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Linear Accelerator

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In strict terminology the 'linear accelerator' is a machine in which electrons are accelerated up to the required energy, which may be from 4 MeV for a low-energy machine to a few tens of MeV for a higher energy machine. Electrons by virtue of their low mass become relativistic already at energies of the order of an MeV. Circular machines such as the cyclotron, the betatron or the synchrotron are not very suitable to accelerate them to energies higher than a few hundred MeV. This is because of the strong radiation emitted by charged particles under accelerated motion, the synchrotron radiation. The energy loss by synchrotron radiation varies as the fourth power of the energy of the particles and inversely with the radius of the orbit. Thus, at some stage in a circular machine, the amount of energy the particles lose by synchrotron radiation becomes greater than the energy they gain from the rf source. Clearly the method to cut the synchrotron radiation losses is to avoid using circular machines and accelerate the particles in linear machines instead.


Definition

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The linear accelerator can be used to accelerate electrons, protons or even heavier ions. It also uses multiple pushes given to the particles in the beam to accelerate them to high energies. Modern linear accelerators make use of the electromagnetic field established inside a hollow tube of conducting material, called wave guide. Considerations of phase stability in linear accelerators proceed much as those in circular accelerators. It is achieved during that part of the cycle of the rf when the potential increases rather than when it decreases.

 Linear Accelerator
  • The first proton linear accelerator was built in Berkeley in 1946.
  • The first electron linear accelerator was successfully put into operation in Stanford around 1955.

Linear accelerators which accelerate electrons and positrons with high intensity to 50GeV of energy.

Magnetic Linear Accelerator

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The main idea of this type of macroparticle accelerator is that a premagnetized magnetic dipole is accelerated in a traveling wave of magnetic field gradient. The propagation of the wave is controlled by the velocity and position of the dipolar projectile in such a way that a stabilized path with the optimum accelerating condition persists throughout the acceleration process. The dipole orientation is stable if the force is exerted as a drag from a magnetic pole of opposing polarity; it is unstable if it is a pushing force between two poles of the same polarity. In other words, a stably oriented dipole is pulled into a peak-field zone and not pushed away from it.

Linear Particle Accelerator

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It might be expected that the term linear particle accelerator should refer to any device in which particles are accelerated along a straight line. However, through common usage in the accelerator field the term linear particle accelerator has been reserved for an accelerator in which charged particles move on a linear path, and are accelerated by time dependent electromagnetic fields. Generally, a particle accelerator provides energy to a beam of charged particle by the application of an electric field. The ideal particle orbit in an RF accelerator may be either a straight line for a linac, a spiral for a cyclotron or a circle for a synchrotron.