相对论返波管中击穿现象粒子模拟

随着相对论返波管(RBWO)输出功率的提高,RBWO内部击穿问题日益突出。击穿过程中产生的等离子体,会降低输出功率并导致脉冲缩短,大大限制了RBWO的输出单脉冲能量。采用3维粒子模拟,在反射器、慢波结构、提取腔局部区域产生等离子体,建立了RBWO单点击穿及多点击穿模型,获得了等离子体产生的区域和密度对微波输出性能的影响规律。模拟结果表明,输出微波功率随等离子体密度增加而迅速降低,多点击穿相对于单点击穿情况更容易引起输出微波脉冲提前终止,且发射器击穿产生的等离子体效应更为明显。     

相对论返波管中击穿现象粒子模拟

随着相对论返波管(RBWO)输出功率的提高,RBWO内部击穿问题日益突出。击穿过程中产生的等离子体,会降低输出功率并导致脉冲缩短,大大限制了RBWO的输出单脉冲能量。采用3维粒子模拟,在反射器、慢波结构、提取腔局部区域产生等离子体,建立了RBWO单点击穿及多点击穿模型,获得了等离子体产生的区域和密度对微波输出性能的影响规律。模拟结果表明,输出微波功率随等离子体密度增加而迅速降低,多点击穿相对于单点击穿情况更容易引起输出微波脉冲提前终止,且发射器击穿产生的等离子体效应更为明显。     

无外加引导磁场相对论返波振荡器粒子模拟

设计了一种无外加引导磁场S波段相对论返波振荡器,采用阳极网提取电子,并设计了非均匀慢波结构。通过Karat 2.5维全电磁粒子模拟程序研究了器件内束-波作用的物理过程。典型模拟结果为:当二极管工作电压330 kV、电流2.83 kA时,器件在频率2.79 GHz处获得较高的微波输出,经27 ns后饱和,输出微波的功率达158 MW,效率约为16.8%。     

无外加引导磁场相对论返波振荡器粒子模拟

设计了一种无外加引导磁场S波段相对论返波振荡器,采用阳极网提取电子,并设计了非均匀慢波结构。通过Karat 2.5维全电磁粒子模拟程序研究了器件内束-波作用的物理过程。典型模拟结果为：当二极管工作电压330 kV、电流2.83 kA时, 器件在频率2.79 GHz处获得较高的微波输出,经27 ns后饱和,输出微波的功率达158 MW,效率约为16.8%。     

Particle-in-cell simulation of ion-acoustic solitary waves in a bounded plasma

We study some nonlinear waves in a viscous plasma which is confined in a finite cylinder.By averaging the physical quantities on the radial direction in some cases,we reduce this system to a simple one-dimensional model.It seems that the effects of the bounded geometry(the radius of the cylinder in this case)can be included in the damping coefficient.We notice that the amplitudes of both Korteweg–de Vries(KdV)solitary waves and dark envelope solitary waves decrease exponentially as time increases from the particle-in-cell(PIC)simulation.The dependence of damping coefficient on the cylinder radius and the viscosity coefficient is also obtained numerically and analytically.Both are in good agreement.By using a definition,we give a condition whether a solitary wave exists in a bounded plasma.Moreover,some of potential applications in laboratory experiments are suggested.     

Phase-lock of a submillimetric carcinotron

In this paper the problem of phase stabilization of submillimetric backward wave oscillators (BWO's) is considered. Experimental results are given about the phase-lock of a 600 GHz BWO to a quartz crystal reference, via a frequency multiplier chain of high phase spectral purity. The spectral analysis of the locked BWO is performed both on the IF and on the submillimetric output signal.     

