Electron Plasma Waves Research Articles

Electron plasma wave excitation by a q-Gaussian laser beam and subsequent electron acceleration

In this paper, we theoretically study the propagation dynamics of a q-Gaussian laser beam in a plasma by considering the relativistic and ponderomotive nonlinearities. The q-Gaussian laser beam exhibits unique characteristics while interacting with the plasma. The q-Gaussian laser beam redistributes the plasma density in a different way, which affects the laser self-focusing. A comparative study of the self-focusing for Gaussian and q-Gaussian laser beams is reported. The results obtained from numerical analysis reveal a stronger self-focusing of the q-Gaussian laser beam in plasmas, which is desirable to excite a large amplitude plasma wave for electron acceleration by extending the interaction length. We then extended this study to investigate the electron plasma wave excitation by the q-Gaussian laser beam. The electron plasma wave is driven more efficiently by the q-Gaussian laser beam. Our results show that the electron plasma wave field intensity enhances more than twofold for the q-Gaussian laser beam in comparison with the case of a Gaussian laser beam. The electron plasma wave excited by a q-Gaussian beam can accelerate the plasma electrons to higher energies. Numerical results are presented for the established set of laser and plasma parameters.

Nonlinear excitation of electron plasma waves trapped in a blob in the O1-mode ECRH experiments

We analyze a scenario of low-threshold parametric decay instability of the pump ordinary wave associated with excitation in a plasma blob of two trapped electron plasma waves at frequencies smaller than the local Langmuir frequency.

Generation of second harmonics of self-focused quadruple-Gaussian laser beams in collisional plasmas with density ramp

This paper presents a scheme for generation of second harmonics of intense laser beams propagating through collisional plasmas. In order to see the effect of uniformity as well as nonuniformity of the irradiance over the cross section of the laser beam on yield of generated harmonics, the field distribution in the medium has been expressed in terms of quadruple Gaussian (Q.G) profile instead of Gaussian profile. Moment theory has been adopted to find semi-analytical solution of the wave equation for the slowly varying envelope of the laser beam. When laser beam with frequency $$ \omega _0 $$ propagates through plasma it makes the plasma electrons to oscillate at pump frequency $$ \omega _0 $$ . These oscillations of the plasma electrons in the presence of thermal velocity generate an electron plasma wave (EPW) at frequency $$ \omega _0 $$ . The generated EPW beats with the pump beam to produce its second harmonics. By using hydrodynamic fluid model of plasma, nonlinear current density for the SHG has been obtained. Emphasis are put on investigation of the effect of various laser and plasma parameters on propagation dynamics of pump beam and conversion efficiency of second harmonics.

Symmetric Airy electron plasma wave

A symmetric Airy electron plasma (SAiEP) wave, which is caused by launching four Airy beams symmetrically in the initial plane in an unmagnetized collisionless plasma, is analytically investigated in this paper. In addition to intensity distributions, evolutions, and the potential of the SAiEP wave with different parameters, the difference between the SAiEP wave and the Airy-like electron plasma wave is studied as well. The results show that the SAiEP wave with different distances between the main lobes in the initial plane behaves differently as the decay factor changes. When the decay factor increases, the frequency and the amplitude of the potential become smaller. Besides, the SAiEP wave has the autofocusing property, while the Airy-like electron plasma wave has the weak diffraction property.

Requirements for a 4ω Thomson scattering system on megajoule scale laser facilities.

With the arrival of megajoule class laser facilities, the features of laser-produced plasmas are evolving toward unprecedented high electron temperatures reached in the environment of a cm-scale indirect-drive Hohlraum for a few tens of nanoseconds. In this context, the need for in situ experimental characterization of the plasma parameters becomes critical in order to test hydrodynamics simulations in these novel conditions. Taking advantage of the progress achieved in the last 40 years, Thomson scattering has become a classic diagnostic in the characterization of laser produced plasmas. However, the many beam configuration of the megajoule scale experiments makes the measurements increasingly complex because the Thomson scattering signals produced by the 351 nm heaters themselves dominate the plasma emission around 263 nm, a wavelength range typically of interest when a 4ω Thomson probe is used. This paper reviews the requirements for and the potential of a 4ω Thomson scattering system to be operated on such 351 nm megajoule scale facilities in order to characterize the hot (Te > 3 keV) plasmas produced in the indirect-drive irradiation of a Hohlraum. It is found that the configuration of the diagnostic could be optimized in order to enable the detection of the ion acoustic resonances over a large domain of plasma parameters. The results for the electron plasma wave resonances are also given.

Propagation properties of the chirped Airy–Gaussian vortex electron plasma wave* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11775083 and 11374108), the Science and Technology Program of Guangzhou City (Grant No. 2019050001), and the Special Funds for the Cultivation of Guangdong College Students' Scientific and Technological Innovation (Grant Nos. pdjh2020a0149 and pdjh2019a0127).

