关键词: 强流, 直线加速器, 混沌, 束晕

Abstract: In recent years, high current ion linacs have become increasingly attractive for applications such as heavy ion fusion and nuclear waste treatment, and these applications have raised strict requirements of low beam losses. During the transport of high current beam in low energy section of linac, a halo surrounding the dense core is one of the main sources of beam losses. In this paper, the test-particle core-interaction model is used to study the beam transport problem of a space-charge-dominated beam in a one-way self-consistency by solving simultaneously the KV envelope and Hill's equations in Hamilton dynamics. The motion of beam particles in phase-space is numerically analyzed by using Poincare mapping technique and Lyapunov exponents. The results show that the envelope oscillations of a mismatched beam can generate parameter resonance of the particle Hamiltonian, and the resonance condition depends only on the effective space charge parameter. The motion of particles near the core can become chaotic with development of the parameter resonance, and the evolution of global chaos will lead more particles near the KV envelope to become halo particles. The results also indicate that the halo can be regenerated, and have a boundary in two dimensional regime.

Key words: high current, linac, chaos, beam halo