电子激励表面等离极化激元的粒子模拟

采用极化电流微分方程,对贵金属中自由电子与外电场的共振过程进行描述。将该微分方程与麦克斯韦方程相结合,运用时域有限差分(FDTD)方法,在粒子PIC模拟软件CHIPIC3D的基础上,实现了电子激励表面等离极化激元(SPPs)的模拟。通过对100 keV电子平行于银薄膜表面运动、激励起表面等离极化激元的模拟,观测并分析了SPPs的场强及模式在银薄膜表面的分布,并验证了模拟结果的正确性。     

圆柱形阳极层霍尔等离子体加速器的质点网格方法模拟

对圆柱形阳极层霍尔加速器内的放电等离子体运用二维质点网格方法（particle in cell）进行数值模拟,用蒙特卡罗碰撞方法处理带电粒子与中性粒子之间的碰撞. 得到了放电通道内离子与电子的分布以及离子流的运动,并且对出口外侧的能量分布进行了统计. 结果发现圆柱形阳极层等离子体加速器的磁场对电子有明显的约束作用,电子集中于阳极附近很小的区域内. 由于电磁场的特殊分布,离子流呈现出双峰式的分布. 离子能量范围从放电电压的20%到接近放电电压,平均能量在放电电压的40%—50%之间. 关键词： 质点网格方法 蒙特卡罗碰撞 数值模拟 阳极层霍尔等离子体加速器     

X波段新型低阻抗高功率微波源的模拟研究

提出了一种新型低阻抗高功率微波源,能在单个器件内产生两束锁相的相干高功率微波,对两束相干微波进行功率合成有望在单个高功率微波器件中实现更高的功率输出.粒子模拟结果显示,在电压687 k V、磁场0.8 T时,该微波源整体阻抗36?,两束微波的频率都为9.72 GHz,输出功率分别为1.20 GW和2.58 GW,功率效率分别为28%和30%;两束输出微波之间频率抖动小于±3 MHz,相位差抖动小于±3?.     

Particle-in-cell simulation of the stopping power in the presence of a magnetic field

In the last years electron cooling has become a well established method to reduce the phase space volume of ion beams in storage rings. We use a Particle-In-Cell (PIC) simulation to study the interaction between the ion beam and the electron plasma in the cooler. We investigate the energy loss of heavy, highly charged ions in magnetized electron plasmas and focus on the influence of the magnetic field. This revised version was published online in July 2006 with corrections to the Cover Date.     

强流电子束聚焦数值模拟

采用粒子模拟（PIC）方法模拟了强流电子束在薄磁透镜中的聚焦。建立了强流电子束的聚焦模型,模拟了神龙一号加速器某次实验的结果,得到的模拟结果非常接近实验值,证明采用建立的PIC模型模拟强流束经过磁透镜时的聚焦是可信的。应用此模型模拟了电子束参数（入射半径、发射度、能散度、相位角等）对焦斑直径的影响, 结果表明：在模拟条件下,电子束平行入射时最佳束包络半径位于20.0~22.5 mm;发射度和能散度对焦斑直径的影响和理论公式吻合得较好;只有入射电子束包络半径和相位角匹配时才能得到小的焦斑直径。     

强流电子束聚焦数值模拟

采用粒子模拟（PIC）方法模拟了强流电子束在薄磁透镜中的聚焦。建立了强流电子束的聚焦模型,模拟了神龙一号加速器某次实验的结果,得到的模拟结果非常接近实验值,证明采用建立的PIC模型模拟强流束经过磁透镜时的聚焦是可信的。应用此模型模拟了电子束参数（入射半径、发射度、能散度、相位角等）对焦斑直径的影响, 结果表明:在模拟条件下,电子束平行入射时最佳束包络半径位于20.0~22.5 mm;发射度和能散度对焦斑直径的影响和理论公式吻合得较好;只有入射电子束包络半径和相位角匹配时才能得到小的焦斑直径。     

Fluid-magnetic helicity in axisymmetric stationary relativistic magnetohydrodynamics

The present work is intended to gain a fruitful insight into the understanding of the formations of magneto-vortex configurations and their role in the physical processes of mutual exchange of energies associated with fluid’s motion and the magnetic fields in an axisymmetric stationary hydromagnetic system subject to strong gravitational field (e.g., neutron star/magnetar). It is found that the vorticity flux vector field associated with vorticity 2-form is a linear combination of fluid’s vorticity vector and of magnetic vorticity vector. The vorticity flux vector obeys Helmholtz’s flux conservation. The energy equation associated with the vorticity flux vector field is deduced. It is shown that the mechanical rotation of vorticity flux surfaces contributes to the formation of vorticity flux vector field. The dynamo action for the generation of toroidal components of vorticity flux vector field is described in the presence of meridional circulations. It is shown that the stretching of twisting magnetic lines due to differential rotation leads to the breakdown of gravitational isorotation in the absence of meridional circulations. An explicit expression consists of rotation of vorticity flux surface, energy and angular momentum per baryon for the fluid-magnetic helicity current vector is obtained. The conservation of fluid-magnetic helicity is demonstrated. It is found that the fluid-magnetic helicity displays the energy spectrum arising due to the interaction between the mechanical rotation of vorticity flux surfaces and the fluid’s motion obeying Euler’s equations. The dissipation of a linear combination of modified fluid helicity and magnetic twist is shown to occur due to coupled effect of frame dragging and meridional circulation. It is found that the growing twist of magnetic lines causes the dissipation of modified fluid helicity in the absence of meridional circulations.     

