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1 Physics and Technology of Particle Accelerators Basics, Overview and Outlook Simone Di Mitri, Elettra Sincrotrone Trieste University of Trieste, Dept. of Engineering 1

2 Prologue This seminar samples the history of particle accelerators, and contents of my Particle Accelerators Course. This is a seminar primarily for students and young scientists. We aim to provide a taste of what particle accelerators are, how they work and why they have been developed. Use a qualitative approach, no mathematics, focus on existing cases (whenever possible), such as Elettra Sincrotrone Trieste. Credits: Physics of Particle Accelerators, Prof. S. Tazzari, University of Roma Tor Vergata,

3 Particle Acceleration Charged Particles: electron, proton, ion and anti-particles E = T + m 0 c 2 = γm 0 c 2 Special Relativity is all we need. Includes 2 p r r = βγm 0 c kinematics and dynamics of relativistic r r r charged particles. = q E + v B γ = 1 1 β 2 F L ( ) Static and time-varying electric field increases the particle kinetic energy. Radiofrequency (RF) accelerating structures: cavities, diskloaded waveguides. Static and time-varying magnetic field bounds the particle motion into the vacuum chamber, possibly on a closed orbit. Dipole, quadrupoleand multi-pole magnetic elements for controlling the particles direction (orbit) and beam size (focusing). 3

4 Why High Energy Particles? 3Li 7 + p = 2 2He4 Proton (p) energy has to overwhelm the Coulomb barrier of the target atoms (He). Rutherford s exp. in 1911 led to investigation of the atomic structure&(sub-)nuclear reactions. x p λ = h p h Heisenberg s Uncertainty Principle + De Broglie Wavelength point that the spatial/energyresolutionfor observing the matter structure is inversely proportional to the particle energy. 4

5 Accelerator Facilities Beam on Fixed Target (p = t): E = 2γ m b c CM 0 2 Collider (p 1 = p 2 ): E = 2γ bm c CM 0 2 Synchrotron Radiation : U turn [ kev ] 3 3 cγ ω b c = 2 R = 88.5 E 4 b R [ GeV ] [ m] 5

6 Colliding Proton Beams: the Tevatron (Chicago, IL) Neutrinos from fixed target exp. The search for Higgs boson 6

7 Synchrotron Radiation Light Source: ESRF (Grenoble, FR) observer matter sample synchrotron light 7

8 Electrostatic Accelerators 5 MeV electrons, Van De Graaf, MIT 1931 Few MeVs protons, Cockroft and Walton, CERN 40 s T = q V Au - ions 15MV Stripper, Q = 15e- T = 14x15MV = 210 MV!! 8

9 Resonant Linear Accelerators Ising(1924), Wideroe(1928), Sloan and Lawrence (1931), Alvarez (1945), Gap Drift-Tubes Disk-Loaded Waveguide Structure 9

10 RF Structure Pill-box (in vacuum) (TM 010 ) Accel. field: Synchronism: Traveling Wave: Energy Gain: 10

11 RF Electron Linac: SACLA (Hyogo Pref., Japan) 50 m Experimental Hall 200 m Undulator Hall 400 m Accelerator Tunnel Klystron Gallery May 2010 Machine Assembly Hall Source: T. Inagaki, T. Shintake 8 GeV e-linac C-band (5.7 GHz) 35 MV/m acc. gradient cells mass production 11

12 RF Proton Linac: TULIP (CERN) Source: A. Degiovanni, U. Amaldi MeV p-linac C-band (5.7 GHz) <38 MV/m acc. gradient Rep.rate, 200 Hz 12

13 Dees Resonant Circular Accelerator: the Cyclotron (E.O.Lawrence & M.S.Livingstone, Berkeley 1931) side view top view Synchronism Energy gain / turn Spiraling motion: 1 T T ρ = ρ = 2 T q cb m0c 2T 2 Lorentz force Maximum kinetic energy: Classical approximation (e.g., massive particles) 13

14 Cyclotron for Relativistic Particles ω = c B q m = B γ q m 1 Cω To maintain the synchronism, which ensures the RF multi/turn acceleration, one has two ways: 0 1. Increase B(t) synchronous to γ(t), ρ(t) sector cyclotron 2. Increase ω RF (t) synchronous to γ(t) sincro-cyclotron N.B.: here the beam is bunched, over one period of modulation of ω RF!! CERN SC TRIUMPH, Canada 14

15 Betatron The focusing issue of the sector cyclotron, to keep the beam orbit stable, had already been faced by R. Wideröe in 1923 ( ray transformer ), but only solved by D.W. Kerst in 1940( betatron ). Few tens of MV/m average accelerating gradient Unlike the cyclotron, the betatron is not resonant, as the accelerating field is here generated by the time-varying magnetic field. Here the beam is bunched, over one period of modulation of B(t)(typically, <50Hz). 15

