Nonlinear Ponderomotive Force Research Articles

Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor

Measured highly elevated gains of proton–boron (HB11) fusion (Picciotto et al., Phys. Rev. X 4, 031030 (2014)) confirmed the exceptional avalanche reaction process (Lalousis et al., Laser Part. Beams 32, 409 (2014); Hora et al., Laser Part. Beams 33, 607 (2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh acceleration above $10^{20}~\text{cm}~\text{s}^{-2}$ for plasma blocks was theoretically and numerically predicted since 1978 (Hora, Physics of Laser Driven Plasmas (Wiley, 1981), pp. 178 and 179) and measured (Sauerbrey, Phys. Plasmas 3, 4712 (1996)) in exact agreement (Hora et al., Phys. Plasmas 14, 072701 (2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell’s stress tensor by the dielectric properties of plasma leading to the nonlinear (ponderomotive) force $f_{\text{NL}}$ resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. This is supported also by other experiments with very high HB11 reactions under different conditions (Labaune et al., Nature Commun. 4, 2506 (2013)).

Effect of dc-magnetic field on the growth rate of Raman backscattering of X-mode laser in magnetized collisional plasma

AbstractStimulated Raman backward scattering of an X-mode laser beam propagating in a homogenous plasma is studied in the presence of a transverse magnetic field. As the laser propagates in its X-mode in plasma, it decays into an upper hybrid wave and a down-shifted sideband wave. Beating the incident laser with the sideband exerts a nonlinear ponderomotive force acting on plasma electrons driving the excited upper hybrid wave. The incident wave then parametrically couples with the upper hybrid wave to drive the sideband. Using the fluid model and nonlinear current density, the nonlinear ponderomotive force is obtained to find the dispersion relation of the scattered sideband wave and the growth rate of the instability in the weakly relativistic regime. It is shown that the growth rate decreases and the cut-off points in the normalized wave number of the upper-hybrid wave become smaller by increasing the static magnetic field.

Self-focusing and defocusing of Gaussian laser beams in collisional underdense magnetized plasmas with considering the nonlinear ohmic heating and ponderomotive force effects

The propagation characteristics of a Gaussian laser beam in collisional magnetized plasma are investigated by considering the ponderomotive and ohmic heating nonlinearities. Here, by taking into account the effect of the external magnetic field, the second order differential equation of the dimensionless beam width parameter is solved numerically. Furthermore, the nonlinear dielectric permittivity of the mentioned plasma medium in the paraxial approximation and its dependence on the propagation characteristics of the Gaussian laser pulse is obtained, and its variation in terms of the dimensionless plasma length is analyzed at different initial normalized plasma and cyclotron frequencies. The results show that the dimensionless beam width parameter is strongly affected by the initial plasma frequency, magnetic strength, and laser pulse intensity. Furthermore, it is found that there exists a certain intensity value below which the laser pulse tends to self focus, while the beam diverges above of this value. In addition, the results confirm that, by increasing the plasma and cyclotron frequencies (plasma density and magnetic strength), the self-focusing effect can occur intensively.

The new possibility of the fusion p + 11B chain reaction being induced by intense laser pulses

We discuss the experimental and theoretical principal schemes of a thermonuclear reactor, based on the fusion reaction p + 11B: beam collisions, fusion in degenerate plasmas, ignition at the plasma, particle acceleration by nonlinear ponderomotive forces and irradiation of the solid 11B target by a proton beam at the Coulomb explosion of hydrogen microdroplets. The fusion reaction p + 11B can be initiated by ultrashort high intensity laser pulses under conditions far from thermodynamic equilibrium. This may result in fusion products containing a small amount of neutrons and other nuclear radiation effects. It was found that the fusion reaction p + 11B produces further nuclear reactions and generates high-energy protons. The latter can support the chain reaction process. Our approach allows us to also investigate nuclear reactions in the early Universe and in stars.

