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The Large Hadron Collider Machine, Experiments, Physics Accelerator physics and the LHC Johannes Haller Thomas Schörner-Sadenius Hamburg University Summer Term 2009 SETTING THE STAGE “Everyman’s accelerator”: Television set! deflection From there it is a long way to the LHC … … we will make it short! diagnostics source acceleration … but accelerators have come a long way: Thompson watched scintillations of particles on screens in glass pipes “cathode rays”. Deflection of electrons with E,B fields! JH/TSS “Livingston plot”: – About a decade in energy per time decade! Trend also for the future? Costs? Space? – What about cosmic accelerators? Astroparticle physics? – Caveat: Plot not precise – many machines run at different energies with different particles … UHH SS09: LHC 2 MOTIVATION, BASICS Basics of all beam-accelerating/–steering elements: dp – Lorentz force: Remember: Quantum mechanics, relativity – DeBroglie: connection between h wave length (resolution power) p and particle momentum: – Einstein: Wish for ever-higher E mc2 center-of-mass energies Want accelerators with ever higher energies to investigate ever smaller constituents of nature and to find new, heavy objects. F q ( E v B) – For the simple case of a perpendicular B field: mv 2 mv p qvB B r qr qr – Which fields for particle deflections? E or B? chose p 0.3GeV / c q e r 1m magnetic fields! B 1T E 300MV / m Basics of accelerators: Electrodynamics, Maxwell: D B 0 E B B j D Electric and magnetic fields are used to accelerate, collect and guide clouds of particles through an accelerator. We will discuss: - History of accelerators - Dipols, quadrupoles, sextupoles, …, focusing - Optical lattices - Accelerations -… JH/TSS dt Circular or linear accelerators? - Linear: + Only focussing elements required. – One acceleration only! + No synchrotron losses! 4 - Circular: + Repeated acceleration! 1E E – More complex layout. Rm – Synchroton losses Particle types? - Electrons: high synchrotron losses ideal point sources well-known initial states. - Protons: necessary B field rises with m (if r const)! UHH SS09: LHC 3 SYNCHROTRON RADIATION Emission is tangential to the orbit and collimated in narrow cone: Power radiated from relativistic particle under centripetal acceleration: e 2c 1 E4 PS 60 (m0c 2 ) 4 R 2 Energy lost per orbit: 2R e 2 1 E4 W PS dt PS c 30 m0c 2 4 R Difference electron/proton for same energy,radius: – Electron with v~c: Ps ,e Ps , p m4p 4 e m 1.13 1013 E 4 [GeV 4 ] W 8.85 10 MeV [km] 5 – Proton with v~c: W 7.8 10 6 E 4 [TeV 4 ] MeV [km] – Numbers: electrons in LEP: 3 GeV/turn protons in LHC: 6.7 keV/turn Issues of radiation protection of humans, experiments, electronics, … At LHC: Radiation will be visible to the eye! JH/TSS UHH SS09: LHC 4 COLLIDER VERSUS FIXED-TARGET Then the collider: Consider the following two scenarios (for protons): – 450 GeV is the maximum SppS energy at CERN! p1 p2 2 E1 E2 2 p1 p 2 2 2 2 2 E 900 GeV 2 s ECM p1 p2 2 2 m ??? m s1 Let’s do the calculation: First fixed-target: p1 p2 2 E1 E2 2 p1 2 E12 E22 2 E1 E2 p12 m 2 p12 m 2 2 E1m p12 2m 2 2 E1m 2m( E1 m) 2m 2 ( 1) 29 GeV 2 JH/TSS If technically possible build colliders! - Fixed-target experiments today used if strong boosts wanted, for example to produce beams of certain particles (pions, kaons, neutrinos, …) or if asymmetry required (BABAR) … UHH SS09: LHC 5 ACCELERATION 1: OVERVIEW Acceleration involves several steps: – Power generation in klystrons generation of very intense, high-frequency electromagnetic fields. – Transport of this energy from the klystron to the accelerator wave guides – Power