BESSY II launches New Filling Pattern in User Mode
The new filling pattern consists of a Hybrid (or Camshaft) bunch at 4 mA (Chopper) in the center of the 200 ns wide ion clearing gap followed by the so-called PPRE-bunch of variable transverse excitation at 3 mA and 84 ns later. Together with the usual multibunch filling and the 3 slicing bunches on top of the multibunch train, now 302 out of 400 possible buckets in the storage ring are filled and topped up. © HZB
Since July 2015 BESSY II has been providing a new bunch filling pattern in Top-Up mode. It will open new opportunities especially for research teams dealing with time-resolved x-ray experiments. It is of significant importance for us and the community anticipating BESSY VSR.
Apart from ultrafast experiments at the Femtoslicing facility (slicing bunches) and x-ray pump-probe applications with the hybrid (or camshaft) bunch, now also time-of-flight experiments with the ARTOF and other instruments that use the pulse selection of the MHz-Chopper [1] can be carried out in normal mode.
The new additional bunch in the dark gap arriving 84 ns after the chopper bunch can be transversally excited to support time-resolved Photoelectron- and X-ray spectroscopy based on the PPRE-technique [2]. Having such time-resolved methods at hand in the regular usermode we are even now able to take a glimpse into future operation modes at BESSY VSR.
- BESSY II: New sample environment allows glimpse into thermocatalytic processesA novel measurement cell allows, for the first time, soft and hard X-ray investigations under high pressures of up to 20 bar and temperatures of up to 400°C. This provides new insights into thermocatalytic processes, such as the Fischer-Tropsch synthesis for producing synthetic fuels. The development of the measurement cell is considered a significant achievement within the Care-O-Sene project.
- Magnetic imaging: Micro-flowers increase the local magnetic fieldMaterials with magnetic nanostructures have many potential applications such as in spintronics. To explore such materials, nanoscale magnetic-sensitive imaging techniques are very useful, but up to now only weak magnetic fields could be applied during the imaging process. Now an international collaboration led by Dr. Sergio Valencia, HZB, has developed an approach that overcomes this limitation. The team designed tiny magnetic flux concentrators (MFCs), into which the sample is placed. The geometry of the MFCs resembles a flower with a number of petals which focus the applied magnetic field into its center. This greatly expands the magnetic field range available during imaging, and so the range of magnetic systems that can be investigated. The micro-flowers, enhancing magnetic fields locally, can find application in different nanometric magnetic microscopy techniques.
- Disorder creates new properties in compound semiconductorsAn international research team has demonstrated that the intrinsic disorder of the compound semiconductor CuInSnS₄ can be exploited to influence its optical properties. While the atomic vibrations also sense the local disorder, their response is averaged over many different local environments and therefore appear isotropic, as expected for a cubic crystal. In contrast, the optical excitations, known as excitons, are much more sensitive to the local arrangement of atoms. Surprisingly, they show a direction-dependent optical response even though the average crystal structure is cubic. These findings shed new light on the relationship between disorder and material properties, opening up new options for targeted 'disorder engineering' in optoelectronic and photocatalytic devices.