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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) Slide 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 Slide 3 III.I. The straight sections SPS (~7 km) LHC (27 km) IR ARC Sector DS MS IR IT IP Slide 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 Slide 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 Slide 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 Slide 7 III.II Momentum and betatron cleaning insertions (IR3, IR7) 14 50 6(9) Settings @7TeV and *=0.55 m Beam size ( ) = 300 m (@arc) Beam size ( ) = 17 m (@IR1, IR5) 77 8.5 Slide 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 Slide 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 Slide 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) x /2** y /2**QxQy Injection182.6182.64464.2859.31 Collision0.552.6332.64964.3159.32 Slide 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 Slide 12 slide 12 III.III. The experiments: High luminosity insertions ATLAS five-storey building CMS Slide 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 Slide 14 LHCb experiment Center of the exp cavern Slide 15 III.III. The experiments: Low luminosity insertions ALICE LHCb Slide 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 Slide 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 Slide 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 Slide 19 III.IV. Squeeze IR2 IR1 IR3IR4 IR5 IR6IR7IR8 IR1 Injection Beta function at top energy and after squeeze Slide 20 III.IV. Squeeze ATLAS=CMS Q1Q3D2Q5 Q2 D1Q4Q6 Q7 2MB Q8 2MB Q9 2MB Q10 2MB Q11 ITMSDS Slide 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 Slide 22 III.IV Colliding with a Xangle Why? to minimize beam-beam interaction effects Vertical Xangle (160 rad @ injection, 142.5 rad @collis) Horizon Xangle (160 rad @ injection, 142.5 rad @collis) Slide 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 Slide 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 () contribution, which for a crossing angle in the horizontal plane (XS, with S the direction of movement) takes the form: F LHC = 0.836 1 (x,y,s,-s 0 ) 2 (x,y,s,-s 0 ) s x Slide 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. Slide 26 III.IV Luminosity optimization Method orthogonal separation scans Example from LEP x y Slide 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