The light, produced by the circulating electrons, is emitted tangentially to the curvature they follow. In the case of bending magnets, the light is tangential to the arc described by electrons. In the case of insertion devices, the light is emitted along the axis of oscillation.

In both cases the vacuum chamber in which the electrons are contained has an aperture allowing light extraction. The aperture is attached to a straight vacuum tube that couples the accelerator with the beamline.

This vacuum tube is called "front end", because it is at the "end" of the accelerator and it arrives at the "front" of the beamline hutch. The Front End starts at the accelerator vacuum chamber and ends immediately after passing through a special window in the wall of the bunker tunnel.

Picture of Front End


Along the length of this vacuum tube, specific pieces of equipment condition the light beam: the slits, the masks and the photon shutter.

  • SLITS. Sometimes, and depending on each sample in the experiment, there is a need to regulate the intensity of the light beam. This is achieved by using movable slits. They are very special because they have to absorb a significant amount of heat while conserving a precise position and alignment.
  • MASKS. Depending on the application of the generated synchrotron light, sometimes not all of the emerging fan is used. So, a fixed mask is used to screen the part of the light that will never be used inside the hutch. Masks are placed in the Front End because the screening of X-rays produces radiation that is better kept inside the tunnel.
  • PHOTON SHUTTER. The opening or closing of the photon shutter controls the sample illumination .

Apart from optical elements, the Front End is also used to install two important safety systems:

  • THE RADIATION SHUTTER is connected to the experimental hutch via an interlocking system designed to avoid radiation exposure to anybody inside the experimental hutches. Only when this device is blocking the light can a person enter and work inside the experimental hutches.
  • THE VACUUM TRIGGER UNIT is linked to a fast closing valve. Its function is to isolate the vacuum in the accelerator in the event that it becomes broken in the experimental hutch. This situation happens sometimes in the case of modifications to, or the malfunctioning of, experimental elements.

Finally, the Front Ends are also equipped with an X-Ray Beam Position Monitor (XBPM) in order to measure the position of the emitted light and use this information to align the accelerator with the set up of the experiment.

Front End layout

Front End layout