Lattice beam dynamics study at low b for SARAF/EURISOL driver 40/60 MEV 4 MA D&P superconducting linac

In this study we examine a lattice for the SARAF superconducting (SC) linac at the low-β range. The SC Half Wave Resonator cavities in the first cryostat are optimized for a geometric β₀=0.09 and hence the β=0.0567 ions coming from the RFQ are mismatched. We developed a semi adiabatic tuning method for the low-β portion of the SC linac. The guidelines were derived from the study of two linac lattices that were considered for the SARAF 40 MeV proton and deuteron linac, extended up to 60 MeV for the low energy part of the EURISOL driver. Simulations were run using the TRACK and GPT codes. The lattices were tested for energy gain along the linac, emittance growth and acceptance. Further, error runs in GPT using a tail emphasis technique to enhance statistics by focusing on the bunch tail allowed us to examine compatibility of the lattices with hands-on maintenance requirements. Our study may be relevant for other linacs that begin with SC cavities immediately following the RFQ, such as SPIRAL2, and perhaps also for IFMIF which is designed to start with similar β-mismatch at the low-β range.