Langmuir Wave Collapse Research Articles

Hot electron scaling for two-plasmon decay in ICF plasmas

We present a parametric scaling of hot electron (HE) generation at quarter critical density from the two-plasmon decay process. The study is conducted with the laser plasma simulation environment code, considering Langmuir decay instabilities (LDI) and laser pump depletion in 2D. The parameter scan is conducted as a function of electron temperature, ion–electron temperature ratio, drive strength, and density scale length. The scaling shows an hot electron (HE) conversion fraction up to 40%, HE fluxes up to 6 × 10 14 W / cm 2, and average temperatures in the range of 30 to 100 keV. The electron angular distributions exhibit two main regions: the plasma “bulk,” characterized by homogeneous emission, up to energies of 30 − 60 keV depending on the individual laser–plasma conditions, and a HE tail after ≃ 50 − 60 keV. The mid-energy electrons are homogeneously emitted toward the end of the plasma bulk and acquire energy through electron plasma wave (EPW) Landau damping from Langmuir wave collapse and LDI cascade. The HE tail has electrons emitted in the forward direction and at low divergence, due to turbulence and EPW Landau damping from multi-staged acceleration. Finally, the laser power transmitted through the quarter critical region reaches values from ∼ 80 % down to ∼ 35 % for increasing HE generation, with absorption due to EPW collisional damping in the range of ∼ 10 % − 35 %.

Rogue waves and solitons of the generalized modified nonlinear Schrödinger equations

Many applications of the classical nonlinear Schrödinger equations with cubic and power nonlinearity are seen in nonlinear optics, plasma physics, superconductivity, propagation of the electric field in optical fibers, self-focusing and collapse of Langmuir waves in plasma physics, to model deep water waves and freak waves in the ocean. Objectives:In this paper, the generalized form of the modified nonlinear Schrödinger equation is proposed with various nonlinearities. Methods:Bernoulli equation method, which is one of the ansatz-based methods, is considered to be obtained as the novel soliton solutions of the modified nonlinear Schrödinger equation with various nonlinearities. Results:With the view of the results, new improvements can happen for applications of the model.

Detection of Extreme and Exceptional Langmuir Wave Packets in Solar Type III Radio Bursts

AbstractWe report the STEREO observations of two extreme and exceptional Langmuir wave packets, which are the most intense wave packets ever detected in solar type III bursts; their peak intensities Et∼ 215 and ∼ 161 mVm−1 beat out the previous 107 mVm−1 record, reported by Thejappa and MacDowall (2018a; https://doi.org/10.3847/1538-4357/aaca3b). These observations provide new evidence for (1) the four‐wave interaction called the oscillating two‐stream instability (OTSI), which is the coupling of two beam‐excited Langmuir waves with an ion sound wave yielding downshifted and upshifted side bands, and (2) Langmuir solitons formed as a result of OTSI, and (3) density cavities created by their ponderomotive forces. The fast Fourier transform spectra of these wave packets provide what is believed to be the first evidence for harmonics of the electron plasma frequency, fpe up to the order of 5 with peak intensities falling off with increasing harmonic number. The higher order spectral analysis indicates that these harmonics probably correspond to the electromagnetic waves excited as a result of various three‐wave interactions. We argue that although the observed characteristics also indicate that these wave packets could be collapsing wave packets formed as a result of nucleation instability, the observed evidence for OTSI and Langmuir solitons trapped inside the self‐generated density cavities strongly favor the OTSI as the route for the spatial collapse of Langmuir waves in the present case. The implication of these findings for theories of solar type III radio bursts is discussed.

Evidence for Oscillating Two-stream Instability and Spatial Collapse of Langmuir Waves in a Solar Type II Radio Burst

Abstract We present the high time resolution in situ observations of Langmuir waves, likely excited by an electron beam accelerated by a coronal-mass ejection-driven super-critical quasi-perpendicular interplanetary shock into its upstream solar wind, which happens to be the source region of a solar type II radio burst. We show that (1) these waves occur as coherent localized magnetic-field-aligned, one-dimensional wave packets with durations of a few milliseconds and with peak intensities well in excess of the threshold for strong turbulence processes, (2) they provide what is believed to be the first evidence for: (a) the oscillating two-stream instability (OTSI) , where L 1 and L 2, U and D, and S are the pump Langmuir waves, up- and down-shifted side bands, and ion sound waves, respectively, (b) a three-wave interaction , where is the second-harmonic electromagnetic wave, (3) they satisfy the threshold condition for formation of collapsing solitons, and (4) they are accompanied by their ponderomotive force induced density cavities with , where is the level of ponderomotive force induced density fluctuations and is that of the ambient fluctuations. These findings strongly suggest that the observed wave packets provide evidence for the collapsing solitons formed as a result of OTSI. The implication is that the strong turbulence processes probably play very important roles in excitation of type II radio emissions as well as in stabilization of shock-accelerated electron beams.

