HEP Accelerators M Cobal Few things about Accelerators
HEP Accelerators M. Cobal
Few things about Accelerators M. Cobal, University of Udine Thanks to Prof. F. Fabbri
Contents • • Introduction - Terms and Concepts Types of Accelerators Acceleration Techniques Current Machines
Rutherford’s Scattering (1909) • Particle Beam • Target • Detector
Results
Sources of Particles • Radioactive Decays – Modest Rates – Low Energy • Cosmic Rays – Low Rates – High Energy • Accelerators – High Rates – High Energy
Why High Energy? Resolution defined by wavelength
Energy Scales • Particles are waves • Smaller scales = HE 1 Me. V electron 1 MV • 1 Ge. V (109 e. V) =1 fm (10 -15 m)
Roads to Discovery • High Energy Probe smaller scales Produce new particles • High Luminosity Detect the presence of rare processes Precision measurements of fundamental parameters
Cross-section • Area of target Hard Sphere - • Measured in barns = 10 -24 cm 2 1 mbarn = 1 fm 2 - size of proton • Cross-section depends upon process about 16 pb (others fb or less)
Luminosity • Intensity or brightness of an accelerator • Events Seen = Luminosity x cross-section Rare processes (fb) need lots of luminosity (fb-1) • In a storage ring Current Spot size More particles through a smaller area means more collisions
Accelerator Physics for Dummies Lorentz Force • Electric Fields – Aligned with field – Typically need very high fields • Magnetic Fields – Transverse to momentum – Cannot change |p|
Types of Accelerators • Linear Accelerator (one-pass) • Storage Ring (multi-turn) • electrons (e+e-) • protons (pp or pp) • Fixed Target (one beam into target) • Collider (two beams colliding)
Circle or Line? • Linear Accelerator – Electrostatic – RF linac • Circular Accelerator – Cyclotron – Synchrotron – Storage Ring
DESY FERMILAB FNAL SLAC CERN SERPUKHOV DUBNA NOVOSIBIRSK KEK LBL LNF CORNELL BROOKHAVEN PECHINO
Name Type ADONE e+ e _ SPEAR e+ e _ DORIS e+ e _ CESR e+ e _ PEP I e II e+ e _ PETRA e+ e _ TRISTAN e+ e _ SLC e+ e _ LEP e+ e _ DAΦNE e+ e _ BEPC II e+ e _ √s (Ge. V) Working years Laboratory 3 1967 - 1993 LNF 8 1972 - 1985 SLAC 10 1974 - 1985 DESY 12 1978 - 1993 Cornell 15 - 30 1980 - 2008 SLAC 12 - 37 1978 - 1993 DESY 55 - 70 1985 - 1995 KEK 91 1988 - 200 SLAC 1989 - 2000 CERN 1. 02 1994 - LNF 2 - 5 2008 - Pechino 86 - 209
Name Type √s (Ge. V) Working years Laboratory PS p 28 - 30 1959 - CERN SPS p 450 1976 - CERN Tevatron p 350 - 1000 1985 - FNAL ISR pp 28 - 63 1972 - 1984 CERN Spp. S pp 450 - 900 1983 - 1989 CERN Tevatron pp 1000 - 2000 1985 - FNAL 30 + 920 nel laboratorio 1990 -2007 DESY 2000 - BNL HERA RHIC e +_ p Heavy ions
Electrons vs Protons
History of accelerator energies e+e- machines typically match hadron machines with x 10 nominal energy
Colliding Beams DESY HERA 1990 s
Center of Mass Energy To produce a particle, you need enough energy to reach its rest mass. Usually, particles are produced in pairs from a neutral object. To produce requires 2 x 175 Ge. V = 350 Ge. V of CM Energy Head-on collisions: One electron at rest: Need 30, 000 Ge. V electron. . .
Secondary Beams • Fixed-target: still useful for secondary beams neutrinos pions -> muons protons Nu. Te. V Neutrino Production
Accelerator Types • • Static Accelerators Cockroft-Walton Van-de Graaff Linear Cyclotron Betatron Synchrotron Storage Ring
Static E Field Particle Source Just like your TV set Fields limited by Corona effect to few MV -> few Me. V electrons
Van-de Graaff - 1930 s Generator and accelerator (1929, Princeton, New Jersey)
Construction of the first big generator Spectacular demonstrations
Non è però usato solo per dimostrazioni spettacolari
Van-de Graaff II First large Van-de Graaf Tank allows ~10 MV voltages Tandem allows x 2 from terminal voltage 20 -30 Me. V protons about the limit Will accelerate almost anything (isotopes)
Cockroft-Walton - 1930 s electric circuit that generates a high DC voltage from a low voltage AC or pulsing DC input. Good for ~ 4 MV FNAL Injector Cascaded rectifier chain
Linear Accelerators • Proposed by Ising (1925) • First built by Wideröe (1928) Replace static fields by time-varying periodic fields
Linear accelerators
Linear Accelerator Timing Fill copper cavity with RF power Phase of RF voltage (GHz) keeps bunches together Up to ~50 MV/meter possible SLAC Linac: 2 miles, 50 Ge. V electrons
LINAC 1 per Protoni del CERN E = 50 Me. V Courtesy: CERN
Linac 2 @ CERN Courtesy: CERN
Linac del Laboratorio Fermi Chicago Courtesy: Fermilab
Stanford Linear Accelerator Center (SLAC) 280 Freeway Campus Research ya 2 miles Linac Linear elettrons accelerator, working in the period: 1962 and 1966. Emax = 30 Ge. V
Electron Linacs
Taylor, Friedman e Kendall Premio Nobel 1990 1968 Deep inelastic scattering of electrons on nucleons. A sort of Rutherford experiment to study the nucleons inner part. Results consistent with the presence ofo 3 diffusion centers with fractional charge,
Cyclotron B
Cyclotron Proposed 1930 by Lawrence (Berkeley) Built in Livingston in 1931 4” 70 ke. V protons Avoided size problem of linear accelerators, early ones ~ few Me. V
“Classic” Cyclotrons Chicago, Berkeley, and others had large Cyclotrons (e. g. : 60” at LBL) through the 1950 s Protons, deuterons, He to ~20 Me. V Typically very high currents, fixed frequency Higher energies limited by shift in revolution frequency due to relativistic effects. Cyclotrons still used extensively in hospitals.
M. S. Livingston e E. O. Lawrence Ciclotrone da 8 Me. V (68 cm, 1934) Courtesy: Lawrence Berkeley Laboratory
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