LHC Workshop, Jan '05 P. Collier AB-OP/LHC 1

450 GeV450 GeVP. Collier AB/OP

Prerequisites First Turn Getting Closure RF Capture Preliminary Commissioning Tuning up Summary

LHC Workshop, Jan '05 P. Collier AB-OP/LHC 2

IntroductionIntroductionBeam commissioning at 450 GeV is planned to take place in three stages:

A sector test with beam through sector 7-8, several months before Preliminary commissioning at 450GeV for the whole ring using a special

cycle (with different working point and a degauss blip) Passage to a ‘normal’ ramping cycle in preparation for commissioning the

ramp

Here will concentrate on the second stage The first part of this is also valid for the sector test. In addition, later parts might take place after initial ramp

commissioning

Many details are contained in the Session VII of Chamonix XII And in the beam commissioning web pages

http://lhc-commissioning.web.cern.ch/lhc-commissioning/… so a more general overview is given here

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PrerequisitesPrerequisitesA set of settings for the magnetic machine:A set of settings for the magnetic machine: Using an optics having an increased tune split –

Qh=64.285, Qy=59.385 With crossing angles, separation schemes, experimental

magnets etc. OFF Minimizing the dynamic effects by using a ‘degauss blip’

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17A cycle for each powering circuit must be defined to allow us to recover to a given condition (reproducibility)Some Circuits will be not needed at first: Spool piece and lattice Octupoles & Decapoles Non-linear correctors in the inner triplets Skew sextupoles Experimental compensation elements …

-140 PC’s Leaves ~1570

to power!L. Bottura

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Convert to Current via a transfer function … Convert to Current via a transfer function … I(t) I(t) Convert strength to integrated field ->bn(t) TF comes from magnetic measurements : warm & cold Need to interpolate between measured points of the

transfer function - or are provided with a model

Prerequisites (2) Prerequisites (2) Settings GenerationSettings Generation

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Other Settings Generation:Other Settings Generation: Power b3,b4, b5 spool piece magnets + skew quads based on magnet measurements

(though only b3 powered for the first turn) The RMS is invoked during settings generation when model predictions are required

Start with:Start with: Baseline Energy function E(t) for the chosen cycle Normalized strengths from MAD – optics file K(t) for each object Description of magnet / magnet family e.g. magnetic length

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In this case only need the injection settings for beam but still need a ‘cycle’ for reproducibility

& ‘reset’

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Prerequisites (3)Prerequisites (3)Other Things:Other Things:

Beam instrumentation: auto-triggering for the BPM’s. DC-BCT should just work Beam loss monitors, radiation monitors ready to go Beam down the pipe from the SPS at the right energy and injected [Bren] Collimators, Protection elements etc. out of the way

- including TL collimators Screens – will use matching screens in IR4 to see the beam pass by … Beam Interlock system –

- configured to a minimum level – to match our minimum situation. RF Power OFF Initially – used once we have multiple turns. RF Low-level system for synchronization tested and available.

- used to provide timing reference to fire kickers. Mountains of Software – the usual stuff Software interlock system … and so on …

And of course the basics from machine checkout … cold, powered magnets, access system, controls, technical services

and the like

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Automated Threading

Not very successful in LEP – but not pushed too much. Tends to be perturbed by:

BPM’s with large unphysical offsetslarge unphysical offsets, calibration errorscalibration errors, or cabling errorscabling errors (Ring, Plane or Sign)

Correctors with wrong polaritywrong polarity

Large quadrupole misalignmentsquadrupole misalignments – or settings errors

First TurnFirst Turn

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LEP TrajectoryThreading …

A reasonable 1st turn in LEP

Bad Pickups cause headaches for automatic threaders

Manual Threading Expect beam to pass 4-5 half-cells before being lost

(LEP ~1 octant) Expect large offsets before beam is lost Correct over a relatively small range of BPM’s Iterate many, many times Hope beam goes further each time! Needs careful thinking and experience useful!

