SuperKEKB test operation with skew sextupole magnets

SuperKEKB is an asymmetric-energy electron-positron collider aiming at the integrated luminosity of 50 ab-1 as the successor to KEKB. To achieve this goal, SuperKEKB adopted the "nano-beam scheme," in which two low emittance beams collide at the interaction point (IP) with a large crossing angle. To realize such low emittance beams at IP, Chromatic x-y coupling at IP has to be corrected frequently. In SuperKEKB positron ring (LER), twenty-four rotating sextupole magnets were installed to generate skew sextupole magnetic fields for the chromatic x-y coupling correction. In December 2021, a few setups of tilting angles of the 24 rotating sextupole magnets varied the chromatic x-y coupling parameters. It was found that the vertical emittance growth at the primary and secondary synchro-beta resonance lines can be controlled by rolling the sextupole magnets. The tilting system of the rotating sextupole magnet is described, and the results of the beam study are summarized in this report. (author)