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.
- Only at BESSY II worldwide: IR nanoscopy at very long THz wavelengthsThe team at the IRIS beamline at BESSY II has created a new experimental option: They achieved infrared nanoscopy with a spatial resolution of around 50 nm at very long THz wavelengths. This was possible thanks to a temporal pattern of light pulses known as the low-alpha operating mode at BESSY II. Worldwide, BESSY II is the only synchrotron light source at which users could perform nanoscopy in a single setup from 25 to 4000 cm-1, a unique opportunity for ultra-broadband characterisation of complex materials at the nanoscale in both the life sciences and materials sciences.
- Ultrafast demagnetisation - Thinner iron, stronger effectThe thinner an iron film, the more easily it can be demagnetised by a laser pulse. Researchers at the University of Duisburg-Essen, working with Helmholtz-Zentrum Berlin and other partners, have discovered why: the key lies in the magnetic order at the material's interfaces. In the long term, these findings could contribute to the development of new technologies for magnetic data storage. The results have been published in the scientific journal Advanced Science.
- Patterns of polar vortices in lead-free superlattices on siliconA team at HZB has, for the first time, reported polar vortices in (BaTiO3/SrTiO3)10 superlattices on silicon. These results expand the range of materials and substrates on which polar topological textures can occur and open up new options for incorporating complex ferroelectric states into silicon-based technologies.