Department Undulators
Department
We are the Undulator department of the Helmholtz-Zentrum Berlin für Materialien und Energie. We operate the insertion devices for the BESSY II and MLS synchrotron light sources. BESSY II houses 13 permanent magnet undulators: 7 APPLE II devices, 5 out of vacuum planar devices, and 1 cryogenic permanent magnet undulator (CPMU). The MLS is home to one planar undulator.
All devices have been modelled, designed, built and measured in house and continue to act as brilliant photon sources to many of HZBs beamlines. Our in-house undulator expertise allows us to continue to push at the cutting edge of undulator development, with current developments including in-vacuum APPLE II devices (both room temperature and cryogenic), as well as developing advanced techniques for magnetic field characterization.
What are Undulators ?
Undulators are in the core of synchrotron light sources, being the device responsible for producing highly collimated and intense X-ray beams for the wide range of applications at BESSY II. It dates back to the mid-20th century, when scientists first explored the radiation emitted by moving charged particles, like electrons, traveling at nearly the speed of light. An undulator is a periodic array of magnets that forces the fast-moving electrons into a serios of small oscillations as they pass through. These designed „wiggling“ causes electrons to emit synchrotron radiation coherently, resulting in light with unique properties such as high brightness, narrow spectral bandwidth, tunable wavelenght and polarization.
A type of undulator is the Advanced Planar Polarized Light Emitting (APPLE) Undulator such as the UE 56. The diagram shows linear polarization without any shift, meaning the magnetic fields are aligned in a way that produces horizontally polarized light (top). The middle section represents the circular polarization mode, where the magnetic fields are shifted by a quarter period. This creates equal amplitudes for both the horizontal and vertical magnetic fields, resulting in circularly polarized light. The bottom section displays the linear mode again, but this time with a half-period shift of the magnetic structure, producing linearly polarized light at an azimuthal angle due to the 90° phase difference between horizontal and vertical magnetic fields.
Design & Characterization
The BESSY II undulators produce brilliant photon beams which are limited only by the electron beam emittance and energy spread. Since the devices are integral parts of the machine the interaction with the electron beam must be minimized. Sophisticated strategies have been developed for passive and active compensation schemes. Advanced software packages have been developed at the HZB to describe the beam optic effects as well as the spectral undulator performance and its propagation along the beamline. The existing know-how in the field of undulator construction and fabrication is the basis for new challenging undulator projects for storage ring upgrades or future light source. Click here for more.
