THE INFLUENCE OF HIGHER ORDER MULTIPOLES OF IR MAGNETS ON LUMINOSITY FOR SuperKEKB

In SuperKEKB, the value of beta function is extremely small at interaction point (IP) to achieve higher luminosity. As magnets in interaction region (IR) have very strong focusing effect, they make a large disturbance to beams. Higher order multipoles and their skew components of IR magnets are located at a very high beta section with 7/2 phase difference from IP. Since the beta in IR magnets has largest value, multipole components of x-y coupling can give critical effect to beam dynamics at IP and reduce luminosity on SuperKEKB design. In this study, we calculated beam dynamics for the nonlinear effect of multipole components and estimated the influence on luminosity deteriorated by them. The present result suggested that the unknown luminosity loss calculated by the SAD library can be explained by the contribution of the skew sextupole term.