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5th Particle Physics Workshop National Centre for Physics Quaid-i-Azam University Campus, Islamabad PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE Hans-H. Braun, CERN ¾ History and Physics Principles of Particle Accelerators Origins From Zyklotron to Synchrotron Defocusing + Focusing = Focusing Particle Colliders ¾ An Overview of Accelerator Applications Synchrotron Radiation, from Nuisance to Bright Light Beams for Medicine Particle Accelerators for Particle Physics ¾ Introduction to Linear e+/e- Colliders and CLIC Linear Colliders - Motivation and Concept Technical Challenges for Linear Colliders CLIC 5th Particle Physics Workshop National Centre for Physics Quaid-i-Azam University Campus, Islamabad PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE Hans-H. Braun, CERN 1st Lecture History and Physics Principles of Particle Accelerators o Origins o From Zyklotron to Synchrotron o Defocusing + Focusing = Focusing o Particle Colliders Origins One of the first particle beam set-up’s (Marsden didn’t get a stamp) The Rutherford-Geiger-Marsden Experiment (1906-1913) Showed that the Thomson (or Plum Pudding) model of the atom is wrong ! Atoms consists of extremely small nucleus of positive electric charge, carrying almost all the mass of the atoms. The nucleus is surrounded by a diffuse cloud of almost weightless electrons with negative charged. Rutherford experiment started interest in subatomic length scales Ernest Rutherford cajoled for years British industry to push development of high voltage sources as replacement for the α-emitters in his experiments. Why ? • Higher flux of particles • Particles of higher velocity ⇔ higher momentum ⇔ higher kinetic energy Motivations for higher beam energies I Theory of microscope: Only objects larger than the wavelength λ of light can be resolved Louis De Broglie 1923: Particles have wave properties with wavelength given by h h h = λ= = P 2m E KIN 2m q U de Broglie wavelength of α particles vs. kinetic energy -14 10 λ (m) strongest α sources size of proton -15 10 -16 10 6 10 7 8 10 10 Accelerating Voltage (MV) 9 10 Motivations for higher beam energies II Coulomb barrier for charged-particle reactions + elect ric forc e + + + + Motivations for higher beam energies III Einstein* 1905: Energy equivalent to mass E = m c2 ⇒ Collisions of energetic particles can create new particles, if kinetic energy is sufficient Traces of particles produced in collision of gold atoms at 100 GeV *many stamps Electrostatic Generators Van de Graaff Generator, 1931 Limited to K20MV by electrical sparking Linear accelerator (Rolf Wideroe 1928) … and half an RF period later L= Lengths of drift tubes follow increasing velocity Particle gains energy at each gap, total acceleration Applied acceleration is N 1 v 2 f NGAP ·VRF times higher than electric voltage ! Wiederoe’s first LINAC In 1928 voltage from RF oscillators was small and the linear accelerator, (or LINAC ) not competitive with electrostatic accelerators RADAR technology boosted the development of RF sources during World War II. This eventually made LINAC’s the accelerator of choice for many applications. Fermilab proton linac (400MeV) Inside proton linac Electron Linacs Because of higher particle velocity (≈c0), higher frequency (1.3-30 GHz) and different accelerating structure types. Most common building block it traveling wave structure. pulsed RF Power source Electric field RF wall currents d Electrically coupled TM010 resonant cavities Condition for acceleration Δϕ = ω/c·d, with Δϕ the phase difference between adjacent cells RF load TM 010 "pill box cavity mode" E 0 J 0 ( ωc r ) cos(ωt ) EZ = Bφ E0 J 1 ( ωc r ) sin(ωt ) c Resonant frequency given by 1st zero c of Bessel function, ω = 2.405 R ω independent of d ! Bφ = − EZ R d Stored Energy ∫∫ 0 0 0 = π 2 2 ( E + c Bφ ) r dr dφ dz 2 Z ε 0 d E Z2 R 2 J 1 (2.405) 2 Power loss given by P=- ω Q W, Q ≈ 100 0.2 50 0.1 2 7 ⋅ 10 8 f (typical Q value for copper accelerating structures) 0 0 0.5 1 ω/c r 1.5 2 0 2.5 Bφ (T) W=∫ ε0 EZ (MV/m) d 2π R d Coupled chain of resonators ″ ″ ″ Ei + ω 0 E + aEi −1 + Ei +1 = 0 i-1 Ansatz i i+1 Ei −1 = e i (ωt +ϕ ) , Ei = e iωt , Ei +1 = e i (ωt −ϕ ) ; ⇒ Dispersion relation wavenumber ⇒ Group velocity ω= k= ω0 1 + 2a cosϕ ϕ d a d ω 0 sin kd dω vG = = 3 dk (1 + 2a cos kd ) 2 ω ω0 vP = ω k = ωd = v ELECTRON ϕ ϕ 3 GHz accelerating structure of CTF3 Input power Pulse length Length Beam current Acceleration Frequency 30 MW 1.5 μs 1m 3.5 A 9 MV 2.99855 GHz Dipole modes suppressed by slotted iris damping (first dipole’s Q factor < 20) and HOM frequency detuning Damping slot SiC load Cyclotron Lawrence & Livingston 1932 The same acceleration gap traversed many times ! Lorentz Force = Centrifugal Force m v2 ev B = R mv Radius of trajectory R = eB 2π R 2π m T= Revolution time = v eB Cyclotron frequency f = eB 2π m Independent of velocity ! R Example: a typical proton Zyklotron B = 1.7 T R = 0.75 m f = EKIN eB = 25.92 MHz 2π m 2 ( e B R) = 2 mP = 1.247 ⋅10 −11 J = 77.86 MeV Cyclotron frequency f = Theo ry relat of ivity eB 2π m Independent of velocity ? meffective ⎛ EKIN ⎞ ⎟ = m0 ⎜⎜1 + 2 ⎟ ⎝ m0c ⎠ ⇒ Cyclotron principle works only for beam energies EKINh m0 c2 For example for protons EKINh 938 MeV (with some tricks ¡600 MeV can be obtained) The Synchrotron Proposed independently and simultaneously 1945 by McMillan in the USA and Veksler in the USSR E.M. McMillan V. Veksler magnetic field Electromagnet of variable strength Magnetic cycle synchrotron ion rat e l e acc injection extraction injection time RF electric field with variable frequency f=g(t) N S Beam on circular orbit with constant radius B(t) To make synchrotron work magnetic field, RF frequency and voltage have to be controlled following a system of coupled equations: dEkin(t) = e VRF f (t ) dt m c ( Ekin(t) + m c 2 ) 2 B (t ) = −1 eR m 2c 4 f(t) VRF EKIN(t) Layout of an early proton synchrotron f (t ) = v(t) 2π R m 2c 4 v(t ) = c 1 − ( Ekin(t) + m c 2 ) 2 Taken relativistic mass increase into account ! ⇒ Synchrotron can be build for very high energies. For proton beams limits are given by achievable magnetic field and size. Largest synchrotron LHC at CERN (under construction), 27km circumference, BMAX=8.3 T, EKIN=7.000.000 MeV Variation of parameters with time in a proton synchrotron Proton Synchrotron, R= 10m, VRF=10 kV, EKinetic at injection=10MeV 2.5 ´ 108 particle velocity m s 4000 EKinetic MeV 3 ´ 108 @ D 5000 3000 2000 1000 2 ´ 108 1.5 ´ 108 1 ´ 108 5 ´ 107 0 0.2 0.4 @ D 0.6 0.8 1 0 0.2 2 @ D 0.4 0.6 0.8 1 Time s Time s @ D 5 1 @ D 1.75 0.75 2 4 1.25 fRevolution MHz magnetic field T 1.5 3 0.5 1 0.25 0 0.2 0.4 @ D 0.6 Time s 0.8 1 0 0.2 0.4 @ D 0.6 Time s 0.8 1 How to keep beam particles together ? In light optics an array of focusing lenses is used to keep light rays together An electromagnet in quadrupole configuration will have a similar effect on a particle beam. Δφ iron yoke x The action of each lens can be described as an angle change of the trajectory x Δφ = − f N S S N coil quadrupole magnet However there is one big difference, considering the direction of Lorentz force you find that it focuses in one plane, but defocuses in the other ! 