LHC Machine Advisory Committee
Commissioning the Beam Dumping System
Brennan Goddard AB/BT
Input from
E.Carlier, L.Ducimetière, M.Gyr, L.Jensen, J.Uythoven, V.Mertens,
R.Assmann, V.Kain, R.Schmidt, M.Lamont , W.Weterings
+ many others
http://proj-lbds.web.cern.ch/proj-lbds/
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Outline
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Beam dumping system overview :
– Principles
– Layout
– Safety critical aspects
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Commissioning without beam :
– Individual System Tests
– Hardware Commissioning
– Reliability Run
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Commissioning with beam:
– Overview of individual LHC Beam Dump System (LBDS) beam tests
– Known problem areas
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Ongoing work
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Conclusion
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LHC beam dump principle (and acronyms)
Dump block
Dilution kickers
Passive diluter
Extraction septum
Passive diluter
Extraction kicker
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Underground kicker installations around P6
UD62
UP62
TD62
Dilution kicker generators,
cables and magnets
UJ62
UJ63
RA63
UA63
RA67
UA67
UJ67
UJ68
TD68
UD68
Extraction kicker generators,
cables and magnets
16 June 2006
UP68
LHC Machine Advisory Committee
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Also a lot of sub-system interconnectivity
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Example: critical triggering/retriggering
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Synchronised to abort gap (internal PLL locks to rev. freq.)
Parallel path with 1 turn delay by-passes synchronisation system
Retriggering system detects any trigger and re-distributes
Large amount of redundancy with crossed trigger lines – all needs commissioning
IR6 BLM
2 of 15 generators shown
User Permits (interlocks) from BIS clients
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Safety critical aspects of the LBDS
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Signal from beam interlock system (test in Hardware Commissioning/Reliability Run)
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Energy tracking (test in HC/RR & with beam)
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Increasing severity
Insufficient dilution could damage dump block, entrance window and screens
Abort gap ‘protection’ (test with beam)
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Dump with bad orbit could damage extraction elements (septa, diluters)
Extraction-dilution kicker connection and sweep form (test in HC/RR & with beam)
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Undetected ‘dead’ extraction kicker severely reduces reliability
Aperture, optics and orbit (test with beam)
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Wrong w.r.t. orbit exposes LHC arc / triplets / collimators.
System self-tests and post-mortem (test in HC/RR & with beam)
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No retriggering could put whole 7 TeV beam at ~10s
Mobile diluter TCDQ setting (test with beam)
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Potentially catastrophic (whole beam at “any” amplitude)
Extraction kicker retriggering (test in HC/RR)
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No trigger = no beam dump
Beam in the abort gaps risks quench, or aperture damage if TCDQ wrongly positioned
Fault tolerance with 14/15 extraction kickers (test in HC/RR & with beam)
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The system is designed to operate safely with only 14 out of the 15 kickers
Nearly all aspects need beam commissioning (validation or optimisation)
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Reminder – staged dilution system
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Dilution kicker system MKB is staged (2/4 H, 2/6 V installed at startup)
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Made for budget profile reasons, with argument that anyway intensity 50% in first 2 years
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Limit on single bunch intensity (not possible to fill 50% of the ring with full intensity bunches…)
Can dump full beam intensity up to ~2 TeV…but safer to limit the intensity at injection
Remaining MKBs installed in 08/09 shutdown (conditional on actual installation/commissioning)
Nominal beam, full dilution
50% nominal beam, staged MKB
I/Inom
Allowed dumped intensity (staged MKB)
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
0
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1000
2000
3000
4000
5000
6000
7000
p [GeV/c]
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Individual System tests
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Equipment groups provide tested sub-systems ready for Hardware commissioning
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Entry/exit condition, procedures & requirements defined with sub-system engineers and HC team
Formal Test Procedures for most LBDS sub-systems presently in preparation
http://proj-lbds.web.cern.ch/proj-lbds/
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Individual System tests
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Example: outline of Individual System Tests for extraction kickers
– Details of Individual System Tests for the equipment
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Pulse the system and check all signals at 450 GeV equivalent voltage;
Measurement of the pulse form (magnet current);
Set up system timing without beam (adjustment of trigger voltage);
Commission Internal diagnostics and post-operational check;
Ramp the system and check all signals up to 7 TeV equivalent voltage;
Set up kick strengths (adjust settings for different beam energies),
Stability and reproducibility measurements at 7 TeV equivalent voltage
– Estimated duration
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4 weeks per beam for MKD, 1.5 weeks per beam for MKB
– Services required
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Electrical distribution system;
Fire detection system;
UPS system;
Ethernet network infrastructure;
Distribution of the LHC timing;
Vacuum (ceramic chambers, interconnects, sector valves, pumps, gauges, bake-out)
– Special safety or access conditions
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•
No access limitations during the HV conditioning and tests (systems designed such that contact with HV is
not possible: All HV components contained in grounded metallic containers or racks, disconnection or
opening not possible without special tools);
Yellow flashers and Emergency Stops in RA and UAs next to equipment
– Impact on transport or other activities in the zone
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16 June 2006
In principle No: however, basic considerations to enhance personnel safety may lead to implementation of
transport restrictions during IST, or other additional safety measures.
