LHC Technical Committee, 14/03/2007 LHC Commissioning Phases Circulating pilot and RF capture presented by G. Arduini for the LHCCWG members Many thanks

LHC Technical Committee, 14/03/2007

LHC Commissioning Phases

Circulating pilot and RF capture

presented by G. Arduini

for the LHCCWG members

Many thanks to the EICs & V. Kain, R. Bailey, P. Baudrenghien, L. Bottura, O. Brüning, A. Butterworth, S. Fartoukh, R. Jones, E. Shaposhnikova, J. Uythoven, J.

Wenninger, F. Zimmermann….


LHC Commissioning Phases: Phase 2 – Circulating pilot and RF capture

• Phase A.2: Circulating pilot and RF capture– Entry and exit conditions– Objectives– Preconditions and tools

• Equipment state/readiness (exit from machine checkout)• Controls, software and tools

– Machine setup• Beams, cycles and modes • Basic settings

– Commissioning procedure• Breakdown• Details of some steps• Possible problems

– Outstanding issues

• Summary


LHC Stage A: Commissioning phases

Phase DescriptionA.1 Injection and first turn: injection commissioning; threading, commissioning beam instrumentation.A.2 Circulating pilot: establish circulating beam, closed orbit, tunes, RF capture A.3 450 GeV initial commissioning: initial commissioning of beam instrumentation, beam dump A.4 450 GeV optics: beta beating, dispersion, coupling, non-linear field quality, apertureA.5 Increasing intensity: prepare the LHC for unsafe beamA.6 Two beam operation - colliding beams at 450 GeV A.7 Snap-back and ramp: single beam A.8 Bringing beams into collision: adjustment and luminosity measurementA.9 7 TeV optics: beta beating, dispersion, coupling, non-linear field quality, apertureA.10 Squeeze: commissioning the betatron squeeze in all IP's A.11 Physics runs: physics with partially squeezed beams, no crossing in IP1 and IP5

Phase Beam time [days] BeamA.1 Injection and first turn 4 1 x pilotA.2 Circulating beam 3 1 x pilotA.3 450 GeV: initial 3 1 x pilot++A.4 450 GeV: optics 4 1 x pilot++A.6a 2 beam operation 1 2 x pilot++A.6b Collisions 1 2 x pilot++

16

Phases for full commissioning Stage A (pilot physics run)

Phases for proposed 2007 engineering run


Circulating pilot and RF capture – exit and entry conditions

• Entry conditions: – First turn completed– RF OFF

• Exit conditions:– Beam circulating for few hundred turns and RF captured– Ready for set-up of the instrumentation for circulating beam and more

detailed optics measurements (following 2 phases)


Circulating pilot and RF capture – basic objectives

• Establish closed orbit• Commissioning of additional instrumentation:

– BPM intensity acquisition

• Preliminary orbit, tune, coupling and chromaticity adjustments

• Obtain circulating beam (few hundred turns at least)• SPS-LHC energy matching• Commissioning of RF capture


Circulating pilot and RF capture – basic objectives

• Tolerances we aim at for this phase:– Closed orbit corrected down to ~1-2 mm r.m.s.– Maximum acceptable radial offset: 0.5 mm– Tune: 64.28/59.38 (tune for commissioning) within few 0.01– Octant-to-octant MB field offset to few 10-4

– Chromaticity to 10-20 units (to minimize decoherence of oscillations – 1000 turn dynamic aperture requires |Q’|<80)

– Coupling to few 0.01– SPS-LHC energy matching to few 10-4

O. Bruning, Chamonix 2003S. Fartoukh, M. Hayes, LCC#31


Circulating pilot and RF capture – Objectives

Objective PriorityO.A.2.1 Machine parameters according to tolerances 1O.A.2.2 Beam captured 1O.A.2.3 Beam instrumentation

