射频电感耦合等离子体在横向磁场中扩散的研究

通过轴向移动朗缪尔探针,考察了外置电磁铁提供的横向磁场对射频感应耦合等离子体(ICP)延轴向扩散过程中的电子温度、离子密度的影响。实验数据表明,与无磁场条件下的结果相比,横向磁场的加入使得扩散区内的电子温度沿轴向迅速下降,研究了横向磁场对电子的过滤作用。     

两种外磁场形式对介质面次级电子倍增的抑制

利用自编1D3V PIC程序,数值研究了不同外加磁场方式对次级电子倍增抑制的物理过程,给出了次级电子数目、平均能量、密度、运动轨迹、渡越时间、介质表面静电场及沉积功率等物理量时空分布关系。模拟结果表明:不同方向外加磁场抑制次级电子倍增的机理有所不同。轴向外加磁场利用电子回旋运动干扰微波电场对电子加速过程,使其碰壁能量降低以达到抑制二次电子倍增的效果;横向外加磁场利用电子回旋漂移过程中,电子半个周期被推离介质表面（不发生次级电子倍增）,半个周期被推回介质表面（降低电子碰撞能量）的作用机理,达到抑制二次电子倍增的效果。讨论了横向磁场在回旋共振下,电子回旋同步加速导致回旋半径增大,电子能量持续增加的特殊过程。两种外加磁场方式都可以通过增加磁场达到进一步抑制次级电子倍增的目的。轴向外加磁场加载容易,但对磁场要求较高;横向外加磁场需要磁场较低,但加载较为困难。     

带轴向引导磁场自由电子激光器中的电子轨迹与稳定性

在对中国工程物理研究院电子学研究所和中国科学院上海光学精密机械研究所所做带引导磁场喇曼型自由电子激光实验进行数值模拟的基础上,本文研究了轴向引导磁场和摇摆磁场联合作用的单电子轨迹,对电子的平衡轨道和一阶微扰轨道进行了仔细分析,揭示了在引导磁场存在的情况下,摇摆磁场横向变化引起的电子感应回旋运动的重要性,推导了带引导磁场情况下的电子感应回旋运动方程,给出了电子感应回旋运动的周期,X方向、Y方向之间的关系。同时,用数值模拟方法研究了电子的运动,两者结果符合很好。 关键词：     

相移光栅磁场传感方案交叉敏感分析

通过相移光栅的偏振相关损耗(PDL)进行磁场测量是一种较为新颖的磁场测量方法,可用于对脉冲交变强磁场的测量。交叉敏感问题是光纤光栅传感中的关键问题。忽略光栅固有双折射,利用传输矩阵法对磁场传感原理进行了推导与仿真,理论分析了温度、轴向应力和压力等对相移光栅透射窗口的影响,并对相应的PDL峰值变化进行了数值仿真。理论和实验表明,透射窗口峰值的波长随温度和轴向应力呈线性变化,PDL谱线发生横向平移,磁场传感系统不受影响。压力的变化改变了光栅的折射率分布,产生应力双折射,PDL谱线发生不规则变化,对磁场测量结果产生严重影响。     

HIRFL–CSR电子冷却装置上的横向电子束温度

从磁场中单电子的轨道运动方程出发,分析并推出了HIRFL-CSR电子冷却装置上的横向电子束温度,并得到了一些重要结论.     

自由电子激光放大器的理论分析

本文从单粒子模型出发,对自由电子激光放大器在小信号情形下的工作机理与参量特性进行了比较详细的分析与讨论,结果表明自由电子激光放大器实质上是电子束与快迴旋波的相互作用,而电子在轴向均匀静磁场及横向周期静磁场中运动的迴旋谐振条件对这种相互作用有重大的影响,本文对放大器的参量(如电子束的电压和电流密度、轴向及横向静磁场强度、横向静磁场波长等)与放大器的中心工作频率、放大带宽、小信号增益和放大电磁波的波数的关系进行了数值计算,并指出了最佳设计的途径,经过适当设计,自由电子激光放大器的小信号增益达到10^-2厘米^-1或1米的e倍距离并有足够的带宽是不难的。 关键词：     

