Toward transparent injection with a multipole injection kicker in a storage ring

Achieving transparent Top-Up injection, characterized by stored beam position perturbations lower than 10% of the root mean square (rms) size of the stored beam, is very challenging for third-generation storage ring-based synchrotron light sources. The standard bump-based injection scheme used at SOLEIL 2.75 -GeV storage ring for daily operation relies on two pulsed septum magnets and four pulsed dipole kickers installed in a 12-m-long straight section. Perfect tuning of the kickers to meet the perturbation tolerances is impossible since it would require at least four identical magnets, Ti-coated ceramic chambers, and electronics. On the way toward transparent injection, the four kickers can be replaced by a single pulsed magnet, benefiting from a field-free region in the stored beam path. This Multipole Injection Kicker (MIK), developed in the frame of a collaboration between SOLEIL and MAX IV, and currently installed in the MAX IV 3-GeV storage ring, has proven to meet the transparency specifications. A copy of the MIK has been installed in a short straight section of the SOLEIL storage ring in January 2021. Perturbations of less than 2% of the rms size of the stored beam were measured using the newly installed high-performance diagnostics. In this article, a start-to-end model of the MIK-based injection is presented as well as major challenges inherent in designing such an innovative magnet. Then, the results of the MIK commissioning are presented in depth along with the high-performance diagnostics, which are essential when such levels of beam stability are to be achieved.