transmission from electromagnetic wave to particles accelerating resonating cavities JH/TSS UHH SS09: LHC 6 ACCELERATION 2: POWER GENERATION Today, acceleration happens with high-frequency RF EM fields. The necessary power is generated in klystrons (field amplifiers): – Low-current electron beam is accelerated and cut into bunches by applying HF fields in first resonating cavity. – Bunched electrons induce high-power HF fields in second cavity that can then be transferred to accelerating cavities in the accelerator ring. JH/TSS UHH SS09: LHC 7 ACCELERATION 3: POWER TRANSFER Power is brought to the cavities in wave guides: – Behaviour of these (and of accelerating cavities) dictated by wave equation: One can show (B parallel, E perpendicular to wall): – General solution of wave equation: f x ( x) A sin( k x x) B cos( k x x) 2 2 E c E 0 E r k E r 0 With wave number: k c f y ( y ) C sin( k y y ) D cos( k y y ) Applying boundary conditions for E,B fields: 2 k x a m k y b n Considering, for simplicity, only z direction and assuming: E x 0 E y E0 sin( … one can show that a solution is given by kz2 k 2 kx2 ky2 k 2 2 2 m,n specify the mode of the guide. Example TE10: E z x, y,z f x x f y y f z z Ez E0 eikz z m n k a b 2 c f x f y fx fy x ikz z )e a Ez 0 Special case: rectangular wave guide: JH/TSS UHH SS09: LHC 8 ACCELERATION 4: ACCELERATING CAVITIES Accelerating cavities: Particles accelerated by `riding’ on standing EM wave: – General solution of wave equation: W (r , t ) A exp i t k r B exp i t k r Alternative (historic): alternating positive and negative electric fields: – If wave completely reflected, then A=B: W (r , t ) 2 A cos k r exp it – Stable standing wave with constant amplitude if for cavity of length l: (n integer) Length l has to match RF Frequency and particle momentum. ln z 2 – Drift tubes alternatingly connected to poles of HF. – Acceleration between tubes. – Drift lengths, energy and frequencies need to be tuned. – No continuous particle flow! Bunched operation! – Efficient for light particles (synchrotron radiation) – Today also with resonating cavities (ILC). – Energy after n drift tubes: En nqU 0 sin (Phase ψ between particles and field). JH/TSS UHH SS09: LHC 9 PARTICLE STEERING (1) Focusing (simple approach): Dipole magnets: – B field perpendicular force perpendicular to velocity v and B field! B p qR Dipoles define beam momentum! Quadrupole magnets: More complicated field shape: Gradient for particles in x and y, no field on axis focusing / defocusing action! JH/TSS Combine two quadrupoles to have net focusing in two dimensions: The FODO structure! UHH SS09: LHC 10 PARTICLE STEERING (2) Dipole and Qaudrupole magnets: – provide stable trajectory for particles with nominal momentum Sextupole magnets: – Correct trajectories of off-momentum particles. Multipole magnets (up to 10 or 12 poles) – Used to compensate field imperfections of the dipoles. Improve beam quality and lifetime. From these elements a “lattice” is build up – aim for regular structures for easy-to-understand machine: Formalism for description: multipole expansion: - use Lorentz force, B=(Bx,By,0), v=(0,0,vs), path length s and mv2 e 1 qvB By ( x, y, s) r p R( x, y, s) JH/TSS Develop B field in vicinity of orbit (x,y << R): 2 3 dB y e e 1 d By 2 1 d By 3 B y ( x) ( B y 0 x x x ...) p p dx 2! dx 2 3! dx 3 1 1 1 kx mx2 x 3 ... R 2! 