HIRFL－CSR电子冷却装置上的横向电子束温度

从磁场中单电子的轨道运动方程出发，分析并推出了ＨＩＲＦＬ－ＣＳＲ电子冷却装置上的横向电子束温度，并得到了一些重要结论．     

HIRFL—CSR电子冷却装置上的横向电子束温度

从磁场中单电子的轨道运动方程出发，分析并推出了ＨＩＲＦＬ－ＣＳＲ电子冷却装置上的横向电子束温度，并得到了一些重要结论。     

铁磁性加载复合管壳电子注聚焦性能的研究

大功率行波管通常利用复合管壳提升高频系统的集成度和散热特性。宽带行波管采用复合管壳高频制造工艺时,由于加载翼片含有铁磁性材料(纯铁)使得聚焦系统的横向磁场分量变大,径向和角向磁场分量呈非均匀性,电子注聚焦困难。本文研究了周期永磁聚焦系统横向磁场产生的原因并建立理论模型,并对磁场分量和其对电子注形态的影响进行了仿真,仿真结果与理论计算结果一致。根据横向磁场分布模型对加载翼片的形状和数量进行优化仿真,结果表明9片齿形加载翼片方案可在保持慢波电路参数的同时,降低聚焦系统的横向磁场分量,改善电子注聚焦效果。     

多注行波管周期永磁聚焦系统

 利用自行开发的3维行波管仿真软件研究了五注耦合腔行波管周期永磁聚焦系统,分析了各个电子注通道内的静磁场分布和电子注聚焦性能。讨论了在有无初始横向速度的情况下各电子注的聚焦情况。并对外层电子注通道内的横向磁场的性质和其造成的对电子注聚焦的影响进行了分析,结果表明:该多注周期永磁聚焦系统具有良好的静磁场分布特性与电子注聚焦性能,在结构设计合理时,横向磁场对外层通道内电子注的聚焦影响很小,可以忽略。     

Coaxial Discharge and Transverse Magnetic Field

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (T_e). The experimental results and the calculations showed that T_e is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.     

Quenching of the nonlocal electron heat transport by large external magnetic fields in a laser-produced plasma measured with imaging thomson scattering

We present a direct measurement of the quenching of nonlocal heat transport in a laser-produced plasma by applying large external magnetic fields (>10 T). The temporally resolved Thomson-scattering measurements of the electron temperature profile show that the heat front propagation transverse to a high-power laser beam is slowed resulting in extremely strong local heating. We find agreement with hydrodynamic modeling when including a magnetic field model that self-consistently evolves the fields in the plasma.     

Ionization formation of plasma inhomogeneity by the near-zone field of a magnetic-type source in a magnetized plasma

An investigations is made of the steady-state structure of a plasma inhomogeneity arising as a result of high-frequency heating and additional ionization of a background magnetized plasma by the near-zone field of a magnetic-type source (ring electric current). It is assumed that the source axis is parallel to an external magnetic field; the source frequency belongs in the low hybrid band. The main attention is focused on the particular case (important for possible applications) when the characteristic longitudinal and transverse scales of density distribution considerably exceed the corresponding scales of distribution of the electron temperature and of the source field. Simplified equations for the near-zone field of the source, the electron temperature, and the plasma density are written for this particular case. Based on the numerical solution of these equations, steady-state distributions of plasma parameters in the formed plasma inhomogeneity are found. It is demonstrated that a plasma inhomogeneity proves to be markedly extended along the external magnetic field. It is found that, for the values of the source current that are attainable under the conditions of active ionospheric and model laboratory experiments, the maximum plasma density in a nonuniform plasma may appreciably exceed the background value.     

纳秒激光烧蚀固体靶产生的等离子体在外加横向磁场中膨胀时的温度和密度参数演化

利用等离子体光学波段自发光成像、光学光谱和光学探针干涉等诊断手段, 观察了纳秒脉冲激光烧蚀固体靶产生的等离子体在外加横向磁场中的膨胀过程. 根据实验参数特征建立了简化的磁流体物理模型, 结合自发光强度的时间演化, 理论计算了等离子体温度和密度参数的时间演化, 理论计算结果与实验测量结果基本符合, 证实了碰撞磁扩散过程在等离子体演化中发挥了关键作用.     

