ACCELERATORS OF PARTICLES
In the beginning of our
century scientists conducted many experiments on charged particles.
The first sources of the particles were radioactive materials. They
send f.e. alpha particles of energies up to 6 Me V. That kind of
particles was used in first controlled nuclear reactions. But those sources
were very expensive and hard to control. And foremost produced
particles had not enough energy to make many of the experiments
possible to conduct. Scientists needed some better ways of
achieving high-energetic particles. Some of the constructions
(these systems are called generally accelerators)
are described above:
- Cockcroft-Walton generator
In 1932 two scientists - J.D. Cockcroft and E.T. Walton - built a
system thanks to which they could accelerate charged particles. The
system consisted of a container filled with gaseous helium. Helium
was shot with electrons, and they caused ionization of that helium.
Free protons were created. They were accelerated by the potential
difference (0,15 MV). Accelerated protons incidence at a thin foil
caused some emission of alpha particles as the formula shows
Each alpha particle achieved energy of 8,6 MeV.
Van de Graffa generator (belt-type generator)
That generator consisted of a source of high voltage and a belt
hanging on two rolls. The electric charge caused by the source was
transferred to the belt thank to some special blades. Another
blades situated in the sphere were collecting the charge and
transferring it to the external surface of the sphere increasing
its potential. The ions created inside the sphere were accelerated
thanks to the potential difference between the sphere and earth.
The ions were moving inside the vacuum tube.
| In the beginning of the
thirties at the Californian University in Berkeley two scientists
E.O. Lawerence and M.S. Livingstone constructed a new type of ions'
accelerator. It consists of the two empty, semicircular chambers-
duants. There is a narrow, empty slot between the chambers. The
chambers are supplied with the voltage of the radio frequency. The
duants are placed in the vacuum chamber, between the poles of the
mighty electromagnet. The creation of ions proceeds in the source
placed in the middle, between the duants. After leaving the source
the ions' path is curved in the strong magnetic field. That is
because they are bound by the magnetic force. In this case, when
the vector of induction is perpendicular with the respect to the
vector of velocity, the magnetic force is given by the formula
According to the Newton's law
for the circular motion it is:
Having those two formulas we can calculate the radius of the
trajectory of the ion leaving the source:
When passing through the slot between the duants each ion undergoes
acceleration thanks to the electric field. That electric field
between the duants is caused by the source of the radio frequency.
So the ion moves a bit faster. That is why in the second duant the
radius of the ion's movement is longer. The source of the variable
current (the current is of the radio frequency) is synchronized, so
every time when the ion passes through the space between duants it
is "pushed". That means that each time it moves faster and the
radius of the movement grows longer. The final velocity of the ion
is its mas, the magnetic field intensity (B) and the duants'
radiuses depended. The final kinetic energy of the particle is
given with the formula:
- In the beginning of the forties D.W.
Kerst of the Illinois University constructed a new machine
accelerating ions - the betatron. It consists of the torus shaped
vacuum chamber placed between the overpoles of a very strong
electromagnet. In the chamber there is a source of electrons. The
variable current fed coils induce a variable electromagnetic field
between the poles of the electromagnet. The field accelerates
electrons ant keeps them on a circular orbit. That is why there is
no such limit as in the cyclotron - the radius of the particle's
movement doesn't get longer.
These are one of the most simple accelerators of particles. Charged
particles (the protons, the electrons) are firstly accelerated in
some other machines (i.e. in a van de Graff generator) and then
shot in a long vacuum tube. The beam of the particles goes through
the many of empty, metallic cylinders and that are connected
alternate (positive - negative) with a radio frequency generator.
So the particles are accelerated by the electric field of the
electromagnetic wave moving along the accelerator. Every next
cylinder has to be longer than the preceding one because of the
increasing velocity of the particle.
| It is a kind of circle
accelerator for charged particles. The particles circulate at
stable orbits, where they are held by the magnetic field increasing
with the increasing velocity of the particles. The particles are
accelerated each time they pass through the place in the
synchrotron called the resonator slot. The slot is fed by a high
Some of the first
accelerators constructed from the thirties to seventies are listed
|Kerst's Betatron Stanford University
|Linear accelerato Stanford University
|Synchrotron Brookhaven National Laboratory
|Synchrotron CERN, Szwajcaria
|SLAC - linear accelerator Stanford University
|Synchrotron Sierpuchow, ZSRR
|Synchrotron National Accelerator Laboratory