C. M. Ryu

Turbulent acceleration of superthermal electrons

In a recent paper it was suggested on the basis of weak turbulence theory that the collisionality of a plasma, coupled with nonlinear wave-particle interaction, is crucial for the acceleration of electrons by Langmuir turbulence to a superthermal energy level. In this Letter, fully nonlinear Vlasov and particle-in-cell (PIC) simulation techniques are employed to further verify this potentially important finding. The previous conclusion is fully confirmed by observing the expected difference between the Vlasov and PIC simulation results in the weak beam regime. However, in the strong beam regime, both the Vlasov and PIC simulations are found to produce a high-energy tail population, which indicates that there may be other mechanisms in the high beam speed situation, that are responsible for the generation the superthermal electrons.

Compressional Alfvénic rogue and solitary waves in magnetohydrodynamic plasmas

Generation of compressional Alfvenic rogue and solitary waves in magnetohydrodynamic plasmas is investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. The reductive perturbation method is used to obtain a Korteweg–de Vries (KdV) equation describing the evolution of the solitary wave. The height of a soliton is proportional to the soliton speed “U” and inversely proportional to plasma “β” (ratio of plasma thermal pressure to pressure of the confining magnetic field) and the width of soliton is proportional to the electron inertial length. KdV equation is used to study the nonlinear evolution of modulationally unstable compressional Alfvenic wavepackets via the nonlinear Schrodinger equation. The characteristics of rogue wave influenced by plasma “β” and the electron inertial length are described.

Oblique ion-acoustic cnoidal waves in two temperature superthermal electrons magnetized plasma

A study is presented for the oblique propagation of ion acoustic cnoidal waves in a magnetized plasma consisting of cold ions and two temperature superthermal electrons modelled by kappa-type distributions. Using the reductive perturbation method, the nonlinear Korteweg de-Vries equation is derived, which further gives the solutions with a special type of cnoidal elliptical functions. Both compressive and rarefactive structures are found for these cnoidal waves. Nonlinear periodic cnoidal waves are explained in terms of plasma parameters depicting the Sagdeev potential and the phase curves. It is found that the density ratio of hot electrons to ions μ significantly modifies compressive/refractive wave structures. Furthermore, the combined effects of superthermality of cold and hot electrons κc,κh, cold to hot electron temperature ratio σ, angle of propagation and ion cyclotron frequency ωci have been studied in detail to analyze the height and width of compressive/refractive cnoidal waves. The findings in...

Electrostatic solitary wave and double layer in a plasma with heavy ions and nonthermally distributed electrons

The existence condition for bump and dip type, as well as double layer (DL), solutions of electrostatic solitary waves (ESWs) in a nonthermal electron plasma with heavy ions is investigated by a pseudopotential method. It is found that the nonthermality of electrons determines the existence of the DL solution and that the amplitude of ESWs is enhanced by the density of heavy ions. When the heavy ion density is beyond a certain critical value, ESWs and DLs cannot exist. It is also found that both the lower and upper critical Mach numbers are reduced by the presence of heavy ions.

Obliquely propagating solitary kinetic Alfven wave in a collisional dusty plasma

An obliquely propagating solitary kinetic Alfven wave in a low beta dusty plasma (β⪡me/mi) is studied by considering the ion motion along the magnetic field and the collisional effect of electrons. The existence condition for a solitary wave for a collisionless dusty plasma is re-examined. It is found that there is an upper limit of the possible Alfvenic Mach velocity, imposed by dust particles. The Mach number lies between lz and lz/Nd, where lz is the directional cosine and Nd is the dust particle charge density. In the collisional case, the same upper limit of the Mach velocity is found, and the solitary wave turns into an oscillating double layer. The damping scale and the size of the oscillation structure increase with increasing dust particle charge density. The damping scale and the size of the oscillation structure are estimated by using the virial theorem.