We introduce a new class of the chirped Airy–Gaussian vortex electron plasma (CAiGVEP) wave which constitutes the exact and continuous transition modes between the chirped Airy vortex and the chirped Gaussian vortex electron plasma wave. The intensity, the phase, and the angular momentum density flow of the CAiGVEP wave are discussed under different distribution factors and different chirp modes.

Saturation of trapped particle instability induced by vortex-merging in electron plasma waves

Phase space vortex merging in electron plasma waves is researched by applying a periodically changing electric field in plasma space with Maxwellian velocity distribution. The pump electric field excites the electron plasma wave with large amplitude and electron phase space vortices are formed. The electron plasma wave can be transited to longer wave modes through vortex merging processes. Excepting the fundamental mode of electron plasma waves, two or more modes appear and grow exponentially before vortex merging. After merging, another mode replaces the initial pumping wave as the strongest wave mode. It is verified that the growth of this new strong mode is related to trapping particle instability. Vortex merging is one of the saturation mechanisms of trapped particle instability.

Two-color laser-plasma interactions for efficient production of non-thermal hot electrons

Efficient production of non-thermal hot electrons has been demonstrated experimentally by interactions of a plasma and two-color lasers with wavelengths of 527 and 1053 nm. The two-color-lasers and plasma interactions caused a 4.8 times enhancement of the temperature of the hot electrons and a 2.7 times enhancement of energy conversion from the lasers to the hot electrons compared with that obtained with only a 527 nm laser. These experimental results can be explained by a staging electron acceleration mechanism realized with a mixture of plasma waves excited by the two-color lasers. The primary 527 nm laser excites at least two electron plasma waves. Those have completely different phase velocities, therefore, staging acceleration cannot occur only with the 527 nm laser. The secondary 1053 nm laser excites other electron plasma waves, of which the phase velocities locate between those of the waves excited by the primary 527 nm laser. Some of the background thermal electrons can be heated contentiously to several hundred kilo-electronvolts by the electron plasma waves excited by the two-color lasers.

Electron plasma wave Thomson scattering on laboratory plasma jets

Plasma jets created from a 15 μm thick Al foil on a 1 MA pulsed power machine were studied using a new electron plasma wave (EPW) Thomson scattering system in conjunction with previously developed ion acoustic wave (IAW) Thomson scattering and interferometry. These diagnostics give multiple ways of measuring the electron temperature and density of the jet. Analysis of the EPW feature found the on-axis density of the jet to be between 5×1018 and 1.4×1019 cm−3, which either matched or was higher than interferometry measurements. Outside of the jet, both of these diagnostics measured a density of 7×1017 cm−3. On one shot, the EPW spectral feature showed two pairs of peaks within a 250 μm scattering length on the edge of the jet, which shows that the boundary of the jet ∼1 mm radius jet is ≲ 0.1 mm. While electron temperature measurements of the plasma jet are complicated by the probe beam producing inverse bremsstrahlung heating of the jet, comparison of the electron temperature measured between IAW and EPW Thomson scattering showed the EPW feature to imply significantly higher electron temperatures than the IAW feature (e.g., 160 eV vs 70 eV in one case). Various sources of this discrepancy (for example, density gradients, collisions, and a lag in ionization) and their impact on the plasma are discussed.

Generation of second harmonics of q-Gaussian laser beams in collisional plasma with upward density ramp

An investigation of frequency up-conversion of a laser beam through the phenomenon of second harmonic generation (SHG) in collisional plasma with an upward density ramp is presented. The variational method has been adopted to find a semi-analytical solution of the wave equation for the slowly varying envelope of the laser beam. When a laser beam with frequency ω0 propagates through plasma it causes the plasma electrons to oscillate at pump frequency ω0. These oscillations of the plasma electrons in the presence of thermal velocity generate an electron plasma wave (EPW) at frequency ω0. The generated EPW beats with the pump beam to produce its second harmonics. By using a hydrodynamic fluid model of plasma, the source term for the SHG has been obtained. Emphasis is put on investigation of the effect of various laser and plasma parameters on the propagation dynamics of the pump beam and the conversion efficiency of second harmonics.

Effects of continuous phase plate on plasma corona homogeneity and laser-plasma instabilities in experiments with three target materials

Corona homogeneity and spectra of scattered light and hot electrons produced by laser-plasma instabilities inside laser-produced plastic, aluminum, and gold plasmas were investigated with and without the use of continuous phase plate (CPP) to the laser beam. Improvement of the corona homogeneity was observed for all three materials after applying CPP, while the inhibition of the intensity of backward-scattered light and the amount of emitted hot electrons was not always synchronous for different materials, which is interpreted as a result of the changes in thresholds of the stimulated Raman scattering (SRS) and the two-plasmon decay (TPD) instability before and after the application of CPP. By comparing the changes of SRS scattered light intensity with the amount of hot electrons in different kinetic energy ranges for all three target materials in our experiments, we conclude that SRS is more responsible for the diagnosed hot electrons between 50–150 keV, and those above 150 keV should be generated by TPD, which could be explained by the difference in phase velocity of electron plasma waves between SRS and TPD calculated from measured and simulated parameters of corona and laser-plasma instabilities.

