Physics (Year 12) - The Standard Model
What are they?
Particle accelerators are devices that use electric and magnetic fields to accelerate charged particles to very high speeds and then are made to collide with other particles, allowing scientists to study the resulting reactions and the particles produced in these reactions.
Particle accelerators are important to the theory of the Standard model because inside such accelerators the mass-energy equivalence principle is put into practice by using the energy of the accelerated particles to create new particles or to study the interactions of existing particles. For example, when high-energy particles collide with a target, they can create new particles or cause existing particles to change their energy or mass, allowing scientists to study the fundamental properties of matter and the forces that govern it. By observing the behaviours of the particles inside a particle accelerator, scientists can test the predictions of the Standard model and search for evidence for phenomenon that may not be explained by the model.
There are two basic types of particle accelerators; linear and circular.
Linear particle accelerator
A linear particle accelerator is sometimes referred to as LINAC. As the name suggests, LINAC accelerate charged particles in a straight line. They consist of a series of hollow metal tubes which are called drift tubes, and each drift tube is connected an alternating power supply. When a charged particle enters the accelerator, it is attracted towards the first drift tube because of the opposite charges of the tube and the particle. Once inside the tube, the electric field of the tubes is dialled down to 0 and the particles continue moving through the tube. As they exit the first tube, the electric field is increased again but this time with the opposite polarity. This allows the particles to be attracted to the second drift tube and repelled from the first drift tube. Once inside the second drift tube, the process repeats again. It is the region between the tubes where the particles accelerate. It is worth noticing that the tubes get longer near the end of the LINAC because the charged particles are travelling faster. The time they spend inside the tubes need to be constant so that the power supply can alternate at the same time the particles enter and exit the tubes.
Linear accelerators are commonly used in medical settings to produce high-energy X-rays for imaging and cancer treatment. Compared to circular accelerators, linear accelerators are more compact and easier to operate because they don’t use powerful magnetic fields as used in circular accelerators. However, they can only accelerate particles to a limited energy.
Circular particle accelerator
Circular particle accelerators use electric and magnetic fields to accelerate charged particles in a circular path. They use the electromagnetic phenomenon of a charged particle travelling in circular motion due to the magnetic force. This phenomenon is described through the relationship;
Circular particle accelerators contain many D-shaped electrodes, called ‘dees’, which create an electric field that accelerates the particles as they pass through the gap between the electrodes. A common type of circular particle accelerator is called a cyclotron. Cyclotrons maintain a constant magnetic and electric field to accelerate the charged particles through a spiral path. A second type of circular particle accelerator is called a synchrotron. Synchrotrons use a varying magnetic and electric field to accelerate charged particles through a single loop; unlike a spiral path in a cyclotron.