High-intensity terahertz generation by nonlinear frequency-mixing of lasers in plasma with DC magnetic field

AbstractWe propose a mechanism of highly focused, tunable and high-intensity terahertz (THz) radiation generation by frequency-mixing of two super-Gaussian lasers with frequencies ω1, ω2 and wave numbers k1, k2 (laser profile index p > 2) in a corrugated plasma in the presence of external static magnetic field ${B_0}\hat z$. In this process, a strong nonlinear ponderomotive force is offered to the plasma electrons at frequency ω′ = ω1 − ω2 and wave number k′ = k1 − k2 by laser beams. The ponderomotive force results in a strong, controllable nonlinear transverse oscillatory current, which can be optimized by optimizing the external magnetic field, ripple parameters, and laser indexes. This controllable current produces focused and intense THz radiation of tunable frequency and power along with a remarkable efficiency ~25%.

Stimulated Brillouin side-scattering of the beat wave excited by two counter-propagating X-mode lasers in magnetized plasma

The stimulated Brillouin scattering (SBS) of nonresonant beat mode in the presence of static magnetic field is investigated in a plasma. Two counter-propagating lasers of frequencies (ω1 and ω2) and wave vectors (k1 and k2) drive a nonresonant space charge beat mode at the phase matching condition of frequency ω0≈ω1∼ω2 and wave number k→0≈k→1+k→2. The driver wave parametrically excites a pair of ion acoustic wave (ω,k→) and a sideband electromagnetic wave (ω3,k→3). The beat wave couples with the sideband electromagnetic wave to exert a nonlinear ponderomotive force at the frequency of ion acoustic wave. Density perturbations due to ion acoustic wave and ponderomotive force couple with the oscillatory motion of plasma electron due to velocity of beat wave to give rise to a nonlinear current (by feedback mechanism) responsible for the growth of sideband wave at resonance. The growth rate of SBS was reduced (from ∼1012s−1 to 1010s−1) by applying a transverse static magnetic field ∼90 T. The present study can be useful for the excitation of fast plasma waves (for the purpose of electron acceleration) by two counter-propagating laser beams.

Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma

A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω1, ω2) and wave numbers (k→1, k→2) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations (n′=nα0eiαz) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ωh (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ω=ω1−ω2 and k→=k→1−k→2+α→. The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters (a0) of super Gaussian lasers. In the present scheme, efficiency ∼10−2 is achieved with the optimization of all these parameters.

Non-linear Alfvén wave interaction leading to resonant excitation of an acoustic mode in the laboratorya)

The nonlinear three-wave interaction process at the heart of the parametric decay process is studied by launching counter-propagating Alfvén waves from antennas placed at either end of the Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. A simple damped, driven oscillator model making use of the MHD equations well-predicts most of the observations, but the width of the resonance curve is still under investigation.

Strong terahertz radiation generation by beating of two x-mode spatial triangular lasers in magnetized plasma

AbstractResonant THz radiation generation is proposed by beating of two spatial-triangular laser pulses of different frequencies (ω1, ω2) and wave numbers $\lpar \vec k_1 \comma \; \vec k_2 \rpar $ in plasma having external static magnetic field. Laser pulses co-propagating perpendicular to a dc magnetic field exert a nonlinear ponderomotive force on plasma electrons, imparting them an oscillatory velocity with finite transverse and longitudinal components. Oscillatory plasma electrons couple with periodic density ripples n′ = nq0eiqz to produce a nonlinear current, i.e., responsible for resonantly driving terahertz radiation at $\lpar {\rm \omega} = {\rm \omega} _1 - {\rm \omega} _2 \comma \; \vec k = \vec k_1 - \vec k_2 + \vec q\rpar $. Effects of THz wave frequency, laser beam width, density ripples, and applied magnetic field are studied for the efficient THz radiation generation. The frequency and amplitude of THz radiation were observed to be better tuned by varying dc magnetic field strength and parameters of density ripples (amplitude and periodicity). An efficiency about 0.02 is achieved for laser intensity of 2 × 1015 W/cm2 in a plasma having density ripples about 30%, plasma frequency about 1 THz and magnetic field about 100 kG.

