Electron energy gain in the transverse electric mode of a coaxial waveguide filled with plasma by microwave radiation

The dynamics and acceleration of an electron in the field of a transverse electric wave propagating inside a cold plasma-filled waveguide by microwave radiation is analytically investigated by considering the existence of a coaxial metallic rod. The relativistic momentum and energy equations are solved for the electron when it is injected along the direction of mode propagation. The deflection angle and the acceleration gradient of the electron in the configuration are obtained. Besides, the results are graphically presented.     

Electron acceleration considering pondermotive force effect in a plasma-filled rectangular waveguide by microwave radiation

The electron acceleration inside the plasma-filled rectangular waveguide is numerically investigated for the externally injected single-electron model considering the effects of density modification under a balance between the ponderomotive force and the pressure gradient force. Using Maxwell’s equations, we evaluate the field components of the fundamental mode in the plasma-filled rectangular waveguide, where the obtained equations are solved numerically using the fourth-order Runge–Kutta method for the electric field amplitude of the microwave. Besides, by solving the relativistic momentum and energy equations using the fourth-order Runge–Kutta method, the deflection angle and the total energy of the electron in the waveguide are obtained. Furthermore, it is shown that the electron energy gain can be controlled using superposing microwave fundamental modes. Effects of various parameters on the results are graphically presented.     

Infrared wave interaction with an electron in the rectangular and circular plasma waveguide

In this article, the effect of the electron collision frequency with background ions on TM mode field components, the trajectory, and the electron energy gain in interaction infrared radiation with collisional plasma is studied. The field components of the TM mode in the rectangular and circular collisional plasma waveguides are obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a plasma waveguide for TM mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the infrared. The results for collisionless and collisional plasma are graphically represented. Finally, the results for rectangular and circular waveguides are compared.     

Application of obliquely interfering TE10 modes for electron energy gain

Two fundamental TE₁₀ modes are considered to interfere at a small angle θ and then propagate along the z-axis in an evacuated rectangular waveguide. The electron trajectory in the resultant field and the expressions for energy gain and the acceleration gradient are obtained, when the electron is injected along the z-axis. A 50 keV electron gains 718 keV energy in a 4.0 cm × 2.5 cm waveguide, when the microwave with intensity of 1 × 10¹⁰ W/cm² and frequency 5.577 GHz is used and the modes superpose at an angle of 10°; here the maximum acceleration gradient is obtained as 251 MeV/m. The energy gain and acceleration gradient are decreased with increasing width of the waveguide and microwave frequency. Higher gradient and larger energy gain are obtained for the higher microwave intensity, smaller angle of superposition and also when the electron is injected with larger initial energy.     

Mechanism of electron violent acceleration by extra-intense lasers in vacuum

The mechanism underlying the electron capture acceleration (Phys. Rev. E 58 (1998) 6575) is studied. It is found that the longitudinal electric field, resulting from the transverse spatial gradient of the laser fields, is responsible for the violent electron acceleration while the transverse fields play the role of confining the electron inside the laser beam.     

Scattering from an elliptical cylindrical plasma for electromagnetic waves with wavelength much greater than the dimensions of the plasma cross-section

The distribution of the electric potential inside and outside a cold plasma column with elliptical cross-section when electromagnetic waves scatter from it are obtained. It is assumed that the wavelength of incident wave is much greater than the dimensions of the cross section of the plasma column. The electrical potential inside and outside a magnetized elliptical plasma column for an anisotropic scattering process are obtained. The graphs of the ratio of the electric field inside the plasma and the incident electric field versus the incident angle, the geometrical dimension of the elliptical plasma column and cyclotron frequency are presented separately. Finally, scattering of the same waves from an elliptical cylindrical inhomogeneous isotropic cold plasma is also investigated.     

Interaction of a supersonic beam of toluene with a resonant RF electric field

Deflection of a cold supersonic toluene beam seeded in He has been observed when these molecules interact with both a static and a resonant oscillating electric field. The toluene beam splits into two beams each one peaking at a deflection angle of 1 degree towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the toluene molecule is 1411 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the toluene dipole moment and the employed RF field gradient. Different hypothesis are suggested to explain the observed strong beam splitting including the possibility of transverse beam interferences induced by both the resonant RF field and the transverse uniform electric field. A theoretical model is presented based on molecular beam interferences induced by the resonant RF field which seems to account satisfactorily for the present observations.     

Energy-gain measurements from a microwave inverse free-electron-laser accelerator

Experiments are reported on inverse free-electron-laser acceleration, including for the first time observations of the energy change as a function of relative injection phase of the electron bunches. The microwave accelerating structure consists of a uniform circular waveguide with a helical wiggler and an axial magnetic field. Acceleration of the entire beam by 6% is seen for 6 MeV electron bunches at optimum relative phase. Experimental results compare favorably, for accelerating phases, with predictions of a three-dimensional simulation that includes large-orbit effects.     