1952 Courant, Snyder and Livingston propose “alternating gradient focusing” focusing + defocusing = focusing E. Courant defocusing + H. Snyder S. Livingston focusing = focusing Introduction of AG focusing had tremendous impact on beam quality and accelerator size and cost ! In turned out that Christofilos from Athens had filed an U.S. patent on this idea already in 1950, but nobody had noticed ! N. Christofilos C l el Quadrupole focusing Dipole (B=Bend) Quadrupole defocusing FODO lattice for synchrotron Particle Colliders Frascati and Novosibirsk, 1961 Reaction products extracted beam Reaction products e acc injection extraction injection time “Interaction point” Storage ring Synchrotron Magnetic cycle synchrotron n tio a r le A. Budker Detectors “Fixed target” magnetic field magnetic field Detectors B. Touschek* Magnetic cycle storage ring e acc injection n tio a r le storage time *with Lola What is the advantage of collider? Fixed target Colliding beams beam particle with energy E new particle of mass mX particle of clockwise beam with energy E interaction new particle of mass mX interaction particle at rest of mass mT particle of counterclockwise beam with energy E Conservation of energy and momentum E> m X 2c 2 2 mT E> mX c2 2 Same pages from Bruno Touscheks 1960 notebook 2007 1961 VEP 1, Novosibirsk, USSR 1971 ISR, CERN, Switzerland 2000 RHIC, Brookhaven, USA e+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ep/p p/p p/p e+/ee+/ee+/ee+/- /p e+/ee+/ee+/ee+/ee+/ep/p and Pb/Pb e-/ep/p ion/ion DAΦNE LNF Frascati 500 MeV e+/e- collider In the tunnel of the CERN SppS proton antiproton collider 450.000 MeV, 7 km circumference 1967 Unified Theory of electromagnetic and weak interaction Field quanta γ, W± and Z0 1979 Nobel price for Glashow, Weinberg, Salam 1983 Discovery of W± and Z0 at SppS /CERN 1984 Nobel price for Rubbia and van der Meer UA1 detector SppS 7 km W event Enabling technologies for accelerators ¾ Electron, proton and ion sources ¾ Vacuum systems ¾ Magnet technology Iron/copper magnets Fast pulsed ferrit magnets Superconducting magnets Permanent magnets ¾ RF power sources ¾ Accelerating RF structures Normal conducting Superconducting ¾ Cryogenic Systems ¾ Electromagnetic sensors ¾ High speed electronics ¾ High precision electronics ¾ Electric power systems ¾ Large scale precision alignment ¾ Large scale computer control systems ¾ Laser ¾ Tunnel construction techniques ¾... Accelerators Many technological developments were promoted by accelerator needs Recommended literature Accelerator physics general H. Wiedemann, “Particle Accelerator Physics,” (2 volumes), Springer 1993 K. Wille, “The Physics of Particle Accelerators : An Introduction,” Oxford University Press, 2001 S.Y. Lee, “Accelerator Physics,” World Scientific, 2004 A. Chao and M. Tigner (editors), “Handbook of Accelerator Physics and Engineering,” World Scientific, 1999 T. Wangler, “RF Linear Accelerators,” John Wiley 1998 M. Minty and F. Zimmermann, “Measurement and Control of Charged Particle Beams,” Springer 2003 Accelerator key technologies M.J. Smith and G. Phillips, “Power Klystrons Today,” John Wiley 1995 M. Sedlacek, “Electron Physics of Vacuum and Gaseous Devices,” John Wiley 1996 H. Padamsee, J. Knobloch, T. Hays, “RF Superconductivity for Accelerators,” Wiley 1998 J. Tanabe, “Iron Dominated Magnets,” World Scientific 2005 K. Mess, P. Schmüser, S. Wolff, “Superconducting Accelerator Magnets,” World Scientific, 1996 For more accelerator book references http://uspas.fnal.gov/book.html PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE Hans-H. Braun, CERN 2nd Lecture Examples of Modern Applications and their Technological Challenges o Synchrotron Radiation, from Nuisance to Bright Light o Beams for Medicine o Particle Accelerators for Particle Physics