Use low intensity – of course!

By the end of LEP we could do the first turn in ~1 hour.

Both should be available for LHC

commissioning

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LHC has 8 sectors - Each has to be matched to the beam energy

1st Turn continued1st Turn continued

-4-3-2-101234

IP1 IP2 IP3 IP4 IP5 IP6 IP7 IP8 ENDLEP

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Separation/Recombination Dipoles will act like very strong correctors during the threading … must correct Transfer Function errors early.. Note: not all have been cold measured

Threading is easier with higher order multipole magnets off. (avoiding feed-down) Cut lattice sextupoles, octupoles, spool piece octupoles, decapoles etc. Probably leave the spool piece sextupoles powered – since we have the b3 anyway.

Checking pickup response is best done using difference trajectories with kicks. Can identify non-responding, polarity reversed and plane inverted BPM OK Calibration errors less easy – do that later. Use several correctors, both signs, both planes (both rings) to sample all cases.

Instrumentation Can have intensity + position from each PU at the same time (for single beam) How much use will the BLM’s be at this point??

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Getting Closure ‘Degauss’ Cycle Q’h Q’v

No Correction +83 -263

80% Dipole Correction Only using spool piece correctors

-75 -105

Natural Q’ Only corrected using lattice sextupoles

+176 -176

Both Corrections +18 -18

1st turn:- Decoherence is only a few turns

Turn the lattice sextupoles on and use them as a ‘knob’ – decoherence time can be used as an observable …Combined with: Continued trajectory correction to decrease the peaks and reduce lossesEstablishing more than a few turns also requires control over the

tunes:Once we have ~10 turns measured …

Average the turns to get an ‘orbit’ – can start correcting that, At this point get the skew quads on and powered from measurement data Can extract from the orbit the integer tune. If the coupling is reasonably well corrected can also extract the fractional

tunes (10 turns 0.01)

80 units Q’ 6 turns

LHC Project Report 308 A. Verdier

With a bit of luck and the wind behind us work up towards ~100 turns

(Q’ corrected to ~10 units) – Ready for Capture. Initial Commissioning of the beam dump can also happen here …

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RF Capture RF Capture

Step 1: Get the energy correct.Step 1: Get the energy correct. Can get reasonably close using the average Horizontal offset in the arcs on the first turn trajectory…1 mm corresponds to ~7x10-4 dB/B

Step 3: Energy Matching – Later … but before any serious tuning Step 3: Energy Matching – Later … but before any serious tuning startsstarts

Choose something to fix (dipole field, or flhc) [in the SPS it is the frequency]Observe 1st turn offset – change SPS energy to centre it. Observe closed orbit offset – change either dipole field, or flhc to correct. Usually needs iteration …

Step 2: Initial CaptureStep 2: Initial CaptureGet the RF ON and phase to the beam. RF will accelerate the beam onto a new orbit to match the LHC energy

Observe the phase slip between RF and the beam Correct using the main field, or the frequency, flhc.

Ignoring a multitude of details!Ignoring a multitude of details!

Wall current monitor

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Preliminary Commissioning (1)Preliminary Commissioning (1)For this we need a captured beam – pilot bunch

Step 1: Get a reasonable lifetime:Step 1: Get a reasonable lifetime: Commission Beam instrumentation- especially Q-meter (single kick) and BLM Use these to measure and adjust Q, Q’ coupling, orbit etc. Later need transverse profile measurements Also, get the External beam synchronized timing working for the BPM’s.