3! Dipole: deflection Quadrupole Focusing Sextupole trajectory Octupole trajectory With multipoles I influence the path in great details. Use mainly dipoles and quadrupoles (“linear optics”, easy to calculate). Description of lattice / behaviour of beams: Matrix formalism: – 6 quantities to describe beam particles: x,x’,y,y’,s,δ – Each optical element corresponds to one 6*6 matrix acting on the 6-vector of the particle. Describe ring by product of “transfer” matrices: UHH SS09: LHC x( s ) x(0) M N ... M 2 M 1 x ( s ) x ( 0 ) 11 PARTICLE FOCUSING (1) (Weak) transverse focusing: – Particles tend to leave orbit horizontally and/or vertically (Coulomb repulsion, starting conditions). – In horizontal plane deflecting dipoles have weak focusing action: Consider particle with distance x to beam: Constant gradient: B field weaker towards larger r, r component! Trajectory is bent towards orbit! Focusing! But oscillations! – Vertically slightly more difficult: constant gradient scheme for magnets with large dipole gaps: Small Br component. Particles perform oscillations around orbit! JH/TSS More efficient: strong focusing and “alternating gradient scheme”: - constant gradient: dipoles opened towards outside. - Idea Livingston et al: Open some dipoles towards inside different focusing effect also smaller dipole gaps and thus higher fields possible. - First used at AGS and CERN PS (30 GeV). - Still one step further: FFAG: Gradient spiraling around orbit not pursued. - Today: Focusing with multipoles (FODO!). UHH SS09: LHC 12 PARTICLE FOCUSING (2) Strong focusing with two quadrupoles in action: Longitudinal focusing and phase stability: – Particles not all in sync with accelerating phase. – Solution: On–time particles should not arrive on the peak: Particle late/slow larger U, acceleration Particle early/fast: Smaller U, acceleration For not too large amplitudes: harmonic oscillation around orbit and phase: synchrotron oscillations! JH/TSS UHH SS09: LHC 13 PARTICLE FOCUSING (3), BEAM CHARACT. Stochastic cooling: … just a few buzz words: - Nobel prize S. v.d. Meer 1984 – β function: Measure for beam diameter; strictly - Active correction to wandering bunches. speaking: β(s) is s-dependent amplitude of - “Nobel prize for finding out that the diameter is less particle oscillations along the orbit. then the circumference …” – Emittance ε: Measure for the divergence of the - especially important for anti-protons! beam (beam quality). – Acceptance: A=min(d2(s)/β(s)), d=Strahlrohrdurchmesser, space for the beam at the narrowest position in s. – Enveloppe E: E(s) (s) – Luminosity: Measure for beam intensity in cm-2s-1. L f JH/TSS UHH SS09: LHC n1n2 4 x x* y y* 14 EXAMPLES OF ACCELERATORS (1) Betatron: - Vacuum pipe with electrons serves as second transformator winding Cyclotron: – constant B field, but r~v orbit timeτ=const. – Particles run on spirals, on each orbit two acceleration steps. – Maximum energy 33 MeV at 2 T (protons). E B - Variable flux in magnet yoke variable B field variable E field for acceleration. - Also guiding field grows with the flux. - Only ¼ of oscillations useable. - Maximum energy limited by synchrotron radiation, ~100 MeV. – relativistic effects: m γm. eB m adapt frequency: synchro-cyclotron. – Also iso-cyclotron: adapt B field with radius. JH/TSS UHH SS09: LHC 15 CYCLOTRON IN ACTION JH/TSS UHH SS09: LHC 16 EXAMPLES OF ACCELERATORS (2) Synchrotron: – With realistic fields and energies E > 1 GeV radius for single magnets gets too large. – Idea: Keep R constant and increase E and B in synchronised way. mv mc 2v E r 2 qB qc B qcB (v c) – Particles travel along orbit many 106 times importance of focusing JH/TSS – finally combine two synchrotrons collider! UHH SS09: LHC 17 OVERVIEW OF HEP ACCELERATORS Collider Start/end Beams Max. energy [GeV] Circumference or length [km] PETRA (DESY) 1978-86 e +e – 23.4 2.304 SLC (SLAC) 1989-99 e +e – 50 1.45 + 1.47 LEP (CERN) 1989-2000 e +e – 104 26.7 ILC (?) 