LHC Workshop, Jan '05P. Collier AB-OP/LHC1 450 GeV P. Collier AB/OP  Prerequisites  First Turn  Getting Closure  RF Capture  Preliminary Commissioning  Tuning up  Summary

LHC Workshop, Jan '05P. Collier AB-OP/LHC2 Introduction Beam 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 … so a more general overview is given here

LHC Workshop, Jan '05P. Collier AB-OP/LHC3 Prerequisites A set of settings for the magnetic machine:  Using an optics having an increased tune split – Q h =64.285, Q y =  With crossing angles, separation schemes, experimental magnets etc. OFF  Minimizing the dynamic effects by using a ‘degauss blip’ A 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

LHC Workshop, Jan '05P. Collier AB-OP/LHC4 Convert to Current via a transfer function …  I(t)  Convert strength to integrated field ->b n (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) Settings Generation Other Settings Generation:  Power b 3,b 4, b 5 spool piece magnets + skew quads based on magnet measurements (though only b 3 powered for the first turn)  The RMS is invoked during settings generation when model predictions are required 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 In this case only need the injection settings for beam but still need a ‘cycle’ for reproducibility & ‘reset’

LHC Workshop, Jan '05P. Collier AB-OP/LHC5 Prerequisites (3) 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

LHC Workshop, Jan '05P. Collier AB-OP/LHC6 Automated Threading Not very successful in LEP – but not pushed too much. Tends to be perturbed by: large unphysical offsetscalibration errorscabling errors  BPM’s with large unphysical offsets, calibration errors, or cabling errors (Ring, Plane or Sign) wrong polarity  Correctors with wrong polarity quadrupole misalignments  Large quadrupole misalignments – or settings errors First Turn LEP Trajectory Threading … A reasonable 1 st 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

LHC Workshop, Jan '05P. Collier AB-OP/LHC7  LHC has 8 sectors - Each has to be matched to the beam energy 1st Turn continued  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 b 3 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??

LHC Workshop, Jan '05P. Collier AB-OP/LHC8 Getting Closure ‘ Degauss ’ Cycle Q’ h Q’ v No Correction % Dipole Correction Only using spool piece correctors Natural Q’ Only corrected using lattice sextupoles Both Corrections st 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 losses Establishing 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 …

LHC Workshop, Jan '05P. Collier AB-OP/LHC9 RF Capture 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 starts Choose something to fix (dipole field, or f lhc ) [in the SPS it is the frequency] Observe 1 st turn offset – change SPS energy to centre it. Observe closed orbit offset – change either dipole field, or f lhc to correct. Usually needs iteration … Step 2: Initial Capture Get 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, f lhc. Ignoring a multitude of details! Wall current monitor

LHC Workshop, Jan '05P. Collier AB-OP/LHC10 Preliminary Commissioning (1) For this we need a captured beam – pilot bunch 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:  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:  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 little by little – and iterate – aim for few More Intensity   More Precision

LHC Workshop, Jan '05P. Collier AB-OP/LHC11 (Examples of Bumps with Everything) Preliminary Commissioning (2) (Examples of Bumps with Everything) Systematic Kicks  Use single kicks – look at difference orbit (similar to during 1 st turn studies) both signsseveral strengths  Use each corrector, with both signs and several 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 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 calibrating the individual BLM’s  Can also be used for calibrating 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 …

LHC Workshop, Jan '05P. Collier AB-OP/LHC12 Preliminary commissioning (3) Preliminary commissioning (3) Other Aspects: 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: 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 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.

LHC Workshop, Jan '05P. Collier AB-OP/LHC13 Tuning-UP (1) 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: Sufficient intensity for good quality measurements ~3x 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

LHC Workshop, Jan '05P. Collier AB-OP/LHC14 Tuning Up (2): Linear Optics Here we enter a 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: 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?

LHC Workshop, Jan '05P. Collier AB-OP/LHC15 Tuning Up (3) : Other Stuff Non-Linear Optics Checks and correction - Examples include (Frank)  |Q”| < ~1500 (a 2 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 aperture… Don’t forget to Study reproducibility after cycling the machine b 3 spool piece checks  Use combination  bumps (to increase the signal) to check and correct b 3 spool piece powering arc-by-arc to ~10% [ Hayes, Bruning ] Tune scans  Get to know the terrain around the chosen WP Get 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 1 st pilot physics runs

LHC Workshop, Jan '05P. Collier AB-OP/LHC16 End Game  2 separated beams in the machine – intensities ~3x  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 b 3 (and maybe b 4 & b 5 ) 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:

LHC Workshop, Jan '05P. Collier AB-OP/LHC17 What we’ve left for later … Anything to do with 25ns or 75ns operation and ‘High’ intensities  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 ( Andy 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 run:  Alignment optics and measurements for inner triplets.  Inner triplet correctors  Special features for ions ( J. Jowett this aft )

LHC Workshop, Jan '05P. Collier AB-OP/LHC18 Summary Start 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 needed  Revisit each system often  Attack only the things we need for the pilot physics goal  The rest can come progressively, later Fast track to complete the phase as quickly 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 beam/machine at each stage