16 Synchrotron RF acceleration in linacs turned out to be very efficient for reaching high energies (T>100s MeV). At the same time, a closed orbit minimized the cost of the facility. But, closed orbit implies transverse focusing, synchronized with the energy ramping. Idea: split the electric and the magnetic action, and distribute it on a ring. The magneticfieldsare ramped withthebeamenergy,forafixedrf. to LEP(1987) and LHC(2007), synchrotron colliders in Geneva, Switzerland. From AdA, e+e-synchrotron collider in Frascati, Rome (1961). 16

17 Livingstone Chart ev Average 10-fold increase in energy every 6 years. New branches correspond to technological advances. 17

18 Resumé Particle accelerators developed from atomic physics research at the beginning of the 20th century (Rutherford, 1911). The nuclear structure of stable atoms was investigated with electrostatic accelerators driving < 30 MeV protons and ions (Cockroft-Walton, Van De Graaf, until 1940s). Nuclear transmutation and radioactive elements were studied. In US, research started being driven by the army(mainly fusion and nuclear bomb). Kinetic energy gain reached 100s of MeV with linear (Ising, Wideroe, Alvarez) and circular(lawrence and Livingstone s cyclotron, 1931) resonant accelerators. Stability issues faced in the sector-cyclotron, the sincro-cyclotron and the betatron. These are currently used for nuclear physics and medical applications. Kinetic energy gain reached the GeV level with resonant accelerators, splitting the accelerating (RF) and the focusing (magnets) action. Stability was ensured over long time periods, in all 3-planes of motion. Synchrotrons are used to store leptons, hadrons and ions. Applications include: particle physics, astrophysics (collider), imaging, biology, lithography, radiology(light sources), medical applications(protons). 18

19 Elettra Sincrotrone Trieste Elettra Sincrotrone Trieste is a nonprofit shareholder company of Italian national interest, established in 1987 to construct and manage synchrotron light sources as international facilities. FERMI@Elettra FEL: nm, fully funded Sponsors: Italian Minister of University and Research (MIUR) Regione Auton. Friuli Venezia Giulia European Investment Bank (EIB) European Research Council (ERC) European Commission (EC) Collaborations: ELETTRA Synchrotron Light Source: up to 2.4 GeV,top-up mode, 768 proposals from 39 countries in 2010 and many others 19

20 High resolution at small spatial scales short wavelength Most of the photons at the same wavelength narrow bandwidth Stroboscopic picture of chimical processes short pulse Large statistics in single-shot large number of photons per pulse Large statistics in multi-shot high repetition rate Science Needs and Goals (examples) multi-color wide source multi-color collimated monochromatic wide source monochromatic collimated = coherent! Coherence Brilliance 20

21 Elettra Synchrotron Light Source Main Ring Dipole Magnet (bend) B Quadrupole(focus) RF cavity (energy) Hill s equation: x' ' + k( s) x = δ ρ( s) electrons ref. orbit \ 21

22 Electron Beam Dynamics in Rings 1. The machine is modelled with codes. 2. From orbit measurements, machine imperfections are evaluated. 3. The machine model is upgraded and corrections applied to the machine. Beam optics along the lattice Multi-turn nonlinear dynamics Other crucial issues: injection into the main ring, beam-beam collisions, collimation, single- and multi-bunch instability (excited modes). 22

23 An accelerated charge particle radiates: Why a Linac-Driven Light Source? P circ e γ = p r & c m 0 2, P circ 2 = γ P Leptons (i.e., electrons) radiate more than hadrons (i.e., protons) when subjected to the same force. Circular acceleration is more efficient (and typically cheaper) than the linear one. lin But, e-beams in SLS reach equilibrium properties that are typically far from providing radiation as wished by FEL users(synchrotron radiation damping of particles velocities is balanced by the quantum excitation due to random emission of photons in time). An electron linac can be used to overcome the SLS equilibrium dynamics and to shape the e-beam as desired. However, a more efficient radiating process is still needed to surpass the SLS s brilliance level 23

24 Undulator Radiation & FEL Gap mm s λ u cm s N Source: T. Shintake, R. Bakker, E. Allaria 24

25 FERMI Free Electron Laser 25

26 FERMI Free Electron Laser 26

27 FERMI Free Electron Laser 27

28 Electron Beam Dynamics in Linacs Emittance compensation : r r qi r Kr r = = 2 2πε mc β γ R R (Figure by P.G. O Shea) slice z r emittance Bunch Length Compression : Wakefield (Impedance) : Electron w/ higher energy is behind = = Electron w/ higher energy travels on shorter path and catches up Reference particle Electron w/ lower energy is ahead = Electron w/ lower energy falls behind Source: J.R. Harris, M. Venturini, P. Craievich 28

29 Achievements and many others in Phys. Rev. Letters. 29

30 Conclusions SLSs are complementary to FELs as for multiple-users access, stability, pulse rate, λ-tunability, brilliance and coherence. Successful (i.e., interesting and delivering) projects are those that reach the right equilibrium between pushing the boundaries and setting achievable goals. The gap between what current technology/proven designs can deliver and what is desirable for the users provides opportunities (R&D! jobs! fun!) for physicists and engineers(and scientists in general). Thank you for Your Attention Contact: Course: Acceleratori di Particelle, in Ing. Elettronica, Laurea Magistrale (6 CU) 30