Effect of the anode-current magnetic field on the motion of electrons in a triode with a virtual cathode

The effect of the anode-current magnetic field on the electron motion in a triode with a virtual cathode is considered. It is shown that the anode-current magnetic field influences the oscillation period and trajectories of electrons. The condition of self-isolation of the electron beam is investigated as a function of the diode parameter. It is shown that the displacement of the beam electrons under the action of the anode-current magnetic field leads to a decrease in the electron phase modulation and an increase in the spread in the electron oscillation amplitude; as a result, the generation efficiency of microwave radiation decreases.     

A confident source of hard X‐rays: radiation from a tokamak applicable for runaway electrons diagnosis

In a tokamak with a toroidal electric field, electrons that exceed the critical velocity are freely accelerated and can reach very high energies. These so‐called `runaway electrons' can cause severe damage to the vacuum vessel and are a dangerous source of hard X‐rays. Here the effect of toroidal electric and magnetic field changes on the characteristics of runaway electrons is reported. A possible technique for runaways diagnosis is the detection of hard X‐ray radiation; for this purpose, a scintillator (NaI) was used. Because of the high loop voltage at the beginning of a plasma, this investigation was carried out on toroidal electric field changes in the first 5 ms interval from the beginning of the plasma. In addition, the toroidal magnetic field was monitored for the whole discharge time. The results indicate that with increasing toroidal electric field the mean energy of runaway electrons rises, and also an increase in the toroidal magnetic field can result in a decrease in intensity of magnetohydrodynamic oscillations which means that for both conditions more of these high‐energy electrons will be generated.     

Ion acceleration by the space charge electric force arising from the radiation pressure in a magnetized electron–positron plasma

It is shown that ions can be accelerated by the space charge electric force arising from the separation of electrons and positrons due to the ponderomotive force of the magnetic field-aligned circularly polarized electromagnetic (CPEM) wave in a magnetized electron–positron–ion plasma. The ion acceleration critically depends on the external magnetic field strength. The result is useful in understanding differential ion acceleration in magnetized electron–positron–ion plasmas, such as those in magnetars and in some laboratory experiments that aim to mimic astrophysical environments.     

电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究. 结果表明: 垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大, 逐渐从一维近周期运动演变为二维折叠运动, 并产生强的微米量级波长的太赫兹辐射; 高能电子垂直或者平行于激光电场方向入射到激光驻波场中, 都会产生波长在几个纳米的高频辐射; 低能电子与激光驻波场作用中, 激光强度影响着电子的运动形式、辐射频率以及辐射强度; 高能电子入射时, 激光强度影响了电子高频辐射的强度, 电子初始能量影响着辐射的频率; 电子能量越高, 产生的辐射频率越大. 研究表明可以由激光加速电子的方式得到不同能量的电子束, 并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源. 研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.     

Acceleration of electrons in an underdense plasma containing fluctuations of magnetic field on a background of a large scale dc-magnetic field

It is shown that scattering of electrons off magnetic field fluctuations can result in acceleration of these electrons along the lines-of-force of a large scale background dc-magnetic field. The mechanism proposed is applied to the underdense corona of a large scale produced plasma.     

Acceleration of electrons by a Bessel-Gaussian beam in vacuum

The acceleration of electrons by using a Bessel-Gaussian (BG) beam in vacuum is studied. It is shown that the axial electric field of a linearly or circularly polarized BG beam of order n = 1 can be used to accelerate electrons. The general features of the acceleration of electrons by using a linearly or circularly polarized BG beam, such as the transversal and axial electric-field components, phase velocity, slippage distance, accelerating potential, and energy gain etc., are analyzed.     