Observational Evidence for Langmuir Wave Collapse in the Source Region of a Solar Type III Radio Burst

Abstract High-time-resolution in situ wave observations show that Langmuir waves associated with solar type III radio bursts often occur as coherent localized one-dimensional magnetic-field-aligned wave packets with short durations of a few milliseconds and peak intensities well above the strong turbulence thresholds. In this paper, we report observations of a wave packet obtained by the time domain sampler of the STEREO WAVES experiment, which is unique in the sense that it is the most intense wave packet ever detected in association with a solar type III radio burst, with a peak intensity E t ∼ 107 mVm−1. We show that this wave packet provides evidence for (1) oscillating two-stream instability (OTSI), (2) a collapsing soliton formed as a result of OTSI, (3) the formation of a soliton–caviton pair, and (4) excitation of second and third harmonic electromagnetic waves. We also show that the peak intensity and spatial width satisfy the threshold condition for this wave packet to be the collapsing Langmuir wave packet formed as a result of nucleation processes even when δn b > δn p , where δn b and δn p are the levels of background and ponderomotive-force-induced density fluctuations, respectively. Thus, these observations provide unambiguous evidence for the spatial collapse of Langmuir waves in the source region of a type III radio burst, and the observed spectral evidence for OTSI and the ponderomotive-force-induced density cavity strongly suggest that OTSI is mostly likely responsible for the collapse of the observed wave packet.

ON THE ORIGIN AND PHYSICS OF GAMMA FLARES IN CRAB NEBULA

We consider parametric generation of electrostatic waves in the magnetosphere of the pulsar PSR0531. The suggested mechanism allows us to convert the pulsar rotational energy into the energy of Langmuir waves. The maximum growth rate is achieved in the superluminal area, where the phase velocity of perturbations exceeds the speed of light. Therefore, electromagnetic waves do not damp on particles. Instead, they create plasmon condensate, which is carried out outside of the pulsar magnetosphere and reaches the Crab Nebula. It is shown that the transfer of the energy of the plasmon condensate from the light cylinder to the active region of the nebula happens practically without losses. Unlike the plasma of the magnetosphere, the one of the nebula contains ions, i.e., it may sustain modulation instability, that leads to the collapse of the Langmuir condensate. Langmuir wave collapse, in turn, leads to the acceleration of the distribution function particles. Furthermore, the processes that lead to self-trapping of the synchrotron radiation are discussed. The self-trapping results in the growth of the radiation intensity, which manifests itself observationally as a flare. The condition for the self-trapping onset is derived, showing that if the phenomenon takes place at 100 MeV, then it does not happen at lower (or higher) energies. This specific kind of higher-/lower-energy cutoff could explain why when we observe the flare at 100 MeV that no enhanced emission is observed at lower/higher energies!

Evidence for generation of unstable suprathermal electron population in the auroral F region

AbstractAnomalous incoherent scatter radar (ISR) spectra confined to narrow altitude ranges near the F region peak and correlated with dynamic auroral precipitation have previously been identified and explained in terms of the cavitating beam‐driven Langmuir turbulence. In this work we used a one‐dimensional Zakharov simulation to constrain the range of physical mechanisms underlying these observational features. We find that although Langmuir wave collapse and caviton formation generated by electron beams with energies of 1 keV can give rise to similar radar echoes, the predicted spectral features and intensities of such echoes are inconsistent with experimental data acquired by various ISRs. Our results suggest that the free energy for the turbulence must be provided by unstable low‐energy (5 − 20 eV) electron populations and that such populations must be produced locally in the F region ionosphere.

Quantum Zakharov model in a bounded domain

We consider an initial boundary value problem for a quantum version of the Zakharov system arising in plasma physics. We prove the global well-posedness of this problem in some Sobolev type classes and study properties of solutions. This means that the quantum Zakharov model is coherent with the observation of an absence of collapse of (quantum) Langmuir waves, hence might be a valid model for the description of electronic plasma waves. In the dissipative case the existence of a finite-dimensional global attractor is established, and regularity properties of this attractor are studied. For this we use the recently developed method of quasi-stability estimates. In the case when external forces are C ∞ functions, we show that every trajectory in the attractor is C ∞ in both time and spatial variables. This can be interpreted as the absence of sharp coherent structures in the limiting dynamics.

