How does a Synchrotron work?


A Synchrotron accelerates charged particles, such as electrons into an orbit at almost the speed of light. When electrons are deflected through magnetic fields they create extremely bright light, million times brighter than sunlight.

A synchrotron uses powerful magnets and radio frequency waves to accelerate charged particles. The powerful magnet and radio frequency waves accelerate negatively charged electron along a stainless steel tube, where they reach high speed.  As the magnets are turned on and off, electrons get pulled along the ring of tubes. Since the fast-moving electrons emit a continuous spectrum of light, with various wavelengths and strength, scientists can pick whatever wavelength they need for their experiments e.g. visible light, ultraviolet light or X-rays (soft or hard x-rays).

Structural features of a Synchrotron

A Synchrotron consists of the electron gun, linear accelerator (LINAC), booster ring, storage ring (or rings), bending magnets (not shown in diagram), beam lines and the end stations (see picture below). Click on the name of each part of the Synchrotron to the left to the diagram to read descriptions.



     Parts of Synchrotron


 (1) Electron gun

 (2) LINAC

 (3) Booster ring

 (4) Storage ring

 (5) Beamline

 (6) End station


Diagram of Synchrotron









                                (Diagram of Synchrotron)


What goes on in each of the parts of a Synchrotron?

1. Electron Gun

In the Basement of the Synchrotron building a transformer feeds approximately 220,000 volts DC  (compare with a  car's battery's 12 volts) of electricity through a cathode causing electrons to boil off the surface. The cathode is a tungsten-oxide disk called a button (tungsten is the same material as light bulb filaments). As electricity flows through the disk, the disk gets heated to about 1000oC the temperature that electrons are released. A screen near the button is given a short, strong positive charge 125 times per second, which pulls the negative charge particles, the electrons, away from the disk. This procedure is similar to that found in a television picture tube (see the picture of the Electron Gun below).

Electron Gun
                        (Electron  Gun)

Back to the parts of the Synchrotron

2.  Linear Accelerator (LINAC)

The Electron gun feeds into the LINAC. Microwave radio frequency fields provide energy to accelerate the electrons to almost the speed of light. The speed of the electrons is approximately 3x108 m/s. The electrons are pushed by the microwaves much like the same way as a surfer is pushed by water waves. The  LINAC  produces electron pulses approximately up to 132 nano seconds (ns) in duration. The electrons (and later photons) must travel in a vacuum to avoid being slowed down by colliding with atoms and molecules. The vacuum chamber pressure is lower than 10-11 torr (1.0 torr =133 pascels). This means that there are fewer molecules in the vacuum chamber than in the space surrounding the International Space Station. Below is a picture of the LINAC.

Linear Accelerator
        (Linear Accelerator)


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3. Booster Ring

As the electrons circulate in the Booster ring, they receive a boost in energy from approximately 250 MeV (Mega electron volt) to approximately 2.9 to 6 GeV (Giga electron volts) power equivalent to about 2 billion flashlight batteries from microwaves generated in a Radio Frequency Cavity. In particle physics, the standard unit to measure energy is the electron volt (eV). One electron volt is the amount of energy that an electron gains when it moves through a potential difference of 1 volt (in a vacuum). A synchrotron generates energy in the realm of 2.9 to 6 GeV and higher!


For comparison, charged particles in a nuclear explosion range from 0.3 to 3 MeV. 


Booster Ring
                              (Booster Ring)


The Booster Ring increases the speed of the electrons close to the speed of light (approximately 99.9999985 percent of the speed of light). There are two types of electro magnets shown in the picture below of the booster ring. The blue dipole magnets weigh over 3000 kg. The Synchrotron uses the magnetic field created by these magnets to direct the electrons around the booster ring. The magnetic field of the green quadruple magnets are used to force the bunches of electrons into a fine beam within the vacuum chamber. Above is a picture of booster ring, and it's magnets.


Back to the parts of the Synchrotron

4. Storage Ring, Beam line, and End Station

When the electrons have enough energy to produce light, an injection system transfers them from the booster ring to the storage ring. The process of transferring electrons from booster to storage ring occurs approximately once per second up to 600 cycles (about 10 minutes) as required to reach an average circulating current of. Once in the storage ring, the electrons will circulate for four to twelve hours producing photons every time the 6800kg dipole magnets change the direction of the flow of electrons. While the ring looks circular, it is really a series of 12 straight sections. After each turn there is a photon port to allow the light to travel down the beamlines to the research stations. The magnets and steerage ring are shown in the picture below.

Each beamline has an optics cabin, the experimental cabin, and the control cabin. The optics cabin has optical instruments used to "tailor" the type of radiation to have the characteristics for the experiment. The experimental cabin contains the support mechanism, and the environment  for  the sample study. Instruments called detectors record the information produced from the sample. the control cabin allows the researchers to control the experiments and collect the data. 

Storage Ring  

                               (Storage Ring)

The Synchrotron described above is a basic Synchrotron. There are Synchrotrons that are even bigger, and brighter. These Synchrotrons achieve this by using multi-magnet insertion devices called undulators and wigglers, and having more storage rings. While dipole magnets change the direction of the electrons, thus producing light, multi-magnet insertion devices called undulators and wigglers move the electrons back and forth creating a narrow beam of much more intense light. For example, Spring_8 of Japan is the brightest synchrotron in the world, and the biggest. 


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