回旋加速器中的空间电荷效应和束晕(英文)

在考虑束团内粒子之间的空间电荷相互作用力的条件下,对日本理化研究所(RIKEN)现有的一台注入器(加速常数为K70的AVF型回旋加速器)中束团的演变过程进行了模拟计算。模拟结果表明,束团的形变、束晕现象同样发生在回旋加速器中,不过,其产生机制不同于直线加速器。它不是由共振和混沌引起,而是由于粒子的排斥运动和束团内粒子的涡流运动引起的。     

强流质子直线加速器中束晕现象研究

从束流包络方程与单粒子运动方程联立模型出发，考虑了纵向能量方程的耦合，研究了强流质子直线加速器中的束晕现象。采用相交间的Ｐｏｉｎｃａｒｅ截面方法和实空间Ｐｏｉｎｃａｒｅ截面方法，研究了周期聚焦系统失配的情况下束晕的形成以及加速对束晕形成的影响。     

周期性聚焦结构中强流束的共振与束晕形成

强流束中的束晕形成是研制下一代高功率加速器必须解决的关键问题之一。为此研究了周期性聚焦结构中强流束的非线性共振、参数共振与束晕形成的关系 ,给出强流束中非线性共振、参数共振的共振范围表达式及其随束流空间电荷效应变化的数值结果和图表曲线 ,提出由非线性共振而激发的束晕形成的空间电荷效应极限 ,为下一代高功率加速器的物理设计提供理论依据。     

空间电荷引起的非线性共振与束晕形成

采用束核－单粒子模型研究强流束中由是电荷引起的非线性共振与束晕形的关系。借助Ｐｏｉｎｃａｒｅ截面技术,对粒子在相空间的运动进行数值分析。从束核包缝振荡的两个本征模出发,推志得到强流束中非线性共振范围随束流空间电荷效应化变化的表达式,以及由非线性共振而激发的束晕形成的空间电荷极限的形式,并给出相应的结果。     

等时性回旋加速器空间电荷效应初步研究

空间电荷效应是回旋加速器设计中一个非常重要的问题，当束流强度达到几mA时，空间电荷力在半径和垂直方向的散焦作用变得很明显，在经典的回旋加速器的中心区，垂直方向的聚焦很弱，因此，空间电荷效应将限制垂直方向的接收度。然而，和横向空间电荷效应相比，在等时性回旋加速器中，人们更关注纵向空间电荷效应。纵向空间电荷效应会增加单个束团的能散，同时在等时性回旋加速器中，纵向运动和径向运动存在着很强的耦合，空间电荷力使束团在径向和纵向的空间中产生扭曲和涡流运动。     

回旋加速器静电引出通道的计算

本文介绍三叶扇形可变能量等时性回旋加速器的束流静电引出通道的设计方法和特点,讨论了静电引出通道设计的基本粒子动力学要求,并根据静电通道的几何参数,对静电引出通道的单粒子运动方程作数值积分,从而确定了通道入口相对扇形磁场的合理方位角、通道分段的跨度及通道经向张口的程度,推导了单粒子运动方程等效的线性化简谐振荡方程。由束流光学的σ矩阵变换方法计算了通道入口的经向接受度及引出束包络,给出了引出束穿越边缘磁场的图象,证明在第一段静电通道内,引出束几乎正交地穿透等高斯线     

CYCIAE-100中心平面的Br对束流发射度的影响计算

在回旋加速器中，如果磁极的镜像对称被破坏，将在加速器的中心平面上产生一水平分量的场Br，在粒子相应轴向共振的作用下，这样的场将使中心粒子的运动偏离中心平面，进而使束流发射度发生变化。在回旋加速器中粒子由于径向磁场作用偏离中心平面运动的方程可表示为：     

CSNS直线加速器空间电荷效应的模拟研究

本文利用三维空间电荷效应程序IMPACT-Z对直线加速器中的空间电荷效应进行了模拟研究,从单粒子动力学和多粒子动力学角度分析了束流在不同峰值流强下的发射度变化。在15 mA流强下,比较了束流初始失配对束流发射度的影响,结果显示横向失配对发射度束流品质影响更大,实际调束过程中应保证束流失配因子不超过1.4。     

束晕-混沌控制的进一步研究:参数影响、粒子跟踪和自适应控制

本工作在以前课题组关于束晕-混沌控制的基础上,进一步研究了强流加速器中调谐衰减因子和真空相移的改变对束晕-混沌控制的影响及束晕-混沌控制对粒子横向运动的影响,并提出了一种新的控制方法——自适应控制方法,实现了对束晕-混沌的较好控制。本文主要介绍以下3方面的工作。1     

小世界同步与束流输运网络同步控制

加速器中束流失匹配、离子的非线性共振等作用都会导致强流离子束产生的束晕．混沌现象，即在强流束中高密度束核的外围弥漫着少量粒子，且出现混沌现象。束晕．混沌现象会在加速器器壁上引起超标的放射性，对加速期间带来损伤，因此具有极大的危害性。尝试在小世界网络的基础上构造束流输运网络，研究束流输运网络中粒子的同步问题。     

脉冲高频加速器束流动力学计算

用增补后的Parmela程序模拟了脉冲高频加速器中粒子的三维运动,给出了粒子在各相平面上的发射度大小和图示,同时简述了谐振腔的载束性能,并讨论了螺线管里束流横向发射度的变化。     

