INTRODUCTION TO SYNCHROTRON LIGHT

 

What is a synchrotron?

A synchrotron is a large machine (about the size of a football field) that accelerates electrons to almost the speed of light. As the electrons are deflected through magnetic fields they create extremely bright light.

The light is channelled down beamlines to experimental workstations where it is used for research.

 

Illustration of the Australian Synchrotron

Synchrotron applications

Synchrotron light is advancing research and development in fields as diverse as:

·         biosciences (macromolecular/protein crystallography and cell biology)

·         medical research (microbiology, disease mechanisms, high resolution imaging and cancer radiation therapy)

·         environmental sciences (toxicology, atmospheric research, clean combustion and cleaner industrial production technologies)

·         agriculture (plant genomics, soil studies, animal and plant imaging)

·         minerals exploration (rapid analysis of drill core samples, comprehensive characterisation of ores for ease of mineral processing)

·         advanced materials (nanostructured materials, intelligent polymers, ceramics, light metals and alloys, electronic and magnetic materials)

·         engineering (imaging of industrial processes in real time, high resolution imaging of cracks and defects in structures, the operation of catalysts in large chemical engineering processes)

·         forensics (identification of suspects from extremely small and dilute samples).

What is synchrotron light?

Synchrotron light is the electromagnetic radiation emitted when electrons, moving at velocities close to the speed of light, are forced to change direction under the action of a magnetic field.

The electromagnetic radiation is emitted in a narrow cone in the forward direction, at a tangent to the electron's orbit.

Synchrotron light is unique in its intensity and brilliance and it can be generated across the range of the electromagnetic spectrum: from infrared to x-rays.

The electromagnetic spectrum, showing the range of the Australian Synchrotron

Properties of synchrotron light

Synchrotron light has a number of unique properties. These include:

·         High brightness: synchrotron light is extremely intense (hundreds of thousands of times more intense than that from conventional x-ray tubes) and highly collimated.

·         Wide energy spectrum: synchrotron light is emitted with energies ranging from infrared light to hard x-rays.

·         Tunable: it is possible to obtain an intense beam of any selected wavelength.

·         Highly polarised: the synchrotron emits highly polarised radiation, which can be linear, circular or elliptical.

·         Emitted in very short pulses: pulses emitted are typically less than a nano-second (a billionth of a second), enabling time-resolved studies.

 

How synchrotron light is created?

1.     electron gun 2.     linear accelerator (linac) 3.     booster ring 4.     storage ring 5.     beamline 6.     end station

Electrons are generated in the centre (electron gun) and accelerated to 99.9997% of the speed of light by the linear accelerator (linac).  The electrons are then transferred to the booster ring, where they are increased in energy.  They are then transferred to the outer storage ring.

The electrons are circulated around the storage ring by a series of magnets separated by straight sections. As the electrons are deflected through the magnetic field created by the magnets, they give off electromagnetic radiation, so that at each bending magnet a beam of synchrotron light is produced.

 

Illustration of a bending magnet.

At each deflection of the electron path a beam of light is produced. The effect is similar to the sweeping of a search light. These beams can be captured and focussed to a specific wavelength appropriate for a particular technique.

Insertion Devices
It was found that the intensity of light can be significantly increased by the use of 'insertion devices' in the straight sections of the ring.

There are two classes of insertion devices. One is a multipole wiggler (MPW) in which a cone of light is emitted at each bend in the 'wiggle' so that the cones of light superimpose on each other, the intensity increasing with the number of bends.

                                                            Illustration of a multipole wiggler.
At the peak of each wave, a beam of light is emitted. These beams reinforce each other and appear as a broad beam of incoherent synchrotron light when viewed in the horizontal plane ahead of the wiggler.

The second type of device is an undulator. It uses less powerful magnets to produce gentler undulations of the beam. In this case, the light cones just overlap and interfere with each other, so that certain wavelengths of light are enhanced perhaps by 10,000 times. These wavelengths can be changed by altering the gap between the component magnets so that the light is tunable to specific wavelengths.

Illustration of an undulator.

The poles produce less deflection of the electron beam. This results in a narrow beam of coherent synchrotron light, with certain frequencies amplified by up to 10,000 times. 

Current ('third generation') designs of synchrotrons aim to optimise the intensity that can be obtained from insertion devices. In particular, attention is given to the size and positioning of the straight sections that accommodate the insertion devices.

The Australian Synchrotron is an advanced 'third generation' design. It uses the three different types of light sources (bending magnets, multipole wigglers and undulators) to enable a wide range of advanced experiments or measurements to be carried out.

 

Source: http://www.synchrotron.org.au

In order to understand clearly about Synchrotron Light, I've compiled two video clips; one of them is SLRI's, Thailand.

 

 

Synchrotron Technology

 

Presentation of Siam Photon @Synchrotron Light Research Institute

(Public Organization)