.01 BPM: acquisition, intensity mode 1

.02 DC-BCT: acquisition, first calibration 2O.A.2.4 Measurements

.01 Polarity/cabling errors check for correctors and BPMs 1

.02 MQs: checked for major errors (integer tune and optics) 1

.03 MBs: Energy mismatch between arcs and SPS to LHC corrected to few 10 -4 1

.04 Fast physical aperture scans, free oscillations with BPM intensity meas. 1

.05 Systematic physical aperture scans with sliding bumps 2

.06 Systematic linear optics measurements 2O.A.2.5 Machine protection

.01 Beam dump synchronization 1

Assume that priority 1 objectives of phase A.1 have been achieved


Circulating pilot and RF capture – Objectives

Objective PriorityO.A.2.6 Controls and applications

.01RF signals and triggers in OASIS (phase pick-up, wall current monitor, peak detected signal, frev, fRF,….) available 1

.02 Synchronization diagnostics tools available 1

.03 RF controls (frequency, voltage, phase, bucket position, …..) 1

.04 Multi-turn trajectory acquisition 1O.A.2.7 RF systems

.01 RF cavities operational with pilot bunches 1

.02 Phase-loop operational 1

.03 Observation equipment set-up (wall-current monitor) 1

.04 Bucket counting and bunch reference numbers set-up 1

.05 Fine synchronization SPS/LHC commissioned 1O.A.2.8 Magnets

.01 List of CODs that are found wrong (polarity and coarse calibration) - systematic 1

.02 MQs: Major errors disturbing integer tune found and possibly corrected 1

.03 MBs: Energy mismatch (inter-arcs, SPS to LHC) corrected to few 10 -4 1

.04 MBs: Stability of injection after recycling magnets 2


Circulating pilot and RF capture – Equipment state and readiness (entry)

Entry conditionE.A.2.1 Full LHC checkout and operations dry run (same as E.A.1.1)E.A.2.2 Application SW

.01 Multi-turn trajectory acquisitionE.A.2.3 Timing system

.01 Interleaved injectionE.A.2.4 Machine protection subsystems (same as E.A.1.4)E.A.2.5 Collimators (same as E.A.1.5)E.A.2.6 Magnets (same as E.A.1.6)E.A.2.7 Injectors and transfer lines

.01 B-field trim tested with beam in SPS/TI2/TI8. E.A.2.8 Injection equipment (same as E.A.1.8)E.A.2.9 Beam Instrumentation

.01 Mobile BLMs calibration, acquisition, applicationE.A.2.10 Experiments (same as E.A.1.10)E.A.2.11 RF system

.01 RF cavities conditioned and operating to max. voltage without beam.

.02 RF synchro-loop commissionedE.A.2.12 Beam Dump system (same as E.A.1.12)E.A.2.13 Technical services available (same as E.A.1.13)

Assume that entry conditions for phase A.1 have been met


Circulating pilot and RF capture – Controls, software and tools

• Some additional key elements for the Circulating beam and RF capture phase:– Fast Analog Signals available in CCC (OASIS) and Pt. 4 (scopes)– Tools to measure the beam phase shift per turn w.r.t. the reference RF

frequency signal– Multi-turn trajectory acquisition– YASP for closed orbit measurement and correction (including closure)– LSA applications, in particular:

• Knob for B-field correction (affecting all magnetic elements) by octant and for the overall machine.

• Knob for Bdl trim with orbit correctors for the two beams– LOCO available for orbit response analysis– Online MADX model available– Online aperture model available


Circulating pilot and RF capture – Beams, cycles, modes,…

• Beam type: pilotIb: 5 109 pn: 0.3 – 3.5 mm.mrad (small n in case of problems)L: 0.25 – 0.8 (we can probably go to 2.5) eV.sp/p: 0.15 – 0.6 10-3 (r.m.s.)

• LHC mode: “inject and dump” (set 10-1000 turns)a) One ring, single injection on demandb) One ring, repeated injectionc) Two rings, interleaved repeated injection

• Available operational cycles, modes and states (as for injection commissioning)

• Cycle: Nominal cycle and wait (> 20 mins after injection level achieved)• Occasional re-cycle (in particular during the energy matching)• Machine protection as for injection commissioning• Beam dump and LHC mode “Inject and Dump” allows screens to be in.

