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Physics and Technology of Particle Accelerators Basics, Overview and Outlook Simone Di Mitri, Elettra – Sincrotrone Trieste University of Trieste, Dept. of Engineering Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 1 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, 2006 – 2007. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 2 Particle Acceleration Charged Particles: electron, proton, ion and anti-particles E = T + m0c2 = γm0c2 r r p = βγm0c 2 r r r FL = q (E + v × B ) Special Relativity is all we need. Includes kinematics and dynamics of relativistic charged particles. 2 γ = 1 1− β 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, quadrupole and multi-pole magnetic elements for controlling the particles direction (orbit) and beam size (focusing). Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 3 Why High Energy Particles ? 3Li 7 + p = 2 2He4 ∆x∆p ≥ h λ =h p 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. Heisenberg’s Uncertainty Principle + De Broglie Wavelength point that the spatial/energy resolution for observing the matter structure is inversely proportional to the particle energy. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 4 Accelerator Facilities “Beam on Fixed Target” (p = t): ECM = 2γ b m0c 2 “Collider” (p1 = p2): ECM = 2γ bm0c 2 “Synchrotron Radiation”: U turn [keV ] = 88.5 Eb4 [GeV ] R [m ] 3 cγ b3 ωc = 2 R Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 5 Colliding Proton Beams: the Tevatron (Chicago, IL) Neutrinos from fixed target exp. The search for Higgs boson Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 6 Synchrotron Radiation Light Source: ESRF (Grenoble, FR) observer matter sample synchrotron light Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 7 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- Seminar on Particle Accelerators, Univ. of Trieste T = 14x15MV = 210 MV !! Simone Di Mitri, 19-05-2014 8 Resonant Linear Accelerators Ising (1924), Wideroe (1928), Sloan and Lawrence (1931), Alvarez (1945),… Gap Drift-Tubes Disk-Loaded Waveguide Structure Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 9 RF Structure Pill-box (in vacuum) • Accel. field: • Synchronism: • Traveling Wave: • Energy Gain: (TM010) Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 10 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 13000 cells mass production Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 11 RF Proton Linac: TULIP (CERN) Source: A. Degiovanni, U. Amaldi 80–210 MeV p-linac C-band (5.7 GHz) <38 MV/m acc. gradient Rep.rate, 200 Hz Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 12 Resonant Circular Accelerator: the Cyclotron (E.O.Lawrence & M.S.Livingstone, Berkeley 1931) “Dees” top view side view Synchronism Energy gain / turn Lorentz force • Spiraling motion: 1 ∆T ∆T m0c 2 ∆ρ = ρ = 2 T q cB 2T • Maximum kinetic energy: Classical approximation (e.g., massive particles) Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 13 Cyclotron for Relativistic Particles ωc = B 1 B = ≡ CωRF q m γ q m0 To maintain the synchronism, which ensures the multi/turn acceleration, one has two ways: 1. Increase B(t) synchronous to γ(t), ∝ ρ(t) CERN SC “sector cyclotron” TRIUMPH, Canada 2. Increase ωRF (t) synchronous to γ(t) “sincro-cyclotron” N.B.: here the beam is bunched, over one period of modulation of ωRF !! Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 14 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). Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 15 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 magnetic fields are “ramped” with the beam energy, for a fixed RF. … to LEP (1987) and LHC (2007), synchrotron colliders in Geneva, Switzerland. From AdA, e+e- synchrotron collider in Frascati, Rome (1961)…. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 16 Livingstone Chart eV Average 10-fold increase in energy every 6 years. New branches correspond to technological advances. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 17 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). Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 18 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. ELETTRA Synchrotron Light Source: FERMI@Elettra FEL: up to 2.4 GeV, top-up mode, 100 – 4 nm, fully funded 768 proposals from 39 countries in 2010 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: and many others… Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 19 Science Needs and Goals (examples) 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 multi-color wide source × × multi-color collimated × monochromatic wide source Coherence × Brilliance monochromatic collimated = coherent ! Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 20 Elettra Synchrotron Light Source Main Ring Hill’s equation: Dipole Magnet (bend) Quadrupole (focus) RF cavity (energy) x ' '+ k ( s ) x = δ ρ ( s ) electrons B ref. orbit \ Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 21 Electron Beam Dynamics in Rings 1. 2. 3. The machine is modelled with codes. From orbit measurements, machine imperfections are evaluated. 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) • …. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 22 Why a Linac-Driven Light Source? An accelerated charge particle radiates: Pcirc 2 e 2 γ 2 r& 2 2 = p , P = γ Plin circ 2 3 3 c m0 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. 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… Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 23 Gap ∼ mm’s Undulator Radiation & FEL λu∼cm’s ∼N Source: T. Shintake, R. Bakker, E. Allaria Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 24 FERMI Free Electron Laser Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 25 FERMI Free Electron Laser Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 26 FERMI Free Electron Laser Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 27 Electron Beam Dynamics in Linacs “Emittance compensation”: r ′′ = r’ r qI r Kr = 2πε 0 mc 3 β 3γ 3 R 2 R 2 z (Figure by P.G. O’Shea) r emittance slice “Wakefield (Impedance)”: “Bunch Length Compression”: 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 Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 28 Achievements … and many others in Phys. Rev. Letters. Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 29 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: [email protected] Course: Acceleratori di Particelle, in Ing. Elettronica, Laurea Magistrale (6 CU) Seminar on Particle Accelerators, Univ. of Trieste Simone Di Mitri, 19-05-2014 30