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# Linear Accelerator

In the particle physics, the particle accelerators are used to accelerate the electrons in a tube for performing experiment on them or to understand their behavior under certain conditions.

The particle accelerators are of two types:
The Electrostatic Accelerators are primitive one used for experimental purposes. These accelerators used single source of high voltage to accelerate the particle in the tube. The main disadvantage of these accelerators is the large energy requirement and the distance traveled by the accelerated particles is very less.

The Oscillating Field Accelerators are the type of particle accelerators, several low energy but oscillating high voltage sources are used to accelerate the particles. In these types of particle accelerators the electrode are arranged either in the linear manner or in the circular manner to accelerate the particle linearly or circularly depending upon the type of experiment required. There are various types of Oscillating Field Accelerators.

The most common of these are Linear Particle Accelerators or Circular (or cyclic) Accelerators. Let us study about this Linear Particle Accelerator in this section.
1. Electrostatic Accelerators
2. Oscillating Field accelerators

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## What is a Linear Accelerator?

The Linear Accelerator was invented separately by two scientists Physicist Rolf Wideroe's and Leo Szilard nearly at the same time.
The Linear Accelerator is the type of oscillating field accelerators. It accelerates a charged particle by making the charged particle pass through the various oscillating voltage sources.
The passage is linear that is the reason why this accelerator is known as linear accelerator. It is also termed in short as Linac.

Operation:
The operation of this device is very simple. It has several voltage plates. When a particle approaches it the voltage at the plate is set such that they attract the particles. The particles accelerated towards the plate cavity. As they approach near the plate cavity, the voltage polarity of the plate is switched such that now they repel particle towards the next plate. In this whole process the particles are greatly accelerated.

1. These devices accelerate the particle nearly to the speed of the light, for this reason the cavity are mostly microwave cavities.
2. These devices have completely replaced Cobalt 60 devices which were used previously for radio treatment of the tumors and cancerous tissues.

Applications:
These devices found there use in various applications like used as the feeder device for the circular accelerators and also used in radiotherapy for curing the tumors in the human body or in radio surgery.

## Linear Particle Accelerator

The linear particle accelerator is also termed as linear accelerator. The name is evident from the fact that these devices are cylindrical in shape and particles are accelerated in the straight paths unlike in some accelerators where the particles accelerate and move in circular fashion.
The largest linear accelerator is SLAC (Stanford Linear Accelerator Center). This device is 3 kilometers long and is capable of accelerating the charged particle up to 25 GeV.

## Linear accelerator Diagram

Below shows the block diagram figure of linear accelerator:

The Linear accelerator consists of following elements:

Particle Source:
The particle source is used to produce a particle which needs to be accelerated. The particle source depends on the type of particle, for electron cathodes are used, for protons ion sources are used.

High Voltage Source:
The high voltage source is required to inject these particle into the linear accelerator.

Hollow pipe vacuum chamber:
The length of hollow pipe vacuum chamber depends on the purpose of the use of linear accelerator. The length of hollow pipe varies from 0.5 meters to tens of meters.

Electrodes:
In the hollow chamber the electrodes are placed such that the particle is accelerated at the desired acceleration towards the target. The lengths of the electrodes are depending on the type of particle to be accelerated. The length of the electrodes near the source of particle is small, while the length of electrodes near the target is large.

To energize the electrodes, radio frequency source are used. The radio frequency sources should be operated at correct voltage, right frequency and phase so as to get the maximum device efficiency.

Appropriate Target:
The target materials used depends upon the type of examination and the particle used in the process. If X – rays are produced by the accelerating electron then the target is water cooled tungsten.