LHC Commissioning Phases

1
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.

2
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

3
LHC Stage A Commissioning phases
Phases for full commissioning Stage A (pilot
physics run)
Phase Description
A.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, aperture
A.5 Increasing intensity prepare the LHC for unsafe beam
A.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 measurement
A.9 7 TeV optics beta beating, dispersion, coupling, non-linear field quality, aperture
A.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
Phases for proposed 2007 engineering run
Phase Beam time days Beam
A.1 Injection and first turn 4 1 x pilot
A.2 Circulating beam 3 1 x pilot
A.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
4
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)

5
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

6
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 Qlt80)
• Coupling to few 0.01
• SPS-LHC energy matching to few 10-4

O. Bruning, Chamonix 2003 S. Fartoukh, M. Hayes,
LCC31
7
Circulating pilot and RF capture Objectives
Assume that priority 1 objectives of phase A.1
have been achieved
Objective Priority
O.A.2.1 Machine parameters according to tolerances 1
O.A.2.2 Beam captured 1
O.A.2.3 Beam instrumentation
.01 BPM acquisition, intensity mode 1
.02 DC-BCT acquisition, first calibration 2
O.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 p bumps 2
.06 Systematic linear optics measurements 2
O.A.2.5 Machine protection
.01 Beam dump synchronization 1
8
Circulating pilot and RF capture Objectives
Objective Priority
O.A.2.6 Controls and applications
.01 RF 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 1
O.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 1
O.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
9
Circulating pilot and RF capture Equipment
state and readiness (entry)
Assume that entry conditions for phase A.1 have
been met
Entry condition
E.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 acquisition
E.A.2.3 Timing system
.01 Interleaved injection
E.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, application
E.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 commissioned
E.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)
10
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

11
Circulating pilot and RF capture Beams, cycles,
modes,

• Beam type pilot
• Ib 5 ?109 p
• en 0.3 3.5 mm.mrad (small en in case of
  problems)
• eL 0.25 0.8 (we can probably go to 2.5) eV.s
• Dp/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 demand
• b) One ring, repeated injection
• c) Two rings, interleaved repeated injection
• Available operational cycles, modes and states
  (as for injection commissioning)
• Cycle Nominal cycle and wait (gt 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.

12
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 configuration

H V
Coupling lt0.1 lt0.1
Chromaticity (spool pieces and lattice sextupoles) assuming 20 error in the b3 estimate 0 /- 20 0 -/ 20
Chromaticity (no correction) -180 0
13
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 2
A.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 p bumps ST 2
A.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
STShift Team
14
Circulating pilot and RF capture Breakdown
Step Activity Priority
A.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 2
A.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 1
A.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 1
A.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
15
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.

16
Circulating pilot and RF capture details

• 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 st 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)

17
Circulating pilot and RF capture details

• 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 DQ0.01
• 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
  sdE/E03.0610-4
• 43 turns for QH-17, QV17. Can be further
  increased by reducing the momentum spread at
  extraction from SPS (88 turns for
  sdE/E01.510-4).
• Adjust the chromaticity empirically by maximizing
  the decoherence time
• If the lifetime would not be sufficient
  systematic linear optics checks might be required

18
Circulating pilot and RF capture details

• 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
19
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 (i1,2) 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

• 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 CLHC¹27/7 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)

20
Circulating pilot and RF capture details

• 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

21
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

22
Circulating pilot and RF capture Possible
problems

• Large path-length difference (gt5 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

23
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

24
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

25
References

• Web documentation
• LHC Commissioning procedures,
• LHC Commissioning pages
• Documentation and Procedures Phase A2
  EICsV. 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, LCC31
  (23/10/02) S. Fartoukh, M. Hayes
• First Turn, LHC Project Note 308 A. Verdier

26

• Americas 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. Zimmermann LHCCWG19