High beam current storage at low energy for compact synchrotron radiation rings

A study of high beam current storage at a low energy is being conducted on the compact electron storage ring NIJI-1. In general, it is said that the stored beam lifetime is rapidly shortened as the beam energy decreases, and the high beam current storage is difficult to obtain. However, a stored beam current above a 350 mA was obtained at an injection energy of 100 MeV, and the lifetime of the stored beam is considerably long. For example, e-folding lifetime is about 2 h at 100 MeV. In this paper, we estimate the beam current decay rate due to the residual gas scattering, the ion trapping effect, and the Touschek effect, and make clear these contributions to the beam lifetime. It was clear that the Touschek lifetime is lengthened according to the bunch size growth, which is roughly explained by the longitudinal coupled bunch instability