1. The Large Hadron Collider Contents: 1. The machine II. The beam III. The interaction regions IV. First LHC beam [R. Alemany] [CERN AB/OP] [Engineer In Charge of LHC] Lectures at NIKHEF (12.12.2008)

2. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Squeeze V.Colliding with a crossing angle VI.Luminosity optimization

3. III.I. The straight sections SPS (~7 km) LHC (27 km) IR ARC Sector DS MS IR IT IP

4. III.I. The straight sections A straight section is composed of: 1.Matching section (MS) 2.Inner triplets (IT) (  there is an experiment) 3.IR: collimators, RF, dump system, experiments

5. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Luminosity optimization

6. III.II Momentum and betatron cleaning insertions (IR3, IR7) Particles with large momentum offset are scattered by the primary collimators in IR3. Particles with large H, V or H&V betatron amplitudes are scattered by the primary collimators in IR7. In both cases the scattered particles are absorbed by secondary collimators. Typical quadrupole strength 30-35 T/m Note: IR3 & IR7 have special DS (arc quadrupoles in series + trim quadrupoles) because of lack of space to place the power converters. IR3 IR7 Q4Q5Q6Q7D3D4 (collimators are not shown) Warm magnets 224 mm

7. III.II Momentum and betatron cleaning insertions (IR3, IR7)  14  50   6(9)  Settings @7TeV and  *=0.55 m Beam size (  ) = 300 µm (@arc) Beam size (  ) = 17 µm (@IR1, IR5) 77 8.5 

8. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Squeeze V.Colliding with a crossing angle VI.Luminosity optimization

9. III.III The experiments: High luminosity insertions The high luminosity insertions are IR1 (ATLAS) and IR5 (CMS) They are identical in terms of hardware and optics The optics design is guided by two main requirements: Large dynamic range of  * values while keeping the total phase advance over the IR constant:  * = 18 m for injection  * = 0.55 m for collisions When changing from injection to collision optics, the quadrupole magnets must change smoothly with  * to have under control the beam size, the beam separation and the chromaticity

10. III.III The experiments: High luminosity insertions The hardware constraints: The beams share the same beam pipe and the same low beta triplet quadrupoles, so the optics solution must have the same triplet gradients. The maximum gradients are constraint The overall beam size must be small enough to fit into the tight aperture of the LHC at this location Optics: * The beams at pre-collision are displaced from the ideal orbit to increase the mechanical aperture of the low beta triplet quadrupoles ** phase advance for the whole insertion region (Q13.R – Q13.L) Optics  * (m) µ x /2π**µ y /2π**QxQy Injection182.6182.64464.2859.31 Collision0.552.6332.64964.3159.32

11. Q2 Q1 Q3 III.III. The experiments: High luminosity insertions IP1 TAS* Q1 Q2 Q3D1 (1.38 T) TAN* D2 Q4 (3.8 T) Q5Q6 Q7 4.5 K 1.9 KWarm Separation/ Recombination Matching Quadrupoles Inner Triplet 1.9 K ATLAS R1 * Protect Inner Triplet (TAS) and D2 (TAN) from particles coming from the IP 4.5 K 188 mm Tertiary collimators 6.45 kA10.63 kA 23.85 18.95 22.5 17.6 29.0 24.0 To provide sufficient aperture for the Xangle The mechanical aperture of the inner triplets limits the maximum  * @IPs and the maximum Xangle  limit peak lumi

12. slide 12 III.III. The experiments: High luminosity insertions ATLAS five-storey building CMS

13. III.III. The experiments: Low luminosity insertions LHCb Q7Q6Q5Q4D2 MKI Q1 Q2 Q3 ALICE IP8 LHCb MSI TDI TCDD D1 Beam 1 Beam 2 Beam 1

14. LHCb experiment Center of the exp cavern

15. III.III. The experiments: Low luminosity insertions ALICE LHCb

16. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Squeeze V.Colliding with a crossing angle VI.Luminosity optimization

17. III.IV. Squeeze Squeeze: change quadrupole currents (magnet strength) in a way that the beta function at the interaction point is very small  to increase luminosity Magnets: matching quadrupoles RB RQD/RQF

18. III.IV. Squeeze So even though we squeeze our 100,000 million protons per bunch down to 16 microns (1/5 the width of a human hair) at the interaction point. We get only around 20 collisions per crossing with nominal beam currents. The bunches cross (every 25 ns) so often we end up with around 600 million collisions per second - at the start of a fill with nominal current. Most protons miss each other and carry on around the ring. The beams are kept circulating for hours  10 hours Squeeze the beam size down as much as possible at the collision point to increase the chances of a collision

19. III.IV. Squeeze IR2 IR1 IR3IR4 IR5 IR6IR7IR8 IR1 Injection Beta function at top energy and after squeeze

20. III.IV. Squeeze ATLAS=CMS Q1Q3D2Q5 Q2 D1Q4Q6 Q7 2MB Q8 2MB Q9 2MB Q10 2MB Q11 ITMSDS

21. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Squeeze V.Colliding with a crossing angle VI.Luminosity optimization

22. III.IV Colliding with a Xangle Why?  to minimize beam-beam interaction effects Vertical Xangle (160 µrad @ injection, 142.5 µrad @collis) Horizon Xangle (160 µrad @ injection, 142.5 µrad @collis)

23. III. The interaction regions Contents: I.The straight sections II.Betatron and momentum cleaning insertions III.The experiments: II.High luminosity insertions (ATLAS & CMS) III.Low luminosity insertions (ALICE & LHCb) IV.Squeeze V.Colliding with a crossing angle VI.Luminosity optimization

24. III.IVLuminosity optimization Luminosity formulae: N i = number of protons/bunch N b = number of bunches f rev = revolution frequency  ix = beam size along x for beam i  iy = beam size along y for beam i Assume Gaussian distributions for the beam distribution functions and equal bunch length. W is a pure beam offset contribution. If the offset is in the horizontal plane beam 1 is displaced by d 1 and beam 2 is displaced by d 2 with respect to their reference orbits, thus W takes the form: F is a pure crossing angle (Φ) contribution, which for a crossing angle in the horizontal plane (XS, with S the direction of movement) takes the form: F LHC = 0.836 Φ ρ 1 (x,y,s,-s 0 )ρ 2 (x,y,s,-s 0 ) s x

25. III.IV Luminosity optimization exp(B 2 /A) is a term that appears when beams collide with a crossing angle and an offset at the same time. For a crossing angle and an offset in the x direction: Luminosity monitors in the machine  BRAN detectors: Luminosity scans: 1: Get the beams into collision (the first days of beam commissioning); 2: Optimize luminosity  every fill 3: Calibrate luminosity based on machine parameters  dedicated runs Each of these is of course applicable at each of the four LHC interaction points.

26. III.IV Luminosity optimization Method  orthogonal separation scans Example from LEP x y

27. III.IV Luminosity optimization Luminosity ≠ cte over a physics run. It decays due to degradation of intensities and emittance. The main cause of lumi decay are the collisions themselves, but there are other contributions like beam-gas scattering, beam-beam interactions   ~ 15 hours (lumi lifetime) 600 million collisions/sec = 20 coll/crossx2808x11000Hz Raw data rate is 10 15 bytes/sec equivalent to >1 million CD-roms/sec Only 0.00025% recorded for analysis experimental “trigger” rejects the rest