Introduction to Accelerators Eric Torrence University of Oregon QuartNet 2005 Special Thanks to Bernd Surrow

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 GeV (10 9 eV) =1 fm ( m) 1 MV 1 MeV electron

Roads to Discovery High Energy High Luminosity Probe smaller scales Produce new particles Detect the presence of rare processes Precision measurements of fundamental parameters

Cross-section Area of target Measured in barns = cm 2 Cross-section depends upon process Hard Sphere - 1 mbarn = 1 fm 2 - size of proton about 16 pb (others fb or less) technically infinite (E field)

Luminosity Intensity or brightness of an accelerator Events Seen = Luminosity x cross-section In a storage ring Rare processes (fb) need lots of luminosity (fb -1 ) Current Spot size More particles through a smaller area means more collisions

Accelerator Physics for Dummies Electric Fields  Aligned with field  Typically need very high fields Magnetic Fields  Transverse to momentum  Cannot change |p| Lorentz Force

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

Synchrotron Radiation Linear Acceleration Circular Acceleration 10 MV/m -> Watts Radius must grow quadratically with beam energy!

LEP Accelerator (CERN ) 27 km circumference 4 detectors e + e - collisions  LEPI: 91 GeV  125 MeV/turn  120 Cu RF cavities  LEPII: < 208 GeV  ~3 GeV/turn  288 SC RF cavities

Protons vs. Electrons Can win by accelerating protons But protons aren’t fundamental Only small fraction at highest energy Don’t know energy (or type) of colliding particles

History of accelerator energies e + e - machines typically match hadron machines with x10 nominal energy

Fixed Target SLAC End Station A GeV electons

Colliding Beams DESY HERA 1990s

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 2x175 GeV = 350 GeV of CM Energy Head-on collisions: One electron at rest: Need 30,000,000 GeV electron...

Secondary Beams Fixed-target still useful for secondary beams NuTeV Neutrino Production protons pions -> muons neutrinos

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 MeV electrons

Cockroft-Walton s FNAL InjectorCascaded rectifier chain Good for ~ 4 MV

Van-de Graaff s

Van-de Graaff II First large Van-de Graaff Tank allows ~10 MV voltages Tandem allows x2 from terminal voltage MeV protons about the limit Will accelerate almost anything (isotopes)

Linear Accelerators Proposed by Ising (1925) First built by Wideröe (1928) Replace static fields by time-varying periodic fields

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 GeV electrons

Cyclotron Proposed 1930 by Lawrence (Berkeley) Built in Livingston in 1931 Avoided size problem of linear accelerators, early ones ~ few MeV 4” 70 keV protons

“Classic” Cyclotrons Chicago, Berkeley, and others had large Cyclotrons (e.g.: 60” at LBL) through the 1950s Protons, deuterons, He to ~20 MeV Typically very high currents, fixed frequency Higher energies limited by shift in revolution frequency due to relativistic effects. Cyclotrons still used extensively in hospitals.

Betatron Variant to cyclotron, keep beam trajectory fixed, ramp magnetic fields instead. 25 MeV protons in 1940s. First fixed circular orbit device...

Synchrocyclotron Fixed “classic” cyclotron problem by adjusting “Dee” frequency. No longer constant beams, but rather injection+acceleration Up to 700 MeV eventually achieved

Synchrotrons Use smaller magnets in a ring + accelerating station 3 GeV protons BNL 1950s Basis of all circular machines built since Fixed-target mode severely limiting energy reach

Storage Rings Two beams counter-circulating in same beam-pipe Collisions occur at specially designed Interaction Points RF station to replenish synchrotron losses

Beamline Elements Dipole (bend) magnets Quadrupole (focusing) magnets Also Sextupoles and beyond

Largest HEP Accelerator Labs NuTev

Fermilab Tevatron Highest Energy collider: 1.96 TeV top quark, Higgs search, new physics

SLAC - SLC and PEPII SLAC Linear Collider ( ) Z-pole, EW physics, B-physics, polarized beams PEPII Asymmetric Storage Ring (1999-present) 3 GeV e + on 9 GeV e - Very high luminosity, CP Violation, B-physics, rare decays

CERN Large Hadron Collider Under construction in old LEP tunnel Will collide pp at 14 TeV (mini-SSC) Higgs, EW symmetry breaking, new physics up to 1 TeV

CERN Complex Old rings still in use Many different programs

Proposed 1 TeV e + e - collider Similar energy reach as LHC, higher precision