Controlling beam halo-chaos

Beam halo-chaos is essentially a complex spatiotemporal chaotic motion in a periodic-focusing channel of a high-power linear proton accelerator. The controllability condition for beam halo-chaos is analysed qualitatively. A special nonlinear control method, i.e. the wavelet-based function feedback, is proposed for controlling beam halochaos. Particle-in-cell simulations are used to explore the nature of halo-chaos formation, which has shown that the beam halo-chaos is suppressed effectively after using nonlinear control for the proton beam with an initial full Gaussian distribution. The halo intensity factor H _av is reduced from 14% to zero, and the other statistical physical quantities of beam halo-chaos are more than doubly reduced. The potential applications of such nonlinear control in experiments are briefly pointed out. © 2001 Chinese Physical Society and IOP Publishing Ltd.