What is a Synchrotron?

Synchrotron

A synchrotron is a source of brilliant light that scientists can use to gather information about the structural and chemical properties of materials at the molecular level.

A synchrotron produces light by using radio frequency waves and powerful electro-magnets to accelerate electrons to nearly the speed of light. Energy is added to the electrons as they accelerate so that, when the magnets alter their course, they naturally emit a very brilliant, highly focused light. Different spectra of light, such as Infrared, Ultraviolet, and X-rays, are directed down beamlines where researchers choose the desired wavelength to study their samples. The researchers observe the interaction between the light and matter in their sample at the endstations (small laboratories).

This tool can be used to probe matter and analyze a host of physical, chemical, geological, and biological processes. Information obtained by scientists can be used to help design new drugs, examine the structure of surfaces to develop more effective motor oils, build smaller, more powerful computer chips, develop new materials for safer medical implants, and help with the clean-up of mining wastes, to name just a few applications.

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About the CLS synchrotron

Aerial-CLS

The CLS is Canada’s national centre for synchrotron research. Located at the University of Saskatchewan in Saskatoon, the CLS is a world-class, state-of-the-art facility that is advancing Canadian science, enhancing the competitiveness of Canadian industry and contributing to the quality of life of people around the world.  READ MORE ⇣

Launched in 1999 and officially opened in 2004, the synchrotron is one of the largest science projects in Canadian history and was the product of an unprecedented collaboration of federal, provincial and municipal governments and agencies, universities from across the country and industry.

The CLS is committed to being a world-leading centre of excellence in synchrotron science and its applications by working with the scientific community to promote the use of synchrotron light, promoting industrial partnerships and innovation, and engaging in scientific and educational outreach.

Currently, the CLS has just under 200 employees including scientists, engineers, technicians and administrative personnel. Located next to Innovation Place, one of Canada’s leading high-tech industrial parks, the CLS provides a much-needed national R&D capability and strengthens Saskatoon’s reputation as Canada’s “Science City.”

CLS Staff Photo

CLS Staff Photo 2013

The mission of the CLS encourages excellence in both basic and applied science, with the mandate to grow the Canadian synchrotron research community and be responsive to its needs. This is accomplished through leadership by an independent board of directors that emphasizes the facility’s national character, with representation from government, universities and industry, as well as advisory committees made up of leading scientists from across Canada and around the world.

Access to the CLS for scientists doing basic research is through a peer-review process that encourages excellence and originality in the science done at Canada’s synchrotron. Research time is also reserved on each beamline for fee-for-service access by industry.

This tool can be used to probe matter and analyze a host of physical, chemical, geological and biological processes. Information obtained by scientists can be used to help design new drugs, examine the structure of surfaces to develop more effective motor oils, build smaller, more powerful computer chips, develop new materials for safer medical implants, and help with clean-up of mining wastes, to name just a few applications.

Quick Facts:

  • More than 40 synchrotron light sources have been built around the world. The Canadian synchrotron is competitive with the brightest facilities in Japan, the U.S. and Europe.

  • CLS was built in three phases: Phase I included the building, the rings, and several beamlines at a cost of $174M; Phase II added seven more beamlines ($56M) including the much-lauded Biomedical Imaging and Therapy beamlines; Phase III, currently under way, adds six more beamlines at an estimated cost of $65M

  • More than 3,000 scientists have used the CLS more than 5,000 times.

  • Beamlines carry the synchrotron light to scientific work stations that operate 24 hours per day, 6 days per week, approximately 42 weeks of the year.

  • The first synchrotrons were additions to facilities built to study subatomic physics. Synchrotron light was an annoyance to those researchers because it meant their electron beams lost energy every time they went through a bending magnet. However, the remarkable qualities of this light were soon recognized and researchers began to come up with ways to use it.

  • CLS utility costs are approximately $1.8M annually including electricity, steam and water. When we are operating the facility with stored beam, consumption is approximately 3.2-3.5 megawatts to produce approximately 200 kW of synchrotron radiation. This translates to approximately $1,000 worth of electricity daily.

  • The six-storey building (Phase I construction) required 1,300 tons of steel and enough concrete to build 160 1,200-square-foot homes. This concrete base has more than 700 piles each 10-20m deep with vibrational isolation from the foundation for the walls in order to ensure stability.

  • An economic impact study estimated that CLS operations directly contributed almost $90M to the Canadian GDP. This means that for every dollar of CLS operating funding (approximately $23M) our operations contributed three to the Canadian economy.

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Synchrotron Light

Though a synchrotron is not the only way to generate IR, UV or X-Ray light, we experience substantial benefits in brightness, experiment quality and speed, along with increased ability to select specific light wavelengths. Synchrotron light is emitted when the path of an electron beam is altered via extremely powerful magnets. . READ MORE ⇣

Brightness or Flux

If you were to expose a 1 mm2 sample, similar to what a researcher might put under a regular light microscope, to a number of different light sources and measure the amount of energy the matter in that sample interacted with, you would find that the energy generated by a synchrotron using insertion devices is considerably higher than what is produced by other light sources.

Brightness Flux

Generally speaking, synchrotron sources pack more photons into a smaller beam of light. This offers researchers more information about their sample and makes a greater variety of techniques available to use to learn about their sample.

In situ experiments

Another advantage to some synchrotron techniques is the ability to conduct experiments in situ, or as they are – without treatment. There are a number of research techniques that require the scientist to treat their sample (crush it; make a solution; slice it; etc). While this is also required for some synchrotron techniques, there are also some that allow for the sample to be analyzed without treatment or with less treatment, which can be a significant advantage.

Tuneability or ability to select specific light

By producing high flux light across a significant portion of the spectrum, a synchrotron offers many different techniques to researchers in one building. In order to gather information, the wavelength of the light has to be appropriate for the size of the matter of interest. Shorter wavelengths allow scientists to gather information about smaller things.

In addition, each element absorbs energy at a known level. Being able to select a specific wavelength, or range of wavelengths, allows researchers the flexibility to direct their research towards specific questions.

Wavelengths and objects

Speed

Due to the extreme brightness of the light, it does not take as long to conduct the same experiment using a synchrotron source of light as it does with a ‘table top’ source for some techniques.

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How does a Synchrotron work?

As a third generation synchrotron, the CLS is comprised of several components including the Electron Gun, Linear Accelerator, Booster Ring, and Storage Ring. Each of these sections contributes to producing a beam of synchrotron light, which is then harnessed in a beamline, using an optics hutch, experimental hutch and work stations. READ MORE ⇣

Electron Gun & Linear Accelerator

Electron-gun

Electron gun

LINAC

Linear accelerator

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. READ MORE ⇣

Electron Gun:

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.

View of electron gun during teacher's workshop

View of electron gun during teacher's workshop

Cathode goes here

Cathode goes here

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.

LINAC:

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.

Linear Accelerator (LINAC)

View from the electron gun down the LINAC

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.

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Booster Ring

Booster

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. READ MORE ⇣

Booster Right

The inner Booster Ring connects to the outer 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

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. READ MORE ⇣

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.

Magnets

Radio Frequency (RF) Cavities

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:

Wiggler

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.

A 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.

 undulator

Left: undulator under development (note the series of small magnets in a row top)
Right: undulator installed in vacuum chamber

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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. READ MORE ⇣

Beamlines

Beamline Process

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.

Monochromator

Monochromator

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 iagram

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Experimental-Hall-2010
Energy-Level