Inside the synchrotron

electron gunElectron Gun 

The electron gun begins the process by running high voltage electricity through a heated tungsten button, electrons are boiled out and enter the Linear Accelerator (LINAC). These electrons are then accelerated to 99.999998% of the speed of light using microwave radio frequency cavities.

The process begins in the basement where high voltage electricity passing through a heated cathode produces pulses of electrons. Heating the cathode to incandescence gives some electrons enough energy to leave the surface (essentially boils them off). The high voltage (approximately 200,000 volts – a car battery has only 12 volts!) repels the electrons, accelerating them toward the Linear Accelerator, or LINAC.

The source of the electrons, the cathode, is a tungsten-oxide disk (tungsten is the same material as light bulb filaments). As electricity flows through the disk, it will heat it until electrons are emitted (at about 1,000 °C). A nearby screen is given a short, strong positive charge (125 times per second) which pulls the electrons away from the disk. The system is similar to that found in a television picture tube.

Linear Accelerator

The electron gun supplies electrons to the Linear Accelerator (LINAC). A series of cavities with microwave radio frequency fields in the 2,856 megahertz LINAC provide energy to the electrons that are accelerated to an energy of 250 million electron volts, or 250 MeV. At this energy the electrons are travelling at 99.9998% of the speed of light (3.0 x 108 m/s).

The microwaves push the electrons much the same way a surfer is pushed by water waves. The LINAC produces pulses of electrons for 2 nanoseconds up to 140 nanoseconds for injection into the storage ring. The short pulses can be used to fill a single "bunch" in the storage ring for use in time-sensitive measurement studies. The long pulses are used to produce a (3x140=) 420 nanosecond pulse train in the storage ring. Pulses of electrons are supplied once per second by the LINAC. After several minutes of operation enough current is accumulated in the storage ring for several hours of operation and the LINAC is turned off until it is required to refill the ring.

Vacuum Chambers

The electrons (and later the photons) must travel in a vacuum to avoid colliding into atoms or molecules and disappearing. The ultimate vacuum chamber pressure is lower than 10-11 torr (1 atm. pressure is 760 torr). This means that there are fewer molecules present in our vacuum system than there are in space around the International Space Station.

Booster Ring 

Electrons travel from the LINAC to the booster ring where a specially designed radio frequency cavity raises the energy of the electrons from 250 MeV to 2900 MeV as they circulate in the ring. Following this boost in energy, the electrons are transferred to the Storage Ring.

In particle physics, the standard unit to measure energy is MeV or mega-electron volts (1*106 eV). One eV (electron volt) is the amount of energy that an electron gains when it moves through a potential difference of 1 volt (in a vacuum). As they circulate, electrons receive a boost in energy from 250 MeV to 2,900 MeV (energy equivalent to about 2 billion flashlight batteries!) from microwave fields generated in the Radio Frequency Cavity at 2,856 MHz. For comparison, the energy of charged particles in a nuclear explosion range from 0.3 to 3 MeV. The typical atmospheric molecule has an energy of about 0.03 eV.

The electrons travel around the 103 m ring approximately 1.5 million times in 0.6 seconds. Each of 68 bunches contains 50 pC (3.1 x 108 electrons) with a total energy of 9.92 J at 2,900 MeV and 10 mA circulating current.

The booster ring cannot increase the speed of the electrons to, or beyond, the speed of light, but the electrons travel at about 99.999998% of light speed.

Storage Ring

The high energy electrons are transferred from the Booster Ring, to circulate the Storage Ring`s twelve straight sections. The electrons emit synchrotron light every time their path is bent by the magnets inside the Storage Ring. In each straight section there are also special magnets series called Insertion Devices that increase the brightness of the beam before entering the beamline.

When the electrons reach 2,900 MeV, an injection system transfers them from the booster ring to the 171m storage ring. The process repeats once per second up to 600 cycles (about 10 minutes), as required, to reach an average circulating current of 250 mA.

Once in the storage ring, the electrons will circulate for four to 12 hours producing photons every time the 6800 kg dipole magnets change the direction of the flow of electrons. While the ring looks circular, it is really a series of 12 straight sections each with 2 dipole magnets, and a series of four-pole and six-pole magnets to narrow the beam.

Some straight sections also include space for special magnets called Insertion Devices. After each turn there is a photon port to allow the light to travel down the beamlines.

Over time, the number of electrons stored in the ring will decline. This is inevitable because the vacuum isn’t perfect. Electrons collide with the few particles that are present and are lost. As a result, CLS must either empty the ring and re-inject electrons, or add more electrons to maintain the necessary current.