多光子非线性Compton散射对等离子体中电子运动的影响

应用多光子非线性Compton散射模型,研究了多光子非线性Compton散射对激光等离子体中电子运动的影响,提出了将入射激光和Compton散射光形成的耦合光、耦合光与等离子体产生的自生磁场形成的混合场作为加速电子的新机制,对电子动量和能量方程进行了修正和数值模拟。结果表明,当混合场的电场振幅与磁场振幅相等时,回旋共振电子在与混合场作用时间内能被加速到很高的能量;电子加速能量随耦合光幅值的增大而增大,随电子耦合初始角度的增大而周期变小,随电子横向耦合归一化初始速度的增大,开始时较快增加,之后缓慢增加,最后趋于稳定。     

Impact of nonlinear absorption on propagation of microwave in a plasma filled rectangular waveguide

In collisional and ponderomotive predominant regimes, the propagation of microwave in rectangular waveguide filled with collisional plasma is investigated numerically. The dominant mode is excited through an evacuated waveguide and then enters a similar and co-axis waveguide filled with plasma. In collisional predominant regime, the amplitude of electric field is oscillated along propagation path; outset of propagation path due to the electron-ion collision, the intensity oscillations are reduced. Afterward, under competition between the collisional nonlinearity and absorption, the intensity is increased, so the electron density peak is created in middle of waveguide. In ponderomotive predominant regime, the intensity is slowly decreased due to collision, so the electron density is ramped. Control parameters, like the frequency, input power, collision frequency, and background electron density are surveyed that can be used to control propagation characteristics of microwave. This method can be used to control heating of fusion plasma and accelerate charged particle.     

强激光与柱腔靶作用下准直高能电子束的产生

利用二维PIC粒子模拟程序研究了超短超强激光脉冲与柱腔靶相互作用产生的表面超热电子加速现象。采用光强为1021 W/cm2量级的超高斯激光脉冲掠入射进入柱腔靶,在靶的内壁上观察到了GeV量级的表面超热电子。超热电子束被准静态的电场和磁场约束在内壁表面附近,保证了电子束的准直性,发散角仅为1.6°;并且由于超热电子束在纵向激光电场中加速了mm级的距离,激光到高能电子(100 MeV)的转换效率达到了26.6%。另外,通过多参数模拟和理论解析讨论了激光的光强以及横向空间分布对这种表面超热电子加速的影响。     

x强流相对论环形电子束在低磁场中传输分析

 用理论和粒子模拟相结合的方法分析了强流薄环形相对论电子束在低磁场导引下，在均匀波导，无箔二极管，以及锥形波导和渐减磁场位形条件下的传输过程，研究了束包络的波动和如何减少波动的问题。分析表明：在无箔二极管中一个适当渐增的磁场位形可以有效地抑制束电子的径向运动，从而减少电子在波导中的波动幅度；电子束在锥形波导和渐减磁场位形中运动，不会增加束电子的波动。因此适当的磁场位形可以降低微波器件对导引磁场的要求，有利于实现永磁包装微波器件。     

圆波导硅探测结构对X波段电磁波模式的响应

采用数值模拟和理论分析方法,研究了圆波导内置n-Si探测结构对X波段几种常用电磁波模式的电场响应。首先基于强电场下的热载流子效应,设计了一种利用n-Si进行高功率脉冲实时测量的圆波导探测结构。接着采用三维并行电磁场时域有限差分方法,模拟研究并分析了TE11(两种极化方向)、TM01和TE01模式作用下圆波导探测结构内的横向电场分布特点。结果表明:不同模式下探测芯片内的横向电场均以径向电场为主,径向和角向电场幅度比约为10,而芯片在圆波导内引入的横向电场驻波比均不大于1.3。最后推导了圆波导探测结构在不同模式电场作用下的灵敏度表达式,理论分析指出了探测结构的最大承受功率与圆波导模式有关,最高可达422MW,响应时间则均为ps量级,初步证实了该探测结构可用于X波段百MW级脉冲波源在线探测的可行性。     

