Weak electron beams in inhomogeneous plasma
Inhomogeneous plasma containing weak electron beam using Vlasov equation, noting wave-wave coupling effect
Baker, J. C.↗
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Inhomogeneous plasma oscillations in streaming plasmas
Inhomogeneous plasma oscillations in counterstreaming plasmas analyzed for electric fields and resonant frequencies from Vlasov equation
Baker, J. C.↗
Two-dimensional studies of relativistic electron beam plasma instabilities in an inhomogeneous plasma
Relativistic electron beam propagation in plasma is fraught with several micro instabilities like two stream, filamentation, etc., in plasma. This results in severe limitation of the electron transport through a plasma medium. Recently, however, there has been an experimental demonstration of improved transport of Mega Ampere of electron currents (generated by the interaction of intense laser with solid target) in a carbon nanotube structured solid target [G. Chatterjee et al., Phys. Rev. Lett. 108, 235005 (2012)]. This then suggests that the inhomogeneous plasma (created by the ionization of carbon nanotube structured target) helps in containing the growth of the beam plasma instabilities. This manuscript addresses this issue with the help of a detailed analytical study and 2-D Particle-In-Cell simulations. The study conclusively demonstrates that the growth rate of the dominant instability in the 2-D geometry decreases when the plasma density is chosen to be inhomogeneous, provided the scale length 1/k{sub s} of the inhomogeneous plasma is less than the typical plasma skin depth (c/ω{sub 0}) scale. At such small scale lengths channelization of currents is also observed in simulation.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Laser pulse driven terahertz generation via resonant transition radiation in inhomogeneous plasmas
An intense, short laser pulse propagating across a plasma boundary ponderomotively drives THz radiation. Full format PIC simulations and theoretical analysis are conducted to investigate the properties of this radiation. Simulation results which show the THz emission originates in regions of varying density and covers a broad spectrum with maximum frequency close to the maximum plasma frequency. In the case of a sharp vacuum-plasma boundary, the radiation is generated symmetrically at the plasma entrance and exit, and its properties are independent of plasma density when the density exceeds a characteristic value determined by the product of the plasma frequency and the laser pulse duration. For a diffuse vacuum-plasma boundary, the emission from the plasma entrance and exit is asymmetric: increasing and decreasing density ramps enhance and diminish the radiated energy, respectively. Enhancements by a factor of 50 are found and simulations show that a 1.66 J, 50 fs driver pulse can generate ∼400 μJ of THz radiation in a 1.2 mm increasing density ramp. We present a model that attributes this effect to a plasma resonance process in the density ramp. The results from the model match those of the simulations for ramp lengths less than 600 μm. For longer ramps for which simulations are too time consuming, the model shows that the amount of radiation reaches a maximum at a ramp length determined by collisional absorption.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Channeling of multikilojoule high-intensity laser beams in an inhomogeneous plasma
Not Available
Ivancic, S.↗
PROBABILISTIC MODEL OF BEAM–PLASMA INTERACTION IN RANDOMLY INHOMOGENEOUS PLASMA
We propose a new model that describes beam–plasma interaction in the presence of random density fluctuations with a known probability distribution. We use the property that, for the given frequency, the probability distribution of the density fluctuations uniquely determines the probability distribution of the phase velocity of waves. We present the system as discrete and consisting of small, equal spatial intervals with a linear density profile. This approach allows one to estimate variations in wave energy density and particle velocity, depending on the density gradient on any small spatial interval. Because the characteristic time for the evolution of the electron distribution function and the wave energy is much longer than the time required for a single wave–particle resonant interaction over a small interval, we determine the description for the relaxation process in terms of averaged quantities. We derive a system of equations, similar to the quasi-linear approximation, with the conventional velocity diffusion coefficient D and the wave growth rate γ replaced by the average in phase space, by making use of the probability distribution for phase velocities and by assuming that the interaction in each interval is independent of previous interactions. Functions D and γ are completely determined by the distribution function for the amplitudes of the fluctuations. For the Gaussian distribution of the density fluctuations, we show that the relaxation process is determined by the ratio of beam velocity to plasma thermal velocity, the dispersion of the fluctuations, and the width of the beam in the velocity space.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Radiation from accelerated Alfven solitons in inhomogeneous plasmas
In a weakly inhomogeneous plasma, the large-amplitude Alfven waves propagating parallel to the ambient magnetic field are shown to evolve into accelerated Alfven solitons. Nonlinear interaction of the accelerated Alfven solitons with the Langmuir waves results in the emission of coherent radiations. Analytical expression for the power radiated per unit solid angle from a soliton is derived for two inhomogeneity profiles, namely the linear profile and the parabolic profile. For the case of uniform plasmas, the emission occurs via a decay-type process or resonant modes. In the presence of inhomogeneity, nonresonant modes provide a new channel for the emission of radiation. The power radiated per unit solid angle is computed for the parameters relevant to Comet Halley's plasma environment. For the nonresonant modes it is found to be several orders of magnitude higher than that for the case of resonant modes.
