LHC Machine Advisory Committee

1. 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 LHC Machine Advisory Committee

2. Outline • Beam dumping system overview : • Principles • Layout • Safety critical aspects • Commissioning without beam : • Individual System Tests • Hardware Commissioning • Reliability Run • Commissioning with beam: • Overview of individual LHC Beam Dump System (LBDS) beam tests • Known problem areas • Ongoing work • Conclusion LHC Machine Advisory Committee

3. LHC beam dump principle (and acronyms) Dump block Dilution kickers Passive diluter Extraction septum Passive diluter Extraction kicker LHC Machine Advisory Committee

4. Underground kicker installations around P6 Dilution kicker generators, cables and magnets Extraction kicker generators, cables and magnets UD62 TD62 UP62 UJ62 UJ63 RA63 UA63 RA67 UA67 UJ67 UJ68 TD68 UD68 UP68 LHC Machine Advisory Committee

5. Also a lot of sub-system interconnectivity 2 of 15 generators shown • Example: critical triggering/retriggering • 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 LHC Machine Advisory Committee

6. Safety critical aspects of the LBDS • Signal from beam interlock system (test in Hardware Commissioning/Reliability Run) • No trigger = no beam dump • Energy tracking (test in HC/RR & with beam) • Potentially catastrophic (whole beam at “any” amplitude) • Extraction kicker retriggering (test in HC/RR) • No retriggering could put whole 7 TeV beam at ~10s • Mobile diluter TCDQ setting (test with beam) • Wrong w.r.t. orbit exposes LHC arc / triplets / collimators. • System self-tests and post-mortem (test in HC/RR & with beam) • Undetected ‘dead’ extraction kicker severely reduces reliability • Aperture, optics and orbit (test with beam) • Dump with bad orbit could damage extraction elements (septa, diluters) • Extraction-dilution kicker connection and sweep form (test in HC/RR & with beam) • Insufficient dilution could damage dump block, entrance window and screens • Abort gap ‘protection’ (test with beam) • 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) • The system is designed to operate safely with only 14 out of the 15 kickers Increasing severity Nearly all aspects need beam commissioning (validation or optimisation) LHC Machine Advisory Committee

7. Reminder – staged dilution system • Dilution kicker system MKB is staged (2/4 H, 2/6 V installed at startup) • Made for budget profile reasons, with argument that anyway intensity 50% in first 2 years • 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 Allowed dumped intensity (staged MKB) LHC Machine Advisory Committee

8. Individual System tests • Equipment groups provide tested sub-systems ready for Hardware commissioning • 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/ LHC Machine Advisory Committee

9. Individual System tests • Example: outline of Individual System Tests for extraction kickers • Details of Individual System Tests for the equipment • 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 • 4 weeks per beam for MKD, 1.5 weeks per beam for MKB • Services required • 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 • 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 • 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

10. Hardware Commissioning • Hardware Commissioning to provide commissioned LBDS system to LHC OP • Defined with HC Team and system engineers • Formal HC Test Procedures exist in draft form; still to be finalised and approved LHC Machine Advisory Committee

11. Hardware Commissioning ? • Main emphasis will be on testing the interconnections between the sub-system components and the connections to external systems • 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 Machine Advisory Committee

12. Reliability Run • System “burn-in” by AB/BT and LHC OP in final configuration from CCC. • System debugged, and reliability assumptions measured. • Discover hidden flaws • Check sub-system interdependencies • Test pulsed systems after realistic waiting times; • 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 • obvious/frequent faults are found and repaired. • ‘Statistics gathering’ phase • ‘operational’ system reliability can be estimated and compared to calculated values. • ‘Fault injection’ phase • 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 • 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 LHC Machine Advisory Committee

13. Reliability Run – what can be learnt? • Draft programme exists but detailed and coherent methodology to be elaborated • Schedule: need 3 months to make any meaningful conclusions • 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). • 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. LHC Machine Advisory Committee

14. Beam Commissioning • 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 sub-system engineers and HC team. • Formal Test Procedures for most LBDS sub-systems presently in preparation – to be finalised and approved. • 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 • Implications with collimation being addressed • e.g. Halo load on TCDQ diluter for reduced collimation scheme LHC Machine Advisory Committee

15. Entry conditions for beam commissioning defined • LHC Commissioning Procedures repository http://lhccwg.web.cern.ch/lhccwg/procedures/overview.htm LHC Machine Advisory Committee

16. LBDS beam commissioning – pilot beam • Extraction kicker waveform measurements • Importance: high (defines aperture at TCDS/MSD) • Tools: BPMD, BTVDD and BLMs. • Mode: inject & dump. • Intensity: Pilot bunch • Method: vary injected bunch bucket (6 measurement points). Calculate kick at MKD and compare to tolerance limits from MKD system measurements 89 ms LHC Machine Advisory Committee

17. LBDS beam commissioning – intensity increase • Each commissioning step (intensity increase, # bunches) needs LBDS (re)tests • 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 LHC Machine Advisory Committee

18. Known “problem” areas – TCDQ • TCDQ diluter (+ TCS collimator) protects aperture against particles in abort gap • unsynchronised dumps, extraction kicker pre-triggers, uncaptured beam • Setting-up of this diluter will be time-consuming • 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 • 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) • Can then (if needed) delay full commissioning (final orbit feedback, fine TCDQ / beam positioning, SW interlock) to b* <2 m • Will be simpler and should improve operational efficiency during stage I • Need to check optics control/knowledge, plus orbit at aperture limitations LHC Machine Advisory Committee

19. Areas where work is still ongoing • Formalisation of the various commissioning procedures • 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 • Inject-and-dump mode • Needed from first extractions, for efficient commissioning • Concept exists: details to finalise (timing, multiple injections, turn delays, HW,SW, logging) • Diagnostics • Internal and External post-operational checks – definition and prototyping phase now in progress • Configuration management • 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 • 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 • 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 • FLUKA energy deposition simulations results show TCDQ is a concern – intense study ongoing • Operation with ions - intercepting devices (diluters, dump block, entrance window) • 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 LHC Machine Advisory Committee

20. Conclusion LHC Beam Dump system commissioning : • Starts with the Individual System Tests; • Will depend heavily on careful Hardware Commissioning; • Many key elements and connections will be fully commissioned without beam; • 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; • 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; • Still a lot of work to be done LHC Machine Advisory Committee