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1 Accelerator Physics Aspects LHCb Accelerator Physics Aspects LHCb CERN SL/AP n Layout n Crossing Scheme n Luminosity n Collision Scheme n Electron Cloud n Impedances n Official Schedule

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2 Layout of the LHC

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3 Layout of IR8 Dispersion SuppressorTripletMatching

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4 A few definitions Beam transverse density, proportional to the beam-beam parameter Proportional to the beam current Inversely proportional to * Beam-Beam Parameter:

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5 A few definitions Head-on + Long range Beam-Beam Tune Shift Parameter: n Spread of the transverse oscillation frequencies n High order transverse resonances and a tune shift n It is limited by the space between dangerous resonances n Difficult to compensate for: all particles do not have the same tune shift Independent of * n Its nominal value is

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6 Crossing Angle n Avoid unwanted bunch collisions n Must be larger than the divergence of the beam envelope n Limited by the excursions of the beam trajectories (aperture limitations in the triplet) n In the expression for the luminosity there is a reduction factor for the crossing angle (0.1)

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7 Beam Separation and crossing scheme n Spectrometer magnet compensation: 3 correction magnets to make local bump n Horizontal crossing n Vertical separation when not in collision Spectrometer Correctors End of triplet Correctors D2 D1 IP

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8 Beam Separation and crossing scheme n Limitations by Aperture n Accomodate spectrometer -> 11.22m shift towards IP7 n Beam Separation 2 mm tot = spec + ext tot =345 rad / 75 rad depending on spectrometer polarity spec =135 rad positive or negative ext =210 rad constant n Crossing scheme only one direction n Ramping of spectrometer magnet important to permit both polarities of spectrometer (limitations at injection)

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9 Beam Separation and crossing scheme =1m 10mm 1mm 0.5mm

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10 Optics IR8 Beam Size =Sqrt ( * gamma) =70 m, =10m =400 m =160 m, =50

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11 Nominal Luminosity vs * n Wanted luminosity range for LHCb cm -2 s -1 Tunability 1m < * < 35m Luminosity requirements fulfilled dynamically by varying * Limited to 35m % of Nominal 10 % of Nominal

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12 Luminosity Lifetime n Scattering from residual gas ignored ( torr) n The beam-beam effect and the intrabeam scattering produce emittance increase but this is compensated by synchrotron radiation damping. The net result is a decrease of emittance. n We are left with the formula above giving a lifetime of 26 hours n Beam-gas induced lost rate into the pipe at the triplet under study Number of Interaction points Total cross section ( cm 2 )

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13 Luminosity Life Time n No Beam-Beam Blow up n No synchrotron radiation damping decreases L = 11hours n Synchrotron radiation (theory) constant L = 25hours n Synchrotron radiation (theory) decreases because of beam blow up (SppS Collider) L = 10hours n Run on Beam-beam limit

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14 Collision scheme n Distance between IPs = 891 half buckets: collision scheme has to repeat from one IP to the other n “Holes” (empty buckets) due to injection kickers SPS and LHC, dump Kicker LHC n There are 2808 filled buckets out of 3564 according to following scheme: {[(72b+8e)*3+30e]*2+[(72b+8e)*4+31e]}*3{[(72b+8e)*3+30e]*3+81e} n “Pacman” bunches: do not encounter bunches of the other beam in one or several parasitic collision points n “Superpacman” bunches: as “pacman” but not even at the collision point

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15 Filling scheme

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16 Horizontal orbit offsets Horizontal offset at IP1, in IP8 the situation is similar, need to scale so that the spread 1/10 of the beam size Zooming up Effects coming from the very start of train where there is a “big hole” Effects coming from the “small holes”

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17 Collision scheme n IP8 shifted by 3 half buckets which means 124 extra superpacman bunches in IP8 n Double bunch spacing no encounters in IP8 n Triple spacing means less luminosity (bunch current has to be increased by 3 1/2 to keep luminosity constant) Bunch offsets within at collision point, small effects IP8

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18 Longitudinal Impedance n Longitudinal impedance can cause longitudinal instabilities of the beam n The geometry of an element is crucial n All elements in the machine are optimized to give a minimum contribution to the impedance budget. n Longitudinal impedance budget is very tight n No feedback system in the LHC for longitudinal instabilities n A longitudinal feedback system is technically very difficult and expensive n The evaluation of the LHCb experimental beam pipe longitudinal impedance is done by Nikhef. Has to fit into total budget of the LHC! Examples of critical geometries Sharp edges not good

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19 Transverse Impedance n A transverse feedback system is required in the LHC to cure the effect of transverse impedance (resistive wall instability). n Aluminum, copper and beryllium are good materials (stainless steel not so good). n Transverse impedance should not exceed budget because of emittance conservation (feedback capabilities are limited)

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20 Higher Order Modes n Depends on the geometry of the object n Frequencey spectrum of loss factor should not overlap, bunch spectrum n Different positioning of the vertex detector gives different resonance conditions n All positions of the detector have to be evaluated n Heating up change resonance conditions, cooling down etc. Pumping effect. Different situations should be carefully evaluated

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21 Electron Cloud n Photons, protons, electrons from gas ionization n Critical dimensions of chamber n Heat Load n Vacuum

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22 Electron Cloud Scale different SEY=1.2 Boxes open, xb=12cm, yb=3cm SEY=2.8 Boxes closed, xb=6mm, yb=6mm

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23 Official Schedule n First Beam 01/02/2006 First Collisions 01/04/2006 L *=0.5 = cm -2 s -1 n Shut Down 01/05-31/07/2006 Physics Run 01/08/ /02/2007 L *=0.5 >= cm -2 s -1

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24 People who Contributed n Optics: Oliver Brüning n Crossing Scheme: Werner Herr, Oliver Brüning n Electron Cloud: Frank Zimmermann, Oliver Brüning n Impedance: Daniel Brandt, Oliver Brüning n Lattice files: Elena Wildner n Aperture: Bernard Jeanneret n Beam-Beam: H.Grote

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25 LHC general parameters

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26 Transverse Parameters

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27 Longitudinal Parameters

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