EVIDENCE FOR THE OSCILLATING TWO STREAM INSTABILITY AND SPATIAL COLLAPSE OF LANGMUIR WAVES IN A SOLAR TYPE III RADIO BURST

We present observational evidence for the oscillating two stream instability (OTSI) and spatial collapse of Langmuir waves in the source region of a solar type III radio burst. High time resolution observations from the STEREO A spacecraft show that Langmuir waves excited by the electron beam occur as isolated field structures with short durations ~3.2 ms and with high intensities exceeding the strong turbulence thresholds. These short duration events are identified as the envelope solitons which have collapsed to spatial scales of a few hundred Debye lengths. The spectra of these wave packets contain an intense peak and two sidebands, corresponding to beam-resonant Langmuir waves, and down-shifted and up-shifted daughter Langmuir waves, respectively, and low-frequency enhancements below a few hundred Hz. The frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI. The observed high intensities, short scale lengths, sideband spectral structures, and low-frequency enhancements strongly suggest that the OTSI and spatial collapse of Langmuir waves probably control the nonlinear beam-plasma interactions in type III radio bursts.

Arrest of Langmuir wave collapse by quantum effects

The arrest of Langmuir wave collapse by quantum effects, first addressed by Haas and Shukla [Phys. Rev. E 79, 066402 (2009)] using a Rayleigh-Ritz trial function method is revisited, using rigorous estimates and systematic asymptotic expansions. The absence of blow up for the so-called quantum Zakharov equations is proved in two and three dimensions, whatever the strength of the quantum effects. The time-periodic behavior of the solution for initial conditions slightly in excess of the singularity threshold for the classical problem is established for various settings in two space dimensions. The difficulty of developing a consistent perturbative approach in three dimensions is also discussed and a semiphenomenological model is suggested for this case.

A microwave detector based on an MCT photodiode for subthermonuclear plasma research

A microwave detector including a single-element infrared (IR) photodiode mounted in a cooled Dewar and a preamplifier is developed. An IR photodiode of the n +-p type is created on the basis of mercury-cadmium telluride (HgCdTe or MCT) heteroepitaxial structures grown by means of molecular beam epitaxy. A special profile of MCT structures throughout the MCT layer thickness ensures a low series resistance of less than 10 Ω and a high quantum efficiency at a level of 0.65 without any antireflection coating. For the spectral range of 8 to 12 μm, IR photodiodes are characterized by a low threshold power of 3.8·10−13 W·Hz−1/2 and 10−19 W·Hz−1 in the direct and heterodyne regimes, respectively. The cooled Dewar maintains the operating temperature of the IR photodiode in the interval of 77 to 80 K for 8. The preamplifier operates in a frequency range up to 1 GHz. With the use of this microwave detector, a method is developed for detection of intensity of a CO2 laser beam on plasma fluctuations caused by heating by a relativistic electron beam (REB). At high REB intensities, dips of the turbulence signal with a duration of several nanoseconds are observed, which is interpreted as a collapse of Langmuir waves.

Energy mode distribution: An analysis of the ratio of anti-Stokes to Stokes amplitudes generated by a pair of counterpropagating Langmuir waves

Results from plasma wave experiments in spacecrafts give support to nonlinear interactions involving Langmuir, electromagnetic, and ion-acoustic waves in association with type III solar radio bursts. Starting from a general form of Zakharov equation (Zakharov, V.E., 1985. Collapse and self-focusing of Langmuir waves. Hand-book of Plasma Physics Cap.2, 81–121) the equations for electric fields and density fluctuations (density gratings) induced by a pair of counterpropagating Langmuir waves are obtained. We consider the coupling of four triplets. Each two triplets have in common the Langmuir pump wave (forward or backward wave) and a pair of independent density gratings. We numerically solve the dispersion relation for the system, extending the work of (Alves, M.V., Chian, A.C.L., Moraes, M.A.E., Abalde, J.R., Rizzato, F.B., 2002. A theory of the fundamental plasma emission of type- III solar radio bursts. Astronomy and Astrophysics 390, 351–357). The ratio of anti-Stokes ( AS ) ( ω 0 + ω ) to Stokes ( S ) ( ω 0 - ω * ) electromagnetic mode amplitudes is obtained as a function of the pump wave frequency, wave number, and energy. We notice that the simultaneous excitation of AS and S distinguishable modes, i.e., with Re { ω } = ω r ≠ 0 , only occurs when the ratio between the pump wave amplitudes, r is ≠ 1 and the pump wave vector k 0 is < ( 1 3 ) W 0 1 / 2 , W 0 being the forward pump wave energy. We also observe that the S mode always receives more energy.