Electronic transport of Lorentz plasma with collision and magnetic field effects

The electronic transverse transport of Lorentz plasma with collision and magnetic field effects is studied by solving the Boltzmann equation for different electron density distributions. For the Maxwellian distribution, it is shown that transport coefficients decrease as ? increases, ? is the ratio of an electron's magneto-cyclotron frequency to plasma collision frequency. It means that the electrons are possible to be highly collimated by a strong magnetic field. For the quasimonoenergetic distribution with different widths, it is found that the transport coefficients decrease greatly as εˉ decreases.In particular when the width approaches to zero the transverse transport coefficients are hardly affected by the magnetic field and the minimal one is obtained. Results imply that the strong magnetic field and quasi-monoenergetic distribution are both beneficial to reduce the electronic transverse transport. This study is also helpful to understand the relevant problems of plasma transport in the background of the inertial confinement fusion.     

Occurrence of a gap in the spectrum of magnetoplasma excitations of a two-dimensional electron disk subjected to a strong in-plane magnetic field

The effect of a parallel magnetic field on the dispersion of bulk and edge magnetoplasmons in a disk-shaped two-dimensional electron system is investigated. It is found that the anisotropy of the electron effective mass that appears in a parallel magnetic field lifts the degeneracy of plasma oscillations in the disk. This is accompanied by the occurrence of a gap in the spectrum of magnetoplasmons, and the magnetic dispersion of these excitations changes from a linear to a parabolic one. The width of the gap is determined by the difference between the frequencies of plasma oscillations along the field and transverse to the field and grows quadratically with the in-plane field strength.     

Quasistatic magnetic fields generated by a nonrelativistic intense laser pulse in uniform underdense plasma

Quasistatic magnetic fields generated by nonrelativistic intense linearly polarized (LP) and circularly polarized (CP) laser pulses in an initially uniform underdense plasma in the collision-dominated limit are investigated analytically. Using a selfconsistent analytical model, we perform a detailed derivation of quasistatic magnetic fields in the laser pulse envelope in the collision-dominated limit to obtain exact analytical expressions for magnetic fields and discuss the dependence of magnetic fields on laser and plasma parameters. Equations for quasistatic magnetic fields including both axial component B_z and the azimuthal one B_θ are derived simultaneously from such a selfconsistent model. The dependence of quasistatic magnetic field on incident laser intensity, transverse focused radius of laser pulse, electron density and electron temperature is discussed.     

Magnetic control of particle injection in plasma based accelerators

The use of an external transverse magnetic field to trigger and to control electron self-injection in laser- and particle-beam driven wakefield accelerators is examined analytically and through full-scale particle-in-cell simulations. A magnetic field can relax the injection threshold and can be used to control main output beam features such as charge, energy, and transverse dynamics in the ion channel associated with the plasma blowout. It is shown that this mechanism could be studied using state-of-the-art magnetic fields in next generation plasma accelerator experiments.     

HIRFL-CSR实验环电子冷却装置磁场测量

 在HIRFL-CSR实验环电子冷却装置上采用了独立的高精度螺线管串联产生纵向磁场的设计,获得很高的冷却段磁场平行度。使用霍尔片测量磁场的分布,使用磁针测磁方法测量冷却段磁场的磁轴偏角,并根据测量及计算结果对单个线圈磁轴进行微调。测量及调试结果表明,在施加电流为额定电流的一半时,冷却段磁感应强度为0.078 T,剩余磁场小于2×10^-4 T,磁场不平行度小于1×10^-4,达到了预期的设计目标。     

螺线管磁场缺陷对电子束横向温度的影响

分析了直螺线管磁场缺陷的来源,考虑了电子束的空间电荷作用,采用数值方法模拟计算了磁场缺陷对电子束横向温度的影响 ,获得了电子冷却装置中直螺线管磁场的均匀性要求.结果表明,当相对磁场缺陷小于1× 1 0-3时 ,影响可以被忽略.In order to obtain the tolerance requirement for the magnetic field homogeneity of the solenoids in electron cooling device, the source of the magnetic imperfection and its influence on the transverse temperature of electron beam were investigated by means of numerical simulation, and taking the space charge effect of electron beam into account. The calculated result shows that the influence of the imperfection of magnetic field will be negligible when the relative magnetic field...