Report on the results of the first experiments on a nonlinear collimator for SuperKEKB

SuperKEKB requires a small vertical beam size at the interaction point (IP) and a higher beam current to achieve higher luminosity. One of the challenges is how to manage beam backgrounds for the Belle II detector. Several sets of movable collimators are used to reduce the beam backgrounds. When the distance between the collimator head and beam position is too small, an impedance effect may induce beam instabilities. Thus, we decided to adopt a nonlinear collimator to reduce the beam backgrounds for the Belle II detector as well as to reduce the collimator impedance, then the beam instabilities due to the short-range wake field can be suppressed. The nonlinear collimator has been utilized since February 2024. In the article, we report the results of impedance effects, beam backgrounds reduction, and beam lifetime when the nonlinear collimation system is turned on and off, respectively.