Linear Accelerator

Particle accelerator

A machine that uses electromagnetic fields to propel charged particles to very high speeds is a particle accelerator. The largest particle accelerator is located in Geneva, near Switzerland, known as the Large Hadron Collider (LHC).

There are two types of particle accelerators: electrostatic and electrodynamics accelerators. Linear accelerator belongs to the category of electrodynamics (also known as electromagnetic particle accelerator) accelerator. This class of accelerators were first developed in 1920. In electromagnetic particle accelerators, the particles cannot pass through the same accelerating field again and again. As a result, the output energy is not limited by the strength of the accelerating field.

Linear accelerator

Linear accelerators belong to the category of electrodynamic accelerators. It is also known as a linear particle accelerator and has numerous advantages, like the generation of X-rays, high energy charged particles for medical purposes, radiotherapy, etc. Linear accelerators also serve as a particle injector for high energy accelerators, which are used to achieve high energy electrons and protons.

A linear particle accelerator is also referred to as linac. Leo Szilard developed a method of particle acceleration. In this method, the linear particle accelerator increases the kinetic energy of charged ions and subatomic particles by subjecting them to a linear beamline series of oscillating potential.

Parts of a linear accelerator

A linear accelerator consists of the following parts:

1. Vacuum chamber – It is a hollow pipe used for the acceleration of particles. It is evacuated using a vacuum pump so that no particle collides.
2. Particle source – It produces particles that are charged and accelerated inside the drift tube. There are many sources, such as cold cathode, hot cathode, photocathode, radiofrequency ions, etc.
3. Oscillator and amplifier – These are needed to produce an accelerating field, which accelerates the charged particles within a linear particle accelerator. They have very high AC voltages and potentials.
4. Measuring units – Various precise and large electronic devices are installed to measure the readings and values of the experiment performed. These are regulated from time to time to check the results of the experiment.

Working of a linear accelerator

The ion source in the linear particle accelerator throws a bunch of electrons, which are charged and accelerated in the direction of the first drift tube. This movement of particles occurs due to the attraction between the negative and positive potentials inside the tube.

The radiofrequency source shifts the polarity of particles as soon as the particles come inside the drift tube. The first drift tube becomes negatively charged with the effect of polarity, while the second one becomes positively charged. Due to inertia, the electrons may tend to come out of the first tube and get attached to the second tube. This causes a drift of electrons from the first to the second tube.

As the electrons accelerate, their velocities increase. As a result, they can travel a farther distance then. For such conditions, drift tubes must be made long enough for the movement of particles so that they can travel a longer distance. Greater velocity is needed to move the charged particles to travel a farther distance.

How safe is a linear accelerator?

1. Several tests and treatments are done before the experiment to check the quality of the linear particle accelerator. From design to its plan, everything is done very carefully. Radiation oncologists, physicists and dosimetrists work together to maintain safety.
2. The plan is checked multiple times before execution. Quality tests and procedures should meet the quality standards as set during the planning stage.
3. The experiment or procedure of curing is tracked with precision. The person in charge must check the readings thoroughly and maintain the report timely.
4. Regular weekly and monthly checks must be done of the linear particle accelerator.

Applications of particle accelerators

1. The high beams used in the particle accelerators are widely used in research in science, industrial and technical fields.
2. The world has over 30,000 accelerators, out of which 80-85% are mainly used for ion implantation and radiotherapies. The remaining are used for biomedical applications, industrial processing, and high and low energy research.
3. The highest possible energies developed by these accelerators are used to study fundamentals of time and space, the structure of matter or any other kind of interaction that may exist.
4. Investigation of interaction, properties and structure of nuclei at high temperatures and densities is possible with the beam of bare atomic nuclei.
5. Physicists and cosmologists use a particle accelerator to study the universe's origin by colliding particles and studying particle-particle interactions.
6. The beams of the accelerated particles at low energies are used in radiotherapy to cure cancer.