# Ion beams and particle accelerators

The linac is made up of a series of positive and negatively charge tubes which have an alternating p.d. sent through them. Each tube is a di erent charge to the last and the tubes are sized such that as the charged particle enters each tube the p.d. switches so that it is attracted to the next tube, in order for this to work, the tubes must get longer because the particle is moving faster as it is accelerated. This is because the particle is only accelerated when it is not in a tube and it must therefore have a charge pulling it towards the next tube just as it leaves.

2.3.2 Cyclotron

The cyclotron also uses an electric eld to accelerate charged particles. The source is place in the middle between to D-shaped (semi-circular) hollow plates, and the particle is accelerated across the gap (between the plates) by the electric eld. A magnetic eld is used to ensure that the particle is in circular motion, but since the speed of the particle increases, it spirals outwards and eventually leaves the cyclotron, this limits speed which the particle can be accelerated to. We can use circular motion formulae to work out the frequency of the particle:

2.3.3 Synchrotron
A synchrotron is similar to a cyclotron, except that it keeps the motion circular. It still uses an alternating pd to accelerate the particles, but it uses 4 charged tubes to accelerate it, so it is charged 4 times per ‘orbit’. In order to keep the particle performing circular motion (in contrast to a cyclotron) it must also increase the B- eld strength and (also in contrast to a cyclotron) it must have the AC supply increase in frequency increase as the particle increases in speed.

(large accelerators like LHC use a small accelerator and then a large storage right before colliding particles and they used bending magnets as depicted above; but the same thing can be achieved on a small scales with 4 portions of charged tube to accelerate the particles and 4 magnets going around those 4 tubes to maintain a circular path)