How Does a Synchrotron Work

The synchrotron was developed by elementary particle physics in order to accelerate electrons, positrons, protons and other particles. It consists of a ring with a diameter of about a few meters up to more than 100 m in which a vacuum of 10 mbar can be sustained and to which strong electric and magnetic fields can be applied (see Fig. 1). A bunch of electrons or positrons is first accelerated in a linear accelerator to an energy usually lying between 40 MeV and 380 MeV. 

After the particles have reached the energy one wants (for example 3 GeV) they are injected into the storage ring. 

While the energy of the particles can be kept constant, the average intensity of the current decreases with time. This is due to collisions with atoms which occur in a small amount even in a very good vacuum and to collisions with the wall of the ring because the focussing is not perfect etc. As an example, Fig. 5 shows the current at DORIS as a function of time as it occurred under experimental conditions. 

Of special interest is the time structure of the particle current illustrated in Fig. 4. The duration of the puls Tp depends on the length and the velocity of the bunch. At the 

1 In some cases, for example at the photon factory in Japan the particles are accelerated in the linear accelerator already to the energies of more than 1 GeV and are injected from here directly into the storage ring. 

---