SEAlab accelerator project completed: Achievements and outlook

The SEAlab accelerator project successfully completed its final measurement campaign in summer 2026. The facility is now being dismantled, with many components set to be reused. The two accelerator physicists, Axel Neumann and Thorsten Kamps, explain what the project has achieved and provide an outlook for the future.

The final measurement campaign lasted eight weeks. How did it go? 

Axel Neumann: Very well. We were even able to carry out long-term operational studies. At the end of June, when it was very hot in Berlin, we ran the machine continuously over the weekend without interruption or problems. We kept glancing at our smartphones from time to time, but everything looked fine on the control system. This showed that the accelerator, infrastructure and building are all working together. We’ve filled a lot of gaps as a result. 

What were your objectives with SEAlab?  

Axel Neumann: SEAlab grew out of BERLinPro, which was launched in 2011. At that time, we were working on a new type of accelerator that recovers a large proportion of the energy used: an Energy Recovery Linac, or ERL for short. We set up a new building to house the prototype accelerator. However, due to supply issues with critical components and other delays caused by the pandemic and the cyberattack, we had to keep modifying the project plans. This would have required even more staff, time and money.

Thorsten Kamps: And in the meantime, it became clear that BESSY III, HZB’s next light source, would not be based on the ERL principle, but on a different technology that cannot be tested with BERLinPro. For this reason, in 2021, we at SEAlab focused on a key component of BERLinPro: the photoinjector, which is the actual electron source with its first acceleration section. Photoinjectors are highly relevant for free-electron lasers, ultra-fast electron diffraction and other applications.

What is the function of the injector?

Neumann: In the photoinjector, electron bunches are generated via the photoelectric effect. We extract these electrons from a special photocathode material using intense laser pulses. These electrons are then accelerated using the electric field of a superconducting radio-frequency (SRF) resonator. Our new task at SEAlab was therefore to develop such an injector and to study the beam parameters for a number of applications.

Did you manage it? 

Kamps: Yes, we actually built and set up an SRF photoelectron injector. This injector is unique worldwide. Axel developed the design, and it allows many new applications. I was amazed at how well it also suits applications such as the treatment of water with ‘eternity chemicals’ or electron scattering experiments.

Neumann: We have also developed new methods to eliminate interference in the superconducting radio-frequency resonators. These SRF resonators are extremely sensitive, and even the slightest trace of contamination can impair their functionality. We now know how to address this issue, which benefits accelerator physics as a whole. 

Kamps: We have also developed a new material for the photocathodes in the injector that copes very well with the demanding environment of an SRF high-frequency resonator. It is a compound of sodium, potassium and antimony, and we can deposit these elements as a polycrystalline film onto a substrate. This process is now highly automated and offers a high degree of reproducibility. Many laboratories with photoinjectors are interested in our results, for example for the DALI project at the HZDR.

This project also involved materials research?

Kamps: Yes, of course. We also conduct materials research for accelerators here. In winter of 2025, we investigated our cathode materials at the EMIL laboratory at BESSY II, both for depth and surface information. We have the huge advantage of being able to use these methods at BESSY II. 

SEAlab has now completed its final measurement campaign. Where are you applying your expertise now?

Neumann: I am involved in setting up an SRF photoinjector for DALI at the Helmholtz Centre Dresden-Rossendorf. I am also working on energy-efficient accelerator technologies as part of the European ISAS Framework Programme. CERN has expressed an interest in collaborating with us on test facilities for the Future Circular Collider project. In Germany, an ERL for nuclear physics applications is being built in Mainz. The team in Mainz is very interested in SRF photoinjectors as a potential source for their ERL. Although the ERL concept for new synchrotron radiation sources has not caught on, there is now a renaissance, namely for applications in nuclear physics, high-energy physics, free-electron lasers or even for industry. 

Kamps: For example, efforts are now underway in the USA and also in Japan to build Energy Recovery Linacs for microchip lithography. They are drawing on the research expertise to which we have contributed. We can utilise much of this expertise for BESSY III too. I am currently investigating laser-plasma accelerators, which are extremely compact and require far less energy to accelerate electron bunches. In the long term, these mini-accelerators could potentially replace the conventional pre-accelerators in modern light sources. 

Can components from SEAlab still be used? 

Neumann: Yes, some components can be used for BESSY II+.  Other teams have also got in touch, specifically from the HZDR and the University of Mainz, and we’re in contact too with a project in Orsay, France, and Milan, Italy. We already know where some components will be needed; we’re still in discussions about others.