gap Pre-fire of one of the 15 kicker modules (hard-wired
system triggers all remaining 14 in 0.7-1.3 µs ) Frequency: once per year possible Solution: dedicated passive protection;
– TCDQ (movable) and TCS protect Q4 and general LHC apertures
– TCDS protects the MSD septa In case of problems during extraction coupled with
TCDQ settings, orbit or optics errors, “some” beam loss at the tertiary collimators/triplets in IR5 may occur.
Difficult to quantify - detailed analysis ongoing. PhD thesis of Thomas Kramer, AB/BT.
If abort gap (re-)population => caught by TCDQ and interlocking on abort gap monitor signal
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Possible failures with circulating Possible failures with circulating beambeam
(magnet failures including operation mistakes)(magnet failures including operation mistakes)
Usually slow and detected first in the aperture restrictions of the machine (cleaning insertions)
Potential danger for the experiments (VELO and RP): uncontrolled closed bumps since they could affect only experimental areas. However:– Extremely difficult to create at 7 TeV (less difficult
at 450 GeV)– They build up slowly: first losses seen by the BLMs
and beam extraction before damage threshold– Only critical if combined with a fast failure => low
probability
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Summary of machine Summary of machine failuresfailures
Errors/failures which may drive the beam into the experimental areas;– Settings errors at injection– Undetected closed bump & fast magnet failures
(highly unprobable) Errors/failures which may drive the beam in
the aperture restrictions in the LSS:– Injection errors (IR2, IR8)– Asynchronous beam dump (IR5)
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Experiments (1)Experiments (1) ATLAS
– BCM+ LUCID used for beam abort– Injection errors: ok for pilot bunch, concern for Safe
Beam. What is the structure of Safe Beam?– Questions: mechanism for beam blow up at the IP? How
loss of vacuum close to IP is treated? ALICE
– BCM used for beam dump (same system developed by LHCb). Position dictated by available space. Needs failures/error simulations to show the position is valid for the most relevant scenarios
– Consequences of injection errors: old analysis. Still valid?– During injection: only BCM ON and possibly a few
detectors at safe setting to monitor the losses in the experimental areas
– Concern about Safe Beam
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Experiments (2)Experiments (2) CMS
– BCM with standard LHC BLM Readout and Interface
– Worry particularly about high rates of loss rather than integrated doses
– Needed updated simulation (most realistic worst case scenario) for asynchronous beam dump and injection
– IF BCM OFF (no protection system) => no beam allowed in the machine
– IF CMS OFF but BCM ON => beam allowed– BCM and CIBU on machine power (no local UPS)– Concern about Safe Beam
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Experiments (3)Experiments (3) LHCb
– BCM for beam dump. Readout front end same as BLMs
– Entire BCM system under UPS– Concern On Safe Beam– Needs simulation for beam failures
LHCf– Beam dump based on the detector itself. All
scintillators hit => beam dump– The experiment will run only for a few days per
year: disconnected from the BIC when not in the TAN
– The whole system is on ATLAS UPS– Scintillators always ON at injection
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Experiments (4)Experiments (4)
TOTEM– T1 and T2 should be protected by the CMS
system– RP: simulation for bunch hitting the pot:
• For β*=1540 m only ok for bunch <= 6x1010 p• For β*=90-0.5 m beam wider, depends on number of
bunches
– TOTEM CIBU only used for the positioning of the RP. The other CIBU forced TRUE, may be used later
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Open issues and action list Open issues and action list (1)(1)
Safe Beam– This is a concern for all experiments. If not absolutely
needed, experiments ask to lower to 1.1-1.5x1011 p. Is this OK or just a feeling? Can be simulated/calculated?
– Action: MPWG Post Mortem Data
– Data from the experiments for all dumps– Experiments need PM Data from the Machine?– Details to be discussed– Action: AB/CO+ AB/OP + LEADE
Safe Beam Flag to the experiments– Technically all experiments can receive it via the GMT
receiver– Only LHCb has requested it– Action: BISU
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Open issues and action list Open issues and action list (2)(2)
Injection inhibit– By SW: decide on protocol– New idea for HW with fiber-CIBU– Action: MPWG + AB/CO + LEADE
CIBU (and Protection System) Power– On UPS on two different power sources– Survive a power cut for 10 minutes– CMS philosophy: BCM must be ON whenever the
machine is ON => machine power and not CMS power
– Apply to all experiments?– Action: MPWG + LEADE + BISU
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Open issues and action list Open issues and action list (3)(3)
CMS Philosophy– No beam allowed if CMS protection system is OFF– Beam allowed if CMS not operational– Adopted by all experiments?– What is the reliability of the experiment’s
protection system? Is it there a backup solution? How many unjustified dump per
experiments?– Aim for 1/year/exp?
Procedure after emergency beam dump– CMS request to latch their input until PM check is
done. Check re-arm time scale
Action?
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Open issues and action list Open issues and action list (4)(4)
How to detect direct hit in experimental area at injection if detector off?– Possible with BCM even if may be not always
sufficient– A few additional detectors ON at safe settings?– Action: BISU
TCTs for 2008– Missing Vertical TCT in IR2 and IR8. Is this a problem
for small *?– Action: MPWG + Collimation WG
Bump scenarios and wrong settings at injection– Software Interlock surveillance of D1/D2/correctors
in the experimental insertions at injection & collision– Action: SIS + MPWG
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Open issues and action list Open issues and action list (5)(5)
Abort gap monitor– Status + connection to BIC– Action: MPWG + AB/BI
Simulations– Asynchronous beam dump (including RP) => AB/BT– Consequences of the failure scenarios at injection
=> (AB/BT? TS/LEA? BISU?)– Error settings at injection (in particular IR2/IR8) => (TS/LEA?)- Additional failure scenarios when circulating beam
(beam steering) => (AB/ABP?, AB/CO/MI??)- RP: simulations including mechanical stresses =>
(TS/LEA-MME?)
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To be done in addition…To be done in addition…
Get more information and check consistency of the radiation damage threshold for similar detectors in different experiments
Better define the injection inhibit philosophy
Define/organize the test procedures Define/organize the commissioning
procedures together with the Commissioning of the Machine Protection System Sub-Working-Group