LHC Machine Advisory Committee
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Hardware Commissioning
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Hardware Commissioning to provide commissioned LBDS system to LHC OP
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Defined with HC Team and system engineers
Formal HC Test Procedures exist in draft form; still to be finalised and approved
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Hardware Commissioning
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Main emphasis will be on testing the interconnections between the sub-system
components and the connections to external systems
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Critical link to beam permit loop
Signals from other systems (RF, PO)
Control and data exchange
Direct triggers (access, local BLM)
Links to Safe LHC parameters and Injection kickers
Internal and External Post-Mortem processes
LHC control system
Ethernet
BPM IR6
TCDQ
position
DCCTs
Access
Fast timing
(RF synch)
BLM6
Abort gap
monitor ?
IR6 orbit
feedback
Direct triggers
(to TSU)
LBDS
Slow
timing
Emergency
stop status
IR6 PM
trigger
Mains &
UPS status
External
outputs
External
inputs
Software
interlock
SLP
Injection
BIC
interface
Machine
Protection
interfaces
LHC beam permit loop
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Reliability Run
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System “burn-in” by AB/BT and LHC OP in final configuration from CCC.
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Test pulsed systems after realistic waiting times;
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test (where feasible) functioning of error/fault detectors, fault tolerance and surveillance
After each dump action perform full Internal and External post-operational
checks on pulse generators and power converters
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‘operational’ system reliability can be estimated and compared to calculated values.
‘Fault injection’ phase
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obvious/frequent faults are found and repaired.
‘Statistics gathering’ phase
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Generate statistics to give upper bounds on failure rates
Validate reliability calculations;
Bathtub reliability curve: if problems found, take time to repair and check statistics again
‘Debugging’ phase
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System debugged, and reliability assumptions measured.
Discover hidden flaws
Check sub-system interdependencies
Check all currents and voltages in tolerance, relative to look-up tables.
Look for trends and correlations in measured signals
Determine if any parameter is outside margin
Impact of final LHC HC scenario and planning needs to be evaluated
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Reliability Run – what can be learnt?
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Draft programme exists but detailed and coherent methodology to be elaborated
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Schedule: need 3 months to make any meaningful conclusions
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Needs system operating with connections to external components
Much shorter period will not allow quantification of reliability assumptions
Estimate MKD failure rate upper bound for test duration T, to try to demonstrate
the design hypothesis: (failure rate per MKD branch ≤10-4/h).
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Expect ~4 failures in 3 months for assumed 10-4 /h rate.
A type I censored reliability testing with fixed duration T and pulsing frequency f is performed.
The sampling distribution is Binomial.
The curves in the figure are the one-sided 95% failure rate confidence intervals for 75%
effective running time, f =1/h, T = 1,2,3 and 4 months and number of failures from 0 to 30.
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Beam Commissioning
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AB/BT and LHC OP to provide dump system ready for each new
operational phase
– LBDS will be “commissioned” for a defined operational parameter space.
– Entry/exit condition, procedures & requirements fairly well defined with subsystem engineers and HC team.
– Formal Test Procedures for most LBDS sub-systems presently in preparation –
to be finalised and approved.
