Acta Scientiarum Naturalium Universitatis Pekinensis

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Formation of Global Chaos and Halo in High Current Ion Linacs

LIU Pukun, FANG Jiaxun, CHEN Chiaerh   

  1. Institute of Heavy Ion Physics, Peking University, Beijing, 100871
  • Received:1996-11-15 Online:1997-09-20 Published:1997-09-20


刘濮鲲, 方家训, 陈佳洱   

  1. 北京大学技术物理系,重离子物理研究所,北京,100871

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

摘要: 强流离子直线加速器因其可作为次临界装置的驱动器,近来在放射性洁净核能系统等方面的应用中出现了一些新的动向,引起人们极大的关注。同时,这些新的应用对加速器低束损也提出了苛刻的要求,使得对粒子损失的主要来源之一的束晕问题的研究成为当前加速器物理研究中的热点。本文采用束核-试验粒子模型,通过在哈密顿动力学系统中同时求解KV包络方程和Hill方程,单向自洽地研究了空间电荷控制的束流的传输问题。借助Poincare映射技术和Lyapunov指数,对粒子在相空间的运动进行了数值分析。结果表明,失配的包络振荡是引起粒子哈密顿参量共振的前提,而共振条件则只决定于有效空间电荷参数。参量共振的发展导致束核附近的粒子运动出现混沌。随着球形混沌的演化,使更多位于KV包络附近的粒子成为束晕粒子。结果同时显示,束晕具有再生性,而且在二维情况下是有界的。

关键词: 强流, 直线加速器, 混沌, 束晕

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