Enhanced second harmonic generation of Hermite–Gaussian laser beam in plasma having density transition

Under the combined effect of relativistic and ponderomotive nonlinearity, resonant second harmonic generation of an intense Hermite–Gaussian (H–Gaussian) laser beam in a plasma having upward density ramp profile has been theoretically investigated. Under WKB approximation and with the use of the moment theory approach the coupled differential equations are derived which govern the spot size of the H–Gaussian laser beam. The ponderomotive force creates the density gradient in the background plasma electrons which is responsible for the excitation of the electron plasma wave. The large-amplitude electron plasma wave interacts with the fundamental beam which produces coherent radiations with double the frequency of the incident beam. In addition, the Gouy phase shift is observed for the H–Gaussian laser beam in plasma under the effect of density transition. The analysis shows the vital role of the different modes of the H–Gaussian laser beam and density ramp on the efficiency of generated harmonics and self-phase shift of laser beams in plasma.

Control of ordinary and extraordinary waves excitation by an axial magnetic field in motional plasma

The propagation of transverse Electromagnetic (EM) waves along a high energy relativistic electron beam passing through a neutralizing heavy ion background is investigated in the presence of an external axial magnetic field. By making use of the linearized fluid equations coupled with Maxwell’s equations the dielectric tensor and the dispersion relation of excited modes are derived. Since the electron motion is considered relativistic and fluid theory of plasma is used to describe the system, the obtained results are applicable to a vast range of high energy density regime. The mutual interaction between EM and Electron Plasma Waves (EPWs) is studied numerically. In the absence of the axial magnetic field, the EPWs and the Extraordinary Electromagnetic (EOEM) waves interact due to the existence of the self-generated magnetic field. The instability caused by this interaction has already been reported [Phys. Plasma.16, 062107 (2009) ]. We found that applying an axial magnetic field will cause deflection to plasma oscillations which enables coupling between EPWs and Ordinary Electromagnetic (OEM) waves as well. The results show that increasing the external magnetic field strength suppresses the growth rate caused by the coupling of EPWs-EOEM and passes it to the growth of EPWs-OEM. Therefore by adjusting the external magnetic field strength, the growth of EOEM and OEM modes can be controlled.

Axion excitation by intense laser fields in a plasma

We study the excitation of axions by intense laser pulses propagating in a plasma. We assume that the pulses propagate along the direction of a static magnetic field. We examine two different configurations. One is that of a long pulse, with a duration Δt much longer than the electron plasma period, Δt ≫ 1/ωp. In this case, the axion field couples with the electron plasma waves (or plasmons) which are excited by the laser pulse, due to a modulational instability. The dispersion relation of the coupled axion-plasmon modes, the unstable regimes and the instability growth rates are established. The other configuration is that of a very short laser pulse, with a duration of the order of (or shorter than) the electron plasma period. In this case, the modulational instability is absent, but a laser wakefield can be excited. The latter consists of both electron density and axion field perturbations. The amplitude of this wakefield is described with a simple one-dimensional model. The two configurations (long and short pulse) can eventually be used to create axions in the laboratory and we suggest that laser plasma experiments could shed some light on the existence of these hypothetical dark matter particles.

Evolution of the Electron Distribution Function in the Presence of Inverse Bremsstrahlung Heating and Collisional Ionization.

The picosecond evolution of non-Maxwellian electron distribution functions was measured in a laser-produced plasma using collective electron plasma wave Thomson scattering. During the laser heating, the distribution was measured to be approximately super-Gaussian due to inverse bremsstrahlung heating. After the heating laser turned off, collisional ionization caused further modification to the distribution function while increasing electron density and decreasing temperature. Electron distribution functions were determined using Vlasov-Fokker-Planck simulations including atomic kinetics.

