Accelerator Physics Aspects LHCb Elena.Wildner@cern.ch CERN SL/AP

1. Accelerator Physics Aspects LHCbElena.Wildner@cern.ch CERN SL/AP • Layout • Crossing Scheme • Luminosity • Collision Scheme • Electron Cloud • Impedances • Official Schedule

2. Layout of the LHC

3. Layout of IR8 Dispersion Suppressor Matching Triplet

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

5. A few definitions Beam-Beam Tune Shift Parameter: Head-on + Long range • Spread of the transverse oscillation frequencies • High order transverse resonances and a tune shift • It is limited by the space between dangerous resonances • Difficult to compensate for: all particles do not have the same tune shift • Independent of b* • Its nominal value is 0.0035

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

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

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

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

10. Optics IR8 s =400mm s =70mm, b=10m s =160mm, b=50 Beam Size s =Sqrt (e*b/gamma)

11. Luminosity vs b* • Wanted luminosity range for LHCb 1-5 1032 cm-2 s-1 • Tunability 1m < b* < 35m • Luminosity requirements fulfilled dynamically by varying b* Limited to 35m 5 1032 Nominal 1 1032 50% of Nominal 10 % of Nominal

12. Luminosity Lifetime • Scattering from residual gas ignored (10-12 torr) • 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. • We are left with the formula above giving a lifetime of 26 hours • Beam-gas induced lost rate into the pipe at the triplet under study Number of Interaction points Total cross section (10-25 cm2)

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

14. Collision scheme • Distance between IPs = 891 half buckets: collision scheme has to repeat from one IP to the other • “Holes” (empty buckets) due to injection kickers SPS and LHC, dump Kicker LHC • 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} • “Pacman” bunches: do not encounter bunches of the other beam in one or several parasitic collision points • “Superpacman” bunches: as “pacman” but not even at the collision point

15. Filling scheme

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

17. Collision scheme • IP8 shifted by 3 half buckets which means 124 extra superpacman bunches in IP8 • Double bunch spacing no encounters in IP8 IP8 • Triple spacing means less luminosity (bunch current has to be increased by 31/2 to keep luminosity constant) • Bunch offsets within +-0.1s at collision point, small effects

18. Longitudinal Impedance • Longitudinal impedance can cause longitudinal instabilities of the beam • The geometry of an element is crucial • All elements in the machine are optimized to give a minimum contribution to the impedance budget. • Longitudinal impedance budget is very tight • No feedback system in the LHC for longitudinal instabilities • A longitudinal feedback system is technically very difficult and expensive • 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

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

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

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

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

23. Official Schedule • First Beam 01/02/2006 • First Collisions 01/04/2006 L b*=0.5=5 1032cm -2 s-1 • Shut Down 01/05-31/07/2006 • Physics Run 01/08/2006-28/02/2007 L b*=0.5>= 2 1033cm -2 s-1

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

25. LHC general parameters

26. Transverse Parameters

27. Longitudinal Parameters