BESSY II is ready for user service
A view of what had been the practically empty segment at EMIL in the experimental hall; the beam tubes for EMIL are already being marked out on the brand-new flooring. Photo: Ingo Müller/HZB
BESSY II was shut down as scheduled from February 9th until the end of March for refurbishment and modernization. The accelerator is operational once again, and has been running since the beginning of April, beginning with beam scrubbing to increase the lifetime of the electrons in the storage ring and to improve operation. At the same time teams have been working on the calibration and commissioning of their instruments. BESSY II will be ready for user service once again on April 21 2015.
The new flooring shines - it desperately needed to be re-done in heavily worn areas. But that is just the most obvious update undertaken during this shutdown. At least five major projects were coordinated since the beginning of February. „Our best thanks to the staff, who worked overtime to get everything ready“, says Prof. Anke Kaysser-Pyzalla, scientific director of HZB, „now User Service can start again as planned.“
As a result BESSY II is now equipped with a state-of-art Personal Safety Interlock to ensure safe operation. “The interlock shuts off the machine immediately or brings it to a safe state if someone makes an error while in operation or opens a door to a restricted area”, explains Müller. The new interlock system is based on modern safety PLCs. These programmable logic controllers are certified and the operation of the entire system was inspected and accepted by the radiation safety officer.
Vacuum Sement rebuilt for EMIL
The EMIL laboratory has been added, therefore a vacuum segment in the storage ring needed to be completely re-built. "During this shutdown we also prepared the vacuum system needed for both undulators that have been designed by the Undulator-team specifically for EMIL", Christian Jung (Scientific-Technical Infrastructure II) explains. This is because energies of up to 10,000 eV will be needed for EMIL instead of just the normal 60 to 2000 eV for nominal BESSY II operations.
Modern RF amplifyers and a multipole wavelength shifter have been installed
The replacement of two out of the four klystron-based RF amplifiers, used to power the RF cavities was also very elaborate. They were replaced by newly designed Solid State RF amplifiers. The multipole wavelength shifter on the EDDI beamline, which was damaged last year, has now also been repaired and re-installed.
Dipole front-end systems will get new absorbers
“In addition, we installed new beam line absorbers on a quarter of the dipole front-end systems during this shutdown. That was necessary because we have a 300 mA beam current present at all times in the ring due to operating in top-up mode", Jung explains.
User service resumes April 21, but the next shutdown is already being planned. The work that began during the 2013 shutdown should be completed by the end of 2015. Still on the agenda: replacement of the last two “old” RF cavities in the machine with new RF cavities, installation of the two new undulators for EMIL, changeover of the remaining klystron-based RF amplifiers to Solid State technology as well as fitting new absorbers in the remaining dipole front-end systems.
- 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.