Fundamental Electromagnetic Emissions by a Weak Electron Beam in Solar Wind Plasmas with Density Fluctuations

The generation of Langmuir wave turbulence by a weak electron beam in a randomly inhomogeneous plasma and its subsequent electromagnetic radiation are studied owing to two-dimensional particle-in-cell simulations in conditions relevant to type III solar radio bursts. The essential impact of random density fluctuations of average levels of a few percents of the background plasma on the characteristics of the electromagnetic radiation at the fundamental plasma frequency ω p is shown. Not only wave nonlinear interactions but also processes of Langmuir waves’ transformations on the density fluctuations contribute to the generation of such emissions. During the beam relaxation, the amount of electromagnetic energy radiated at ω p in a plasma with density fluctuations strongly exceeds that observed when the plasma is homogeneous. The fraction of Langmuir wave energy involved in the generation of electromagnetic emissions at ω p saturates around 10−4, i.e., one order of magnitude above that reached when the plasma is uniform. Moreover, whereas harmonic emission at 2ω p dominates over fundamental emission during the time evolution in a homogeneous plasma, fundamental emission is strongly dominant when the plasma contains density fluctuations, at least during several thousands of plasma periods before being overcome by harmonic emission when the total electromagnetic energy begins to saturate.

Полноволновое двумерное моделирование распространения и поглощения геликонов в плазме сферического токамака Глобус-М2

Numerical modeling of propagation and absorption of fast waves (helicons) with frequency 200 MHz in 2D inhomogeneous plasma of the spherical tokamak Globus-M2 was carried out with 2D full-wave code. Toroidal effects, poloidal magnetic field and the actual shape of the flux surfaces were taken into account. The full wave electric field and RF power absorption profiles were computed by solving plasma wave equation with electron Landau damping term. The modeling demonstrated a fairly high efficiency of helicons absorption in the bulk plasma within a wide range of experimental parameters. The waves propagate to the inner regions of the plasma column and are mainly absorbed there; less than 20% of RF energy returns back to the plasma periphery.

Analytical Model Nonequilibrium Inhomogeneous Plasma of the Heliosphere

We prove that a nonequilibrium inhomogeneous giant gas discharge is realized in the heliosphere with huge values of the parameter <i>E</i>/<i>N</i>, which determines the temperature of electrons. This quasi-stationary discharge determines the main parameters of the weak solar wind (SW) in the heliosphere. In connection with the development of space technologies and the human spacewalk, the problem of the nature of the SW is acute. The study of the interference of gravitational and electrical potentials at the Earth's surface began with the work of Hilbert 1600. Such polarization effects – the interference of Coulomb and gravitational forces – have not been studied well enough even in the heliosphere. Our article is devoted to this problem. Pannekoek-Rosseland-Eddington model do not take into account the important role of highly energetic running (away from the Sun) electrons and, accordingly, the duality of electron fluxes. According to an alternative model formulated by we, highly energetic (escaping from the Sun) electrons leave the Sun and the heliosphere, and weakly energetic ones, unable to leave the Coulomb potential well (hole) – the positively charged Sun and the heliosphere, return to the Sun. The weak difference between the opposite currents of highly energetic (escaping from the Sun) electrons and weakly energetic (returning to the Sun) electrons is compensated by the current of positive ions and protons from the Sun – SW. These dynamic processes maintain a quasi-constant effective dynamic charge of the Sun and the entire heliosphere. At the same time, quasi-neutrality in the Sun and heliosphere is well performed up to 10^-36. According to experiments and analytical calculations based on our model: 1) the plasma in the corona is nonequilibrium; 2) the maximum electron temperature is T_e ~ 1-2 million degrees; 3) T_e grows from 1000 km away from the Sun and 4) the role of highly energetic electrons escaping from the plasma leads to a significant increase in the effective: solar charge and electric fields in the heliosphere in relation to the Pannekoek-Rosseland-Eddington model. This is due to the absence of a compensation layer that screens the effective charge of the Sun. It is not formed at all due to the escape of highly energetic electrons (as in a conventional gas discharge) in the entire heliosphere with high temperatures exceeding the temperature of the Sun's surface. Thus, the process of escape of highly energetic electrons forms the internal EMF of the entire heliosphere. Interference of gravitational and Coulomb potentials in the entire heliosphere is considered, it is being manifested in generation of two opposite flows of particles: 1) that are neutral or with a small charge (to the Sun), and 2) in the form of high-energy electrons (escaping from the positively charged Sun) and a solar wind (from the Sun). Calculated values of the registered ion parameters in the solar wind were compared with experimental observations. Reasons for generating the ring current in inhomogeneous heliosphere and inapplicability of the Debye theory in describing processes in the solar wind (plasma with current) are considered.

