The Large Hadron Collider Machine, Experiments, Physics Accelerator physics and the LHC

1. The Large Hadron ColliderMachine, Experiments, PhysicsAccelerator physics and the LHC Johannes HallerThomas Schörner-Sadenius Hamburg UniversitySummer Term 2009

2. SETTING THE STAGE diagnostics deflection source acceleration “Everyman’s accelerator”: Television set! … 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! From there it is a long way to the LHC … … we will make it short! “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

3. MOTIVATION, BASICS • Basics of all beam-accelerating/–steering elements: • – Lorentz force: • – For the simple case of a perpendicular B field: • – Which fields for particle deflections? E or B? •  chose magnetic fields! • Circular or linear accelerators? • Linear: + Only focussing elements required.– One acceleration only!+ No synchrotron losses! • Circular: + Repeated acceleration!– More complex layout. – 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)! • Remember: Quantum mechanics, relativity • – DeBroglie: connection between wave length (resolution power) and particle momentum: • – Einstein: Wish for ever-higher center-of-mass energies • Want accelerators with ever higher energies to investigate ever smaller constituents of nature and to find new, heavy objects. Basics of accelerators: Electrodynamics, Maxwell: 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 • … UHH SS09: LHC

4. SYNCHROTRON RADIATION Emission is tangential to the orbit and collimated in narrow cone: Issues of radiation protection of humans, experiments, electronics, … Power radiated from relativistic particle under centripetal acceleration: Energy lost per orbit: Difference electron/protonfor same energy,radius: – Electron with v~c: – Proton with v~c: – Numbers: electrons in LEP: 3 GeV/turn protons in LHC: 6.7 keV/turn At LHC: Radiation will be visible to the eye! UHH SS09: LHC

5. COLLIDER VERSUS FIXED-TARGET Then the collider:  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) … Consider the following two scenarios (for protons): – 450 GeV is the maximum SppS energy at CERN! Let’s do the calculation: First fixed-target: UHH SS09: LHC

6. 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 UHH SS09: LHC

7. 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. UHH SS09: LHC

8. ACCELERATION 3: POWER TRANSFER One can show (B parallel, E perpendicular to wall): – General solution of wave equation: Applying boundary conditions for E,B fields: m,n specify the mode of the guide. Example TE10: Power is brought to the cavities in wave guides: – Behaviour of these (and of accelerating cavities) dictated by wave equation: With wave number: Considering, for simplicity, only z direction and assuming: … one can show that a solution is given by Special case: rectangular wave guide: UHH SS09: LHC

9. ACCELERATION 4: ACCELERATING CAVITIES Accelerating cavities: Particles accelerated by `riding’ on standing EM wave: – General solution of wave equation: – If wave completely reflected, then A=B: – Stable standing wave with constant amplitude if for cavity of length l: (n integer)  Length l has to match RF Frequency and particle momentum. Alternative (historic): alternating positive and negative electric fields: – 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: (Phase ψ between particles and field). UHH SS09: LHC

10. PARTICLE STEERING (1) Focusing (simple approach):  Combine two quadrupoles to have net focusing in two dimensions: The FODO structure! Dipole magnets: – B field perpendicular  force perpendicular to velocity v and B field!Dipoles define beam momentum!Quadrupole magnets: More complicated field shape: Gradient for particles in x and y, no field on axis focusing / defocusing action! UHH SS09: LHC

11. PARTICLE STEERING (2) • Develop B field in vicinity of orbit (x,y << R): • 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: 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 Sextupoletrajectory Octupoletrajectory Dipole:deflection QuadrupoleFocusing UHH SS09: LHC

12. 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:  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! Constant gradient: B field weaker towards larger r, r component! • 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

13. 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: For not too large amplitudes: harmonic oscillation around orbit and phase: synchrotron oscillations! Particle late/slow larger U, acceleration Particle early/fast:  Smaller U, acceleration UHH SS09: LHC

14. PARTICLE FOCUSING (3), BEAM CHARACT. Stochastic cooling: - Nobel prize S. v.d. Meer 1984- Active correction to wandering bunches.- “Nobel prize for finding out that the diameter is less then the circumference …”- especially important for anti-protons! … just a few buzz words: – β function: Measure for beam diameter; strictly speaking: β(s) is s-dependent amplitude of particle oscillations along the orbit. – Emittance ε: Measure for the divergence of the beam (beam quality). – Acceptance: A=min(d2(s)/β(s)), d=Strahlrohrdurchmesser, space for the beam at the narrowest position in s. – Enveloppe E: – Luminosity: Measure for beam intensity in cm-2s-1. UHH SS09: LHC

15. EXAMPLES OF ACCELERATORS (1) • Betatron: • Vacuum pipe with electrons serves as second transformator winding • 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. 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). – relativistic effects: m γm.   adapt frequency: synchro-cyclotron. – Also iso-cyclotron: adapt B field with radius. UHH SS09: LHC

16. CYCLOTRON IN ACTION UHH SS09: LHC

17. 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. – Particles travel along orbit many 106 times  importance of focusing – finally combine two synchrotrons  collider! UHH SS09: LHC

18. OVERVIEW OF HEP ACCELERATORS UHH SS09: LHC

19. DESY ACCELERATORS Hermes H1 ZEUS Petra/DESY UHH SS09: LHC

20. FERMILAB AND SLAC ACCELERATORS UHH SS09: LHC

21. CERN ACCELERATORS LEP, LHC SppS PS ISR UHH SS09: LHC

22. LHC ACCELERATOR SYSTEM UHH SS09: LHC

23. LHC UHH SS09: LHC

24. LHC REALISATION • Enveloppe of the LHC: • Regular pattern in the arcs. • Straight sections: max. focusing at IR: • Collision point beam size (rms, defined by β* ) - CMS & ATLAS: 16 μm, LHCb: 22-160 μm, - ALICE: 16 μm (ions), >160 μm (p) 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: UHH SS09: LHC

25. LHC: REALISATION UHH SS09: LHC

26. LHC IMPRESSIONS UHH SS09: LHC

27. LHC IMPRESSIONS – AND AN ACCIDENT UHH SS09: LHC

28. LHC IMPRESSIONS – AND AN ACCIDENT UHH SS09: LHC

29. LHC IMPRESSIONS – AND AN ACCIDENT UHH SS09: LHC

30. LHC IMPRESSIONS – AND AN ACCIDENT UHH SS09: LHC

31. LHC DETAILS • Increase with respect to existing accelerators : • A factor 2 in magnetic field • A factor 7 in beam energy • A factor 200 in stored energy In : – We UHH SS09: LHC

32. 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 ! UHH SS09: LHC

33. 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. UHH SS09: LHC

34. 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”, … Applications of accelerators: – Cancer therapy – TV, monitors – production of radio-active substances (radio chemistry). – material sciences – … UHH SS09: LHC

35. 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 UHH SS09: LHC