Magnets

There are two types of electro-magnets in the booster ring. The blue dipole magnets weigh over 3000 kg. The magnetic field created by the magnets is used to direct the electrons around the booster ring. The field of the green quadrupole (four-pole) magnets is used to force bunches of electrons into a fine beam within the vacuum chamber.

 

Radio Frequency (RF) Cavities

There are two cavities that use microwaves to boost the electron’s energy. A cylindrical cavity in the booster ring delivers a high-energy kick to the electron bunches during each turn around the ring. It operates with a radio frequency (RF) of 500 MHz.

The purpose of the cavity, pictured left, in the storage ring is to replace the energy lost by the electrons to light production. Superconductivity is the flow of electric current without resistance in certain metals and alloys at temperatures near absolute zero. The operating temperature is -270°C (-273°C is 0 K or absolute zero, the point at which all motion stops). Operating at such cold temperatures eliminates most power loss, while the RF field provides energy.

Insertion Devices

The CLS is one of the brightest synchrotrons in the world despite being roughly one tenth the size of similarly bright synchrotrons. One of the ways that we achieve this is through insertion devices. 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 many times creating a narrow beam of much more intense light.

insertion device wigglerA wiggler or undulator consists of a periodic series of magnets, placed in a straight section of the storage ring. The magnetic fields force the electrons to ‘wiggle’ around the straight path. The result is a very high flux of photons along the beamline.

A wiggler produces a wide range of high energy X-rays. An undulator produces even higher intensity X-rays with a narrower range of energies.

Beamlines and Experimental Stations

A beamline has several major components including sections that focus and select the required wavelength of light, select the appropriate technique for the experiment, and detect or measure effects of the light as it interacts with the sample.

Beamlines

The CLS has 13 beamlines accessible for “users” or scientists from other institutions using this equipment as part of their research programs. A beamline (#6 above) consists of a optics hutch (#7) where synchrotron light is focused and wavelength is selected, an experimentation hutch (#8) where the appropriate technique is selected for the experiment, and work stations (#9) where scientists operate the beamline and measure light as it is absorbed, reflected, refracted, or scattered by the sample.

MonochromatorMonochromator

Synchrotron light passes through the optics hutch on its way to the sample. There, the monochromator enables researchers to choose the wavelength of light best-suited to the experiment they are conducting. The monochromator is the device that separates different wavelengths (much like a prism). This is done using either optical dispersion (as in a prism), or of diffraction, using a grating which separates the wavelengths of light and filters out the light that isn’t required. Each of the beamlines at CLS is unique and have markedly different monochromators specific to their design.

Endstations

Endstation

The selected wavelengths of synchrotron light are focused by the mirrors in the optics hutch onto the sample in an endstation located in the experimental hutch. Each endstation is designed specifically for the types of experiments conducted on that beamline. In general, each one consists of a sample holder and a detection system, unique to the technique employed by the scientist, as well computers through which the researchers control the mechanisms involved in the experiments and view the data as it is recorded.

Synchrotron Source to Computer diagram

Beamlines

Note: For more detailed information regarding specific beamlines, please see our Beamlines tab

Salute to Safety!

CLS is committed to providing a safe working environment for all staff and protecting the general public and environment from risks. As part of our commitment to safety, we utilize personnel safety systems, equipment protection systems and emergency shutdown processes.

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Engineering Highlights

The CLS uses state-of-the-art technology. From controlling vibrations and temperature in the facility to vacuum systems and advances in cryogenics, we were able to expand on previous improvements in synchrotron science.

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Far Infrared Spectroscopy (Far IR)

Mid Infrared Spectroscopy (Mid IR)

High Resolution Spherical Grating Monochromator (SGM)

Variable Line Spacing Plane Grating Monochromator (VLS-PGM)

Soft X-Ray Spectromicroscopy (SM)

Resonant Elastic and Inelastic X-Ray Scattering (REIXS)

Canadian Macromolecular Crystallography Facility (CMCF)

Very Sensitive Elemental and Structural Probe Employing Radiation from a Synchrotron (VESPERS)

Soft X-Ray Microcharacterization Beamline (SXRMB)

Hard X-Ray MicroAnalysis (HXMA)

Synchrotron Laboratory for Micro and Nano Devices (SyLMAND)

Biomedical Imaging and Therapy (BMIT)

Brockhouse X-Ray Diffraction and Scattering Sector (BXDS)

Quantum Materials Spectroscopy Center (QMSC)

Biological X-Ray Absorption Spectroscopy (BioXAS)

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