Terahertz generation by two cross focused Gaussian laser beams in magnetized plasma

This paper presents a theoretical model for terahertz (THz) radiation generation by two cross-focused Gaussian laser beams in a collisionless magnetoplasma. The plasma is redistributed due to the ponderomotive nonlinearity which leads to the cross focusing of the laser beams. The focusing of the copropagating laser beams increases with increasing the externally applied static magnetic field which is perpendicular to the wave propagation direction. The nonlinear current at THz frequency arises on account of nonlinear ponderomotive force as a result of beating of the two lasers. The generated THz radiation amplitude increases significantly with increasing magnetic field. The cross focusing of two laser beams enhances the THz yield. Optimization of laser-plasma parameters gives the radiated normalized THz power of the order of 10 kW.

Erratum to: Kilotesla Magnetic Assisted Fast Laser Ignited Boron-11 Hydrogen Fusion with Nonlinear Force Driven Ultrahigh Accelerated Plasma Blocks

Nuclear fusion with confinement by available kilotesla magnetic fields allows improved performance for Inertial Confinement Fusion. The combination of this approach with the established ultrahigh laser acceleration of plasma blocks driven by nonlinear (ponderomotive) forces of ps laser pulses of exawatt power may permit high gain boron-11 fusion with protons. This potentially provides a path to very attractive fusion power stations based on aneutronic fusion.

Highly focused and efficient terahertz radiation generation by photo-mixing of lasers in plasma in the presence of magnetic field

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ω1, ω2 and wave numbers k1, k2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ω′=ω1−ω2 and wave number k′=k1−k2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ωUH=(ωp2+ωc2) (where ωc is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field.

Effects of transverse static electric field on terahertz radiation generation by beating of two transversely modulated Gaussian laser beams in a plasma

AbstractResonant excitation of terahertz (THz) radiation by nonlinear coupling of two filamented spatial-Gaussian laser beams of different frequencies and wave numbers is studied in plasma having transverse static electric field. The static ponderomotive force due to filamented lasers is balanced by the pressure gradient force which gives rise to transverse density ripple, while, the nonlinear ponderomotive force at frequency difference of beating lasers couples with density ripple giving rise to stronger transverse nonlinear current which results into the excitation of THz radiation at resonance. The coupling is further enhanced by the presence of static electric field and spatial-Gaussian nature of laser beams. An increase of six-fold in the normalized amplitude of THz is observed by applying a direct current field of about 50 KV. Effects of frequency, laser beam width, and periodicity factor of modulated laser amplitude are studied for the efficient THz radiation generation. These results can be utilized for generating controlled tunable THz sources for medical applications using low filament intensities (~ 1014 W/cm2) of beating lasers.

Nonlinear effects associated with the finite frequency pump kinetic Alfvén wave and turbulent spectrum in solar wind

The paper contains a numerical simulation of the nonlinear coupling between the kinetic Alfven wave and the ion acoustic wave for an intermediate β-plasma (me/mi≪β≪1). For this study, we have introduced the nonlinear ponderomotive force (due to the finite frequency (ω0<ωci) kinetic Alfven wave) in the derivation of the ion acoustic wave. The main aim of the present paper is to study the nonlinear effects associated with the different driving finite frequencies (ω0<ωci) of the pump kinetic Alfven wave on the formation of localized structures and a turbulent spectrum applicable to the solar wind around 1 AU. As a result, we found that the different driving frequencies of the pump kinetic Alfven wave affect the formation of the localized structures. We have also studied the turbulent scaling which follows (∼k−3.6) for ω0/ωci≈0.2, (∼k−3.4) for ω0/ωci≈0.3 and (∼k−3.2) for ω0/ωci≈0.4, at small scales. Further, we have also found that different finite driving frequencies of the pump kinetic Alfven wave affect the turbulence scaling at small scales, which may affect the heating of the plasma particles in solar wind. The present study is correlated with the observation made by the Cluster spacecraft for the solar wind around 1 AU.

