Transcript Accelerator - Kalanand Mishra

Physics of Particle Accelerators
Kalanand Mishra
Department of Physics
University of Cincinnati
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

Physics of a Particle Accelerator
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Beam production
Bunching
Electron guns
Beam focusing
Colliding and Detecting
Beam production
Electron Beam
Thermoionic
Emission
Proton Beam
Ionizing Hydrogen
•Glow Discharge Column
•From H- Ion
Other Beams
Secondary Beams:
• Proton
• Antiproton
• Other Particle Beams
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).
Colliding
•Fixed target
E=
(2mEp)
•Colliding beam
E = 2Ep
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.
Two Types
Accelerator
Linear
Circular
•Linear Path
•Circular Path
•Travel once
•Travel several times
Linear Accelerator
LINAC Operation
Methods of Acceleration in
Linear Accelerator
SLC Polarized Electron Gun
Methods of Acceleration in
Linear Accelerator
•Basic idea
•Synchronization
•Length of the tube
•Shielding
LINAC cont’d
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.
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:
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 E&B fields, which
form an E/M wave traveling down the
accelerator.
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.
Circular Accelerator
Methods of Acceleration in
Circular Accelerator
Cyclotron
•The Ds
•Electric field across the gap
•Circular orbit
•Increasing radius
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
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
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/qB
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
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.
Storage Rings

Similar to a synchrotron, but designed to keep
particles circulating at const. energy not increase
energy further
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SPEAR : 3 GeV
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PEP I : 9 GeV
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PEP II : e- 9 GeV
e+ 3.1 GeV
Detection
•Tracking bubble, radiation
•Tracking curvature (charged particle)