A hybrid model of primary radiation damage in crystals

The paper offers a hybrid model which combines molecular dynamics and Monte Carlo (MD+MC) methods to describe primary radiation damage in crystals, caused by particles whose energies are no higher than several tens of keV. The particles are tracked in accord with equations of motion with account for pair interaction. The model also considers particle interaction with the mean-field potential (MFP) of the crystal. Only particles involved in cascading are tracked. Equations of motion for these particles include dissipative forces which describe energy exchange between cascade particles and electrons. New particles - the atoms of the crystal in the cascade region - have stochastic parameters (phase coordinates); they are sampled by the Monte Carlo method from the distribution that describes the classic canonical ensemble of non-interacting particles subjected to the external MFP. The introduction of particle interaction with the MFP helps avoid difficulties related to crystal stability and the choice of an adequate interparticle interaction potential in the traditional MD methods. Our technique is many times as fast as the traditional MD methods because we consider only particles which are involved in cascading and apply special methods to speedup the calculation of forces by accounting for the short-range pair potential used.     

Effect of Ion Engine Exhaust on the Radiation Field of a Dipole Antenna Part I: Infinite Slab Model for the Exhaust Ion Beam

A theory of the effect of an ion rocket engine exhaust on the radiation pattern of a dipole antenna is presented. The electromagnetic equations are combined with those describing the exhaust plasma beam to calculate its equivalent effective dielectric constant. In part I of this paper, the beam is represented by an infinite slab of a homogenous plasma medium, as is usually considered in space charge neutralization studies of this type of engine. The equations of propagation of electromagnetic waves through the beam medium, are used to calculate the total dipole radiation field. The method of steepest descent is applied for the evaluation of the integrals. It is found that the dipole radiation pattern depends greatly on the beam characteristic parameters.     

腰-腰传输中强流束包络线方程的近似计算

研究了广义导流系数Π <1× 1 0 - 3 时的低能强流束包络方程的近似计算问题 ,在非线性条件下 ,导出相应的数学表达式和特征长度。使用腰 腰传输公式的包络计算结果与强流束包络方程计算结果基本一致。     

Effect of Ion Engine Exhaust on the Radiation Field of a Dipole Antenna Part II: Cylindrical Configuration for the Engine Exhaust Beam

In part II, a cylindrical configuration is used to represent the engine exhaust beam. The dipole, considered as a linear current source, is transformed by means of a Fourier series to an equivalent cosinusoidally distributed current sheet surrounding the beam. A radiation pattern function is presented to give the azimuthal beam synthesis of the dipole. It is found that the antenna radiation pattern is affected seriously by the presence of the exhaust beam. Plasma waves in the exhaust beam are found to be excited by the dipole field. The Boltzman and Poisson equations are used to investigate the existence and nature of these waves.     

Space Charge De-Bunching in Charged-Particle Beams

One of the factors influencing the properties of a pulsed beam is the growth of the charge bunches due to space charge forces. The growth along the direction of motion of the bunch degrades the time-structure of the pulsed beam and the growth transverse to the direction of motion de-focuses the beam. Although the space charge effect is only important at high current densities, it must be considered a limiting factor in any pulsed beam system. A general method of obtaining the field in the bunch to second order in v/c was developed. From this the motion of charges in the bunch was obtained by numerical integration for the case of a Gaussian distribution of space charge under the assumption that the charge distribution remains Gaussian. Solutions are presented in a dimensionless, graphical form which can easily be scaled for a particular problem.     

Power Consumption in Positive Ion Beam Converter with Electrostatic Electron Suppressor

The power recovery characteristics of an in-line direct beam converter provided with electrostatic electron suppressor were studied numerically by tracing the orbits of fast primary ions and secondary charged particles generated along their beam path by collision with background gas molecules. It is shown that, in reference to the electrostatic field potential at the point of impact, the energy distribution of secondary ions impinging on the suppressor has two peaks—one corresponding to a zone of high positive potential surrounding the collector and the other to one of slightly negative potential around the electron suppressor. Secondary electron emission from the suppressor is ascribed mainly to the latter peak, associated with impingement of slower secondary ions. Far much power consumed in secondary particle acceleration is spent for emitting electrons from the suppressor than for secondary ions generated by beam-gas collision. The upper limit of background pressure is discussed on the basis of criteria prescribed for restricting the power consumed in this secondary particle acceleration, as for practical convenience of electrode cooling. Numerical examples are given of calculations based on particle trajectory analysis of both primary ions and secondary particles, for the case of a 100 keV-proton sheet beam 10 cm thick of 35mA/cm² current density.     

Stimulated Brillouin Scattering of Gaussian Laser Beam in Relativistic Plasma

This paper presents an investigation of stimulated Brillouin scattering (SBS) of Gaussian laser beam in relativistic plasma. The pump beam interacts with a pre-excited ion-acoustic wave thereby generating a back-scattered wave. In the high intensity laser beam, electron oscillatory velocity becomes comparable to the velocity of light, which modifies the refractive index of plasma due to increase in the electron mass. This modification of refractive index affects the incident laser beam, ion-acoustic wave and back scattered beam. We have set up non-linear differential equations for the beam width parameters of the main beam, ion-acoustic wave, back-scattered wave and derived expression of SBS-reflectivity by taking full non-linear part of the dielectric constant of relativistic plasma with the help of moment theory approach. It is observed from the analysis that focusing of waves greatly affects the SBS reflectivity.     

直线加速器中电荷束团的耦合包络线方程

采用直线加速器中有限圆柱空间电荷模型，利用电荷束团所产生的纵向和横向空间电荷力，推导得到了直线加速器中计入纵向与横向耦合效应的电荷束团的耦合包络线方程；通过数值计算，给出了纵向和横向几何因子变化的计算实例。