Transcript An Introduction To Particle Accelerators A-Level Physics

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
1 eV = 1.602x10-19 J
An industrial sized Van de Graaff
generator can accelerate electrons up to a
few Mega electron-Volts
The Van de Graaff Generator
 This shows Robert Van de Graaff’s original high voltage generator at
MIT in 1933
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!
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.
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.
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
Accelerating Particles 2
 The particles can also be considered to be
‘surfing’ the electromagnetic wave…
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!
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
Linac or Synchrotron?!
The largest Linac is at Stanford University,
USA.
It can accelerate particles up to 50 GeV
Particle energy at Fermilab, USA:
Linac or Synchrotron?!
Vaan de Graaf:
Linac:
The
H- ions to about 1 MeV
- ions to about 500 MeV
H
beams
particle
fromsynchrotron:
a circular protons to about 10 GeV
Booster
accelerator
Main
injector:
protons to about 150 GeV
(synchrotron) can be
Tevatron synchrotron
protons (and p-) to 1 TeV
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
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
What can they do?
Linacs and Synchrotrons can be used
together or alone:
Accelerating Particles 3
 Heat energy provides the work function for
thermionic emission.
 Electric fields accelerate particles:
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
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?
A. Mass increases! (Velocity can never equal the
speed of light).
 KE = ½ mv2 still applies.
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.
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/t
ech/accelerators/index.ht
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