New cavities successfully installed
The new cavities during their installation. © C. Jung /HZB
A glimps at the water circuits. © C. Jung / HZB
At the heart of BESSY II are four cavities, hollow resonators, providing the energy that electrons in the storage ring re-absorb after they have released it as light packets. The old cavities were still from the 1970s and were employed at DESY in Hamburg, then at BESSY I, and finally at BESSY II beginning in 1998. “However, the limit of their operating life has been reached”, says Dr. Wolfgang Anders from the HZB Institute of SRF – Science and Technology. Anders, an expert in the field, was responsible for replacing two of the four old cavities with new units during the summer shutdown.
The new cavities have been developed as an EU Project under the supervision of HZB. They are constructed of copper, as before, but have a somewhat more complex shape that is optimised to effectively avoid exciting undesirable oscillations, known as “higher-order modes”. These higher modes are excited by high beam energies and can lead to instabilities.
“The new cavities are significantly more robust and can store up to 80 kilowatts – twice as much as the old cavities. As a result, the requirements for cooling have increased as well”, explains Anders, pointing out the multitude of coolant pipes around the new cavities.
The beam energy at BESSY II is presently still restricted because the vacuum in the new cavities is still improving slowly. “We will be normalising the vacuum conditions over Christmas so that we can operate BESSY II at full beam energy afterwards”, says Anders.
Both of the other old cavities will be replaced during the 2015 summer shutdown so that all the advantages of the new cavities can come into play.
- Fascinating archaeological find becomes a source of knowledgeThe Bavarian State Office for the Preservation of Historical Monuments (BLfD) has sent a rare artefact from the Middle Bronze Age to Berlin for examination using cutting-edge, non-destructive methods. It is a 3,400-year-old bronze sword, unearthed during archaeological excavations in Nördlingen, Swabia, in 2023. Experts have been able to determine how the hilt and blade are connected, as well as how the rare and well-preserved decorations on the pommel were made. This has provided valuable insight into the craft techniques employed in southern Germany during the Bronze Age. The BLfD used 3D computed tomography and X-ray diffraction to analyse internal stresses at the Helmholtz-Zentrum Berlin (HZB), as well as X-ray fluorescence spectroscopy at a BESSY II beamline supervised by the Bundesanstalt für Materialforschung und -prüfung (BAM).
- Element cobalt exhibits surprising propertiesThe element cobalt is considered a typical ferromagnet with no further secrets. However, an international team led by HZB researcher Dr. Jaime Sánchez-Barriga has now uncovered complex topological features in its electronic structure. Spin-resolved measurements of the band structure (spin-ARPES) at BESSY II revealed entangled energy bands that cross each other along extended paths in specific crystallographic directions, even at room temperature. As a result, cobalt can be considered as a highly tunable and unexpectedly rich topological platform, opening new perspectives for exploiting magnetic topological states in future information technologies.
- MXene for energy storage: More versatile than expectedMXene materials are promising candidates for a new energy storage technology. However, the processes by which the charge storage takes place were not yet fully understood. A team at HZB has examined, for the first time, individual MXene flakes to explore these processes in detail. Using the in situ Scanning transmission X-ray microscope 'MYSTIIC' at BESSY II, the scientists mapped the chemical states of Titanium atoms on the MXene flake surfaces. The results revealed two distinct redox reactions, depending on the electrolyte. This lays the groundwork for understanding charge transfer processes at the nanoscale and provides a basis for future research aimed at optimising pseudocapacitive energy storage devices.