Here screens should be OUT and we should have an alarm or interlock when they are IN.


Circulating pilot and RF capture – Machine set-up

• Machine set-up as for first turn commissioning, in particular:– Sextupole spool pieces ON and at nominal settings (from magnetic

measurements)– Lattice sextupoles ON and at nominal setting (to correct for natural

chromaticity)– Skew quads ON and at nominal settings (from magnetic measurements)

• Expected machine settings with this configurationH V

Coupling <0.1 <0.1Chromaticity (spool pieces and lattice sextupoles) – assuming ~20% error in the b3 estimate 0 +/- 20 0 -/+ 20

Chromaticity (no correction) ~ -180 ~ 0


Circulating pilot and RF capture – Breakdown

Step Activity Priority

A.2.1 Instrumentation and corrector checks (unless completed in phase A.1) (Interleaved)

.01 Commission interleaved injection ST/CO 1

.02 Commission BPM intensity measurement mode BI 1

.03 Systematic BPM/corrector polarity/plane/ring checks and repairs ST 1

.04 Systematic BPM/corrector preliminary calibrations (by-product – offline) ABP/OP 2A.2.2 Establish closed orbit (one beam at a time)

.01 Close the trajectory ST 1

.02 Closed orbit measurement and correction to get few turns ST 1

.03 Fast physical aperture scans, free oscillations with BPM intensity meas. ST 1

.04 Systematic physical aperture scans with sliding bumps ST 2A.2.3 Measurements with few turns (one beam at a time)

.01 Integer tune measurement and correction from difference orbit ST 1

.02 Fractional tune measurement from injection oscillation ST 1

.03 Adjustment of chromaticity to reduce de-coherence ST 1

.04 Adjustment of the coupling to reduce CTA ST 1

.05 Systematic linear optics checks ABP/OP 2

ST=Shift Team


Circulating pilot and RF capture – Breakdown

Step Activity PriorityA.2.4 Offsets between different sectors (interleaved)

.01 Correction of the orbit to 1-2 mm r.m.s. ST 1

.02 Correction of the Bdl sector-by-sector down to few 10 -4 ST 1

.03 Correction MQ-MQ offsets sector-by-sector from phase advance measurement ST 2A.2.5 RF commissioning with beam (one beam at a time)

.01 Set-up observation equipment and bunch reference numbers RF 1

.02 Synchronize beam dump kickers RF/BT 1A.2.6 SPS-LHC Energy matching (mostly interleaved)

.01 Centre first turn in both rings ST 1

.02 Measure revolution frequency for both beams ST/RF 1

.03 Correct (BdlSPS, BdlLHC1,BdlLHC2, fRF_SPSLHC) ST/RF 1

.04 RF ON and Adjust RF phases ST/RF 1

.05 Set-up phase loop (gain, offsets, etc) RF 1

.06 Measure residual energy error and correct ST/RF 1A.2.7 Measurement with captured beam (interleaved)

.01 Check orbit (average from multi-turn) after capture ST/RF 1

.02 Correct tune-split ST/RF 1


Circulating pilot and RF capture – details

• Instrumentation and corrector checks (unless completed in phase A.1)– BPM intensity measurement is surely important at this stage (if not earlier) to

determine potential bottle-necks (in particular soft ones) and to select the data to be retained for the turn-by-turn trajectory data averaging

– Systematic BPM sanity check (polarity, control chain, plane, ring and other cabling errors) ~2 shifts (R. Steinhagen, F. Zimmermann) is necessary for the following steps.

– This could also provide BPM and corrector calibration and data for off-line linear optics check that could then be made available early in the commissioning in case of problems.



