The Linac (Linear Accelerator)
Radio frequency power makes an electric field,
polarized in the same direction in all the gaps. Particles are accelerated in the
gaps, and "hide" inside the drift tubes when the electric field reverses.
If a particle was in the gap when the polarity was reversed it would be decelerated.
As the velocity of the particles increases, the drift tubes (and the gaps between them)
become longer and longer. This is called an Alvarez type linear
accelerator after its inventor.
A useful analogy is pushing a kid on a swing.
Each time the kid comes back to you you give it a push and on that swing the kid goes
higher.
The advantage of the
Linac over the Crockoft-Walton
is that the DC voltage of the Linac is zero. The beam is bunched instead of a continuous
ribbon of beam that is in the Crockoft-Walton. In the Linac, there must be
dead spaces where there is no beam. These dead spaces coincide
with where the electric field is pointing in the wrong direction. |