Step 2: Initial System Commissioning:Step 2: Initial System Commissioning: Beam dump: orbit, timing, kick and septum strength – observe trajectory in dump line

May not require MKB for initial commissioning. Verify synchronization, establish ‘inject & dump’ operation

Commission Beam Interlock System – add inputs as they come into play

Step 3: Collimation and Protection elements:Step 3: Collimation and Protection elements: Start moving individual collimators. find beam with each jaw to calibrate the position. Get the primaries loosely set – for single stage collimation Close injection protection elements (TDI) again loosely set. TCDS can also be roughly adjusted to protect the arc

Step 3: Should allow us to increase the intensity of the pilot Step 3: Should allow us to increase the intensity of the pilot little by little – and iterate – aim for few 10little by little – and iterate – aim for few 10+10+10

More Intensity

More

Precision

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Preliminary Commissioning (2)(Examples of Bumps with Everything)(Examples of Bumps with Everything)

Systematic KicksSystematic Kicks Use single kicks – look at difference orbit (similar to during 1st turn studies) Use each corrector, with both signsboth signs and several strengthsseveral strengths to can check the response of all of

the pickups and the correctors. Polarity and Calibration Stay below ~1-2 mm in order to avoid non-linear fields

Systematic BumpsSystematic Bumps Use sliding 3-bump around each ring and each plane. Both +ve and –ve bumps Start with ~1mm and increase bump until a) bad lifetime, b) beam dumped or lost.

Gives a measure of the aperture – at least any serious restrictions Can also be used for calibrating the individual BLM’scalibrating the individual BLM’s for known localized losses

Measure Lifetime, tune, non-closure, orbit (both planes) etc. as a function of amplitude First look at the quality of the optics. Local Coupling and sextupole polarity etc.

Powering the non-linear correctors in the bump – check the corrector polarity Can also use bumps in the insertion regions & DS for the corrector elements there.

Including the inner triplet correctors – even though we don’t plan to use them for a while …

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Preliminary commissioning Preliminary commissioning (3) (3) Other Aspects:

Alignment:Alignment:Reposition mis-aligned quads based on analysis of orbit kicks ..How can we detect misaligned dipoles – unless v. bad? Feed down?? Of course any aperture bottlenecks will have to be thoroughly investigated…

Two beams:Two beams: Can extract extra information by commissioning both beams in parallel Complimentary measurements – e.g. tune in each ring Comparisons between behaviour in each ring – big kicks Common elements – e.g. dog-legs, recombination dipoles Can have both beams at the same time by placing the ‘collision point’ in an arc

Progressive Commissioning:Progressive Commissioning:Progressive commissioning of beam instrumentation as the need arises for wire scanners, BCT calibration, matching monitors, etc. etc. Most of the activities will be iterative and re-visited several times as the quality of the diagnostics improve.

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Tuning-UP (1)Tuning-UP (1)

More System Commissioning:More System Commissioning: RF System ‘tuning’ Multiple injection synchronization & rotation systems Longitudinal FB (may be needed for multi-bunch operation) TFB – just commission injection damping part for the moment Transverse profile measurements Revisit beam dump – activate orbit FB and dump trigger Tighten collimation and protection settings if needed for the intensity … Injection tuning and matching of the transfer lines to LHC. BLM’s revisit calibration and thresholds … Other BI – e.g. PLL Q-measurements

Prerequisite: Prerequisite: Sufficient intensity for good quality measurements ~3x10+10

Initially 1 bunch, then either 1x4, or multiple injections from SPS

Initially beam 1, then beam 2 then 1 & 2 non-colliding final step with correct separation in the experiments

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Tuning Up (2): Linear OpticsTuning Up (2): Linear OpticsHere we enter a Here we enter a measure-fest … Measurement Programme:measure-fest … Measurement Programme:

Also Measure the dynamic aperture as a

function of just about

everything

LEP After correction: V in red

LEP : 8 knobs SC quads

LHC: ~100 knobs

Linear Optics Checks and correction to tighter tolerances: Linear Optics Checks and correction to tighter tolerances: Examples include:Examples include:

Tune ~0.001, Q’ ~2 units, |c-| < 0.01, Dispersion few cm? Orbit < 1mm rms. Even better in specific areas. Orbit FB activated. Beta-beating measurement – 1000-turns measurements system a la LEP

LEP ~20% - corrected *v , for the rest we didn’t care …

But correction more difficult in LHC : many (hopefully small) sources – Insertion Quads Analysis tools and Correction Algorithms being worked on

Phase advance, * measurement etc. K-modulation for PU offsets?

