Electron Gun

The Electron Gun begins the process by running high voltage electricity through a heated cathode which produces pulses of electrons that enter the Linear Accelerator (LINAC).

electron gunThis is done by using a tungsten-oxide disk (tungsten is the same material as incandescent light bulb filaments) as the cathode. As electricity flows through the cathode, it becomes heated (at about 1000°C) to incandescence which gives some electrons enough energy to leave the surface of the cathode, essentially boiling electrons off. As this is happening, a nearby screen is given a short, strong positive charge (125 times per second) which pulls the electrons away from the cathode towards the LINAC. (This process is similar to that found in a cathode ray tube (CRT) television). The high voltage electricity running through the cathode (approximately 200,000 volts – a car battery has only 12 volts) also repels the electrons being produced by the cathode and accelerates them towards the LINAC.

Linear Accelerator

The LINAC is a series Radio Frequency Cavities with fields at 2,856 MHz. Electrons produced by the Electron Gun enter the LINAC and the Radio Frequency Cavities accelerate the electrons 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 LINAC produces pulses of electrons ranging from 2 nanoseconds up to 140 nanoseconds for injection into the Storage Ring.  During normal operations, long pulses are used to produce a 420 nanosecond pulse train in the Storage Ring. These pulses of electrons are supplied once per second by the LINAC. After several minutes, enough electrons are accumulated in the Storage Ring that the synchrotron can operate for several hours and the LINAC can be turned off until more electrons are required to refill the ring. The LINAC can also produce short pulses to fill a single “bunch” of electrons in the Storage Ring, which is used for more sensitive studies.

Vacuum Chambers

Everything from the Electron Gun to the Beamlines is under vacuum. The electrons (and later the photons) must travel in a vacuum to avoid colliding into particles and disappearing. The Storage Ring vacuum chamber pressure is lower than 10-11 torr (1 atmosphere pressure is 760 torr). This means that there are less than 10 particles per cubic centimeter present in our vacuum system than there are in space around the International Space Station!

Booster Ring 

Eelectrons travel from the LINAC to the Booster Ring where a specifically designed Radio Frequency Cavity raises the energy of the electrons from 250 MeV to 2900 MeV as they circulate in the Booster Ring. Following this boost in energy, the electrons are transferred to the Storage Ring.

As electrons circulate the 103 m Booster Ring approximately 1.5 million times in 0.6 seconds, they receive a boost in energy from microwave fields generated in the Radio Frequency Cavity at 2,856 MHz to reach a total energy of 2900 MeV. Each of the 68 bunches contains 50 pC (3.1*108 electrons) with a total energy of 9.92 J at 2900 MeV and 10 mA circulating current. How much energy is 2900 MeV? It is equivalent to the energy of about 2 billion flashlight batteries! For comparison, the typical atmospheric molecule has an energy of about 0.03 eV and the energy of charged particles in a nuclear explosion range from 0.3 to 3 MeV.

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 the speed of light.

*In particle physics, the standard unit to measure energy is mega-electron volts or MeV which is 1*106 eV. One eV is the amount of energy that an electron gains when it moves through a potential difference of 1 volt in a vacuum.*

Storage Ring

The high energy electrons from the Booster Ring are transferred into the Storage Ring and circulate the Storage Ring’s twelve straight sections. Electrons prefer to travel in a straight line, but their path is bent by magnets found in the Storage Ring which causes the electrons to emit photons producing synchrotron light. Also, in each of the twelve straight sections there are special magnet series called Insertion Devices that increase the brightness of the light produced by the electrons before entering the beamline.   

In the Booster Ring, when the electrons reach 2900 MeV an injection system transfers them into the 171 m Storage Ring. The process repeats once per second up to 600 cycles (about 10 minutes), as required, to reach an average circulating current of 220 mA.

Once the electrons are in the Storage Ring, they circulate for 4 to 12 hours producing photons every time the direction of the flow of electrons is changed by the 6800 kg dipole magnets. While the Storage 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 electron beam.

