Particle Accelerators

A particle accelerator is a device, which is used to project sub-atomic particles at very high speeds. High energy (of many GeV or more) beams of particles are useful for applied researches in sciences. Scientific investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at several GeV.

The main principle behind particle accelerators is that they are designed to impart kinetic energy on charged particles by means of an applied electric field. When a charged particle is subjected to an electric field it experiences a force proportional to the magnitude of the field, and therefore, acceleration. Once the particles have gained a sufficient amount of energy they are collided with other particles (either matter or anti-matter) and the particles resulting from the collision are observed by a detector array. Another necessity of accelerator is that the region where particles are accelerated is kept at high vacuum to prevent them from being scattered out of beam and getting lost through collisions with gas atoms or molecules.

There are mainly two types of accelerators. Linear high-energy accelerators called Linac and circular accelerators.

The Linac uses a linear array of plates which are supplied with alternating current. Just as the particles are accelerated towards the oppositely charged plate the polarity of the plates is changed and the particles are attracted by the next plate. Due to this specially monitored AC current, a group of particles are accelerated through many plates. This is known as Resonance Acceleration. Generally there is a circular accelerator attached to Linac.

The largest Linac is at Stanford, it has a 3km long underground linear accelerator which is also claimed to be the world’s straightest object. It is an electron-positron collider.

DC accelerators, which are the simplest type of accelerators, can sufficiently speed up neutrons for nuclear reactions, Cockcroft-Walton voltage multiplier and Van De Graff generator.

In a circular accelerator particles are accelerated in spirals or curves which are almost circles (using very strong electromagnets). Cyclotrons have a single pair of hollow ‘D’-shaped plates to accelerate the particles and a single large dipole magnet to bend their path into a circular orbit. It is a characteristic property of charged particles in a uniform and constant magnetic field that they orbit with a constant period, at a frequency called the cyclotron frequency, so long as their speed is small as compared to the speed of light. Circular accelerators are preferred over Linacs because of its relatively small size and its ring topology which allows continuous accelerations.

In India, we have the IUAC in New Delhi. Doctorate students from all across the India come to perform their experiments with accelerated particles. DRDO has developed many versions of accelerators under the name of KALI. The latest accelerator was started in June 2004.