NSLS-II Storage Ring Injection Using a Nonlinear Injection Kicker
The NSLS-II has been operating successfully with top off injection since September 2015. Measurements of the stored beam show a transient of 200 μm in the long straight sections during top off injections. This transient is not desirable for some users, particularly those who specialized in imaging or are otherwise sensitive to beam motion. Users are provided with a signal with which they can gate their detectors, but it is desirable to reduce or eliminate this motion all together. Studies have been performed to reduce the transients, and it is clear that the power supplies require more tunability in the pulse shape in order to reduce the transient across the entire bunch train. Other light sources have explored the possibility of using pulsed quadrupoles and sextupoles as the injection magnet. The stored beam receives no kick as the on-axis fields in these magnets is zero, but the injected beam would see a kick as it is off-center. One drawback of the pulsed quadrupole is that the stored beam experiences a size oscillation. Another issue with a nonlinear kicker is the gradient seen by the injected beam. The transport line needs to be tuned for this gradient, and depending on the strength of the nonlinearity, this gradient may change greatly with injected beam position. Therefore, other facilities have explored other magnet configurations that are nonlinear but have a gradient with less positional dependence. The prospect of using a sextupole kicker was investigated during the design phase of the NSLS-II. It was decided that the idea would not be pursued for several reasons. In particular, the design that was studied the most in depth was not compatible with the standard four bump injection design and the tolerances required were deemed too tight at the time. Other ideas were discussed as well and ultimately none were accepted into the design. In this report we discuss the possibility of placing a nonlinear kicker in the first straight section after the injection straight instead of using the injection bumps. The design of the kicker is based on a design that has been used successfully at BESSY and MAX IV. Our conceptual kicker design is compatible with the existing ring optics and power supply requirements. We show that the transport line is capable of being matched to the required optics. The design does not have restrictive tolerances and is a viable option for a facility upgrade.