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Methods, requirements and steps already analysed in detail for LHC
phase I (up to 156 bunches)
– Still to be fitted in to overall machine protection and beam commissioning plan
– Procedures and steps now being formalised with LHC OP – substantial work
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Implications with collimation being addressed
– e.g. Halo load on TCDQ diluter for reduced collimation scheme
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Entry conditions for beam commissioning defined
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LHC Commissioning Procedures repository
http://lhccwg.web.cern.ch/lhccwg/procedures/overview.htm
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LBDS beam commissioning – pilot beam
LBDS beam commissioning activity
LHC mode
With initial 450 GeV/c circulating beam
IR6 optics measurements
Commission dedicated LBDS BDI in IR6
Beam type
Energy GeV
Extraction
kicker
waveform
Injection
Circulating
1 pilot measurements
450
Extraction element aperture measurements
Commission SW interlock on beam position at TCDQ
Commission IR6 orbit BPM interlock
Commission abort gap watchdog
TCDQ “injection setting” positioning
Orbit feedback / stability checks at TCDQ
-
Importance: high (defines aperture at TCDS/MSD)
Injection
Circulating 1 pilot
450
Tools: BPMD, BTVDD and BLMs.
Injection
Circulating 1 pilot
450
Mode: inject & dump.
Injection
safe beam
450
Intensity: Pilot Circulating,
bunch
Method: vary injected
bunch
bucket
Injection
Circulating,
safe
beam (6 measurement
450
points). Calculate kick at MKD and compare to
Injection
beam
450
tolerance limits Circulating,
from MKD safe
system
measurements
Injection
Circulating, safe beam
450
Injection
Circulating, safe beam
450
With 450 GeV/c extracted beam
First extractions: rough timing adjustment
TD line BDI commissioning
Extraction trajectory and aperture measurements
Inject & dump
Inject & dump
Inject & dump
Check of aperture and trajectory with 14/15 MKD
450
450
450
Inject & dump
Extract 1 pilot
Extract 1 pilot
Extract 1 pilot
ms
Extract89
1 pilot
Data diagnostics: IPOC, logging, FDs, PM
Inject & dump
Extract 1 pilot
450
Verification of post-operational checks (IPOC, XPOC)
MKD waveform overshoot measurements
MKB sweep measurements
Fine timing and amplitude adjustment
Inject & dump
Inject & dump
Inject & dump
Inject & dump
Extract 1 pilot
Extract 1 pilot
Extract 1 pilot
Extract 2 pilots
450
450
450
450
Through the energy ramp 450 – 7000 GeV/c
Energy tracking measurements
TCDQ position function through ramp
Fine timing and amplitude in ramp
Ramp
Ramp
Ramp
Extract 1 pilot
Circulating, safe beam
Extract 2 pilots
450-7000
450-7000
450-7000
At 7000 GeV/c
TCDQ positioning function through squeeze
Adjust/squeeze
Circulating, safe beam
7000
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LHC Machine Advisory Committee
450
16/20
LBDS beam commissioning – intensity increase
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Each commissioning step (intensity increase, # bunches) needs LBDS (re)tests
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Must be completed before operation with the new beam conditions can be allowed
Method to enforce this ‘allowed’ LHC operational configuration still to be finalised
LBDS beam commissioning activity
LHC mode
Beam type
Energy GeV
With 450 GeV/c circulating beam
Orbit feedback / stability checks at TCDQ
Checks of EMC on BI and control signals
Test response of abort gap monitor
Check abort gap cleaning
Injection
Injection
Injection
Injection
Circulating
Circulating
Circulating
Circulating
450
450
450
450
With 450 GeV/c extracted beam
Extraction trajectory checks
Inject & dump
Extract
450
TD line beam instrumentation checks
Data diagnostics: check XPOC response
Define new references for correctly executed beam dump
TDE thermal response
Beam loss profiles (extraction, TD lines and TDE)
Inject & dump
Inject & dump
Inject & dump
Inject & dump
Inject & dump
Extract
Extract
Extract
Extract
Extract
450
450
450
450
450
Through the energy ramp
Energy tracking and abort gap timing checks
Ramp
Extract during ramp
450-7000
At 7 TeV
Checks of EMC on BI and control signals
Test response of abort gap monitor
Check abort gap cleaning
Data diagnostics: check XPOC response
Define new references for correctly executed beam dump
TCDQ positioning at 7 TeV
Adjust/squeeze
Adjust/squeeze
Adjust/squeeze
Adjust/squeeze
Adjust/squeeze
Adjust/squeeze
Circulating
Circulating
Circulating
Extract
Extract
Circulating
7000
7000
7000
7000
7000
7000
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Known “problem” areas – TCDQ
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TCDQ diluter (+ TCS collimator) protects aperture against particles in abort gap
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Setting-up of this diluter will be time-consuming
