Transcript Slide 1 - StCPhysicsDept

Particle Accelerators
Designed to accelerate charged particles to higher
energies . These high energy particles can then be
smashed into a target to probe the nature of matter
or the wave properties of the fast moving particles
can be used to probe( electron microscope )
Principles of Accelerators
Regardless of whether the particle accelerator is
linear or circular, the basic parts are the same:
1. a source of particles (this may be another
accelerator)
2. beam pipes (a guide along which the particles will
travel whilst being accelerated)
3. accelerating structures (a method of accelerating
the particles)
4. a system of magnets (either electromagnets or
superconducting magnets as in the LHC)
5. a target (in the LHC the target is a packet of
particles travelling in the opposite direction).
LHC Large Hadron Collider
Electric Fields
A charged particle inside an Electric field
experiences a force.
The field does work on the charged particle.
The electric work is turned into kinetic energy
work done = charge x potential difference
W =QxV
=
½ mv2
Example
-200V
a) Calculate the work done on the
proton by the electric field.
W=QxV
W = 1.6x10-19 x 500
W = 8.0x10-17 J
b) Calculate the speed
of the proton at the
–ve plate if it was
initially stationary
+300V
proton
Ek gained = work done on proton
Ek = 8.0x10-17 = ½ mv2
2Ek = mv2
2Ek/m =v2
2 x Ek  m x v 2
v
2 x Ek
2 x Ek
v
m
v
2 x8.0 x10 17
5
1
v

3
.
1
x
10
m
s
1.67 x10  27
b) Calculate the speed of the proton at the
–ve plate if it was initially stationary
Ek gained = work done on electron
Ek = 8.0x10-17 = ½ mv2
2Ek = mv2
2Ek/m =v2
2 x Ek  m x v
2
2 x Ek
2 x Ek
v
v
m
m
2 x8.0 x10 17
5
1
v

3
.
1
x
10
m
s
 27
1.67 x10
Another unit for Energy
Particle Physicists measure energy in
electronvolts, eV.
1eV is the energy gained by an electron when
accelerated through a p.d. of 1V.
1eV = Q x V
= 1.6 x10-19 x 1 = 1.6 x10-19eV
To probe the nucleus we need particles in the
GeV range
Electric Field patterns
http://www.physicsclassroom.com/class/estatics/u8l4c2.gif
The arrow shows the direction a free positive
charge would accelerate in. The closer the lines
the stronger the field.
For a point –ve charge the arrows would point
towards the charge
More field patterns
http://physicscatalyst.com/elec/chr_fig6.gif
An +ve and –ve charge of equal magnitude
( similar to the magnetic field around a bar
magnet )
And more patterns
2 equal charges. Null
point between them, no
force is experienced
here.
http://upload.wikimedia.org/wikimedia/en-labs/a/ab/Fhsst_electrost18.png
Field is uniform for parallel
plates.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Field_lines_
parallel_plates.svg/524px-Field_lines_parallel_plates.svg.png
Magnetic Fields
A moving charge has a magnetic field about it. This can
interact with another magnetic field . The direction of
the charged particle can be controlled.
The magnetic field does no net work on the charged
particle, its speed remains constant.
Field pattern around a moving charge
direction of
electron flow
© Douglas Morrison
Left hand grip rule. The
thumb points in the direction
of the North Pole,
Movement of charged particles
Right Hand Motor Rule : Hold the thumb
and first 2 fingers at 900 to each other.
Thumb ; direction of motion
1st finger : points North to South
2nd finger : points direction of current