Lakhina, G. S.↗
Laser-driven electron acceleration in an inhomogeneous plasma channel
We study the laser-driven electron acceleration in a transversely inhomogeneous plasma channel. We find that, in inhomogeneous plasma channel, the developing of instability for electron acceleration and the electron energy gain can be controlled by adjusting the laser polarization angle and inhomogeneity of plasma channel. That is, we can short the accelerating length and enhance the energy gain in inhomogeneous plasma channel by adjusting the laser polarization angle and inhomogeneity of the plasma channel.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
On the asymptotic kinetic equation for inhomogeneous plasmas.
Asymptotic kinetic equation for inhomogeneous plasma compared to results for initial value problem and Bogoliubov method
ASYMPTOTIC FUNCTION↗
Propagation in a planar inhomogeneous plasma medium
Propagation in planar inhomogeneous plasma medium
Norgard, J. D.↗
Excitation of plasma resonances by a small pulsed dipole in a weakly inhomogeneous plasma
Plasma resonance excitation by small pulsed dipole in weakly inhomogenous plasma determined using WKB solutions and stationary phase approximations
Fejer, J. A.↗
Electron density measurements of an inhomogeneous plasma using millimeter wave Fabry-Perot interferometers.
The electron density of a laboratory generated inhomogeneous plasma was measured using 60-90, GHz flat-plate and 150 GHz semi-confocal Fabry-Perot interferometers. The plasma was a negative glow-type and had a measured parabolic electron density profile. An analytical comparison between the derived equations of electron density for an assumed homogeneous plasma slab and an inhomogeneous plasma with parabolic distribution showed that the slab approximation was valid for such a profile. Comparison of measured values of electron density with those using X-band and K-band interferometers for the same plasma indicated good agreement.
Kendall, B. M.↗
Generalised model of a sheath of a plasma bubble excited by a short laser pulse or by a relativistic electron bunch in transversely inhomogeneous plasma
An analytical model of a plasma bubble (a wake wave in the strongly nonlinear regime) in transversely inhomogeneous plasma is generalised to an arbitrary profile of an electron sheath at its boundary. Within the framework of this generalisation we have found the potential within the bubble and shown that its envelope is described by a second-order equation, similar to the equation of a less general theory. We have also determined the domain of parameters at which this equation is considerably simplified and no longer depends on the profile of the electron sheath. (extreme laser radiation: physics and fundamental applications)
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff
This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density n e (r), which will modify the wave propagation in the direction of the gradient rn e (r).
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Variational calculations for resonance oscillations of inhomogeneous plasmas
The electrostatic resonance properties of an inhomogeneous plasma column are reported by application of the Rayleigh-Ritz method. A description of the rf equation of motion and pressure term that expresses the system of equations in Euler-Lagrange form is presented. The Rayleigh-Ritz procedure is applied to the corresponding Lagrangian to obtain approximate resonance frequencies and eigenfunctions. An appropriate set of trial coordinate functions is defined, which leads to frequency and eigenfunction estimates.
Peng, Y. K. M.↗
Variational calculations for resonance oscillations of inhomogeneous plasmas
The electrostatic resonance properties of an inhomogeneous plasma column are treated by the Rayleigh-Ritz method. In contrast to Parker, Nickel & Gould (1964), who carried out an exact computation, the present treatment uses a description of the RF equation of motion and pressure term that allows one to express the system of equations in Euler-Lagrange form. The Rayleigh-Ritz procedure is then applied to the corresponding Lagrangian, to obtain approximate resonance frequences and eigenfunctions. An appropriate set of trial coordinate functions is defined, which leads to frequency and eigenfunction estimates in excellent agreement with the work of Parker et al. (1964).
Peng, Y.-K. M.↗
Laser acceleration of electrons in two-dimensionally inhomogeneous plasma at the boundary of a metal foil
The electron acceleration mechanism associated with the generation of a plasma wave due to self-modulation instability of laser radiation in a subcritical plasma produced by a laser prepulse coming 10 ns before the arrival of the main intense femtosecond pulse is considered. Three-dimensional particle-in-cell simulations of the interaction of laser radiation with two-dimensionally inhomogeneous subcritical plasma have shown that, for a sufficiently strong plasma inhomogeneity and a sharp front of the laser pulse, efficient plasma wave excitation, electron trapping, and generation of collimated electron beams with energies on the order of 0.2–0.5 MeV can occur. The simulation results agree with experiments on the generation of collimated beams of accelerated electrons from metal targets irradiated by intense femtosecond laser pulses.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Time dependent evolution of linear kinetic Alfvén waves in inhomogeneous plasma
The propagation of linear Kinetic Alfvén waves (KAWs) in inhomogeneous magnetized plasma has been studied while including inhomogeneities in transverse and parallel directions relative to the background magnetic field. The propagation of KAWs in inhomogeneous magnetized plasma is expected to play a key role in energy transfer and turbulence generation in space and laboratory plasmas. The inhomogeneity scale lengths in both directions may control the nature of fluctuations and localization of the waves. We present a theoretical study of the localization of KAWs, variations in magnetic field amplitude in time, and variation in the frequency spectra arising from inhomogeneities. The relevance of the model to space and laboratory observations is discussed.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