Accelerators: Types, Techniques, and Physics

1. HEP Accelerators M. Cobal

2. Few things about Accelerators M. Cobal, University of Udine Thanks to Prof. F. Fabbri

3. Contents • Introduction - Terms and Concepts • Types of Accelerators • Acceleration Techniques • Current Machines

4. Rutherford’s Scattering (1909) • Particle Beam • Target • Detector

5. Results

6. Sources of Particles • Radioactive Decays • Modest Rates • Low Energy • Cosmic Rays • Low Rates • High Energy • Accelerators • High Rates • High Energy

8. Why High Energy? Resolution defined by wavelength

9. Energy Scales • Particles are waves • Smaller scales = HE • 1 GeV (109 eV) =1 fm (10-15m) 1 MeV electron 1 MV

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

11. Cross-section • Area of target • Measured in barns = 10-24 cm2 • Cross-section depends upon process Hard Sphere - 1 mbarn = 1 fm2 - size of proton about 16 pb (others fb or less)

12. 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

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

16. 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)

17. Circle or Line? • Linear Accelerator • Electrostatic • RF linac • Circular Accelerator • Cyclotron • Synchrotron • Storage Ring

18. DESY SERPUKHOV DUBNA FERMILAB FNAL SLAC CERN NOVOSIBIRSK KEK LBL PECHINO LNF CORNELL BROOKHAVEN

21. Electrons vs Protons

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

23. Colliding Beams DESY HERA 1990s

24. 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...

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

26. Accelerator Types • Static Accelerators • Cockroft-Walton • Van-de Graaff • Linear • Cyclotron • Betatron • Synchrotron • Storage Ring

27. Static E Field Particle Source Just like your TV set Fields limited by Corona effect to few MV -> few MeV electrons

29. Van-de Graaff - 1930s Generator and accelerator (1929, Princeton, New Jersey)

30. Construction of the first big generator Spectacular demonstrations

31. Non è però usato solo per dimostrazioni spettacolari

32. Van-de Graaff II First large Van-de Graaff Tank allows ~10 MV voltages Tandem allows x2 from terminal voltage 20-30 MeV protons about the limit Will accelerate almost anything (isotopes)

33. Cockroft-Walton - 1930s 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

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

35. Linear accelerators

36. 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

37. LINAC 1 per Protoni del CERN E = 50 MeV Courtesy: CERN

38. Linac 2 @ CERN Courtesy: CERN

39. Linac del Laboratorio Fermi Chicago Courtesy: Fermilab

40. Stanford Linear Accelerator Center (SLAC) Campus 280 Freeway Research yard 2 miles Linac Linear elettronsaccelerator, working in the period: 1962 and 1966. Emax = 30 GeV

41. Electron Linacs

42. Taylor, Friedman e Kendall Premio Nobel 1990 1968 Deepinelasticscattering of electrons on nucleons. A sort of Rutherford experiment to study the nucleonsinner part. Resultsconsistent with the presenceofo 3 diffusion centers with fractionalcharge,

43. Cyclotron B

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

45. “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. Cyclotronsstillusedextensivelyinhospitals.

46. M.S.Livingston e E.O.Lawrence Ciclotrone da 8 MeV (68 cm, 1934) Courtesy: Lawrence Berkeley Laboratory