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In this paper, we investigate the long time existence of the classical solution to 2D one-fluid Euler-Poisson system of electrons with non-zero vorticity in the standard Sobolev spaces so that both the local solution and long time solution lie in the same Sobolev space framework without any extra restrictions of space-decay rates at infinity. It is shown that the lifespan of the classical solution is at least T ε , δ = min ⁡ { e ε − 2 | l n ε | − α , κ δ } , where ε > 0 is the size of the initial perturbed density and velocity, δ > 0 is the size of the initial vorticity, α > 0 is any fixed number, κ > 0 is a suitable constant. We decompose the Euler-Poisson system into three bilinear interaction parts: dispersion–dispersion, vorticity–dispersion, and vorticity–vorticity. Based on the Strichartz inequality, the related quartic energy estimates, the conservation of specific vorticity along the streamline and some delicate analysis, the precise bound of lifespan T ε , δ is obtained. By the way, for the 2D irrotational one-fluid Euler-Poisson system with small amplitude ε of the perturbed initial data in the Sobolev spaces, we obtain an interesting long time existence result with lifespan T ε ≥ e ε − 2 | l n ε | − α (α > 0 is any fixed constant). [ABSTRACT FROM AUTHOR]

Spectral properties of a single type III burst in the wide frequency band from 10 to 70 MHz are studied in detail. It is shown that electrons corresponding to different levels of type III emission move with different velocities. Moreover, these electron velocities decrease from the maximum value, which corresponds to the 0.1 level of the maximum type III flux at its front, to the minimum value, corresponding to the 0.1 level of the maximum type III flux at its back. The velocity of electrons corresponding to the maximum type III flux was approximately 0.31 c. This value equals 0.6 of maximum velocity, and, namely, it was predicted by the gas dynamic theory of electron propagation through the coronal plasma. In addition, we adduce arguments that the type III radio emission is the harmonic emission. In supposition that type III electrons move through the Newkirk coronal plasma, we find electron velocities for every level of the type III burst. The duration dependence on frequency obtained from the observations is close to Elgaroy-Lingstad dependence. We discuss the contribution of electron velocity dispersion to the type III burst duration. In addition, we derived type III flux dependence on frequency in the frequency bands of 10-33 MHz and 33-62 MHz. [ABSTRACT FROM AUTHOR]

Nonlinear kinetic structures, called electron phase-space holes (EHs), are regularly observed in space and experimental magnetized plasmas. The existence of EHs is conditioned and varies according to the ambient magnetic field and the parameters of the electron beam(s) that may generate them. The objective of this paper is to extend the 3D Bernstein–Greene–Kruskal model with cylindrical geometry developed by L.-J. Chen et al. ["Bernstein–Greene–Kruskal solitary waves in three-dimensional magnetized plasma," Phys. Rev. E 69, 055401 (2004)] and L.-J. Chen et al., ["On the width-amplitude inequality of electron phase space holes," J. Geophys. Res. 110, A09211 (2005)] to include simultaneously finite effects due to (i) the strength of the ambient magnetic field B 0 , by modifying the Poisson equation with a term derived from the electron polarization current, and (ii) the drift velocity ue of the background plasma electrons with respect to the EH, by considering velocity-shifted Maxwellian distributions for the boundary conditions. This allows us to more realistically determine the distributions of trapped and passing particles forming the EHs, as well as the width-amplitude relationships for their existence. [ABSTRACT FROM AUTHOR]

The paper is devoted to a comparison of the results of an experimental study of a 28 GHz/25 kW gyrotron with a magnetically shielded system and the results of calculating the electron–wave interaction with the use of the ANGEL software code on the basis of a self-consistent model with an unfixed radio-frequency field structure. The good agreement between the results confirms the validity of using the developed code for creation of new gyrotrons. Comparison of various experimental data with the calculation results for the electron–wave interaction as well as for electron optics makes possible implicit reevaluation of the actual values of some important gyrotron parameters (the electron pitch factor, transverse velocity spread, etc.). [ABSTRACT FROM AUTHOR]

The drift velocity of photo-generated electrons in CdTe by lasers with wavelengths of 532, 355, and 266 nm is studied by the Monte Carlo method. The effects of laser wavelengths on the electron drift velocity are systematically investigated under various laser fluxes, doping densities, and temperatures. It is found that the drift velocity as a function of electric field v d (E) has a close relationship with the laser wavelengths: the electron drift velocity in CdTe becomes larger when a longer photoexcitation wavelength is used. On the other hand, the doping effect, as well as the effect of the laser energy flux, on the v d (E) dependence demonstrates different characteristics for different laser wavelengths. The difference in electron drift velocity caused by the various wavelengths reduces with increasing temperatures. In the case of a low laser energy flux, doping in CdTe plays a remarkable role in v d (E) relations. These new results are helpful in understanding the microscopic mechanism of relaxation processes of photo-excited carriers and applications of CdTe-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Evaluations of the current output from emitter arrays have been carried out based on time-dependent kinetic simulations that include many-body Coulombic contributions from the electron swarm, geometric field enhancements with shielding based on a line charge model, and dynamic screening due to the evolution of the swarm in the position and velocity space. Numerical evaluations are applied to different multi-emitter array arrangements having a hexagonal lattice, with a focus on bimodal distributions. Our results show the expected role of field screening with reductions in emitter separation and positional dependence within the array based on connectivity. Different patterns were examined within a hexagonal lattice structure. For a bimodal distribution, output current optimization is shown for alternating arrangements with three or more successive emitters of the same length along primitive axes predicted to have an advantage. [ABSTRACT FROM AUTHOR]

