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

Abstract

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.

Figures (10)

• Figure 1: Normalized revolution frequencies in a scaling FFA plotted as a function of $\beta\gamma$. Each curve was normalized so that its maximum or asymptotic value was 1. Different colors indicate different values of the field index $k$.
• Figure 2: Ratio of one-turn energy gains, $\Delta E_2/\Delta E_1$, as a function of the dimensionless synchronous momentum $\beta\gamma$, in the below-transition regime. Different colors indicate different values of the field index $k$.
• Figure 3: Comparison of longitudinal acceptances between $h=1$ and general $h$, plotted as a function of $R_h$.
• Figure 4: Simulated RF pattern: (A) frequency; (B) RF amplitude (solid line) and synchronous phase (dashed line).
• Figure 5: Synchronous energies as a function of time for $h = 1$, 2, 4, and 8. Each curve shows the evolution of the synchronous particle's kinetic energy under the RF pattern in Fig. \ref{['fig:SimRfPattern']}.