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Tuning Up (3) : Other StuffTuning Up (3) : Other Stuff

Non-Linear Optics Checks and correction - Examples include Non-Linear Optics Checks and correction - Examples include (Frank)(Frank) |Q”| < ~1500 (a2 correction using skew sextupoles to ~20%)

{measure Q” + tune vs. Vertical bump amplitude} Powering of octupole spools: global correction to 20%

{minimize Q’’, then detuning with amplitude} Decapole spools: arc-by-arc correction to 50% (global 20%)

{minimize Q’’’, then off-momentum tuning with amplitude} ?

Much of this can take place later – after initial ramp commissioning?

… and probably on the normal cycle

After should probably re-visit aperture checks with bumps and dynamic After should probably re-visit aperture checks with bumps and dynamic aperture…aperture…

Don’t forget to Study

reproducibility after cycling the machine

bb33 spool piece checks spool piece checks Use combination bumps (to increase the signal) to check and correct b3 spool piece powering

arc-by-arc to ~10% [Hayes, Bruning]

Tune scansTune scans Get to know the terrain around the chosen WP

Get the separation bumps on and well closedGet the separation bumps on and well closed Re-optimize and re-measure with bumps working Get the experiments on and check compensation

Might not be needed before

1st pilot physics runs

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End GameEnd Game 2 separated beams in the machine – intensities ~3x10+10. Well adjusted beam parameters – at least on the degauss cycle Polarity cabling, etc. checked for pickups and magnets. Alignment checked – corrected if necessary. Physical aperture known. Good understanding of static field errors at injection in the machine.

Correction checked for b3 (and maybe b4 & b5) spool pieces Optics checked and (hopefully) corrected including static beta-beating to <20%

Fully functioning beam instrumentation (at low energy) With the specified beam intensity and bunch structure Including Q-history measurements.

Multiple injections tried and tested. Machine protection shaken down – sufficiently well to consider ramping.

Collimator/ protection settings sufficient for low intensity operation Orbit feedback activated – at least in beam dump & collimation regions

Application Software thoroughly tested in anger …

Exit conditions:Exit conditions:

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What we’ve left for later …What we’ve left for later …

Anything to do with 25ns or 75ns operation and ‘High’ Anything to do with 25ns or 75ns operation and ‘High’ intensitiesintensities

Crossing angles RF, BI, LFB, Dump, Injection, Collimator & protection commissioning for trains and higher

intensities Transverse feedback and especially its interaction with the BI. Beam abort gap cleaning. Electron cloud

Anything to do with the normal machine cycle Anything to do with the normal machine cycle ((Andy NextAndy Next)) Dynamic effects - persistent currents – decay on the flat bottom

But we should have a good ‘baseline’ of the static effects. Software, algorithms and corrections to cope with decay Reproducibility of the machine on the nominal cycle

Anything else not needed for the initial pilot physics Anything else not needed for the initial pilot physics run:run:

Alignment optics and measurements for inner triplets. Inner triplet correctors Special features for ions (J. Jowett this aft)

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SummarySummaryStart as simple as possibleStart as simple as possible Make clear definition of where we want to get to and the path to take Cut the bits we don’t need.

Progressive commissioning of systems as Progressive commissioning of systems as needed needed

Revisit each system often Attack only the things we need for the pilot physics goal The rest can come progressively, laterFast track to complete the phase as Fast track to complete the phase as

quickly as possiblequickly as possible But don’t cut corners – these would come back to bite us Thorough checks and measurements – especially polarity,

aperture and beta-beating.

Online Machine Protection to Assist LHC Operators

Machine protection tailored to the Machine protection tailored to the beam/machine at each stagebeam/machine at each stage