Accelerator Physics: First electron beam in SEALab
The small spot on the screen is the electron beam. The large cloud to its left is caused by the reflection of the laser beam from the photocathode. © SEALab/HZB
The SEALab team has achieved this breakthrough after years of work. Here you can see the commissioning team. © SEALab/HZB
The SEALab team at HZB has achieved a world first by generating an electron beam from a multi-alkali (Na-K-Sb) photocathode and accelerating it to relativistic energies in a superconducting radiofrequency accelerator (SRF photoinjector). This is a real breakthrough and opens up new options for accelerator physics.
This success paves the way for the further development of superconducting radio-frequency accelerators (SRF photoinjectors) for high-brilliancy electron sources. The achievement holds significant potential for applications in free-electron lasers, energy recovery linac (ERL) class accelerators, detector development and ultrafast electron scattering experiments (UED).
Years of dedicated work, first in the bERLinPro project and then in the SEALAB team, have been invested to achieve this success. There were numerous challenges along the way, including delays due to the COVID-19 pandemic and the cyber attack. Despite this, the team has made great progress. The successful test generated an average current in the microampere range at a repetition rate of 1 MHz, demonstrating the viability of the sodium-based photocathode in combination with SRF acceleration.
Axel Neumann, SEALab project manager, emphasises: ‘This great success is the result of many dedicated individuals who contributed to bERLinPro and SEALab over the past years, often under high levels of stress. We also thank all former team members who were involved in the original project.’
Thorsten Kamps, deputy project manager, now sees the fruits of the intensive work for the photoinjector: ‘We have completely revamped the preparation and characterisation of photocathodes in recent years and are now seeing the success. This will have a significant impact on similar projects.’
With this successful test, the SEALab team has demonstrated that it is possible to use a robust multi-alkali photoemissive source to accelerate an electron beam in an SRF photoinjector to relativistic energies and at a high repetition rate. These results could help to further improve the performance of the next generation of electron injectors. The SEALab team will now also investigate the different beam parameters to expand the possibilities of SRF photoinjectors.
- Green fabrication of hybrid materials as highly sensitive X-ray detectorsNew bismuth-based organic-inorganic hybrid materials show exceptional sensitivity and long-term stability as X-ray detectors, significantly more sensitive than commercial X-ray detectors. In addition, these materials can be produced without solvents by ball milling, a mechanochemical synthesis process that is environmentally friendly and scalable. More sensitive detectors would allow for a reduction in the radiation exposure during X-ray examinations.
- BESSY II: Insight into ultrafast spin processes with femtoslicingAn international team has succeeded at BESSY II for the first time to elucidate how ultrafast spin-polarised current pulses can be characterised by measuring the ultrafast demagnetisation in a magnetic layer system within the first hundreds of femtoseconds. The findings are useful for the development of spintronic devices that enable faster and more energy-efficient information processing and storage. The collaboration involved teams from the University of Strasbourg, HZB, Uppsala University and several other universities.
- Battery research: visualisation of aging processes operandoLithium button cells with electrodes made of nickel-manganese-cobalt oxides (NMC) are very powerful. Unfortunately, their capacity decreases over time. Now, for the first time, a team has used a non-destructive method to observe how the elemental composition of the individual layers in a button cell changes during charging cycles. The study, now published in the journal Small, involved teams from the Physikalisch-Technische Bundesanstalt (PTB), the University of Münster, researchers from the SyncLab research group at HZB and the BLiX laboratory at the Technical University of Berlin. Measurements were carried out in the BLiX laboratory and at the BESSY II synchrotron radiation source.