What makes synchrotron light sources so superior to ordinary X-ray emitters?
This can be understood by comparing car headlights to a normal light bulb. Driving at night requires a powerful illumination concentrated ahead of the car. A high flux of light helps, but is not enough: the light must also be collimated with parabolic mirrors -- increasing what is called its brightness.
This is precisely what a synchrotron light source does: it produces a high flux, and concentrates it into a narrow beam, as required for most applications of X-rays.
The principles of synchrotron light are a fascinating consequence of Einstein's relativity. Let us understand them in simple terms.
Imagine a stainless steel tube forming a ring, kept under ultrahigh vacuum (one tenth of a billionth of an atmosphere or less) by special pumps. A bunch of electrons - charged elementary particles - circulates inside the ring almost at the speed of light.
Left free, the electrons would move in a straight line; in the ring, however, a system of magnets bends their path and keeps them in a nearly-circular trajectory. Now visualise the bunch of electrons from the side of the ring: they seem to oscillate in a straight line, just as in the antenna of a radio emitter.
Like the electrons in an antenna, those in the ring emit electromagnetic waves. The reason is that in both cases the electrons are accelerated, i.e., their velocity (direction and/or magnitude) changes with time; for the electrons in the ring, the changes in direction are required to stay in a circular trajectory, and the emitted waves are known as "bremsstrahlung".
The basic difference with respect to a radio antenna is that the electrons in the ring move at a much higher speed - almost the speed of light - and project the emitted waves ahead, due to the Doppler effect of their relativistic motion An electron circulating in the ring is thus like a moving torchlight, producing a narrow (synchrotron) light beam in the direction tangential to the ring.
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Imagine now a straight tube departing from the ring. When the electron-torchlight passes through it, synchrotron light is conveyed along a straight tube.
On ELETTRA, many such tubes are attached to the main ring, and each one of them is equipped with special instruments to use synchrotron light for specific experiments. These tubes and their instruments are called beamlines. Dozens of users simultaneously work on the many beamlines of ELETTRA, performing a wide variety of experiments.