Characteristics of Lattice and Magnet System of TARN II

TARN II is a ring which is designed to be operated both as a synchrotron and a cooler ring for ions. Its mean radius is ~12.4 m and is to be able to accelerate protons up to 1300 MeV and ions with charge to mass ratio of 1/2 up to 450 MeV/u. The ring consists of 24 dipole and 18 quadrupole magnets, which compose the lattice with sixfold symmetry for synchrotron acceleration (Synchrotron Mode) and another one with threefold symmetry to realize doubly achromatic sections for beam cooling (Cooler Ring Mode). These modes can be transferred between each other keeping the operating point at the position of (νH, νV)~(1.75, 1.25). The acceptance for beam cooling experiment at TARN II is expected to be improved from 70π to 400π mm·mrad by application of pre-cooling of horizontal betatron amplitude by stochastic method with Synchrotron Mode before moving to Cooler Ring Mode. Main magnets of the ring with AC characteristics have already been fabricated. Dipole magnets with H-type are found to have realized required good field region of ±100 mm from the result of static field measurement.