Accelerator Physics: HF-Couplers for bERLinPro prove resilient
For the measurement campaign, two couplers were mounted in a horizontal test position under a local clean room tent. © A. Neumann/HZB
To generate the HF power, a 270 kW klystron is needed, among other things. © A. Neumann/HZB
In synchrotron light sources, an electron accelerator brings electron bunches to almost the speed of light so that they can emit the special "synchrotron light". The electron bunches get their enormous energy and their special shape from a standing electromagnetic alternating field in so-called cavities. With high electron currents, as required in the bERLinPro project, the power needed for the stable excitation of this high-frequency alternating field is enormous. The coupling of this high power is achieved with special antennas, so-called couplers, and is considered a great scientific and technical challenge. Now, a first measurement campaign with optimised couplers at bERLinPro shows that the goal can be achieved.
These couplers should supply the cavities with 230 kW in continuous operation at 1.3 GHz. The connection between the ultra-high vacuum of the cavities and the high-frequency transmission link must be guaranteed, both at liquid helium temperature (-269 degrees Celsius or 4 Kelvin) and at room temperature. In addition, clean room conditions must be maintained and particles down to the micrometre range must be removed. The power is to be transferred to the cavity by two couplers each, in order to reduce the individual load, but also to improve the stability of the electron trajectory in the accelerator.
High-performance couplers modified
Now, the team led by Axel Neumann from the HZB Institute SRF (Superconducting Radio Frequency Technologies) has been able to show that this goal is realistic. To do so, they modified the design of the high-performance couplers of a research group from the National Research Centre for High Energy Physics in Japan (KEK).
Measurements up to 45 kW
For the measurement campaign, two of the newly developed couplers were set up in tandem with a test box as a cavity substitute. The measurements started with low power, which was gradually increased up to 45 kW. Initially, only short pulses were transmitted from the couplers to the cavity at longer intervals, here even up to powers of 100 kW. Then the intervals between the power pulses became shorter and shorter up to continuous operation.
Good News: heat can be dissipated
The heat development was 0.25 Kelvin per kilowatt of power. At a final power of 120 kW, the material would heat up by about 30 degrees Kelvin. This is good news, because such amounts of heat are technically dissipatable through the planned cooling. "With the original Japanese design, the heat generation was higher by a factor of four than with our adapted form," explains Neumann.
Outlook: 120 kW
"We initially limited the measurements to power levels below 45 kW. Only when all couplers have been successfully tested at these powers will the next steps come. However, we are now very optimistic. If you extrapolate the figures, the coupler should indeed manage 120 kW in continuous operation without any problems," says Prof. Dr. Jens Knobloch, who heads the HZB Institute SRF Science and Technology.
Helmholtz-Programme for Accelerator Physics (ARD)
With its work on high-frequency cavities, HZB is contributing to the Helmholtz Association's research programme for accelerator physics (ARD = "Accelerator Research and Development"). A central topic of ARD is the development of superconducting high-frequency systems for accelerating high currents in continuous wave operation. Just recently, ARD was evaluated by an international panel and received top marks in all categories.
- Porous Radical Organic framework improves lithium-sulphur batteriesA team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.
- Metallic nanocatalysts: what really happens during catalysisUsing a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY's NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This configuration allows a better understanding of structural changes in, for example, rhodium-platinum catalysts for emission control. The results show that under typical catalytic conditions, some of the rhodium in the shell can diffuse into the interior of the nanoparticles. However, most of it remains on the surface and oxidises. This process is strongly dependent on the surface orientation of the nanoparticle facets.
- Shedding light on insulators: how light pulses unfreeze electronsMetal oxides are abundant in nature and central to technologies such as photocatalysis and photovoltaics. Yet, many suffer from poor electrical conduction, caused by strong repulsion between electrons in neighboring metal atoms. Researchers at HZB and partner institutions have shown that light pulses can temporarily weaken these repulsive forces, lowering the energy required for electrons mobility, inducing a metal-like behavior. This discovery offers a new way to manipulate material properties with light, with high potential to more efficient light-based devices.