Electron acceleration and electron-positron pair production by laser in tunnel ionized inhomogeneous plasma

A high intensity laser short pulse causes rapid tunnel ionization of an inhomogeneous gas. The tunnel ionization of the gas causes a defocusing of the laser pulse. The electron experiences an unequal ponderomotive force due to the trailing and rising part of the laser pulse, hence, gains net energy. The net acquired electron energy is reduced due to the inhomogeneity in gas density. If the accelerated electrons are targeted to a low-Z material nucleus, the electron-positron pair will be created via a trident process.

Modulational instability and associated rogue structures of slow magnetosonic wave in Hall magnetohydrodynamic plasmas

The modulational instability and associated rogue structures of a slow magnetosonic wave are investigated for a Hall magnetohydrodynamic plasma. Nonlinear Schrodinger equation is obtained by using the multiple scale method, which shows a modulationally unstable slow magnetosonic mode evolving into bright wavepackets. The dispersive effects induced by the Hall electron current increase with the increase in plasma β and become weaker as the angle of propagation increases. The growth rate of the modulational instability also increases with the increase in plasma β. The growth rate is greatest for the parallel propagation and drops to zero for perpendicular propagation. The envelope wavepacket of a slow magnetosonic is widened with less oscillations as plasma β increases. But the wavepacket becomes slightly narrower and more oscillatory as the angle of propagation increases. Further a non-stationary envelope solution of the Peregrine soliton is analyzed for rogue waves. The Peregrine soliton contracts temporally and expands spatially with increase in plasma β. However, the width of a slow magnetosonic Peregrine soliton decreases both temporally and spatially with increase of the propagation angle.

Ion-acoustic solitary waves in ion-beam plasma with Boltzmann electrons

Particle simulations and a pseudopotential method were used to study ion-acoustic solitary waves in a plasma composed of Boltzmann electrons and kinetic beam ions. Pseudopotential theory was first applied to determine how ion-acoustic solitary waves can exist in a two-component plasma. Then, particle simulations were carried out, wherein ion-acoustic solitary waves were excited by modulating the bias grid voltage in a double plasma model. For the modulation, the potential of the grid bias was rapidly decreased, such that hump-type ion-acoustic solitary waves with good Gaussian shape were excited one after another, forming a train of waves. The simulation also showed that the phase velocities of ions decrease sharply when the solitary wave occurs, which indicates that the solitary ion-acoustic wave is excited via the inverse Landau damping process.

Stimulated Raman forward scattering of laser in a pre-formed plasma channel

Stimulated Raman forward scattering (SRFS) of an intense short pulse laser in a plasma channel formed by two pre-laser pulses is investigated. The density nonuniformity of a plasma channel increases the focusing of main laser pulse. Main laser pulse excites a plasma wave and two electromagnetic sideband waves. Laser and the sidebands exert an axial ponderomotive force on electrons driving the plasma wave. The nonlinear currents arise at sideband frequencies. The density perturbation due to plasma wave beats with the oscillatory velocity due to pump to drive the sidebands. The normalized growth rate of SRFS increases with the density nonuniformity of a plasma channel. However, in the presence of a deep plasma channel the focusing is ineffective to laser intensity, but the growth rate increases with the intensity of main laser pulse.

Large amplitude inertial compressional Alfvénic shock and solitary waves, and acceleration of ions in magnetohydrodynamic plasmas

Large amplitude inertial compressional Alfvenic shock and solitary waves in magnetohydrodynamic plasmas are investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. A Sagdeev-potential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed, M (Mach number), plasma β (ratio of the plasma thermal pressure to the pressure in the confining magnetic field), and electron inertia, wherein solitary waves may exist, are determined. Depth of the potential increases with increasing the Mach number and plasma β, however decreases with the increasing electron inertia. The height of soliton increases with increasing in Mach number and decreases with plasma β. And with increasing electron inertial length, the width of soliton increases. The electron-ion collisional dissipation results a dissipative inertial compressional Alfven wave, which can produce a shock like structure and can efficiently accelerate ions to the order of the local Alfven velocity. The shock height increases with the increasing collision frequency, but shock height decreases with increasing plasma β.