Physics of Particle Accelerators

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Physics of Particle Accelerators Kalanand
Mishra Department of Physics University of
Cincinnati
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How a Particle Accelerator Works

• Speed up particle with E/M field
• Smash particles into target or other particles
• Record collisions with detectors
• Able to identify product particles

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Physics of a Particle Accelerator

• Beam production
• Bunching
• Electron guns
• Beam focusing
• Colliding and Detecting

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Beam production

• Electron Beam

• Thermoionic Emission

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Proton Beam

• Ionizing Hydrogen

• Glow Discharge Column

• From H- Ion

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Other Beams
Secondary Beams

• Proton
• Antiproton
• Other Particle Beams

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Bunching
Bring the Particles in phase.
As spread out beam gives fewer collisions than a
narrowly focused one, e- e bunches are sent
into damping rings (e- to north, e to south).
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Colliding

• Fixed target
• E ?(2mEp)

• Colliding beam
• E 2Ep

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Beam Focusing
u As spread out beam gives fewer collisions than
a narrowly focused one, e- e beams have
to be focused. u This is done by bent
magnets.
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Two Types

• Linear Path
• Travel once

• Circular Path
• Travel several times

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Linear Accelerator
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LINAC Operation
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Methods of Acceleration in Linear Accelerator
SLC Polarized Electron Gun
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Methods of Acceleration in Linear Accelerator

• Basic idea
• Synchronization
• Length of the tube
• Shielding

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• LINAC contd
• Klystron Microwave generator
• 1. Electron gun produces a flow of
• electrons.
• 2. Bunching cavities regulate speed of
• electrons so that bunches arrive at the
  output cavity.
• 3. Bunches of electrons excite microwaves
  in output cavity of the klystron.
• 4. Microwaves flow into the waveguide ,
  which transports them to the accelerator. 5.
  Electrons are absorbed in beam stop.

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Overall Operation of LINAC Electrons are
Accelerated in a Copper Structure
Bunches of electrons are accelerated in the
copper structure of the linac in much the same
way as a surfer is pushed along by a wave.
Changing Electric and Magnetic Fields

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Klystron Operation

• E/M waves that push the electrons in the linac
  are created by higher energy versions of the
  microwaves used in the microwave ovens in
  our kitchens.
• The microwaves from the klystrons in the
  Klystron Gallery are fed into the accelerator via
  waveguides.
• This creates a pattern of EB fields, which
  form an E/M wave traveling down the
  accelerator.

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LINAC Structure
The 2-mile SLAC linear accelerator (linac) is
made from over 80,000 copper discs and cylinders
brazed together.

• Microwaves set up currents that cause E
  pointing along accelerator and B in a
  circle around interior of accelerator.
• Want e- and e to arrive in each cavity at
  right time to get max. push from E.
• e needs to arrive when field polarity is
  opposite.

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Circular Accelerator
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Methods of Acceleration in Circular Accelerator
Cyclotron

• The Ds
• Electric field across the gap
• Circular orbit
• Increasing radius

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Cyclotron

• The maximum speed a proton could have
• in a dee of radius R and strength B is given
• by (ignoring relativistic effects.)
• vm BeR / mp

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Methods of Acceleration in Circular Accelerator
Synchrotron (synchro-cyclotron)

• Electromagnetic resonant cavity
• Magnetic field for circular orbit
• Field synchronization with increasing
  particle energy
• Synchrotron radiation
• Storage ring

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Synchrotron

• The radius of curvature of the path of particles
  of momentum p and charge q in a synchrotron is
  given by the formula
• R p / q B
• where B is the field strength.
• If a synchrotron of radius R has 4 straight
  sections of length L each and period of the radio
  frequency oscillator corresponds to the time of
  one revolution then
• (a) The speed of the particles is
• v ( 2pR 4L ) f

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Synchrotron
(b) By considering the relativistic momentum
of particles of mass M, the magnetic field
strength of the synchrotron is given by
where f is the frequency.
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Storage Rings

• Similar to a synchrotron, but designed to keep
  particles circulating at const. energy not
  increase energy further
• SPEAR 3 GeV
• PEP I 9 GeV
• PEP II e- 9 GeV
• e 3.1 GeV

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Detection

• Tracking bubble, radiation
• Tracking curvature (charged particle)

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