Some straight sections also include space for special magnets called Insertion Devices. After each bent 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 one another and the few particles that are present causing them to become 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 three types of electro-magnets used at the CLS. There are the dipole magnets, the quadrupole magnets, and the sextupole magnets. The magnetic field created by the blue dipole magnets is used to direct the electrons around the Booster and Storage Ring. The field of the green quadrupole (four-pole) and red sextupole (six-pole) magnets are used to force bunches of electrons into a fine beam within the vacuum chamber. The Booster Ring uses dipole and qudrupole magnets, where as the Storage Ring uses dipole, quadrupole, and sextupole magnets. 

Radio Frequency Cavities

The CLS uses two Radio Frequency Cavities, one in the Booster Ring and one in the Storage Ring. The purpose of the Radio Frequency Cavities is boost the energy of electrons using microwaves.

The Booster Ring has a cylindrical cavity that 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 Storage Ring uses a Radio Frequency Cavity to replace the energy lost by electrons as they produce light. The Radio Frequency Cavity in the Storage ring is also superconductive. Superconductivity means that there is no resistance in the flow of electric current in certain metals and alloys at temperatures near absolute zero. The operating temperature of the Storage Ring Radio Frequency Cavity 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 Radio Frequency field provides energy.

Insertion Devices

The CLS is one of the brightest synchrotrons in the world despite being one tenth the size of similarly bright synchrotrons. insertion device wigglerOne of the ways that CLS achieves its brightness is through Insertion Devices. While dipole magnets change the direction of the electrons producing light, the multi-magnet Insertion Devices called Wigglers and Undulators placed in the straight section of the Storage Ring move or ‘wiggle’ electrons back and forth multiple times creating a narrow beam of highly intense light.

  • 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

The CLS has 15 beamlines accessible for “users” or scientists from other institutions using the synchrotron as part of their research. A Beamline consists of an optics hutch where synchrotron light is focused and wavelength is selected, an experimentation hutch where the appropriate technique is selected for the experiment, and work stations where scientists operate the beamline and measure light as it is absorbed, reflected, refracted, or scattered by the sample. MORE INFORMATION ON BEAMLINES

Monochromator

Monochromator

At the beamline, the 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 of light (much like a prism). This is done using either optical dispersion (as in a prism), or as 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

The selected wavelengths of synchrotron light are focused by the mirrors in the optics hutch onto the sample in an end station located in the experimental hutch. Each end station 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

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.

Control Room

Control Room management is an important part of ensuring personnel safety throughout the facility. From the control room we monitor:

  • Personnel Safety Systems (PSS) - includes Fire Alarms System, Accelerator Access Interlock Systems, Oxygen Monitoring System
  • Equipment Protection Systems (EPS) - includes beam position, size and quality, cooling/heating systems, vacuum systems, power supplies and magnet settings, timing systems, and valve controls
  • Accelerator operators disable/enable all or individual beamlines including start and shutdown processes and select mode of accelerator operation such as normal (beam available to users) versus accelerator studies

In the case of an emergency the synchrotron can be shut down automatically in less than 20 milliseconds from the control room and from several other locations manually.

Radiation Safety 

Radiation is energy that comes from a source and travels through material or through space. Sources of radiation include light, heat and sound. There are many natural sources of radiation, including the sun and various elements in the earth. When dealing with sources of radiation, there are safety concerns that must be addressed.

Since the CLS is a source of light radiation, thermoluminescent detectors are used to record any possible radiation that escapes the shielding surrounding the rings and end stations. These are located throughout the facility as well as carried by personnel. The national limit from natural sources (background radiation) is 3 milli-Sieverts (mSv) per year. CLS measures very little above what is detectable in the background and is well within the annual regulatory limit imposed by the Canadian Nuclear Safety Commission which is 50 mSv - equivalent to approximately 500 chest X-rays per year. 

Experiments and Safety 

CLS will authorize an experiment only after the activities associated with the experiment have been defined, hazards have been identified, and adequate hazard controls have been implemented. A scientific proposal would be submitted for review and if it has been expected and has met all applicable requirements, a permit is issued identifying the users of safety requirements. 

Explore Education 

Important Dates

  • Student on the Beamlines
    Next Submission
    TBA
  • Student on the Beamlines
    Poster Submission
    March 31, 2019

Contact Us

Tracy Walker
Education Program Lead 
 
Email:  tracy.walker@lightsource.ca
Phone: 306-657-3525

Anna-Maria Boechler 
Education Program Coordinator

Email:  anna-maria.boechler@lightsource.ca
Phone: 306-657-3745

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