Plasma Model of Generation and Slip of Linear Defects in Crystalline Materials

In dielectrics and semiconductors, a plasma model of the generation and slip of dislocations is considered, where under shock loads in a generalized space of rectangular pulses an alternating field forms a distribution of pairs of photoelectrons and cations; these electrons with velocities Ve create δ-collisions with cold plasma from free electrons and holes with masses me and mh (mh ≫ me), they emit and absorb longitudinal electron plasma waves whose phase velocities wpw / kpw are close to or are equal to the velocities Ve, while the frequencies wpw and wave numbers kpw of the wave packet of plasma waves are complex, the short-wave components of this wave packet at kpw ⋅ ae ≫ 1 (ae -Debye screening radius) decay in the core linear defect, and its long-wavelength components propagate in the region of the medium surrounding the core of the defect at kpw ⋅ ae ≅ 1. When a defect is generated, the distribution of cations under the influence of the internal Coulomb field shifts to the region of the first peak (protrusion) of the electron plasma wave, thereby forming a vacancy valley. When sliding under the influence of an external electric field, a cationic plasma wave consisting of a vacancy valley and two cationic protrusions moves against the background of an additional potential relief created by an electron plasma wave near the core of the defect. It has been shown that δ-collisions create flows of dynamic large-scale correlations of plasma fluctuations in the form of asymptotics of different-time correlators of density and potential fluctuations as t → +∞.

Stimulated Raman scattering in a non-eigenmode regime

Stimulated Raman scattering (SRS) in plasma in a non-eigenmode regime is studied theoretically and numerically. Different from normal SRS with the eigen electrostatic mode excited, the non-eigenmode SRS is developed at plasma density $n_{e}>0.25n_{c}$ when the laser amplitude is larger than a certain threshold. To satisfy the phase-matching conditions of frequency and wavenumber, the excited electrostatic mode has a constant frequency around half of the incident light frequency $\unicode[STIX]{x1D714}_{0}/2$ , which is no longer the eigenmode of electron plasma wave $\unicode[STIX]{x1D714}_{pe}$ . Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero. Super-hot electrons are produced by the non-eigen electrostatic wave. Our theoretical model is validated by particle-in-cell simulations. The SRS driven in this non-eigenmode regime is an important laser energy loss mechanism in the laser plasma interactions as long as the laser intensity is higher than $10^{15}~\text{W}/\text{cm}^{2}$ .

Second harmonic generation of high power laser beam in cold quantum plasma

Second harmonic generation of high power laser beam in cold quantum plasma (CQP) is investigated in present communication. In order to derive 2nd order differential equations governing the behavior of laser beam against normalized distance, paraxial theory and WKB approximation are adopted. There is self-focusing of beam on account of relativistic increase in mass of electron, which further results in production of intensity gradients in transverse direction. The electron plasma wave (EPW) gets excited due to these intensity gradients at pump wave frequency. Further, there is an interaction of EPW with pump beam thereby producing to second harmonics. In order to study the effect of various parameters of laser and plasma medium on self-focusing of pump beam and second harmonic yield, we have carried out numerical simulations. The comparison of present results is made with classical relativistic plasma (CRP).

Enhanced second harmonic generation of dark hollow Gaussian laser beam in collisionless magneto-plasma

This paper presents an analysis and subsequent discussion of self-focusing and second harmonic generation (SHG) of a dark hollow Gaussian (dhG) laser beam in a magneto plasma, considering ponderomotive non-linearity. As a result of collisionless non-linearity, non-uniform distribution of plasma electrons takes place due to non-uniform irradiance of intensity along the wavefront of the laser beam which leads to the self-focusing of laser beam and production of density gradient in the transverse direction. As a result of density gradient, an electron plasma wave is excited at pump frequency that interacts with the pump beam to produce its second harmonics of frequency twice that of latter. To envision the spot size and dynamics of propagation of dhG laser beam, moment theory in Webtzel-Kramers-Brillouin (WKB) approximation has been used. The nature of self-focusing and second harmonic yield (SHY) is highlighted through critical curves as a plot of dimensionless beam width parameter and power of second harmonic radiation versus the dimensionless distance of propagation. The effect of magnetic field on self-focusing and SHY of various orders of dhG laser beam has also been explored.

Coupling Instability of a Warm Relativistic Electron Beam with Ion-Channel Guiding

In this paper, the coupling instability of warm relativistic electron beam (WREB) propagating through the ion channel guiding is investigated in detail. Obtaining the equilibrium state of the system by considering the self-electric and azimuthal magnetic field, the fluid-Maxwell equations as well as linear perturbation theory are employed to derive the dispersion relation of the excited modes in the system. Numerical analysis of the obtained dispersion relation shows that the electromagnetic (EM) instability can be induced nearly the center of the beam through coupling between the fast electron plasma wave (FEPW), originated from the longitudinal oscillation of WREB, and fast forward electromagnetic wave (FFEW). In this sense, growing the perturbation amplitude occurs due to transport the kinetic energy of WREB to the EM wave at the specific frequency range, where the phase velocity of FEPW and FFEW is coincided. The results of the present investigation will greatly contribute to the understanding of the stability of the warm relativistic electron beam in laboratory experiments, such as in free electron laser experiments, where the ion-channel guiding is used to confine the electrons against the self-repulsive forces generated by the beam itself.