A transparent injection scheme using a multipole injection kicker was successfully brought into routine operation in the MAX IV 3 GeV ring. It is the first such implementation on a fourth-generation ultralow emittance storage ring light source. The results were recently published by the team of researchers from MAX IV and the French synchrotron facility SOLEIL.
At MAX IV, high-energy electrons circulate in a storage ring. As the electrons pass through insertion devices installed around the ring, they produce beams of synchrotron light that are delivered to the beamlines. The stream of electrons revolves turn after turn around the ring, guided by strong electromagnets. Processes intrinsic to the storage of electrons, such as scattering, will, however, lead to a slow decrease in stored current over time. Therefore, new electrons need to be injected regularly with top-up injections while keeping the disturbance to the synchrotron light beam delivery as low as possible. A magnet device that was designed and built at the French synchrotron SOLEIL was installed to achieve extremely low disturbance of the beam on injection.
“This was the first time a multipole injection kicker was implemented in an ultralow emittance storage ring light source. It has since then been proven to deliver both high injection efficiency and low disturbance of the stored electron beam,” says Jonas Breunlin, researcher at MAX IV and one of the authors of the paper.
For many beamlines in their usual beamline settings, the electron beam perturbation from the multipole injection kicker is not detectable, so the injection is now what is called ‘transparent’. This allows the beamlines to operate regardless of top-up injections occurring at 10-minute intervals.
Only for especially source size sensitive modes of beamline operation, a gating approach must be considered in which the data acquisition is paused during the top-up injections. The multipole injection kicker is working so well it has even surprised the installation and operations team.
“With an optimal positioning of the multipole injection kicker, using beam-based alignment, its momentary effect on the horizontal electron beam size becomes nearly undetectable – even when monitoring carefully with sophisticated electron beam diagnostics,” says Breunlin.
Even after the successful installation, work is always ongoing to reach even better beams to be delivered to the users of the MAX IV beamlines.
“The research and development of transparent injection schemes at MAX IV do not stop with the multipole injection kicker. Especially with investigating lattice upgrades to further reduce the emittance of the 3 GeV storage ring,” concludes Breunlin. “Our 1.5 GeV ring is also an interesting candidate for an injection kicker upgrade. The feasibility of an adaptation of the multipole injection kicker to this smaller ring is currently being investigated and would bring transparent injections to the remaining MAX IV storage ring beamlines.”
Patrick Alexandre, Rachid Ben El Fekih, Antoine Letrésor, Serge Thoraud, José da Silva Castro, François Bouvet, Jonas Breunlin, Åke Andersson, and Pedro Fernandes Tavares, Transparent top-up injection into a fourth-generation storage ring, Nuclear Inst. and Methods in Physics Research, A 986, 164739 (2021), DOI: 10.1016/j.nima.2020.164739
Frontpage photo: Max Kleinen, Unsplash