用拉盖尔-高斯激光对真空中电子直接加速

对用拉盖尔-高斯(LG)光束加速电子作了研究.结果表明，仅模指数为p和l=1的LG光束的纵向电场可用于加速电子.模指数为p和l=1的线偏振和圆偏振LG光束都对电子有加速效果.对轴上光场的相速度和群速度以及电子能量增益等物理特征作了讨论.给出了轴上光场的相速度和群速度、加速电位及电子能量增益等的解析表达式，并作了数值计算和分析. 关键词： 激光电子加速 拉盖尔-高斯光束 线偏振和圆偏振 能量增益     

Collective modes and the far-infrared absorption of the two-dimensional electron gas in a periodic quantizing magnetic field

We investigate the far-infrared (FIR) absorption of a two-dimensional electron gas in a periodically modulated quantizing magnetic field. The magnetic field varies along only one spatial direction and the external time-dependent electric field is linearly polarized along that axis. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. The effects of the magnetic material on top of the heterostructure as a grating coupler is included in the time-dependent incident FIR electric field. We show that, similar to an electric modulation, the absorption can be directly correlated to the underlying electronic energy bands. In addition, the magnetic modulation leads to absorption spectra with a richer structure due to the quite different static response of the electron density to the modulation.     

场向传播的内磁层哨声波对辐射带高能电子的共振扩散

基于高斯分布的哨声波谱密度分布、偶极子背景磁场模型以及建立在卫星观测数据基础上的半经验电子密度纬度分布模型,对于等离子体层顶以外区域(4≤L≤7),计算了准线性当地及弹跳平均电子共振扩散系数,并估算了与磁层哨声波回旋共振导致的辐射带电子损失及加速时间尺度.结果表明,波粒共振相互作用区域取决于电子能量、波谱分布、电子赤道抛射角以及当地电子密度及背景磁场.哨声波共振频率除了与以上5个参量有关外,还与地磁纬度有关.赤道哨声波主要影响较低能量辐射带电子的加速,中高纬度哨声波主要作用于较高能量辐射带电 关键词： 共振波粒相互作用 地球辐射带 哨声波 回旋共振加速及散射沉降     

外加静电场的聚焦激光脉冲真空加速电子方案

采用五阶修正的聚焦激光光场方程模拟研究了由Singh提出的在电子和激光脉冲作用尾部阶段施加外场的加速方案,将Singh方案中采用的外加磁场改成了外加电场,并且考虑了光束的纵向电场和光束衍射效应.模拟结果显示,电子可以从加速相位阶段被外场导入下一个加速相位阶段而不进入减速相位阶段,因此电子能获得比不加外场方案更高的净能增益. 关键词： 强激光 激光加速     

Particle acceleration in relativistic current sheets

Relativistic current sheets have been proposed as the sites of dissipation in pulsar winds, jets in active galaxies, and other Poynting flux dominated flows. It is shown that the steady versions of these structures differ from their nonrelativistic counterparts because they do not permit transformation to a de Hofmann-Teller frame with zero electric field. Instead, their generic form is that of a true neutral sheet with no linking magnetic field component normal to the sheet. The maximum energy to which such structures can accelerate particles is derived, and used to compute the maximum frequency of the subsequent synchrotron radiation. This can be substantially in excess of standard estimates. In the magnetically driven gamma-ray burst scenario, acceleration of electrons is possible to energies sufficient to enable photon-photon pair production after an inverse Compton scattering event.     

Electric-and magnetic-field strengths in the Fresnel zone of a microradiator formed by an electric and a magnetic dipole

The propagation of electric and magnetic fields and of the Poynting vector in the near zone (Fresnel zone) of an electric dipole, a loop, and a dipole-loop pair is considered. The dimensions of all radiators are much smaller than the radiation wavelength. It is shown that the ideas of the field distribution (polar diagram) in the far zone cannot be applied to the properties of the field in the Fresnel zone. The radiated-power fraction that is absorbed by an object whose electrodynamic properties are close to those of biological media is found at a distance from the radiator to the absorbing object on the order of several millimeters.     

On the possibility of forming electric-field-controlled fluxes of cold neutrons in crystals

It has been shown previously that the giant electron energy loss in cold cathodes is due to the localization of electrons in polaron states and their emission of a coherent flux of phonons (which is similar to the Cherenkov radiation) during motion in strong electric fields. The scattering of cold neutrons from a coherent-phonon flux is investigated.     

