Weng Jia-Qiang

Control of Beam Halo-Chaos for an Intense Charged-Particle Beam Propagating Through Double Periodic Focusing Field by Soliton

We study an intense beam propagating through the double periodic focusing channel by the particle-core model, and obtain the beam envelope equation. According to the Poincare–Lyapunov theorem, we analyze the stability of beam envelope equation and find the beam halo. The soliton control method for controlling the beam halo-chaos is put forward based on mechanism of halo formation and strategy of controlling beam halo-chaos, and we also prove the validity of the control method, and furthermore, the feasible experimental project is given. We perform multiparticle simulation to control the halo by using the soliton controller. It is shown that our control method is effective. We also find the radial ion density changes when the ion beam is in the channel, not only the halo-chaos and its regeneration can be eliminated by using the nonlinear control method, but also the density uniformity can be found at beams centre as long as an appropriate control method is chosen.

Nonlinear Control of Beam Halo-Chaos in Accelerator-Driven Clean Nuclear Power System*

Beam halo-chaos in high-current accelerators has become a key concerned issue because it can cause excessive radioactivity from the accelerators therefore significantly limits their applications in industry, medicine, and national defense. Some general engineering methods for chaos control have been developed in recent years, but they generally are unsuccessful for beam halo-chaos suppression due to many technical constraints. Beam halo-chaos is essentially a spatiotemporal chaotic motion within a high power proton accelerator. In this paper, some efficient nonlinear control methods, including wavelet function feedback control as a special nonlinear control method, are proposed for controlling beam halo-chaos under five kinds of the initial proton beam distributions (i.e., Kapchinsky–Vladimirsky, full Gauss, 3-sigma Gauss, water-bag, and parabola distributions) respectively. Particles-in-cell simulations show that after control of beam halo-chaos, the beam halo strength factor is reduced to zero, and other statistical physical quantities of beam halo-chaos are doubly reduced. The methods we developed is very effective for suppression of proton beam halo-chaos in a periodic focusing channel of accelerator. Some potential application of the beam halo-chaos control in experiments is finally pointed out.

Controlling Beam Halo-Chaos via Time-Delayed Feedback*

The study of controlling high-current proton beam halo-chaos has become a key concerned issue for many important applications. In this paper, time-delayed feedback control method is proposed for beam halo-chaos. Particle in cell simulation results show that the method is very effective and has some advantages for high-current beam experiments and engineering.

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 halo-chaos. 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 Hav 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.

Control of Beam Halo-Chaos by Fraction Power-Law Function in Hackle Periodic-Focusing Channel

The Kapchinsky–Vladimirsky (K-V) beam through a hackle periodic-focusing magnetic field is studied using the particle-core model. The beam halo-chaos is found, and an idea of fraction power-law function controller is proposed based on the mechanism of halo formation and the strategy of controlling halo-chaos. The method is applied to the multi-particle simulation to control the halo. The numerical results show that the halo-chaos and its regeneration can be eliminated effectively by using the fraction power-law function control method. At the same time, the radial particle density is uniform at the beams center as long as the control method and appropriate parameter are chosen.

Control of Beam Halo-Chaos Based on Self-Field-Intensity of Particle Beam

The KV beam through an axisymmetric periodic-focusing magnetic field is studied using the particle-core model A new variable of the self-field-intensity of particle beam is selected, and an idea of self-field feedback controller is proposed based on the variable for controlling the halo-chaos. We perform multiparticle simulation to control the halo by using the self-field feedback controller. The numerical results show that the halo-chaos and its regeneration can be eliminated effectively, and that the density uniformity can be found at the centre of beam as long as an appropriate control method is chosen. The control method may be operated in the experiment, because field intensity measurement is easy.

Control of beam halo-chaos by Gauss function in the triangle periodic-focusing channel

This paper studies the Kapchinsky?Vladimirsky (K?V) beam through a triangle periodic-focusing magnetic field by using the particle-core model. The beam halo-chaos is found, and an idea of Gauss function controller is proposed based on the strategy of controlling the halo-chaos. It performs multiparticle simulation to control the halo by using the Gauss function control method. The numerical results show that the halo-chaos and its regeneration can be eliminated effectively, and that the radial particle density is uniform at the centre of the beam as long as the control method and appropriate parameter are chosen.

Control of Beam Halo-Chaos by Soliton

The Kapchinsky–Vladimirsky beam through an alternating-gradient quadrupole magnetic field is studied using the particle-core model. The beam halo-chaos is found, and the soliton controller is proposed based on the mechanism of halo formation and strategy of controlling halo-chaos. We perform a multiparticle simulation to control the halo by soliton controller, and find that the halo-chaos and its regeneration can be eliminated. It is shown that our control method is effective.

Controlling Beam Halo-Chaos by Adaptive Control Exterior Magnetic Field*

In this paper, the parametric adaptive method for controlling the beam halo-chaos in the periodic focusing channels of high-current proton linacs is presented. The study of proton beam halo-chaos based on controlled beam envelope equation and the results of particles-in-cell simulations for macro-particle beam show that the proton beam chaotic envelope as well as the beam rsm radius can be controlled to the beam matched radius using this method. For the Kapchinskij-Vladimirskij (K-V) distribution of initial proton beam, all statistical physical quantities of the beam halo-chaos are largely reduced. This control method has an advantage of the control halo-chaos since the exterior magnetic field as controlled parameter can be rather easily adjusted in the periodical magnetic focusing channels for the experiment.

The Screening Behavior in Diffusion-Limited Aggregation

The measure of the screening behavior of the diffusion-Limited aggregation in 100 clusters by computer simulations shows that the screening length is not inversely proportional to the number density of particles [97] or to the square root of the number density of particles[10] quantitatively.