Tomonori Uesugi | Searcharxiv

arXiv2026

Wide frequency-range acceleration using second harmonic RF bucket in fixed field accelerators

We propose a novel acceleration scheme for fixed-field accelerators (FFAs), in which RF buckets with harmonic numbers $h = 1$ and $h = 2$ are time-sequenced to form a single, continuous acceleration path. This approach completes acceleration in two RF frequency sweeps, thereby reducing the total frequency sweep range and shortening the repetition period. The feasibility of this method is demonstrated through longitudinal simulations based on parameters of the FFA at the Institute for Integrated Radiation and Nuclear Science, Kyoto University (KURNS). We also establish operational conditions under which the second harmonic rf bucket remains stable and practically usable.

physics.acc-ph↗

arXiv2025

Design of a Storage Ring based on a Fixed Field Alternating Gradient Configuration with an Internal Target for Heavy-Ion Beams with Stochastic Charge State Conversions

In the general use of a heavy-ion accelerator, an accelerated beam impinged on a target is spoiled into a beam dump. To make more efficient use of the beam, recycling of the beam passed through the target is proposed in the framework of the so-called energy recovery internal target (ERIT). In the ERIT system, the target is irradiated inside the circulating beam by recovering the energy lost in the target using rf cavities. So far, such a system has been realized only for proton beams. Here, the ERIT system for heavy-ion beam is demonstrated for the first time. A challenging issue is the circulation of all ions with different atomic charge. An ion has a probability of equilibrated charge state distribution after passing through the target, independent of the initial charge state. This phenomenon of stochastic charge state conversion (SCSC) causes rapid beam-emittance growth. To solve this problem, we developed a method to match the closed orbits and betatron functions of the beams in different charge states at the target location in a ring based on a scaling fixed field alternating gradient (FFA) lattice structure. We present the design of such an FFA ring and show, through full 6D beam tracking simulations, that transverse emittance growth can be effectively suppressed even in the presence of SCSC.

physics.acc-ph↗