Oleg V. Polomarov

Revisiting the anomalous RF field penetration into a warm plasma

Radio frequency (RF) waves do not penetrate into a plasma and are damped within it. The electric field of the wave and plasma current are concentrated near the plasma boundary in a skin layer. Electrons can transport the plasma current away from the skin layer due to their thermal motion. As a result, the width of the skin layer increases when electron thermal velocity is taken into account. This phenomenon is called the anomalous skin effect. The anomalous penetration of the RF electromagnetic field occurs not only for the electric field parallel to the plasma boundary (inductively coupled plasmas), but also for the electric field normal to the plasma boundary (capacitively coupled plasmas). Such anomalous penetration of the RF field modifies the structure of the RF sheath in capacitive coupled plasma. Recent advances in the nonlinear, nonlocal theory of the capacitive sheath are reported. It is shown that separating the electric field profile into exponential and nonexponential parts yields an efficient qualitative and quantitative description of the anomalous RF field penetration in both inductively and capacitively coupled plasmas

Collision-driven negative-energy waves and the weibel instability of a relativistic electron beam in a quasineutral plasma.

A new model describing the Weibel instability of a relativistic electron beam propagating through a resistive plasma is developed. For finite-temperature beams, a new class of negative-energy magnetosound waves is identified, whose growth due to collisional dissipation destabilizes the beam-plasma system even for high beam temperatures. We perform 2D and 3D particle-in-cell simulations and show that in 3D geometry the Weibel instability persists even for collisionless background plasma. The anomalous plasma resistivity in 3D is caused by the two-stream instability.

Landau damping and anomalous skin effect in low-pressure gas discharges: Self-consistent treatment of collisionless heating

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for t...

Computationally efficient description of relativistic electron beam transport in collisionless plasma

A reduced approach to modeling the electromagnetic Weibel instability and relativistic electron beam transport in collisionless background plasma is developed. Beam electrons are modeled by macroparticles and the background plasma is represented by electron fluid. Conservation of generalized vorticity and quasineutrality of the plasma-beam system are used to simplify the governing equations. The method is suitable for modeling the nonlinear stages of collisionless beam-plasma interaction. A computationally efficient code based on this reduced description is developed and benchmarked against a standard particle-in-cell code. The full-scale two-dimensional numerical simulation of the Weibel instability saturation of a low-current electron beam is presented. Using the present approach, linear growth rates of the Weibel instability are derived for the cold and finite-temperature beams.

Effectiveness of electron-cyclotron and transmission resonance heating in inductively coupled plasmas

The electron-cyclotron and transmission resonances in magnetically enhanced low-pressure one-dimensional uniform inductively coupled plasmas are studied analytically within a simple model of two driven electrodes. The results of our approach are also applicable to the case of one grounded electrode. It is shown that, for a high discharge frequency, the plasma resistance is greatly enhanced at electron-cyclotron and transmission resonances, but normally does not exhibit a sharp peak at the electron-cyclotron resonance (ECR) condition. For a low discharge frequency, the ECR heating is not effective. Conditions of strong transmission resonances are identified. A transition from a bounded to semi-infinite plasma with overlapping of transmission resonances is also considered.

Three-dimensional filamentary structures of a relativistic electron beam in fast ignition plasmas

The filamentary structures and associated electromagnetic fields of a relativistic electron beam have been studied by three-dimensional particle-in-cell simulations in the context of fast ignition fusion. The simulations explicitly include collisions in return plasma current and distinctly examine the effects of beam temperature and collisions on the growth of filamentary structures generated.

Relativistic dynamical bistability and adiabatic excitation of strong plasma waves

Adiabatic evolution of the nonlinear resonantly driven dynamical system generic to a variety of plasma physics problems, including generation of large-amplitude plasma waves in a plasma beat-wave accelerator, is studied. The properties of the resonant Hamiltonian and the dynamics of its phase space for adiabatically varying parameters are considered. It is shown that the system can exhibit bistability and the Hamiltonian of a bistable system always follows the same trajectory for the adiabatically varying driver regardless of whether the system is excited or left quiescent. Descriptions of the bistability, autoresonance, and their possible combination based on the properties of the resonant Hamiltonian are given.

Adiabatic bistable evolution of dynamical systems governed by a Hamiltonian with separatrix crossing

Adiabatic evolution of a nonlinear resonantly driven dynamical system generic to a variety of plasma physics problems is studied. The corresponding Hamiltonian, depending on the strength and frequency of the slowly varying driver, has a variable number of fixed points and the dynamical system can be bistable due to repeated separatrix crossing in the phase space. It is analytically shown that the oscillation periods along the “sister” trajectories corresponding to the same value of the Hamiltonian are equal and the sum of the corresponding areas under them does not depend on the driver amplitude. As a consequence of that, the Hamiltonian of a bistable system always follows the same trajectory for an adiabatically varying driver, regardless of whether the system is excited or left quiescent.

Relativistic Dynamical Bi-Stability of Plasma Waves in a Plasma Wakefield Accelerator

Adiabatic evolution of a nonlinear resonantly driven dynamical system generic to a variety of plasma physics problems, including generation of large‐amplitude plasma waves in a plasma heatwave accelerator, is studied. The corresponding Hamiltonian, depending on the strength and frequency of a slowly varying driver, has a variable number of fixed points and the dynamical system can be bi‐stable due to repeated separatrix crossing in the phase space. It is shown that the Hamiltonian of a bi‐stable system always follows the same trajectory for adiabatically varying driver regardless of whether the system is excited or left quiescent. The descriptions of the bi‐stable and auto‐resonant methods of excitation of a large plasma wake, based on the aforementioned properties of the bi‐stable Hamiltonian, are given.

Novel Computational Approach to Weibel Instability and Beam Transport in Overdense Plasma

A reduced approach to modeling the electromagnetic Weibel instability and relativistic electron beam transport in dense background plasma is developed. Beam electrons are modelled by macro‐particles and the background plasma is represented by electron fluid. Conservation of generalized vorticity and quasineutrality of the plasma‐beam system are used to simplify the governing equations. The method is suitable for modeling a nonlinear stage and long‐time behavior of beam‐plasma interaction.