BESSY II changes over to solid state RF amplifiers
One of the new solid state transmitters: the power supplies are located in the left rack (black), the RF section is located behind the grey doors in the middle and in the right rack the control units can be seen. © HZB
BESSY II storage ring has four cavity resonators that are excited with high-power oscillating electromagnetic fields to compensate for the energy lost by the electron beam. Four Klystrons, as they are called (large high-power linear RF vacuum tubes), have provided extremely pure 500-MHz RF power for exciting these cavity resonators up to now. But there are no replacement klystrons available on the market. Wolfgang Anders and his team at the HZB’s Institute SRF – Science and Technology have therefore used the shutdown to replace two of the klystrons with modern solid-state RF amplifiers. The other klystrons are to be replaced until the end of the year.
“This technology was first developed and employed at the SOLEIL synchrotron in France. However, SOLEIL operates with an excitation frequency of 350 MHz. By comparison, we work with a frequency of 500 MHz like most synchrotron light sources. We had to develop a new design for that reason. The development and manufacture of the RF amplifiers was carried out by a German company named Cryoelectra. We're the first photon source with this technology to have reached an excitation power of 75 kilowatts per amplifier for 500 MHz”, explains Anders.
While the vacuum-tube klystrons required a supply voltage of 26 kilovolts, the solid-state semiconductor RF amplifiers operate at just 50 Volts, but require much higher current. The energy saved is a big advantage. This is because klystron vacuum-tube RF amplifiers constantly draw full power from the mains, whereas the semiconductor RF amplifiers’ current draw is demand-follow and they only pull as much power from their mains connection as needed to compensate for the electron beam energy losses. In addition, the new RF units produce much less RF-noise, because the cavity resonators are excited more purely, which in turn improves the beam quality.
“My team has been working on implementing the new technology at BESSY II for three years. Just the extensive programming for connecting up to the control system interface and performing the signal processing for the solid-state amplifiers took a year for the engineer we hired specially for this. Now we have a very robust solution that is probably of interest to other synchrotron light sources as well”, says Anders.
- BESSY II: Magnetic ‘microflowers’ enhance local magnetic fieldsA flower-shaped structure only a few micrometres in size made of a nickel-iron alloy can concentrate and locally enhance magnetic fields. The size of the effect can be controlled by varying the geometry and number of 'petals'. This magnetic metamaterial developed by Dr Anna Palau's group at the Institut de Ciencia de Materials de Barcelona (ICMAB) in collaboration with her partners of the CHIST-ERA MetaMagIC project, has now been studied at BESSY II in collaboration with Dr Sergio Valencia. Such a device can be used to increase the sensitivity of magnetic sensors, to reduce the energy required for creating local magnetic fields, but also, at the PEEM experimental station, to study samples under much higher magnetic fields than currently possible.
- Innovative battery electrode made from tin foamMetal-based electrodes in lithium-ion batteries promise significantly higher capacities than conventional graphite electrodes. Unfortunately, they degrade due to mechanical stress during charging and discharging cycles. A team at HZB has now shown that a highly porous tin foam is much better at absorbing mechanical stress during charging cycles. This makes tin foam an interesting material for lithium batteries.
- BESSY II: Building block of the catalyst for oxygen formation in photosynthesis reproducedIn a small manganese oxide cluster, teams from HZB and HU Berlin have discovered a particularly exciting compound: two high spin manganese centres in two very different oxidation states and. This complex is the simplest model of a catalyst that occurs as a slightly larger cluster in natural photosynthesis, where it enables the formation of molecular oxygen. The discovery is considered an important step towards a complete understanding of photosynthesis.