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unsynchronised dumps, extraction kicker pre-triggers, uncaptured beam
Interdependency on collimation settings, and on orbit feedback
Iterations (changes of orbit, b-beat, b*) to finalise TCDQ reference/interlock function
Can by-pass some setting-up stages for early operation
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450 GeV - set TCDQ/TCS system up at ±10 s
• Rely on ±4 mm interlock to protect arc (maximum excursion at TCDQ is ≈2 s )
• Asynch dump with 156b, max. 1 bunch in interval 7-12 s  Safe for 450 GeV
7 TeV - pilot near to damage level - set TCDQ/TCS at ±10 s
• Rely on 2-jawed TCS to protect the TCTs – don’t worry about the orbit
• Keep TCTs at ≈20 s  protected for any orbit in IR6 (limits b* to 2 m)
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Can then (if needed) delay full commissioning (final orbit feedback, fine TCDQ /
beam positioning, SW interlock) to b* <2 m
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Will be simpler and should improve operational efficiency during stage I
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16 June 2006
Need to check optics control/knowledge, plus orbit at aperture limitations
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Areas where work is still ongoing
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Formalisation of the various commissioning procedures
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Inject-and-dump mode
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Details still to be worked out (limits, how to operate damper for cleaning, losses)
Halo at TCDQ - effect of “minimum collimation” strategy on energy deposition in Q4
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Operational states and allowed LHC beam conditions still to be defined in adequate detail
Wider issue of OP software for machine protection (MCS, SIS, sequencer, …) outstanding
Abort gap monitoring and cleaning
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Measurement, test and commissioning results to be maintained, plus operational data and settings
Management of critical settings (MCS) – reference management needs subset of MCS presently in definition
Ensuring that only ‘authorised’ beam can be used
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Internal and External post-operational checks – definition and prototyping phase now in progress
Configuration management
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Needed from first extractions, for efficient commissioning
Concept exists: details to finalise (timing, multiple injections, turn delays, HW,SW, logging)
Diagnostics
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Individual system tests – outline drafted –Test Procedures to be made and approved
Hardware Commissioning – draft Test Procedure to be updated and approved
Reliability Run – Test Procedure to be written
Beam Commissioning – details exist – being incorporated in LHC OP commissioning procedures
FLUKA energy deposition simulations results show TCDQ is a concern – intense study ongoing
Operation with ions - intercepting devices (diluters, dump block, entrance window)
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Checks of effects of BI response and optics/orbit control – FLUKA work now being defined
Wide-ranging and heavy workload for LBDS project – low in dedicated resources in AB/BT and rely
heavily on various collaborators
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Conclusion
LHC Beam Dump system commissioning :
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Starts with the Individual System Tests;
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Will depend heavily on careful Hardware Commissioning;
– Many key elements and connections will be fully commissioned without beam;
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Requires a Reliability Run to guarantee safety of the system;
– Validation of subsystem interconnectivity and reliability assumptions;
– Debugging and fault finding in initial ‘simulated’ operational period;
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Requires careful tests and checks with beam;
– A lot can be done with pilot beam;
• At 450 GeV before extraction, to check the optics and aperture;
• At 450 GeV in “Inject & Dump” mode, to check system functionality;
• During the ramp, to check the energy tracking and timing;
– Requires specific checks when LHC beam conditions change;
• To verify instrument response, diagnostics and losses;
– Can be somewhat relaxed for difficult TCDQ/TCS positioning in early stages;
• Take advantage of limited b* squeeze and limited number of bunches;
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Still a lot of work to be done
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