20??-?? e +e – 500? 15+15 (?) KEKB (KEK) 1999-?? e +e – 8 x 3.5 3.0 PEP-II (SLAC) 1999-?? e +e – 9 x 3.1 2.2 HERA (DESY) 1991-2007 ep 27.5 x 820/920 6.3 SppS (CERN) 1981-1990 ppbar 315 6.9 TEVATRON (FNAL) 1987-2009/10 ppbar 1000 6.28 LHC (CERN) 2008-?? pp 7000 26.7 ???? JH/TSS UHH SS09: LHC 18 DESY ACCELERATORS Hermes H1 ZEUS Petra/DESY JH/TSS UHH SS09: LHC 19 FERMILAB AND SLAC ACCELERATORS JH/TSS UHH SS09: LHC 20 CERN ACCELERATORS LEP, LHC Spp S ISR JH/TSS PS UHH SS09: LHC 21 LHC ACCELERATOR SYSTEM JH/TSS UHH SS09: LHC 22 LHC JH/TSS UHH SS09: LHC 23 LHC REALISATION Enveloppe of the LHC: - Regular pattern in the arcs. - Straight sections: max. focusing at IR: LHC RF system: – operates at 400 MHz. – 16 SC cavities, 8 per beam. – peak accelerating voltage: 16 MV / beam (for comparison: LEP at 104 GeV: 3600 MV) reason: synchrotron loss: LEP: 3 GeV / turn LHC: 6.7 keV / turn LHC dipoles: - Collision point beam size (rms, defined by β* ) - CMS & ATLAS: 16 μm, LHCb: 22-160 μm, - ALICE: 16 μm (ions), >160 μm (p) JH/TSS UHH SS09: LHC 24 LHC: REALISATION JH/TSS UHH SS09: LHC 25 LHC IMPRESSIONS JH/TSS UHH SS09: LHC 26 LHC IMPRESSIONS – AND AN ACCIDENT JH/TSS UHH SS09: LHC 27 LHC IMPRESSIONS – AND AN ACCIDENT JH/TSS UHH SS09: LHC 28 LHC IMPRESSIONS – AND AN ACCIDENT JH/TSS UHH SS09: LHC 29 LHC IMPRESSIONS – AND AN ACCIDENT JH/TSS UHH SS09: LHC 30 LHC DETAILS Increase with respect to existing accelerators : In : • A factor 2 in magnetic field – We • A factor 7 in beam energy • A factor 200 in stored energy JH/TSS UHH SS09: LHC 31 POWER IN THE LHC Comparison: – Energy of A380 at 700 km/h corresponds to energy stored in the LHC magnet system! – Sufficient to heat up and melt 12 tons of copper! Energy in the beams: – corresponds to 90 kg of TNT – 8 litres of gasoline – 15 kg of chocolate It’s how easy the energy is released that matters ! JH/TSS UHH SS09: LHC 32 HISTORY AND STATUS OF THE LHC History: – 1982: First studies for LHC project – 1983: Z/W discovery at SppS – 1989: Start of LEP operation – 1994: Approval of CERN project by CERN Council – 1996: Final decision to start LHC construction – 1996: LEP operation > 80 GeV (W factory) – 2000: Final year of LEP operation – 2001: CERN financial crisis: 1B CHF missing extension of LHC program – 2002: Removal of LEP equipment – 2003: Start of LHC installation – 2005: Start of hardware commissioning – 2007: Magnet failure 6 months delay – 2008: Beam commissioning - 10 September 2008: First beams - 19 September 2008: Helium leak - Expected restart: October 2010. JH/TSS UHH SS09: LHC 33 THINGS NOT COVERED (IN DETAIL) … due to time constraints or lack of interest: – Interlock – Quenching and machine protection – Beam dumping – Superconductivity – Collimation and lifetime – Commissioning and operation – Interaction region layout – Comparison to Tevatron – Preacceleration and injection – old accelerator principles as cascade accelerators (Cockcroft-Walton), “Band-Generator”, … JH/TSS Applications of accelerators: – Cancer therapy – TV, monitors – production of radio-active substances (radio chemistry). – material sciences –… UHH SS09: LHC 34 LITERATURE Some literature on accelerators (for HEP): E. Wilson, “An Introduction to Particle Accelerators”, Oxford 2001 H. Wiedemann, “Particle Accelerator Physics” I & II, Springer 1993/1995 K. Wille, Physik der Teilchenbeschleuniger, Teubner 1992 (auch auf Englisch) Particle Data Group, Phys. Rev. D66 (2002) 010001-1, http://pdg.lbl.gov SLAC Linear Accelerator Center, http://www2.slac.stanford.edu/vvc/accelerators/ CERN, http://public.web.cern.ch/Public/ACCELERATORS/accintro.html JH/TSS UHH SS09: LHC 35