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An Introduction To Particle Accelerators

An Introduction To Particle Accelerators. A-Level Physics. A Question . Q. Where is the nearest particle accelerator to this classroom? A. . Accelerating with high voltages. Particles can be accelerated to high speeds and thus high energy The energy is measured in electron-Volts

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An Introduction To Particle Accelerators

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  1. An Introduction To Particle Accelerators A-Level Physics

  2. A Question • Q. Where is the nearest particle accelerator to this classroom? • A.

  3. Accelerating with high voltages • Particles can be accelerated to high speeds and thus high energy • The energy is measured in electron-Volts 1 eV = 1.602x10-19 J • An industrial sized Van de Graaff generator can accelerate electrons up to a few Mega electron-Volts

  4. The Van de Graaff Generator • This shows Robert Van de Graaff’s original high voltage generator at MIT in 1933

  5. Why do we need particle accelerators? • If particles have large velocity, the wavelength decreases. So they can be used to study atomic spacing. • High energy particles can be smashed into each other, allowing other particles to be studied!

  6. How do accelerators work? • Electric fields (creating electromagnetic waves) attract charged particles and speed them up. • Magnetic fields can be used to change their direction.

  7. Obtaining particles to accelerate • Electrons: Heating a metal causes electrons to ‘boil off’ – thermionic emission. • Protons: They can easily be obtained by ionizing hydrogen. • Antiparticles: High energy particles are collided with solid materials and antiparticles are ultimately produced.

  8. Accelerating Particles • In a Linear Accelerator (Linac), a carefully selected frequency of alternating voltage is placed across a series of cylindrical electrodes to accelerate a particle. • Linac Game

  9. Accelerating Particles 2 • The particles can also be considered to be ‘surfing’ the electromagnetic wave…

  10. Accelerator Design • There are two main types of accelerator experiment: • Fixed Target - e.g. Rutherford’s alpha scattering experiment. • Colliding Beams - can use much more energy!

  11. Linac or Synchrotron?! • Linear accelerators (Linacs) are used for fixed-target experiments, as injectors to circular accelerators, or as linear colliders. A Linac at the University of California

  12. Linac or Synchrotron?! • The largest Linac is at Stanford University, USA. • It can accelerate particles up to 50 GeV

  13. Linac or Synchrotron?! Particle energy at Fermilab, USA: Vaan de Graaf: H- ions to about 1 MeV Linac: H- ions to about 500 MeV Booster synchrotron: protons to about 10 GeV Main injector: protons to about 150 GeV Tevatron synchrotron protons (and p-) to 1 TeV • The particle beams from a circular accelerator (synchrotron) can be used for particle colliding experiments or extracted from the ring for fixed-target experiments. This is the European Synchrotron Radiation Facility (ESRF) in Grenoble, France

  14. CERN Accelerators at CERN LINAC2+3 – Hadron Linacs PSB – Proton Synchrotron Booster PS – Proton Synchrotron SPS – Super Proton Synchrotron LHC – Large Hadron Collider Other things AD – Antiproton Decelerator CMS – Compact Muon Solenoid ALICE – A Large Ion Collider Experiment

  15. What can they do? • Linacs and Synchrotrons can be used together or alone:

  16. Accelerating Particles 3 • Heat energy provides the work function for thermionic emission. • Electric fields accelerate particles:

  17. Accelerating electrons • PE lost = KE gained • qV = ½ mv2 e.g. A thermionic diode has a p.d. of 5kV placed across its electrodes. Calculate the maximum velocity of the electrons. v = (2qV/m) ½ v = (2 x 1.6x10-19 x 5000 / 9.1x10-31) ½ v = 4.2x107 ms-1

  18. Accelerating electrons • The greater the acceleration of the electron, the greater its energy. • KE = ½ mv2 Q. What happens when velocity approaches the speed of light? • Mass increases! (Velocity can never equal the speed of light). • KE = ½ mv2 still applies.

  19. Bending Beams of Particles • For a beam of particles to move through a circular path, they must each experience a centripetal force. Q. Does this force increase the energy of the particles? • The centripetal force is provided by a magnetic field perpendicular to the direction of the particles. Demo: Bending a beam of electrons in a CRT monitor or Teltron tube.

  20. The Cyclotron • Cyclotrons accelerate particles in a circular path up to around 10MeV. • They are relatively small and so can be used in hospitals to provide beams of (deuterons creating) neutrons for cancer therapy. • http://www.nscl.msu.edu/tech/accelerators/index.html

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