• Establish closed orbit:– Measure integer tune from first turn difference for two different injection

settings and correct if necessary– Close the trajectory on itself with 2 correctors from difference of 2

consecutive turns (at least a few BPMs after the injection point must provide data in the second turn) YASP

– Closed orbit measurement (average of turn-by-turn data over the number of turns available). The BPM system can cope with an increase in r.m.s. bunch length t from 0.4 to 1.3 ns.

– 140 turns for nominal momentum spread. About 280 turns by reducing the momentum spread at extraction from the SPS by using pilot with 0.25 eV.s and reducing the RF voltage to ~2MV at SPS extraction.

– We should then aim to correct the orbit with a small number of correctors to avoid biasing the momentum offset determination among sectors later (A.2.4)

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• Measurements with few turns: – If it has not been determined from first turn data the integer tune can be

measured from the difference of two orbits (one of them with a distortion from a kick) and harmonic analysis.

– Fractional part can be measured by exciting injection oscillations and comparing turn-by-turn trajectories or turn-by-turn phase advance measurements obtained combining the turn-by-turn data from pairs of BPM separated by 900 in phase advance. The precision of this measurement is expected to be Q=0.01

– Adjust the coupling empirically by minimizing the CTA– Any oscillation will die-out rapidly because of the de-coherence due to

chromaticity:

– e-folding time = 4 turns for QH’=-179 for E/E0=3.06×10-4

– 43 turns for Q’H=-17, Q’V=17. Can be further increased by reducing the momentum spread at extraction from SPS (88 turns for E/E0=1.5×10-4).

– Adjust the chromaticity empirically by maximizing the decoherence time– If the lifetime would not be sufficient systematic linear optics checks might be

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• Offsets between the different sectors:– Once the beam can circulate for a few hundreds turns the orbit can be

measured and corrected possibly down to 1 mm r.m.s.– In these conditions it should be possible to correct the relative octant-to-

octant MB field offset to few 10-4

– The B-field trim should be “propagated” to the multipoles (at least quadrupoles) to keep the correct MQ-MB tracking

– MQ-MQ tracking might be difficult to correct at this stage unless the coupling has been minimized

J.Wenninger LHCCWG #17


Circulating pilot and RF capture – details• SPS-LHC energy matching

– Before the energy matching can start the beam must survive for at least ¼ of a synch. period (~45 turns at nominal voltage – 8MV, about ~35 turns at 16 MV).

– Starting point beam centred in the SPS at extraction and in the LHC for both rings (RF OFF). Pilot beam with small momentum spread.

– Assumed common frequency for B1 and B2 in SPS-LHC (fSPSLHC). Assume same magnetic field at extraction from the SPS for B1 and B2

– Measure frevLHCi (i=1,2) by observing bunch slip w.r.t. SPS-LHC reference frequency fSPSLHC/hLHC (either looking at bunch on longitudinal pickup or at phase detector) vs. time

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– Trim fSPSLHC, the LHC integrated field for B1 and B2 (via the CO correctors only), and the magnetic field at extraction in the SPS

– There will be a radial offset at extraction in the SPS if CLHC27/7 CSPS (this seems to be the case)

– There will be a radial offset in the LHC after capture only if the two “rings” have a different circumference (~0.1 mm for ~1.5 mm difference)



• SPS-LHC energy matching (continued)– Switch the RF ON. It might be worth starting at maximum voltage (16 MV).– Adjust the RF phases (by using the phase pick-up signal)– Set-up the phase loop (gain, offsets, etc.)– Check residual momentum mismatch by observing the phase pick-up signal

(sinusoidal oscillation with amplitude proportional to the momentum mismatch)

– Iterate– Reduce the voltage to 8 MV (nominal injection value) or lower


Circulating pilot and RF capture – Possible problems

• Very low lifetime (few tens of turns)– Causes: Thin obstacle (a “phantom” valve or other objects with thickness in the mm

range, pressure bumps), poor optics control– Diagnostic tools: check performance with probe pilot beam (with small transverse and

longitudinal emittances) BLMs, mobile BLMs and display, BPM intensity mode, radiation survey piquet, systematic optics measurements from orbit response analysis.

