ISLA Spectrometer Beam Focus and Mass Resolving Power Higher Order Optimization~

Nuclear physics plays a significant role in our modern life such as cancer treatment and national security. The product beams produced by certain nuclear reactions still remain unknown. Therefore, it is necessary for us to build a spectrometer that can separate the product beams in order to conduct further scientific research. ISLA (Isochronous Spectrometer of Large Acceptance) will allow experimental studies of reactions from re-accelerated rare isotope beams at the Facility for Rare Isotope Beams (FRIB), and enables us to distinguish different product beams (separating by mass-to-charge ratio) by looking at distributions of particles' time of flight through ISLA, instead of more commonly used physical separation. ISLA initial design consists of four magnetic dipoles and four magnetic quadrupoles, but as to how to achieve a high mass resolving power (the ability of the machine to identify nuclei by time-of-flight difference) in ISLA and how to produce a better focus at the end of ISLA still remained questioned. Recent progress has shown that the proposed solutions of adding multipoles or changing dipole quality do not contribute significantly to improving the resolving power but changing the dipole fringe field shape achieves our goals.