Cyclotron

Particle accelerators are special devices or machines that increase the charged particles' velocity by using electromagnetic fields. There are two types of particle accelerators:

• Electrostatic accelerators
• Electrodynamic accelerators

Electrostatic Accelerators

The accelerating voltage limits electrostatic accelerators. These particle accelerators are similar to the cathode ray tube, and since the speed is dependent upon the accelerating voltage, the final speed can not be very high due to electrical breakdown.

Electrodynamic Accelerators

Electrodynamic Accelerators depend upon dynamic fields where these fields remove the dependence upon the accelerating voltage. As a result, the same particle passes through the field multiple times, constantly gaining speed. These accelerators can either be linear or circular.

Cyclotrons are machines that accelerate charged particles to high energies. The world credits E.O Lawrence and M.S Livingston for the invention of the cyclotron in 1934. They constructed the device to investigate the nuclear structure.

Charged particles are accelerated using both magnetic fields and electric fields in the cyclotron. They are perpendicular to each other, and thus, they are known as cross fields. The spiral path of a cyclotron accelerates charged particles outward from its centre. Static magnetic fields and rapidly varying electric fields bind these particles into a spiral trajectory.

Cyclotrons: How do they work?

Cyclotrons use a high-frequency alternating voltage to accelerate the charged particles. The machine holds this voltage between two hollow D-shaped metal electrodes. These electrodes are known as dees, and you can find these inside a vacuum chamber. The placement of these electrodes (face to face) with a small gap creates a cylindrical space inside the dees. The centre of this space is the location for injecting the particles for acceleration purposes. In DEES, a static magnetic field B is applied perpendicular to the electrode plane by the poles of the electromagnet. Lorentz force perpendicular to the direction of the particle's motion bends the particle's path in a circle. It involves applying several thousand volts of alternating voltage between the dees. In the gap between the electrodes, a voltage produces an oscillating electric field that accelerates the particles. The voltage frequency allows particles to complete one circuit during each voltage cycle. The cyclotron meets this condition by setting the voltage frequency to the particle's cyclotron frequency.

Applications of Cyclotron

Compared to linear accelerators, cyclotrons are much more effective because they accelerate particles more than once in one set-up and because their cylindrical shape requires less space than linear accelerators. Below are some examples of the common uses of cyclotrons.

• For nuclear physics experiments and bombarding atomic nuclei, cyclotrons are widely used to accelerate charged particles.
• Different cyclotrons find their usage in radiation therapy for cancer treatment.
• It is possible to transmute nuclear structures using cyclotrons.

The limitations of Cyclotrons

• Electric or magnetic fields do not interact with neutral particles (e.g. neutrons). Therefore, a cyclotron (no matter how powerful) can accelerate these particles.
• The small mass of electrons causes their speed to rise rapidly so that the high voltage and the particle quickly lose their resonance. As a result, a cyclotron cannot accelerate an electron to very high speeds.
• Cyclotrons can accelerate particles to speeds much less than light speed. Thus, studies related to relativity theory are not possible using a simple cyclotron.

Frequently Asked Questions about a Cyclotron

Ques: Why can't we use cyclotron to accelerate an electron?
The mass of an electron is about 1/1836 times of a proton, and thus, it is a very light particle that attains very high speeds very quickly, and the resonance between the particle and the field is lost. During such a phase, the behaviour of the electron in the fields of the cyclotron become unpredictable.

Ques: What do you mean by cyclotron frequency?
Cyclotron frequency is the rotation frequency of the charged particle. This charged particle rotates with this frequency in a perpendicular direction to the static magnetic fields in the cyclotron.