Electromagnetic Waves In Magnetized Plasma Research Articles

Plasma concept for generating circularly polarized electromagnetic waves with relativistic amplitude

Propagation features of circularly polarized (CP) electromagnetic waves in magnetized plasmas are determined by the plasma density and the magnetic field strength. This property can be applied to design a unique plasma photonic device for intense short-pulse lasers. We have demonstrated by numerical simulations that a thin plasma foil under an external magnetic field works as a polarizing plate to separate a linearly polarized laser into two CP waves traveling in the opposite direction. This plasma photonic device has an advantage for generating intense CP waves even with a relativistic amplitude. For various research purposes, intense CP lights are strongly required to create high energy density plasmas in the laboratory.

Spatial damping of parallel propagating electromagnetic waves in magnetized plasmas

Spatial damping of electromagnetic (EM) waves propagating parallel to the ambient magnetic field in collisionless plasmas is discussed for thermal distribution of electrons. By using the exact numerical analysis, it is shown that the spatial damping properties in hot plasma can be significantly different than the customary cold plasma analysis. The discrepancy comes from the wave-particle interaction (cyclotron resonance) and higher order thermal effects. The response of plasma to the interacting EM radiation depicts the variety of changes in different frequency domains. The comparison with the analytical results based on the expansion of plasma dispersion function is also made in order to validate the approximate treatment and to under what regime full kinetic treatment is called for.

Large-amplitude circularly polarized electromagnetic waves in magnetized plasma

We consider large-amplitude circularly polarized (LACP) waves propagating in a magnetized plasma. It is well-known that the dispersion relation for such waves coincides with the dispersion relation given by the linear theory. We develop the model of LACP wave containing a finite population of Cerenkov resonant particles. We find that the current of resonant particles modifies the linear dispersion relation. Dispersion curves of low-frequency (i.e., whistler and magnetosonic) waves are shifted toward larger values of the wave vector, i.e., waves with arbitrarily large wavelengths do not exist in this case. Dispersion curves of high-frequency waves are modified so that the wave phase velocity becomes smaller than the speed of light.

Enhanced propagation and focusing of an intense laser beam in high density magnetized plasma

In the present communication, the steady state propagation of an intense, circularly polarized Gaussian electromagnetic beam in high-density magnetized plasma is studied analytically and numerically. The relativistic oscillation of the mass of the electrons in the field of the pump and longitudinal magnetic field are shown to have a major effect on the dynamics of the propagation of intense electromagnetic wave. The wave equation has been solved under WKB and paraxial approximation by expanding the dielectric tensor for arbitrary large intensity. The propagation of electromagnetic waves in magnetized plasma, in the so-called extraordinary mode has been explicitly considered in the analysis. The variation of beamwidth parameter with distance of propagation has been obtained for chosen values of critical parameters in different regimes. These regimes are steady divergence, oscillatory divergence and self-focusing. Numerical computations are performed for a wide range of dimensionless parameters. It is seen that the laser beamwidth tends to attain a constant value depending upon plasma electron density, axial inhomogeneity and laser irradiance for different strength of magnetic field. Further, enhanced propagation, focusing and penetration of an intense laser beam is evident through plots from slightly underdense to overdense plasma with different types of density profiles.

Heating of ions by high frequency electromagnetic waves in magnetized plasmas

The heating of ions by high frequency electrostatic waves in magnetically confined plasmas has been a paradigm for studying nonlinear wave-particle interactions. The frequency of the waves is assumed to be much higher than the ion cyclotron frequency and the waves are taken to propagate across the magnetic field. In fusion type plasmas, electrostatic waves, like the lower hybrid wave, cannot access the core of the plasma. That is a domain for high harmonic fast waves or electron cyclotron waves—these are primarily electromagnetic waves. Previous studies on heating of ions by two or more electrostatic waves are extended to two electromagnetic waves that propagate directly across the confining magnetic field. While the ratio of the frequency of each wave to the ion cyclotron frequency is large, the frequency difference is assumed to be near the ion cyclotron frequency. The nonlinear wave-particle interaction is studied analytically using a two time-scale canonical perturbation theory. The theory elucidates the effects of various parameters on the gain in energy by the ions—parameters such as the amplitudes and polarizations of the waves, the ratio of the wave frequencies to the cyclotron frequency, the difference in the frequency of the two waves, and the wave numbers associated with the waves. For example, the ratio of the phase velocity of the envelope formed by the two waves to the phase velocity of the carrier wave is important for energization of ions. For a positive ratio, the energy range is much larger than for a negative ratio. So waves like the lower hybrid waves will impart very little energy to ions. The theoretical results are found to be in good agreement with numerical simulations of the exact dynamical equations. The analytical results are used to construct mapping equations, simplifying the derivation of the motion of ions, which are, subsequently, used to follow the evolution of an ion distribution function. The heating of ions can then be properly quantified in terms of the wave parameters and can be conveniently used to find ideal conditions needed to heat ions by high frequency electromagnetic waves.