Conditions for existence of a stationary relativistic compact beam torus

Conditions of creating an absolute magnetic trap for controllable thermonuclear fusion with the help of a high-current relativistic beam of charged particles are considered. It is demonstrated that these conditions are realized for a compact beam torus (CBT) in an intrinsic electromagnetic field. On the other hand, from the virial theorem it follows that for positive beam pressure and positive energy density of the electromagnetic field, no strictly stationary state exists in the empty Minkowski flat space-time. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 75–78, February, 2009.     

时变等离子体高功率微波频率上转换的粒子模拟

基于电磁波与时变介质相互作用能够实现电磁波频率上转换的原理,通过粒子模拟(PIC)方法对电磁波与时变等离子体薄层相互作用进行模拟,实现了频率由2.45 GHz提升至130 GHz,功率转化效率约为0.39%。探究了等离子体参数(包括等离子体密度、有限的等离子体上升时间以及等离子体薄层厚度)对频率上转换的影响。模拟结果验证了等离子体密度决定上转换频率,与理论结果相符。模拟结果表明,等离子体薄层厚度越大,得到的上转换波的能量越大;等离子体的上升时间越小,上转换波的转换效率和频谱纯度越高。采用等离子体密度21020 cm-3,等离子体厚度1 cm,等离子体上升时间0.04 ns 可以得到可观的130 GHz上转换波输出。     

时变等离子体高功率微波频率上转换的粒子模拟

基于电磁波与时变介质相互作用能够实现电磁波频率上转换的原理,通过粒子模拟(PIC)方法对电磁波与时变等离子体薄层相互作用进行模拟,实现了频率由2.45 GHz提升至130 GHz,功率转化效率约为0.39%。探究了等离子体参数(包括等离子体密度、有限的等离子体上升时间以及等离子体薄层厚度)对频率上转换的影响。模拟结果验证了等离子体密度决定上转换频率,与理论结果相符。模拟结果表明,等离子体薄层厚度越大,得到的上转换波的能量越大;等离子体的上升时间越小,上转换波的转换效率和频谱纯度越高。采用等离子体密度21020 cm-3,等离子体厚度1 cm,等离子体上升时间0.04 ns 可以得到可观的130 GHz上转换波输出。     

Relativistic carcinotron with a thermionic injector of electrons

An experimental study directed to the determination of a mechanism for microwave breakdown in a relativistic X-band carcinatron is presented. An electron beam was generated using a thermionic cathode, which provided a stable beam geometry. The use of this cathode decreased the probability of breakdown caused by electron bombardment of the slow-wave structure. An important part played in microwave breakdown are molecules absorbed on the slow-wave structure surface. It is shown that the presence of these molecules, an implementation of conditions for secondary-electron resonant discharge (SERD), can result in a very fast (during 10-20 ns) limitation of the radiation pulsewidth. To remove the adsorbed molecules, heat degassing of the slow-wave structure and a collector of electrons was applied, going on continuously, during a working day of the device. By degassing and choice of slow-wave structure material, output radiation power of the device was increased by a factor of ten (up to 5 MW at the pulsewidth of 10 μs)     

Fundamental processes in relativistic laser plasmas

A review is given of processes fundamental for current relativistic regimes of laser matter interaction such as the generation and evolution of relativistic coherent nonlinear electromagnetic structures; generation of extremely high intensity electromagnetic waves and extremely high energy charged particle beams; novel regimes of electromagnetic wave interaction with matter and of the prospects for using laser accelerators for the high energy physics and for the laboratory relativistic astrophysics with relativistic laser plasmas.