Efficient Generation of Fusion Flames Using PW-ps Laser Pulses for Ultrahigh Acceleration of Plasma Blocks by Nonlinear (Ponderomotive) Forces

Changing the high intensity interaction time of lasers with plasma from nanosecond duration to picoseconds results in a categorically different regime. With high intensity picoseconds laser pulses, the optical energy is converted directly into kinetic energy of plasma blocks without thermal losses, without delays by collisions, and with exclusion of most of the instabilities. Following the long known theory by the nonlinear (ponderomotive) force, the plasma receives a predicted ultrahigh acceleration in agreement with measurements by Sauerbrey. Interaction of the generated plasma blocks with solid state fusion fuel should produce a side-on ignition of a Chu-Bobin fusion flame. Using hydrodynamics with separate electron and ion fluids, detailed properties can be studied about shock generation, including the varying velocity of the flame fronts far . Results from recent computations confirm how the collective nonthermal nonlinear force driven plasma interactions are causing only marginal electron heating.

Nonlinear interaction of proton whistler with kinetic Alfvén wave to study solar wind turbulence

This paper presents the nonlinear interaction between small but finite amplitude kinetic Alfvén wave (KAW) and proton whistler wave using two-fluid model in intermediate beta plasma, applicable to solar wind. The nonlinearity is introduced by modification in the background density. This change in density is attributed to the nonlinear ponderomotive force due to KAW. The solutions of the model equations, governing the nonlinear interaction (and its effect on the formation of localized structures), have been obtained using semi-analytical method in solar wind at 1AU. It is concluded that the KAW properties significantly affect the threshold field required for the filament formation and their critical size (for proton whistler). The magnetic and electric field power spectra have been obtained and their relevance with the recent observations of solar wind turbulence by Cluster spacecraft has been pointed out.

On the electrodynamic model of ultra-relativistic laser-plasma interactions caused by radiation reaction effects

A simple electrodynamic model is developed to define plasma-field structures in self-consistent ultra-relativistic laser-plasma interactions when the radiation reaction effects come into play. An exact analysis of a circularly polarized laser interacting with plasmas is presented. We define fundamental notions, such as nonlinear dielectric permittivity, ponderomotive and dissipative forces acting in a plasma. Plasma-field structures arising during the ultra-relativisitc interactions are also calculated. Based on these solutions, we show that about 50% of laser energy can be converted into gamma-rays in the optimal conditions of laser-foil interaction.

THz generation by cosh-Gaussian lasers in a rippled density plasma

This paper presents a scheme to achieve THz radiation by the beating of cosh-Gaussian lasers in spatially periodic density plasma (ripple density). Here, the lasers exert a nonlinear ponderomotive force along the transverse direction which imparts an oscillatory velocity to electrons that couples with the density ripple to generate a stronger transient transverse current due to the spatial variation of their fields, driving THz radiation. The importance of laser-beam-width parameters, decentred parameter, amplitude and periodicity of the density structure are discussed for THz emission. By changing the decentred parameter the peak intensity of lasers can be shifted in the transverse direction and a notable change is found in the magnitude of THz field amplitude and its conversion efficiency.

Nonlinear Brightness Optimization in Compton Scattering

In Compton scattering light sources, a laser pulse is scattered by a relativistic electron beam to generate tunable x and gamma rays. Because of the inhomogeneous nature of the incident radiation, the relativistic Lorentz boost of the electrons is modulated by the ponderomotive force during the interaction, leading to intrinsic spectral broadening and brightness limitations. These effects are discussed, along with an optimization strategy to properly balance the laser bandwidth, diffraction, and nonlinear ponderomotive force.

Tuning and Focusing of Terahertz Radiation by DC Magnetic Field in a Laser Beating Process

The role of an external DC magnetic held in tuning the frequency and power of terahertz (THz) radiation and obtaining focused radiation is clarified in a beating process using two spatial-triangular lasers, where a nonlinear ponderomotive force acting on the electrons provides oscillating current in longitudinal and transverse directions. The transient transverse current oscillating at the beating frequency produces THz radiations in extraordinary mode, when the beating frequency of lasers matches the upper hybrid frequency for the resonant excitation. Based on the maximum momentum transfer with the application of density ripples, this scheme is realized with high efficiency (>;0.01), where the radiation may attain >;107 V/cm held amplitude. This held can be further enhanced using higher amplitudes of density ripples and lasers fields. The consequences of any deviation from the triangular profile of lasers are also discussed by comparing the results with rounded triangular shape lasers.