To investigate the effects of the optical field and the Fermi velocity on the transport properties of spin and valley electrons, we impose a normal/ferromagnetic/normal (N/F/N) quantum structure based on the monolayer WSe 2. The results indicate that there is a strong switch effect for spin- and valley-related electrons. When left-handed off-resonant circularly polarized light is irradiated in the intermediate ferromagnetic region, 100 % polarization for K valley electrons can be achieved in the entire effective energy spectrum of the optical field. Meanwhile, 100 % polarization of the K ′ valley can also be gained with the right-handed off-resonant circularly polarized light in the junction. Moreover, the perfect polarization of spin-up electrons can be obtained when the ferromagnetic exchange field is applied to the structure. Additionally, the Fermi velocity barrier also changes the energy band of the studied material, which makes the spin and valley transport increase with the increase of the velocity barrier but does not produce spin or valley polarizations. These interesting results clarify that the optical field and the Fermi velocity both make a contribution to the modulation of spin electrons for the two valleys and provide a useful method for the design of novel spintronic and valleytronic devices. [ABSTRACT FROM AUTHOR]

An experimental study of 0.5-5.0 keV-energy H+ ion scattering on Cu(100) has been presented at a grazing scattering angle of 7°. The velocity dependent ion fractions have been measured in this work. The positive-ion fraction increases with the increase of incident velocity, which can be described by the exponential scaling. In particular, the threshold velocity for the positive-ion fraction is observed at about 0.25 a.u., and explained by the Auger ionization process. The negative-ion fraction increases monotonically with the impact velocity, which can be explained by the first type of the parallel velocity effect. Considering the formation of positive ions and the contribution of the parallel velocity effect, the negative-ion fraction is calculated by the modified theoretical model and the general trend is consistent with the experimental data. [ABSTRACT FROM AUTHOR]

We demonstrate three-dimensional velocity map imaging of low energy electrons using a TPX3CAM, where the three-dimensional momentum information [px, py, pz] is encoded in position and timing [x, y, t] of hits on the camera sensor. We make use of the camera sensor for the [x, y] information and a constant fraction discriminator and fast time to digital converter in the camera for the time information. We illustrate the capabilities of our apparatus by presenting above threshold ionization measurements of xenon, which produces well defined structures in the momentum resolved photoelectron yield. [ABSTRACT FROM AUTHOR]

The nuclear velocity perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The research on the space-charge limited current is of great importance for developing insight into the high current diodes. The Child-Langmuir law presents one-dimensional (1D) space-charge limited current density by considering a full electrostatic solution. Jaffe investigated the 1D space-charge limited current density modified by the uniform initial velocity of electrons emitted from the cathode by using the equation of motion for the individual electron. Luginsland et al. presented the two-dimensional (2D) space-charge limited current density by using the particle-in-cell (PIC) codes neglecting initial velocity distribution of the emitted electrons. In this Letter, the effects of initial electrons with the uniform energy distribution and thermal equilibrium distribution on the space charge limited current density are studied by using the full electromagnetic PIC method; the 2D modification factors to the space charge limited current density for the two cases are presented and discussed. [ABSTRACT FROM AUTHOR]

Experimental and modelling study of the pre-breakdown phenomenon in dielectric liquids, generally called 'streamers', is vital for the application of liquids in high voltage and power dense devices. Streamer is characterized into four modes by average propagation velocity, among which the second mode streamer is responsible for breakdowns at a wide range of gap distances and voltage levels. The stable propagation velocity of around 2 km s−1 is one of the key characteristics of the second mode streamer. The most recent study found that streamer branching is not the main reason for the stable velocity of second mode streamer as was assumed previously. Besides, one major drawback of the existing charge-drift model of the second mode streamer is the over-estimation of electron velocity, which leads to the much higher streamer propagation velocity in simulation than that observed in experiments. In this paper, restriction of streamer propagaiton velocity by using electron saturation velocity (ESV) is found to be the key reason for the stable propagaiton velocity of the second mode streamer. The charge-drift model is modified by considering different ESVs. It is found that reducing ESV from 30 km s−1 to 2.5 km s−1 in simulation can greatly constrain positive streamer propagation velocity from 4.15 km s−1 to 0.50 km s−1 in cyclohexane. When ESV is set to be 7.5 km s−1 in cyclohexane, the streamer propagation velocity in simulation increases from 1.59 km s−1 at 80 kV (below breakdown voltage) to 1.91 km s−1 at 100 kV (near to acceleration voltage), which closely matches the experimental observations. [ABSTRACT FROM AUTHOR]

The drift velocity of electrons in mixtures of gaseous water and helium is measured over the range of reduced electric fields 0.1-300 Td using a pulsed-Townsend technique. Admixtures of 1% and 2% water to helium are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. The measured drift velocities are used as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-water vapour cross-sections [K. F. Ness, R. E. Robson, M. J. Brunger, and R. D. White, J. Chem. Phys. 136, 024318 (2012)]. A refinement of the momentum transfer cross-section for electron-water vapour scattering is presented, which ensures self-consistency with the measured drift velocities in mixtures with helium to within approximately 5% over the range of reduced fields considered. [ABSTRACT FROM AUTHOR]

A spark discharge in a 1.5-mm-long tip (cathode)-plane gap in the time interval from the breakdown onset to 200 ns has been studied. Тhe discharge has been found to arise in the form of a bundle of microchannels. The dynamics of the discharge spatial structure, the electron concentration, the gas temperature in the channel, and the velocity of its radial expansion have been determined. [ABSTRACT FROM AUTHOR]