An Introduction

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Particle Accelerators

• An Introduction
• By Zoe Matthews

The Large Hadron Collider Tunnel CERN, Geneva
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Talk contents

• How do particle accelerators work?
• Accelerating particles with electric fields
• Controlling particle beams with magnetic fields
• The first modern accelerators
• Types of particle accelerator
• Linear accelerators
• Cyclotrons
• Synchrotrons
• Accelerators under your nose
• High energy GREAT BIG MAGNETS
• Superconductivity in Particle Accelerator Magnets
  
• Beam focusing and bending using dipoles and
  quadrupoles
• Same-charge particle collisions The LHC Dipole
  Magnet
• The Large Hadron Collider!
• LHC statistics and pictures
• Questions

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Accelerating charged particles Electric fields

• Alternating electric fields along the beam
  attract the particle on its way in and then repel
  when particle has passed
• Oscillations need to remain synchronised with
  particles as they get faster

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Bending charged particles Magnetic fields

• Controlling beam can use magnetic field to bend
  path round corners
• Used in circular accelerators
• Need to use stronger B as particle gets faster
  radius of curvature depends on velocity
• Also loses energy (emits Synchrotron Radiation)

Direction of force
Magnetic field
Direction of current
Photon
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Linear particle accelerator

• Late 1920s Lawrence and Stroud
• The first modern accelerators were made like this
• Sections get longer as the particles get faster
  so that it remains synchronised.
• No synchrotron radiation loss common choice for
  ee- collisions
• No need to bend the particles, but they can get
  really long!

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The Cyclotron
Relativistic limit for cyclotrons!

• 1930s-40s
• Up to 184 inches diameter

Lawrence, 1931 First successful cyclotron (5
inches)

• AC Electric field accelerates particle between
  dees
• Inside dees, magnetic field bends path back out
• Faster particle gets, larger its radius, so has
  same amount of time in the dee frequency can be
  constant

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The Synchrotron

• 1950s onward
• In 1947, Oliphant, Gooden and Hide (members of
  Birmingham University physics department)
  proposed a solution to the problems with the
  cyclotron
• The first proton synchrotron design was done by
  Birmingham University!

Professor M L E (Sir Mark) Oliphant was head of
the Physics department at Birmingham, and went on
to be Governor of Australia!
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The Synchrotron
The first proton synchrotron to be completed in
the world was built here at Birmingham
(in this very place 1953!)
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The Synchrotron
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The synchrotron

• Carefully synchronised so that magnetic field
  gets stronger as particles get faster (and
  heavier!)
• can go up to relativistic speeds, can achieve
  very high energies
• Until you cant increase the magnetic field any
  more
• or until synchrotron radiation losses dominate

Beam pipe must be very good vacuum
Keep particles separate until collision
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Particle accelerators under your nose

• Chemistry/Condensed matter Physics(synchrotron
  radiation!)
• Medical Physics
• Cathode Ray Tubes inside old TVs are miniature
  Particle Accelerators

PET scan of a brain www.nia.nih.gov
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Accelerators and Particle Physics
What is an electron volt?
1.60217646 10-19 joules

• SLAC Stanford Linear ACcellerator (PEPII)
  2.2Km, e 3 GeV) e- 9.1 Gev, (total Y mass)
  BABAR
• LHC Large Hadron Collider p p collisions, 14
  TeV (Pb Pb)
• ATLAS, CMS, ALICE, LHCb

• LEP Large Electron Positron e-e collider, 91
  GeV (Z mass), 130-140 GeV
• OPAL, ALEPH, L3, DELPHI
• DESY, Hamburg (HERA) e- p collisions up to 920
  GeV
• H1, ZEUS

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Introducing the LHC!

• 27Km circumference, up to 100m underground,
  38,000 tonnes (excluding
• detectors)
• Proton-Proton collisions at 14TeV (Consumes 120
  MW power!)
• 1 bunch crossing every 25 nanoseconds
  (eventually)
• Protons circle beam 11245 times per second
• Up to 600 million collisions a second
• 9593 magnets (1232 dipoles, 392 quadropoles)
• Collisions due to start this summer!

• How much IS 14TeV?
• 14,000,000,000,000eV

And the whole beam?
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The LHC Dipole Magnet Design!
Dipole magnets at the LHC are designed to allow
same-charge particles circle the beam in opposite
directions
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Beam Focusing Quadrupoles

• Need to keep beam straight and focused, dont
  want to lose any particles
• Do this using Quadrupole Magnets
• Result is that beam is focused
• in one direction, broadened in
• the other
• Alternating the orientation gives
• overall focused beam

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Superconducting Magnets!

• At high energies, need very strong magnetic field
  to keep beam inside ring Superconducting
  electromagnets are used
• Cryogenics At the LHC, 10,000 tonnes of liquid
  nitrogen and 60 tonnes of super-cold liquid
  helium used to cool magnets to 1.9 K - Colder
  than space (3K)!
• This allows means magnetic field can be very
  strong (8.3 Tesla)!
• Superconducting materials have ZERO resistance,
  so
• Needs no extra power to keep B field, just need
  to keep it cool!

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Progress at LHC installing dipole magnets
Installing each 30 tonne dipole magnet is a big
job!
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Summary

• Accelerators work using
• Charged particles
• Very clean vacuum beam pipes
• Alternating (RF) electric fields
• Magnets to focus and bend the beam
• Accelerators are used
• In everyday life (TV, in Hospitals)
• In research such as Chemistry, Materials, Biology
• For High Energy Collisions for Particle Physics
  Research
• Design choices
• Linear limited by length, cyclotron by
  relativistic limits
• (Proton) Synchrotron is able to go to very high
  energies
• Physics/experimental aims play a big part in
  design choices

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And finally
Any Questions?

• Facts and Figures from
• LHC UK, LHC_at_Home and CERN Public Web pages
• FAQ at LHC The guide http//public.web.cern.ch/Pu
  blic/en/LHC/Facts-en.html
• Images/other information from (many thanks!)
• John Dowell and John Kinson (Birmingham Proton
  Synchrotron)
• Introduction to Accelerators, Elena Wildner,
  LHC UK Teaching Resources http//indico.cern.ch/co
  nferenceDisplay.py?confId9238
• Dr David Evans and Dr Gron Tudor Jones
• Philip Chater (unit cell referring to x ray
  diffraction)
• LHC_at_Home webpage (very informative!)
• CERN, ALICE, DESY, Fermilab, SLAC, Diamond, LHC
  and ILC Galleries
• Not forgetting that silly game

http//microcosm.web.cern.ch/microcosm/RF_cavity/e
x.html
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Future Particle Accelerators Linear Collider?

• E.g. ILC chose to collide electrons and positrons
  
• - Very clean signal, easier to spot interesting
  physics!
• Synchrotron radiation is too much of a problem
  for electrons and positrons
• - Linear collider needed to get to high (1TeV)
  energy
• To reach 1TeV, ILC will need to be very, very
  long 35km in fact!

Artists impression Superconducting Accelerator
Resonator, Linear beam tunnels
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Building a Particle AcceleratorParticle sources
and beams

• Choice of particles (must be charged!)
• Where do we get them from?
• Natures own source of high energy particles

Beta emitters e.g. Yttrium 90
Strip hydrogen of its electron for proton source
Alpha emitters or other radioactive materials
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More on Synchrotrons

• Radio Frequency Cavities Timed so that slower or
  faster particles will get more or less
  acceleration, will be pulled back into the
  bunch and kept together