Mechanism for the streamer propagation toward the anode and cathode due to background electron multiplication

A simple mechanism for the propagation of an ionization wave in a dense gas due to the multiplication of background electrons in a nonuniform electric field is proposed. The mechanism does not depend on the sign of the field projection onto the streamer propagation direction. The streamer propagation is caused by the enhancement of the electric field at the streamer head. It is shown that, in a prebreakdown field, the intense multiplication of electrons takes place in both electropositive and electronegative gases. The prebreakdown multiplication can provide a fairly high density of background electrons; this allows one to treat the background as a continuous medium when considering streamer propagation as a multiplication wave. The initial ionization is enabled by the natural background of ionizing radiation and cosmic rays. An analytical expression for the velocity of the ionization front is obtained based on a simple equation for the multiplication of background electrons. This expression is in good agreement with numerical simulations performed within both a simple model of background electron multiplication and a more comprehensive drift-diffusion model. In particular, the drift-diffusion model predicts the propagation of the ionization front from a small-radius anode to the cathode due to the multiplication of background electrons. The velocity of the ionization wave front is calculated as a function of the electric field at the streamer head for helium, xenon, nitrogen, and sulfur hexafluoride. It is shown that some features of streamer propagation (e.g., its jerky motion) can be related to the recently found nonmonotonic dependence of ionization frequency on the electric field.     

Electron acceleration by two crossed Bessel--Gaussian beams in vacuum

The direct acceleration of electrons by using two linearly polarized crossed Bessel--Gaussian (BG) beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order (0 or 1) with a \textit{\pi }-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.     

Magnetic reconnection and acceleration of particles on the sun

The present-day state of the problem regarding the acceleration of high-energy particles in solar flares is reviewed briefly. It is shown that an analytical solution to the equation of charged-particle motion in a reconnecting current layer with a 3D magnetic field and the electric field caused by magnetic reconnection allows us to offer an explanation for the acceleration of electrons and protons to relativistic energies over very short time intervals. The theoretical results are compared to recent observations of accelerated particles in solar flares.     

Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum

We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.     

Enhanced effectivity of autoresonant acceleration of electrons by Gaussian laser radiation

The autoresonant mechanism of acceleration of relativistic electrons by combined Gaussian laser radiation, which consists of radiation of the lowest and first modes, is considered. It is shown that acceleration by combined radiation is more effective than acceleration by Gaussian beams of the lowest or the first mode.     

Spatial Distribution of Energetic Electrons during Magnetic Reconnection

Electron acceleration by the inductive electric field near the X point in magnetic reconnection is an important generation mechanism for energetic electrons. Particle simulations have revealed that most of energetic electrons reside in the magnetic field line pileup region, and a depletion of energetic electrons can be found near the centre of the diffusion region [Phys. Plasmas, 13 (2006) 012309]. We report direct measurement of energetic electron in and around the ion diffusion region in near-Earth tail by the cluster, and our observations confirm the above predictions: a depletion of the high-energy electron fluxes is detected near the centre of the diffusion region. At the same time, the plasma temperature has a similar profile in the diffusion region. .     

X-ray radiation from the volume discharge in atmospheric-pressure air

X-ray radiation from the volume discharge in atmospheric-pressure air is studied under the conditions when the voltage pulse rise time varies from 0.5 to 100 ns and the open-circuit voltage amplitude of the generator varies from 20 to 750 kV. It is shown that a volume discharge from a needle-like cathode forms at a relatively wide voltage pulse (to ≈60 ns in this work). The volume character of the discharge is due to preionization by fast electrons, which arise when the electric field concentrates at the cathode and in the discharge gap. As the voltage pulse rise time grows, X-ray radiation comes largely from the discharge gap in accordance with previous experiments. Propagation of fast avalanche electrons in nitrogen subjected to a nonuniform unsteady electric field is simulated. It is demonstrated that the amount of hard X-ray photons grows not only with increasing voltage amplitude but also with shortening pulse rise time.