Scattering experiments have always been used to investigate the nature of atoms and subatomic particles. Early particle physicists used alpha particles for scattering experiments. Naturally occurring alpha particle emitters were used as a source for alpha particles.

As the further investigations required particles with higher energies, it was apparent than naturally occurring alpha particle emitters were not enough. There was a need for instrument which could accelerate particles to higher energies and control the energy of the particles.

Particle accelerators solved this problem.

• An early model of particle accelerators were developed by J.D.Cocokroft and E.Walton at the Cavendish laboratory in 1932. It was used to create a large voltage difference that would provide a single “kick” or “force” to the proton and could accelerate it to 770keV. Similar mechanism could be made using a Van-de-Graaff generator also.
• Linear Accelerators : Linear accelerators provide multiple junctions where particles can be accelerated along its path. One of the most famous linear accelerator is at the Stanford Linear Accelerator Center (SLAC).

• Cyclotrons : Like Linear accelerator cyclotrons provide multiple kicks to a charged particle. But instead of a linear path, the particle follows a circular path due to force from a magnetic field. The radius of the circular path keeps on increasing with the increase in Kinetic energy of the particle.

• Synchrotrons :  Synchrotrons follow the same mechanism as cyclotrons , except it keeps the radius of the particle constant by adjusting its magnetic field. Most of the particle accelerators currently in use are Synchrotrons.

Physicist use high energy particles, as a lot of interactions that need to be observed, require a lot of energy to take place. If the final particles which are expected to be observed are heavy particles, it  would require initial particles to have high kinetic energy.

A lot of the particles, including heavy quarks in the early days of standard model and the elusive Higgs boson in the 21st century, required high energy interactions , so that they could be experimentally observed.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)