– Remedies: obstacle removal, optics correction, leak fixes– Issues: activation of components at problem location – cool-down times

• Large coupling– Causes: magnet model uncertainty, wrong MQS settings, polarity/cabling errors,

calibration errors.– Diagnostic tools: cross-plane orbit response with local bumps at the MQS– Remedies: Correction from measurements– Issues: analysis tools

• Large chromaticity– Causes: magnet model uncertainty, wrong MCS/MS settings, polarity/cabling errors,

calibration errors.– Diagnostic tools: phase advance along the ring vs. momentum offset– Remedies: Correction from measurements– Issues: analysis tools


Circulating pilot and RF capture – Possible problems

• Large path-length difference (>5 mm) between beam 1 and beam 2 leading to large offsets after capture

– Causes: Differences in Bdl among apertures larger than expected – Diagnostic tools: measure the revolution frequency of the 2 beams with RF off – Remedies: Need to have different SPS extraction magnetic fields for B1 and B2 (2

different cycles) for the same RF frequency


Circulating pilot and RF capture – Issues

• Software for BPMs in intensity mode…– This is a very useful tool in the SPS at start-up even after 30 years of

operation….– Needed to identify soft bottlenecks and lifetime problems– Some time is required for the commissioning, but well spent

• Recycling– How often is recycling required (e.g. if energy mismatch detected and MBs

adjusted)? – Cycling strategy to be fully defined for each circuit.

• We are trying to have a strategy for the commissioning with beam. Do we have it for the “cold check-out”?– From the “What if” exercise we can learn something for the “cold check-out

strategy” at least to avoid trivial problems (calibration curves, wrong settings, …).

– Need to create a list of possible errors and corresponding methods to trace them


Summary

• Phase A.2: from first turn to basic machine set-up to obtain circulating beam (few hundred turns) for RF capture and to open the way to the next phase focussed on Beam Instrumentation set-up

• Also in this phase aim for simplicity (where possible): – For some of the steps interleaved injection might be required – Stay with single pilot bunch– Systematic measurement limited to the sanity check of the correctors/BPM

required to iron-out the orbit and to adjust the LHC Bdl– Need to commission the BPM intensity measurement to identify localized

losses that might lead to low lifetime

• Some “what-if” scenarios elaborated– We need to create a list of possible errors (cabling, polarity, etc.) with their

effect and possible means to detect them


References

• Web documentationLHC Commissioning procedures, LHC Commissioning pagesDocumentation and Procedures: Phase A2 [EICs+V. Kain]

• LHCCWG minutes and relevant presentations:Circulating Beam and RF Capture [G. Arduini, A.

Butterworth]Circumference Difference Between the 2 LHC Rings [G. Arduini]Beam Instrumentation - BPM, BLM, BCT, Transverse Diagnostics [R. Jones]Commissioning Procedures [V. Kain] Response Matrix Measurements and Analysis [J. Wenninger] Tracking error measurement and correction [J. Wenninger]Summary of Parameter Tolerances [F. Zimmermann]What to Do If We Cannot Get in Tolerance [F. Zimmermann]

• Others:The minimum machine and the first 1000 turns or so [O. Brüning]Commissioning tunes to bootstrap the LHC, LCC#31 (23/10/02) [S. Fartoukh, M. Hayes]First Turn, LHC Project Note 308 [A. Verdier]

http://lhccwg.web.cern.ch/lhccwg/Meetings/2006.04.05/LHCCWG-April2006-BI450GeV.ppt


America’s Marine Corps never makes detailed studies in advance. Leaving important things to the last minute reduces the risk of wasting time on things that may

ultimately prove not important at all.

The Economist, Jan 4th, 2007

F. ZimmermannLHCCWG#19

Documents

LHC Technical Committee, 14/03/2007 LHC Commissioning Phases Circulating pilot and RF capture presented by G. Arduini for the LHCCWG members Many thanks