At the beginning of our century scientists conducted many experiments on charged particles. The first sources of the particles were radioactive materials. They send e.g. alpha particles of energies up to 6 Me V. That kind of particles was used in the 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 obtaining high-energetic particles. Some of the constructions (these systems are called generally accelerators) are described below:
In 1932 two scientists - J.D. Cockcroft and E.T. Walton - built a system thanks to which they were able to 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). The accelerated protons incidence at a thin foil caused some emission of alpha particles as the formula shows below:
Each alpha particle achieved energy of 8,6 MeV.
Van de Graff 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 by means of 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.
At the early thirties at the University of California, in Berkeley two scientists - Ernest Orlando Lawerence and M.S. Livingston constructed a new type of ions' accelerator. It consisted of two empty, semicircular chambers- dees. There is a narrow, empty slot between the chambers. The chambers are supplied with the voltage of radio frequency. The dees are placed in a vacuum chamber, between the poles of a mighty electromagnet. The creation of ions proceeds in the source placed in the middle, between the dees. 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 shown below:
According to 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:
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In the early forties D.W. Kerst from the University of Illinois constructed a new system for 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 electromagnetic field changes in time. The changeable field accelerates electrons and keeps them on a constant circular orbit.
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 kept by a 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.
Accelerators are used for the scientific research in the elementary particle physics and nucleonics. But some kinds of accelerators are used also in medicine, technology, and industry. But these kinds of accelerators are not that strong as the scientific ones.