Synchrotron X-rays
A synchrotron is a large machine (about the size of a football field and even bigger) that generates brilliant beams of light by moving electrons through a strong magnetic field, (see Fig. 2.1 at left).
In a synchrotron, electrons are accelerated to near the speed of light and are confined to a circular orbit by a series of bending magnets, (see Fig. 2.2 at left).
Bending Magnet
(Image courtesy of The Australian Synchrotron Program). |
At each deflection of the electron path a beam of radiation is produced. The electron orbit of a synchrotron is composed of a series of curved sections and straight sections. In addition to bending magnets, other types of magnets are used to enhance various properties of the radiation. These are known as insertion devices and are placed in the straight sections of the electron orbit. There are two types of insertion devices, an undulator and a wiggler, which are comprised of rows of magnets with alternating polarity, and which correspond to weak and strong magnetic fields respectively. |
Undulator
(Image courtesy of The Australian Synchrotron Program). |
A very narrow beam of coherent light is produced that is amplified by up to a 104 increase over that of a bending magnet. |
Wiggler
(Image courtesy of The Australian Synchrotron Program). |
Beams emitted at each pole reinforce each other and appear as a broad beam of incoherent light. (Image courtesy of The Australian Synchrotron Program).
The radiation emitted at a bending magnet or a wiggler insertion device has a very wide spectral range, while undulator radiation is concentrated in more narrow spectral bands. To produce an X-ray beam of narrow wavelength range, optical devices are inserted in the beam produced. |
Monochromator
For diffraction experiments, a monochromator is needed to obtain X-rays of narrow-bandwidth (as shown above). Also, because of the large source-to-sample distances in a synchrotron facility, focusing is required to increase the intensity of the beam over a small area. This is particularly true in the horizontal direction for a bending magnet beam as it diverges outward as it leaves the source.
The X-ray beam is then channeled down “beam lines” to experimental workstations where they can be used in many different avenues of science.
Fig.2.1 The Advanced Photon Source in Illinois, USA.
Fig.2.2 Creating the Light
(1) Electrons are generated and accelerated into the linear accelerator (2). They are then injected into the booster ring (3) and further accelerated to 99.987% of the speed of light. They are then injected into the storage ring (4) where light is created by use of bending magnets or insertion devices. The light is then sent down beam lines (5) where it can be used in experimental work stations (6).
Source: www.lightsources.org