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Particle Accelerators

Particle accelerators were invented to investigate objects with size less then 10-12 cm.
A particle accelerator is a device that uses electric fields to propel electrically-charged particles to high speeds and to contain them. An ordinary CRT television set is a simple form of accelerator. There are two basic types: linear accelerators and circular accelerators.
Linear particle accelerators
In a linear accelerator also known as a linac, particles are accelerated in a straight line with a target at the end. Linacs are very widely used - every cathode ray tube contains one. The longest linac in the world is the Stanford Linear Accelerator, SLAC, which is 3 km long. SLAC is an electron-positron collider.
Linear high-energy accelerators use a linear array of plates to which an alternating high-energy field is applied. As the particles approach a plate they are accelerated towards it by an opposite polarity charge applied to the plate. As they pass through a hole in the plate, the polarity is switched so that the plate now repels them and they are now accelerated by it towards the next plate. Normally a stream of particles are accelerated, so a carefully controlled AC voltage is applied to each plate to continuously repeat this process for each bunch.
As the particles approach the speed of light the switching rate of the electric fields becomes so high that they operate at microwave frequencies, and so RF cavity resonators are used in higher energy machines instead of simple plates.
Linear accelerators are also widely used in medicine, for radiotherapy and radiosurgery. Medical grade LINACs accelerate electrons using a klystron and a complex bending magnet arrangement which produces a beam of 6-30 million electron-volt (MeV) energy. The electrons can be used directly or they can be collided with a target to produce a beam of X-rays. The reliability, flexibility and accuracy of the...