The effect of trapped electrons on large amplitude ion-acousticwaves in a plasma with an electron beam

The nonlinear wave structures of large amplitude ion-acoustic waves are investigated in an electron beam-plasma system with trapped electrons, by the pseudopotential method. The speed of the ion-acoustic wave increases as the effect of trapped electrons decreases and the beam temperature increases. The region of the existence of ion-acoustic waves is examined, showing that the condition of the existence sensitively depends on the parameters such as the effects of the electron beam density and temperature, electrostatic potential, and the effect of trapped electrons. It turns out that the region of existence spreads as the effect of trapped electrons decreases and beam temperature increases. New findings of large amplitude ion-acoustic waves in an electron beam-plasma system with trapped electrons are predicted     

Observation of trapped and passing runaway electrons by infrared camera in the EAST tokamak

In EAST, synchrotron radiation is emitted by runaway electrons in the infrared band, which can be observed by infrared cameras. This synchrotron radiation is mainly emitted by passing runaway electrons with tens of Me V energy. A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side. However,the deeply trapped runaway electrons cannot reach the high field side in principle. Therefore, in this case, the high field side radiation is expected to be weak. This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image. Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment, the proportion of trapped runaway electrons is very low.     

Photoabsorption by the electron subsystem of a semiconductor nanoparticle

The IR photoabsorption cross section of a semiconductor nanoparticle has been calculated. Light is absorbed by conduction electrons and trapped electrons in the volume and surface of the nanoparticle. Electron concentrations have been obtained by minimizing the total free energy of charges in the system. The photoabsorption cross section has two characteristic maxima corresponding to the absorption by conduction electrons and by trapped electrons in the nanoparticle volume. The number of trapped electrons on the surface is relatively small, so that they do not contribute to the total cross section.     

捕获电子效应对电流驱动影响的数值研究

在考虑到捕获电子效应的情况下,对求解二维Fokker-Planck方程的编程进行了反弹平均的修改,使用了交替方向隐式法来求解方程。分析和计算了在不同扩散系数和不同共振区间的情况下,捕获电子效应对驱动电流的影响。结果显示：随着逆纵横比的增加驱动电流密度有明显的下降,在磁轴附近捕获电子效应对电流驱动影响很小;提高波功率并不能很好的改善捕获电子效应对电流驱动的影响;右移共振区间提高共振电子的速度,也不能很好的改善捕获电子效应对电流驱动的影响。所得结果与理论分析基本一致。     

�������ЧӦ�Ե�������Ӱ�����ֵ�о�

在考虑到捕获电子效应的情况下,对求解二维Fokker-Planck方程的编程进行了反弹平均的修改,使用了交替方向隐式法来求解方程。分析和计算了在不同扩散系数和不同共振区间的情况下,捕获电子效应对驱动电流的影响。结果显示：随着逆纵横比的增加驱动电流密度有明显的下降,在磁轴附近捕获电子效应对电流驱动影响很小;提高波功率并不能很好的改善捕获电子效应对电流驱动的影响;右移共振区间提高共振电子的速度,也不能很好的改善捕获电子效应对电流驱动的影响。所得结果与理论分析基本一致。     

电子回旋波使磁镜中捕获电子与逃逸电子相互转化

在Littlejohn的带电粒子引导中心拉格朗日体系下,讨论了电子回旋波对磁镜等离子体中捕获电子与逃逸电子的影响,给出了捕获电子变成逃逸电子以及逃逸电子被电子回旋波捕获的条件,并计算了它们的相互转化的概率。 关键词：     

Electron injection in laser wake-field acceleration by using near critical layers

A method for enhancing trapped electrons in the laser wake-field acceleration in dilute plasma is proposed. In this method, a thin layer with near critical density is placed in front of the dilute plasma. Upon interaction of this layer with a short and high power laser pulse, a relatively large number of layer electrons are injected in dilute plasma. Some of these electrons are trapped in the wake-field of transmitted laser pulse. Particle in cell simulation is used to demonstrate this method. Simulations showed that in addition to increasing the number of trapped electrons, this mechanism also reduces the energy broadening.     

Radiation dose from reentrant electrons

In estimating the crew exposures during an extra vehicular activity (EVA), the contribution of reentrant electrons has always been neglected. Although the flux of these electrons is small compared to the flux of trapped electrons, their energy spectrum extends to several GeV compared to about 7 MeV for trapped electrons. This is also true of splash electrons. Using the measured reentrant electron energy spectra, it is shown that the dose contribution of these electrons to the blood forming organs (BFO) is more that 10 times greater than that from the trapped electrons. The calculations also show that the dose-depth response is a very slowly changing function of depth, and thus adding reasonable amounts of additional shielding would not significantly lower the dose to BFO.     