Analytical Model Nonequilibrium Inhomogeneous Plasma of the Heliosphere

We prove that a nonequilibrium inhomogeneous giant gas discharge is realized in the heliosphere with huge values of the parameter <i>E</i>/<i>N</i>, which determines the temperature of electrons. This quasi-stationary discharge determines the main parameters of the weak solar wind (SW) in the heliosphere. In connection with the development of space technologies and the human spacewalk, the problem of the nature of the SW is acute. The study of the interference of gravitational and electrical potentials at the Earth's surface began with the work of Hilbert 1600. Such polarization effects – the interference of Coulomb and gravitational forces – have not been studied well enough even in the heliosphere. Our article is devoted to this problem. Pannekoek-Rosseland-Eddington model do not take into account the important role of highly energetic running (away from the Sun) electrons and, accordingly, the duality of electron fluxes. According to an alternative model formulated by we, highly energetic (escaping from the Sun) electrons leave the Sun and the heliosphere, and weakly energetic ones, unable to leave the Coulomb potential well (hole) – the positively charged Sun and the heliosphere, return to the Sun. The weak difference between the opposite currents of highly energetic (escaping from the Sun) electrons and weakly energetic (returning to the Sun) electrons is compensated by the current of positive ions and protons from the Sun – SW. These dynamic processes maintain a quasi-constant effective dynamic charge of the Sun and the entire heliosphere. At the same time, quasi-neutrality in the Sun and heliosphere is well performed up to 10^-36. According to experiments and analytical calculations based on our model: 1) the plasma in the corona is nonequilibrium; 2) the maximum electron temperature is T_e ~ 1-2 million degrees; 3) T_e grows from 1000 km away from the Sun and 4) the role of highly energetic electrons escaping from the plasma leads to a significant increase in the effective: solar charge and electric fields in the heliosphere in relation to the Pannekoek-Rosseland-Eddington model. This is due to the absence of a compensation layer that screens the effective charge of the Sun. It is not formed at all due to the escape of highly energetic electrons (as in a conventional gas discharge) in the entire heliosphere with high temperatures exceeding the temperature of the Sun's surface. Thus, the process of escape of highly energetic electrons forms the internal EMF of the entire heliosphere. Interference of gravitational and Coulomb potentials in the entire heliosphere is considered, it is being manifested in generation of two opposite flows of particles: 1) that are neutral or with a small charge (to the Sun), and 2) in the form of high-energy electrons (escaping from the positively charged Sun) and a solar wind (from the Sun). Calculated values of the registered ion parameters in the solar wind were compared with experimental observations. Reasons for generating the ring current in inhomogeneous heliosphere and inapplicability of the Debye theory in describing processes in the solar wind (plasma with current) are considered.

3D multi-scale modelling of plasma-based seeded soft X-ray lasers

Modelling plasma-based seeded soft X-ray lasers from the creation of the plasma to the propagation of a femtosecond high-order harmonic (HOH) seed throughout several millimetres of inhomogeneous plasma is a complex challenge. Different spatio-temporal scales from the hydrodynamic evolution of the plasma (hundreds of micrometres and nanoseconds) to the propagation of pulses through the plasma (millimetres and tens of picoseconds), electron collisions (picoseconds or even shorter) and the evolution of the envelope of the seeded HOH (tens of femtoseconds) must be tackled in order to fully understand these systems. In this paper, we will present the multi-scale computational paradigm that we have used to perform a full ab initio simulation of a dense, Ni-like Krypton plasma amplifier of soft X-rays. Results of the modelling and expected future applications will also be shown.

One-Dimensional Nonlinear Parametric Instability of Inhomogeneous Plasma: Time Domain Problem

A numerical one-dimensional model of convective parametric instability of inhomogeneous plasma is developed. By using this model, a numerical solution describing spatial and temporal characteristics of interacting waves is obtained. The results obtained are in a good agreement with known analytical models and substantially generalize them. In particular, an important advantage of the proposed model is the possibility of varying initial conditions, analyzing behavior of the system in the presence of incident wave fluctuations that is important for the future study of the absolute instability mode. The model is also provides possibility to simulate absolute parametric instability with a wide range of controllable parameters, as well as to study interacting wave transients.