Geometric phases of the Faraday rotation of electromagnetic waves in magnetized plasmas

Geometric phases of circularly polarized electromagnetic waves in nonuniform magnetized plasmas is studied theoretically. The variation of the propagation direction of circularly polarized waves results in a geometric phase, which also contributes to the Faraday rotation, in addition to the standard dynamical phase. The origin and properties of the geometric phase are investigated. The influence of the geometric phase to plasma diagnostics using the Faraday rotation is discussed as an application of the theory.

Slow packets of electromagnetic waves in magnetized plasma with ferrite grains

The propagation of narrow Gaussian electromagnetic wave packets in the collisionless magnetized plasma with ferrite grains (MPFG) is studied. In this system, in the frequency range close to the frequency of the electron cyclotron resonance, which coincides with the frequency of the ferromagnetic resonance, the dispersion of the electric permittivity (electron subsystem) and magnetic permeability (ferrite grain subsystem) must be taken into account simultaneously. The refractive index η of MPFG can be negative and with increase in frequency becomes positive passing through zero. The strong dispersion of η and the group velocity vg results in the spreading of the wave packets, which propagate with velocity much smaller than the speed of light. Their phase velocity is negative if η<0 and positive if η>0. For η<0, the group velocity can have a maximum at some frequency. The wave packets centered at this frequency are weakly spreading. The existence of slow waves in the frequency range, where η≤0, may be a general property of left handed media.

The anomalous penetration of intense circularly polarized electromagnetic beam through overdense magnetized plasma

The steady state nonlinear propagation of an intense, circularly polarized electromagnetic beam in an inhomogeneous magnetized plasma has been investigated in paraxial approximation. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. Further, rising due to cyclotron resonance effect. The propagation of the electromagnetic waves in magnetized plasma in both the extraordinary and ordinary mode is analyzed. The nonlinearity in dielectric function is considered in presence of external magnetic field due to saturation effects for arbitrary large intensity, which leads to focusing/defocusing of the beam. The focusing effect along with magnetic field helps in the process of anomalous penetration of the beam by enhancing the depletion of the plasma from the axial region. The penetration increases with the incident beam power up to some critical value beyond which it rises abruptly when all electrons have been driven out of the axis. The cyclotron resonance effect awfully supports the laser beam to propagate inside the overdense plasma region. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction applicable for underdense and overdense plasma.

Modulation and suppression of weak Cotton-Mouton effect by Faraday rotation

Polarization of electromagnetic waves in magnetized plasma is studied in conditions, when Cotton-Mouton effect is weak enough as compared with Faraday one. Evolution of polarization state is described by new mathematical approach, namely, by angular variables technique (AVT) which describes evolution of the angular parameters of polarization ellipse in magnetized plasma. The method of consequent approximations is applied, which uses the ratio (Ω ⊥/Ω 3) of Cotton-Mouton and Faraday terms, as a small parameter of a problem and allows obtaining simple analytical expressions for azimuthal and ellipticity angles in frame of the first and second approximations. The phenomenon of ellipticity modulation and suppression by Faraday rotation is revealed, which consists in ellipticity decreasing for stronger Faraday rotation, what makes polarization closer to linear one. Numerical illustration of the phenomenon are presented. It is shown that account of the second-order terms of the method of consequent approximation provides an accuracy better than 1% even in conditions, when small parameter Ω ⊥/Ω 3 achieves the value 1/4.

A finite-mass fluid electron simulation model for low-frequency electromagnetic waves in magnetized plasmas

A finite-mass fluid electron model has been developed for simulating low-frequency electromagnetic waves in finite-β magnetized plasmas. Here, β is the ratio between plasma and magnetic pressures. It is demonstrated in slab geometry that the model successfully exhibits the linear properties of both the kinetic and inertial Alfvén waves as well as the theoretically predicted collisionless tearing-mode instability.

Stimulated Brillouin scattering of electromagnetic waves in magnetized plasmas

AbstractA previous theoretical result on stimulated Brillouin scattering is corrected.

Manipulating Electromagnetic Waves in Magnetized Plasmas: Compression, Frequency Shifting, and Release

A new approach to manipulating the duration and frequency of microwave pulses using magnetized plasmas is demonstrated. The plasma accomplishes two functions: (i) slowing down and spatially compressing the incident wave, and (ii) modifying the propagation properties (group velocity and frequency) of the wave in the plasma during a uniform in space adiabatic in time variation of the magnitude and/or direction of the magnetic field. The increase in the group velocity results in the shortening of the temporal pulse duration. Depending on the plasma parameters, the frequency of the outgoing compressed pulse can either change or remain unchanged. Such dynamic manipulation of radiation in plasma opens new avenues for manipulating high power microwave pulses.