On the possibility of natural formation of a transverse wave with a phase velocity lower than the velocity of light

The formation of a transverse wave with a phase velocity lower than the velocity of light, which can exist in an equilibrium plasma without a slow-wave structure in zero magnetic field, is described. It involves the transformation of a transverse wave with trapped electrons, traveling along the magnetic field, into a slow transverse wave after the removal of the magnetic field. During the evolution of the wave with trapped electrons, the magnetic induction decreases very slowly in the direction of the wave propagation. As a result, the velocity at which electrons are in resonant interaction with the wave increases; therefore, the electrons fall to the bottom of potential wells. Under the influence of the trapped electrons, the phase velocity of the wave decreases and becomes lower than the velocity of light. It becomes equal to the velocity at which the electrons are in resonance interaction with the wave at the instant when the magnetic field vanishes. It is demonstrated that a transverse wave with a velocity lower than the velocity of light can exist in an equilibrium plasma even after the magnetic field vanishes; in this case, the flow of trapped electrons serves as a slow-wave structure.     

Giant electron tails and passing electron pinch effects in tokamak-core turbulence

The anomalous particle transport in a tokamak core is believed to be linked to the advection of magnetically trapped electrons alone, owing to the passing electrons maintaining a thermal equilibrium along the field lines. Surprisingly, in nonlinear numerical studies, the radial flux of passing electrons rivals that of the trapped ones. The strong interaction of passing electrons and electric fluctuations is mediated by long tails of the modes along the magnetic field, which are generated by the passing electrons in the first place.     

Effects of trapped electrons on the line shape in emission Mössbauer spectra

To explain line broadening in emission Mössbauer spectra as compared to the corresponding absorber measurements, the model of trapped electrons has been proposed. Auger electrons (emitted, e.g. after electron capture by ⁵⁷Co or after the converted isomeric transition of ^119mSn), as well as secondary electrons, may be trapped in the proximity to the nucleogenic ion. Electrons captured by lattice traps at different distances from the daughter ion induce an asymmetric distribution of quadrupole splitting in the resulting emission spectra, as shown in a few examples. This model is supported by estimates of quadrupole splitting values which may be caused by such trapped electrons located at specified distances from the nucleogenic atom.     

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa-Maxwellian auroral plasmas

The presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa-Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.     

On the temperature dependence of the phosphorescence of CaF2 : Mn phosphor in different atmospheres

The temperature dependence inthe region of 24–150°C of the phosphorescence of CaF₂ : Mn phosphor in the atmospheres of nitrogen gas, vacuum and moisture-saturated air were studied. A decay formula was found to adequately describe the rate of decay of the trapped electrons — which is assumed to be proportional to the amount of phosphorescence observed — in thermal traps. In nitrogen gas and vacuum the decay constants of the trapped electrons are dependent only on the storage temperature and not on the storage atmosphere of the phosphor. A slight effect of water on the rate of decay of the trapped electrons was also observed.     

Single-stage depressed collectors for gyrotrons

Two 140 GHz gyrotrons with a single-step depressed collector have been operated. The different position of the isolating collector gap in the stray magnetic field causes the electron motion in the retarding region to be in one case adiabatic and in the other case nonadiabatic. The kind of motion within the retarding field influences strongly the behavior of the gyrotron with a depressed collector. In the case of nonadiabatic motion a significant amount of transverse momentum is given to the electrons reflected at the collector potential. This causes the reflected electrons to be trapped between the magnetic mirror and the collector. The electrons escape from the trap by diffusion across the magnetic field to the body of the tube thus contributing to the body current. Despite the high body current there is no observable influence of the collector voltage on the RF output power. In the case of adiabatic motion the reflected electrons do not gain a sufficient amount of transverse momentum to be trapped by the magnetic mirror. They pass the cavity toward the gun and they are trapped between the negative gun potential and the collector. The interaction with the RF field by electrons traveling through the cavity enhances the diffusion in the velocity space thus enabling the trapped electrons to overcome the potential barrier and escape toward the collector. Therefore the body current stays at low values since in this case the reflected electrons do not contribute to it. However, at higher collector voltages a reduction of RF power occurred and some noise in the electron beam was observed     

