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.
- Spintronics at BESSY II: Domain walls in magnetic nanowiresMagnetic domains walls are known to be a source of electrical resistance due to the difficulty for transport electron spins to follow their magnetic texture. This phenomenon holds potential for utilization in spintronic devices, where the electrical resistance can vary based on the presence or absence of a domain wall. A particularly intriguing class of materials are half metals such as La2/3Sr1/3MnO3 (LSMO) which present full spin polarization, allowing their exploitation in spintronic devices. Still the resistance of a single domain wall in half metals remained unknown. Now a team from Spain, France and Germany has generated a single domain wall on a LSMO nanowire and measured resistance changes 20 times larger than for a normal ferromagnet such as Cobalt.
- Fractons as information storage: Not yet quite tangible, but closeA new quasiparticle with interesting properties has appeared in solid-state physics - but so far only in the theoretical modelling of solids with certain magnetic properties. An international team from HZB and Freie Universität Berlin has now shown that, contrary to expectations, quantum fluctuations do not make the quasiparticle appear more clearly, but rather blur its signature.
- Graphene on titanium carbide triggers a novel phase transitionResearchers have discovered a Lifshitz-transition in TiC, driven by a graphene overlayer, at the photon source BESSY II. Their study sheds light on the exciting potential of 2D materials such as graphene and the effects they can have on neighboring materials through proximity interactions.