Relativistic electron beam acceleration by Compton scattering of extraordinary waves

Relativistic transport equations, which demonstrate that relativistic and nonrelativistic particle acceleration along and across a magnetic field and the generation of an electric field transverse to the magnetic field, are induced by nonlinear wave-particle scattering (nonlinear Landau and cyclotron damping) of almost perpendicularly propagating electromagnetic waves in a relativistic magnetized plasma were derived from the relativistic Vlasov-Maxwell equations. The relativistic transport equations show that electromagnetic waves can accelerate particles in the k″ direction (k″=k−k′). Simultaneously, an intense cross-field electric field, E0=B0×vd∕c, is generated via the dynamo effect owing to perpendicular particle drift to satisfy the generalized Ohm’s law, which means that this cross-field particle drift is identical to the E×B drift. On the basis of these equations, acceleration and heating of a relativistic electron beam due to nonlinear wave-particle scattering of electromagnetic waves in a magnetized plasma were investigated theoretically and numerically. Two electromagnetic waves interact nonlinearly with the relativistic electron beam, satisfying the resonance condition of ωk−ωk′−(k⊥−k⊥′)vd−(k∥−k∥′)vb≃mωce, where vb and vd are the parallel and perpendicular velocities of the relativistic electron beam, respectively, and ωce is the relativistic electron cyclotron frequency. The relativistic transport equations using the relativistic drifted Maxwellian momentum distribution function of the relativistic electron beam were derived and analyzed. It was verified numerically that extraordinary waves can accelerate the highly relativistic electron beam efficiently with βmec2≲1GeV, where β=(1−vb2∕c2)−1∕2.

Propagation of electromagnetic waves in the plasma near electron cyclotron resonance: Undulator-induced transparency

Propagation of electromagnetic waves in magnetized plasma near the electron cyclotron frequency can be strongly modified by adding a weak magnetic undulator. For example, both right- and left-hand circularly polarized waves can propagate along the magnetic field without experiencing resonant absorption. This effect of entirely eliminating electron cyclotron heating is referred to as the undulator-induced transparency (UIT) of the plasma, and is the classical equivalent of the well-known quantum mechanical effect of electromagnetically induced transparency. The basics of UIT are reviewed, and various ways in which UIT can be utilized to achieve exotic propagation properties of electromagnetic waves in plasmas are discussed. For example, UIT can dramatically slow down the waves’ group velocity, resulting in the extreme compression of the wave energy in the plasma. Compressed waves are polarized along the propagation direction, and can be used for synchronous electron or ion acceleration. Strong coupling between the two wave helicities are explored to impart the waves with high group velocities ∂ω∕∂k for vanishing wave numbers k. Cross-helicity coupling for realistic density and magnetic field profiles are examined using a linearized fluid code, particle-in-cell simulations, and ray-tracing WKB calculations.

Theory of stimulated scattering of large-amplitude waves

Comprehensive comments on the theory of stimulated scattering instabilities of high-frequency electromagnetic waves in magnetized plasmas are presented. It is shown that our general dispersion relations are appropriate for deducing valuable information regarding the growth rates of scattering instabilities and the long-term evolution of modulationally unstable waves in space and laboratory plasmas as well as in astrophysical settings.

Emission of electromagnetic waves in magnetized plasma in the presence of field aligned currents: A model for occurrence of circular polarizations in the pulsar radiations

The growth rate of electromagnetic waves, in the whistler mode frequency range, in the presence of field aligned currents is calculated. A model for the occurrence of circular polarizations in pulses of pulsars is presented.

Excitation of plasma waves by electromagnetic waves in magnetized plasmas

Three-dimensional equations for the plasma wake fields in the presence of a single frequency, intense circularly polarized electromagnetic (CPEM) wave in a two-component magnetoplasma are derived. For a given CPEM envelope, the axial electric fields of plasma waves are obtained for a one-dimensional model problem in which all the waves are aligned along the magnetic-field lines. It is found that the presence of an external magnetic field can significantly enhance the strength of the plasma wake fields when the right-hand CPEM wave is used for the excitation purposes.

Filamentation instability of electromagnetic waves in magnetized plasmas

The filamentation instability of electromagnetic electron and ion-cyclotron waves is investigated by including the combined effect of relativistic electron mass variation as well as static density and field-aligned magnetic field perturbations that are created by the radiation pressure. Analytical expressions for the critical power at which the instability starts are presented. The relevance of this investigation to radio-frequency wave heating of fusion plasmas is pointed out.

Theory of near-sonic envelope electromagnetic waves in magnetized plasmas.

Theory of near-sonic envelope electromagnetic waves in magnetized plasmas.

Compact dispersion relations for parametric instabilities of electromagnetic waves in magnetized plasmas

The existence of compact dispersion relations for parametric instabilities of coherent electromagnetic waves in magnetized plasmas is addressed here. In general, comprehensive dispersion relations for parametric instabilities in unmagnetized plasmas become more complicated in the presence of an applied time-independent magnetic field. This is demonstrated with a fluid perturbation theory. A compact dispersion relation for parametric instabilities in unmagnetized plasma is heuristically extended here to the case of a magnetized plasma. This dispersion relation gives the correct results in a variety of circumstances of interest in considering electron cyclotron heating applications.