Modulational instability of relativistic ion-acoustic waves in aplasma with trapped electrons

The association between the modified Korteweg-de Vries solitary wave and the modulationally unstable envelope solitary wave in a weakly relativistic unmagnetized plasma with trapped electrons is discussed. The effect of trapped electrons modifies the nonlinearity of the nonlinear Schrodinger equation and gives rise to the propagation of the modulationally unstable ion-acoustic solitary wave. The amplitude of the envelope solitary wave increases while the number of trapped electrons decreases. The velocity of the solitary wave decreases with increasing ionic temperature and increasing particle velocities. The ion oscillation mode, which satisfies the nonlinear dispersion relation, is also derived. The theory is applied to explain space observations of the solar energetic flows in interplanetary space and of the energetic particle events in the Earth's magnetosphere     

Scattering of magnetic mirror trapped fast electrons by a shear Alfvén wave

Laboratory observations of enhanced loss of fast electrons trapped in a magnetic mirror geometry irradiated by shear Alfvén waves (SAW) are reported. A population of runaway electrons generated by second harmonic electron-cyclotron-resonance heating, as evidenced by the production of hard x rays with energy up to 3?MeV, is subjected to SAW launched with a rotating magnetic field antenna. It is observed that the SAW dramatically affect the trapped fast electrons and scatter them out of the magnetic mirror despite any obvious resonance. The results could have implications on the techniques of artificial reduction of energetic electrons in the inner radiation belt.     

Entanglement dephasing of spatially separated multiparticle GHZ states coupled to a squeezed environment

In tokamak plasmas, it is recognized that ITG (ion temperature gradient instability) and trapped electron modes (TEM) are held responsible for turbulence giving rise to anomalous transport. The present work focuses on the building of a model including trapped kinetic ions and trapped kinetic electrons. For this purpose, the dimensionality is reduced by averaging the motion over the cyclotron motion and the “banana” orbits, according to the fact that the instabilities are characterized by frequencies of the order of the low trapped particle precession frequency. Moreover, a set of action-angle variables is used. The final model is 4D (two-dimensional phase space parametrized by the two first adiabatic invariants namely the particle energy and the trapping parameter). In this paper, the trapped ion and electron modes (TIM and TEM) are studied by using a linear analysis of the model. This work is currently performed in order to include trapped electrons in an existing semi lagrangian code for which TIM modes are already taken into account. This study can be considered as a first step in order to include kinetic trapped electrons in the 5D gyrokinetic code GYSELA [J. Abiteboul et al., ESAIM Proc. 32, 103 (2011)].     

Effects of trapped electrons on off-axis lower hybrid current drive in tokamaks

The effects of trapped electrons on off-axis lower hybrid current drive （LHCD） in tokamaks are studied, A computer code for solving the Fokker-Planck equation in a toroidal geometry is developed and employed. The code is suitable for various auxiliary heating and current drive schemes in tokamak plasmas. The influence of the resonance regime on the current drive efficiency as well as the influence of trapped particle fraction on the current drive efficiency are emphasized. It is shown that, as an electrostatic force, the lower hybrid wave causes some of the trapped electrons to be untrapped and lose their energy, which can cut the LHCD efficiency by about 30%. The ITER scaling law is also used to estimate the trapped electron effects.[第一段]     

Influence of Non-Maxwellian Particles on Dust Acoustic Waves in a Dusty Magnetized Plasma

In this paper an investigation into dust acoustic solitary waves(DASWs) in the presence of superthermal electrons and ions in a magnetized plasma with cold dust grains and trapped electrons is discussed. The dynamic of both electrons and ions is simulated by the generalized Lorentzian(κ) distribution function(DF). The dust grains are cold and their dynamics are studied by hydrodynamic equations. The basic set of fluid equations is reduced to modified Korteweg-de Vries(mKdV) equation using Reductive Perturbation Theory(RPT). Two types of solitary waves, fast and slow dust acoustic soliton(DAS) exist in this plasma. Calculations reveal that compressive solitary structures are possibly propagated in the plasma where dust grains are negatively(or positively) charged. The properties of DASs are also investigated numerically.     

A self-consistent Maltsev pulse model

A self-consistent model for an electron pulse propagating through a plasma is presented. In this model, the charge imbalance between plasma ions, plasma electrons and pulse electrons creates the travelling potential well in which the pulse electrons are trapped.