Proposal and design of 81.25 MHz heavy ion drift tube linacs for BISOL

TL;DR

This paper presents the design of 81.25 MHz heavy ion drift tube linacs for the BISOL project, achieving high efficiency and robustness through innovative electromagnetic and dynamics design strategies.

Contribution

It introduces a novel design of CW drift tube linacs based on the KONUS scheme with comprehensive error analysis and optimized electromagnetic tuning for heavy ion acceleration.

Findings

Achieves over 95% transmission efficiency.

Maintains high performance despite beam and cavity errors.

Frequency shifts within acceptable ranges.

Abstract

Based on the design requirements proposed by the Beijing On-Line Isotope Separation project (BISOL), four Sn$^{22+}$-based,81.25MHz continuous wave (CW) drift tube linac (DTL) cavities have been designed. These DTLs are capable of accelerating Sn$^{22+}$ of 0.1 pmA from 0.5 MeV/u to 1.8 MeV/u over a length of 7 m, with an output longitudinal normalized RMS emittance of 0.35$\pi \cdot$ mm$\cdot$mrad, and transmission efficiency higher than 95%. The dynamics design adopted the KONUS (Kombinierte Null Grad Struktur Combined $0^\circ$ Structure) scheme. Comprehensive error study implies that these DTLs can accommodate a wide range of non-ideal beams and cavity alignment errors while maintaining high transmission efficiency. The electromagnetic design employed a Cross-bar H-mode (CH) structure for superior water-cooling characteristics, and a detailed tuning analysis was conducted to derive an optimal tuning scheme. The results of the multiple-physics analysis indicate that the frequency shift of each cavity is within an acceptable range. Comparing the dynamics requirements with the RF design results, similar particle output phase distribution, equivalent energy gain and consistent emittance growth are observed. Detailed designs will be presented in this manuscript.