1,721,041 research outputs found
Vlasov simulations of strongly nonlinear electrostatic oscillations in a one-dimensional electron-ion plasma
No full textThe problem of the microscopic plasma response to the excitation of large amplitude electrostatic perturbations in a two-component plasma is studied by means of the numerical integration of the Vlasov-Maxwell system. The decaying of an initial electron density perturbation as well as the plasma response to an externally applied oscillating electric field are considered for times much longer than the typical ion-plasma times. The interconnections between the microscopic particle dynamics and the macroscopic plasma density and temperature evolutions are investigated. [S1063-651X(98)02811-6]
Electron hole generation and propagation in an inhomogeneous collisionless plasma
No full textThe generation of "trains" of electron holes in phase space due to an external electrostatic disturbance is investigated by using a Vlasov-Ampere code with open boundary conditions. Electron holes are produced mostly during the initial phase of the wave-plasma interaction, with a given drift velocity which is maintained until they exit the integration box, even in the presence of plasma inhomogeneities. They present macroscopic features, a dipolar electrostatic field and an electron density perturbation, which can be exploited for diagnostic purposes. Their equilibrium is intrinsically kinetic, in that they are accompanied by a stationary hole in the electron distribution function
Vlasov-Maxwell numerical simulations of large amplitude Langmuir wave dynamics
No full textThe classical problem of the nonlinear dynamics of one dimensional large Langmuir waves is investigated numerically in the framework of a kinetic model based on the Vlasov equations for plasma electrons and ions, coupled with the Maxwell equations. The field and plasma quantities are followed in time starting from a given spatial electric field distribution with typical scalelength much larger than the Debye length. The temporal evolution of the particle distribution functions and of its moments are investigated during the relaxation of the initial perturbation or under the action of an externally applied oscillating field. The transformation of ordered energy into electron temperature is observed. The frequency spectra of the electron and ion fluctuations are calculated and harmonic generation is studied
Fluid and kinetic (Vlasov) numerical simulations of the wave-plasma interaction in conditions of relevance for rf heating
No full textThe interaction of electrostatic waves of finite amplitude with the plasma which characterizes the edge region of a magnetic confinement device during radiofrequency (rf) heating experiments is investigated on the basis of fluid and kinetic models. In the former case, the time evolution of a two-dimensional initial distribution of the rf energy, coupled with the slow plasma density motion through the action of ponderomotive forces, is investigated. A fluid magnetized plasma is considered and the electric field evolution is treated in the frame of the slowly varying envelope approximation. In the latter case, the Vlasov equations for electrons and ions are integrated together with the Poisson equation in a one-dimensional geometry. An externally applied a.c. forcing term acts on both the species with given frequency and wavevector spectrum, which can be either monochromatic or broad. It is shown that, under conditions typical of the lower hybrid or ion Bernstein heating experiments of tokamak plasmas, numerous nonlinear effects are expected to accompany the wave-plasma interaction, as for example, the formation of strong plasma non-uniformities, the acceleration of charged particles, the nonlinear plasma heating
Vlasov-Maxwell simulations of high-frequency longitudinal waves in a magnetized plasma
No full textThe plasma response to the injection of a propagating purely electrostatic wave of finite amplitude is investigated by means of a kinetic code which solves the Vlasov equations for electrons and ions in the three-dimensional (one spatial and two in velocity, 1D2V) phase space, self-consistently coupled to the Maxwell equations. The plasma is uniformly magnetized, and the wave frequency close to the cold upper-hybrid resonance omega(0)=rootomega(pe)(2)+omega(ce)(2) is considered. Coherent structures are formed in the phase space that would be completely missed by a hydrodynamic analysis. In particular, in the early stage of the interaction, the initially unperturbed equilibrium electron distribution is strongly affected as a whole by the pump, taking a ringlike shape in the velocity plane transverse to the magnetic field. Then, a sort of instability occurs, leading to the broadening and flattening of the electron distribution
Vlasov-Poisson simulations of strong wave-plasma interaction in conditions of relevance for radio frequency plasma heating
No full textThe nonlinear aspects of the interaction between externally applied electrostatic oscillations and a one-dimensional electron-ion plasma is investigated by numerically integrating the Vlasov-Poisson system of equations. The forcing held is in the form of a broad symmetric k spectrum which simulates that used in low-frequency wave-heating experiments in tokamak plasmas. It is shown that, for realistic values of the plasma and field parameters, numerous nonlinear effects accompany the wave-plasma interaction, as, for example, the formation of density cavities by the action of ponderomotive forces, the acceleration of charged particles, and the nonlinear plasma heating
Induced plasma nonuniformities and wave vector cascade in the strong wave-plasma interaction
No full textThe interaction of finite amplitude electrostatic waves with an unmagnetized electron-ion plasma is studied by means of a one-dimensional kinetic code that solves the Vlasov equations for the plasma species coupled with the Poisson equation for the self-consistent electric field. An external force acts upon the charged particles, in the form of the sum of several counterpropagating electrostatic waves, characterized by a unique frequency and a broad wave-vector spectrum which form a standing wave pattern. The interplay between several nonlinear aspects of the interaction, such as the wavebreaking, the particle trapping, the electron heating, the production of ion beams, and the principal role of the wave-induced plasma density nonuniformities as the trigger of the above processes are investigated
Vlasov-Maxwell kinetic simulations of radio-frequency-driven ion flows in magnetized plasmas
No full textThe generation of a coherent ion flow due to the injection in a plasma of a purely electrostatic wave of finite amplitude, propagating at right angle with the ambient uniform magnetic field, is investigated making use of a kinetic code which solves the fully nonlinear Vlasov equations for electrons and ions, coupled with the Maxwell equations, in one spatial and two velocity dimensions. A uniformly magnetized slab plasma is considered. The wave frequency is assumed in the range of the fourth harmonic of the ion cyclotron frequency, and the wave vector is chosen in order to model the propagation of an ion Bernstein wave. The computation of the first-order moment of the ion distribution function shows that indeed a quasistationary transverse average ion drift velocity is produced. The time evolution of the ion distribution function undergoes a "resonant" interaction of Cherenkov type, even if the plasma ions are magnetized (omega(ci)/omega(pi)approximate to0.5). During the wave-plasma interaction, the electron distribution function remains Gaussian-like, while increasing its energy content
Generation of a nonuniform transverse ion flow by a propagating electrostatic wave in a strongly magnetized hot plasma
No full textThe plasma response to an externally driven low-frequency electrostatic wave, propagating perpendicularly to a uniform and static magnetic field, is investigated by means of a kinetic code, which solves the Vlasov equation for ions coupled to the Poisson equation. The aim of the investigation is to simulate the interaction of an ion Bernstein wave (LBW) with a collisionless plasma. The problem is dealt with in the frame of a one-dimensional slab model, where all physical quantities vary in the direction of wave propagation. Electrons constitute a uniform neutralizing background. The analysis shows that a net ion flow, transverse both to the magnetic field and to the wave-vector, is produced, with peak amplitude at frequencies higher than the low-order harmonics of the ion cyclotron frequency. In order to produce a flow spatial profile steep enough to satisfy the criterion for drift-wave suppression, several kV/cm are needed inside the plasma
Turbulence healing via plasma-wave interaction: the results of a study via kinetic codes
No full textThe propagation through a plasma slab of an electrostatic wave with characteristics similar to an Ion Bernstein wave is studied by means of Vlasov simulation codes and grid paradigms. Some interesting results for an application on turbulence healing in fusion devices are illustrated. (c) 2005 Elsevier B.V. All rights reserved
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