介质窗横向电磁场分布下的次级电子倍增效应

本文利用自编P3D3V PIC程序, 数值研究了BJ32矩波导传输TE₁₀模式高功率微波在介质窗内、 外表面引发的次级电子倍增过程, 给出了次级电子3维空间位置分布特征、介质窗表面法向静电场分布规律以及电子数密度分布特性. 模拟结果表明: 对于介质窗内侧, 微波强场区域率先进入次级电子倍增过程; 而对于介质窗外侧, 则是微波弱场区域优先进入次级电子倍增过程. 形成机理可以解释为: 微波坡印廷矢量方向与介质窗外表面法向相同而与内表面法向相反, 内侧漂移运动导致强场区域电子易于被推回表面, 有利于次级电子倍增优先形成; 外侧漂移运动导致强场区域电子易于被推离表面, 不利于次级电子倍增形成. 准3维模型相对1维模型: 介质窗内侧次级电子倍增过程中, 次级电子倍增进入饱和时间长、饱和次级电子数目少、平均电子能量高、 入射微波功率低、沉积功率低; 介质窗外侧次级电子倍增过程中, 次级电子倍增进入饱和时间短、饱和次级电子数目少、平均电子能量低、 入射微波功率低、沉积功率低. 沉积功率与入射微波功率比值与微波模式、强度及介质窗内外侧表面关系不大, 准3维和1维模型计算结果均在1%–2%左右水平. 关键词： 高功率微波 介质表面次级电子倍增 粒子模拟 横向电磁场分布     

Mode-selective amplification in a waveguide free electron laserwith a two-sectioned wiggler

One important issue in waveguide free electron lasers (FELs) involves an interaction of the electron beam with one waveguide mode at two different resonant frequencies. Since the low-frequency mode often has a higher pain, the usually preferred high-frequency mode is suppressed as a result of mode competition. In this paper, possible control of this mode competition is considered using a nonstandard wiggler magnet consisting of two cascaded wiggler sections with different periods and field strengths. It is demonstrated that with an appropriate differentiation between the two wiggler sections the high-frequency mode may be amplified preferentially. This mode-selective amplification may be used to suppress the low-frequency mode. A small signal gain formulation is developed for a waveguide FEL with such a two-sectioned wiggler arrangement and numerical examples are used to demonstrate its applicability to mode control in waveguide FELs. Effects of wiggler field errors and electron energy spread are also considered. It is shown that the requirement for wiggler field errors and electron energy spread in the two-sectioned wiggler arrangement is similar to that in the usual straight wiggler configuration     

电子束空间极限电流的非线性理论研究

从电子束一维稳态传输的电势非线性Poisson方程出发,推导了圆柱波导内实心束和环形束空间极限电流与电子入射电势的依赖关系,给出了数值求解方法和解的特征,分析比较了数值计算与现有解析公式及粒子模拟的结果.考虑电子的横向运动,对数值方法进行了二维修正,计算结果与粒子模拟结果具有很好的一致性.说明利用数值方法计算电子电势非线性微分方程能够得到更精确的电子束在圆柱波导内的空间极限电流;另外,对其他形状的波导,尤其是难以得到解析式的情况,根据实际几何结构设置边界条件,数值方法可以方便地给出束流传输特性,对设计新型结构的高功率微波器件提供理论指导. 关键词： 相对论电子束 圆柱波导 空间极限电流 束流传输     

扇形波导谐振宽边纵缝的归一化电导

扇形波导可作为高功率微波圆柱共形波导缝隙阵天线的基本单元。分析了扇形波导中主模场分量,根据实际情况对主模场进行了合理近似。采用互易定理推导由波导主模横向场分量和缝隙场分量表示的波导场分量的前向或后向散射系数。根据波导传输线理论,将波导宽边纵缝等效为并联导纳,再根据波导边界条件得到扇形波导宽边谐振纵缝的归一化电导与波导散射系数之间的关系式。根据缝隙天线与振子天线的互补关系得到扇形波导谐振缝隙的辐射阻抗,结合波导功率平衡关系得到由波导横向场散射系数表示的缝隙辐射功率表达式,得到归一化电导的与谐振宽边纵缝的偏移位置、缝隙宽度、波导波长以及扇形波导尺寸参数之间的解析表达式。给出了算例,在波导中间区域,通过商用软件计算得到的电导与理论公式结果基本吻合。     

Synchrotron Radiation in a Circular Metallic Waveguide

We study theoretically the influence of a circular metallic waveguide with a longitudinal magnetic field on the synchrotron radiation of a point electric charge moving along a helical trajectory coaxial with the waveguide axis. The main attention is focused on the analysis of the energy characteristics of radiation of electromagnetic E and H waves. We derive the formulas for the radiation powers of E and H waves. It is shown that, under certain conditions, slowly moving electric charges do not radiate any of these electromagnetic waves in the circular waveguide.     

新型反馈式轴向同轴虚阴极振荡器

提出一种利用低磁场导引环形电子束在同轴波导内轴向激励虚阴极振荡的新型虚阴极振荡器.利用反馈式结构,使虚阴极在由反馈环、阳极箔和同轴波导构成的高品质因子准谐振腔内形成.作用腔内环形电子束激励同轴波导TM₀₁模式,在相对低品质因子的同轴提取区转化为TEM主模输出.用25维KARAT粒子模拟软件研究得到束波功率转换效率12%,输出微波平均27 GW,中心频率38 GHz. 关键词： 环形电子束 轴向导引磁场 同轴波导 反馈环