Impossibility of Zakharov's short-wavelength modulational instability in plasmas with intense Langmuir turbulence

An analysis of two experimental observations of Langmuir wave collapse is performed. The corresponding experimental data are shown as evidence against the occurrence of collapses. The physical reason preventing the collapses is found to be the nonresonant electron diffusion in momentum. In this process, plasma thermal electrons are efficiently heated at the expense of wave energy, therefore intense collisionless wave dissipation takes place. The basic reason for the underestimation of nonresonant electron diffusion in the traditional theory is shown to be the substitution of a real plasma by a plasma probabilistic ensemble.A study of nonresonant electron diffusion refraining from ensemble substitution is performed. It is shown that its intensity is sufficient for suppression of Zakharov's short-wavelength modulational plasma instability [Zakharov, V. E., Sov. Phys. JETP35, 908 (1972)]. This explains the nonoccurrence of Zakharov's Langmuir wave collapse in experiments.

Collisionless dissipation of Langmuir turbulence

An analysis of two experimental observations of Langmuir wave collapse is performed. The corresponding experimental data are shown to give evidence against the collapse. The physical reason for preventing the collapses is found to be the nonresonant electron diffusion in momentums. In this process, plasma thermal electrons are efficiently heated at the expense of wave energy, and intense collisionless wave dissipation takes place. The basic reason of underestimation of this phenomenon in traditional theory is shown to be the substitution of real plasma by a plasma probabilistic ensemble. A theory of nonresonant electron diffusion in a single collisionless plasma is developed. It is shown that corresponding collisionless wave dissipation may arrest spectral energy transfer towards small wave numbers.

Quasilinear diffusion as a result of modulational instability in the pulsar plasma.

Quasilinear diffusion due to modulational instability is considered in this paper. Interaction between the high-frequency, nearly transverse O mode (or the transverse X mode) and the low-frequency, nearly longitudinal L-O mode in a pulsar magnetospheric pair plasma can lead to modulational instability. The low-frequency L-O mode is superluminal, which is not subjected to usual Landau damping, and it is possible that excess wave energy is stored in this superluminal mode. The superluminal low-frequency L-O mode can dissipate in a way similar to the process of Langmuir wave collapse, that is, it cascades from the long- to short-wavelength regimes. When the phase speed becomes less than c, the waves can be damped through various resonances. We consider, in particular, damping through cyclotron resonance, which can lead to particle acceleration. The energetic beam particles, which have a very small spread initially, can develop a high-energy distribution tail, acquiring pitch angles through quasilinear diffusion. These particles can emit gamma rays through synchrotron radiation, contributing to the observed pulsar high-energy emission.

Effect of ambient density fluctuations on Langmuir wave collapse and strong turbulence

The effect of ambient density fluctuations on Langmuir wave collapse and strong Langmuir turbulence is investigated. Hamiltonian analysis of the collapse threshold implies that fluctuations with scales near those of nucleating wave packets can disrupt them before they can accumulate enough energy to collapse, provided the ambient fluctuation level is greater than that generated ponderomotively by the Langmuir waves. If packet disruption is effective, Langmuir energy cannot be dissipated via wave collapse and burnout, but must be scattered off density fluctuations directly to high wave numbers, as predicted by previous analyses. Numerical simulations of strong Langmuir turbulence confirm these predictions, with sudden transitions occurring from a strong-turbulence regime to one dominated by scattering or one with relatively rare wave collapses as a result of disruption of nascent wave packets. A corresponding sudden drop in Langmuir energy density is observed. Simulations of individual wave packets near the threshold for collapse show that such packets are easily disrupted by fluctuations with wavelengths near their linear scale, and confirm previous analytic disruption criteria.

Nonlinear saturation of stimulated Raman scattering in laser hot spots

Two-dimensional simulation studies are reported of the nonlinear development of stimulated Raman scattering (SRS) from a compact laser hot spot using a reduced model, which includes saturation by pump depletion, Langmuir wave decay cascades, Langmuir wave collapse, and ponderomotive density profile modification. The needle-like intensity distribution in a speckle arising from a random phase plate processed laser beam promotes backscatter SRS. The dependence of the saturated reflectivity and (the comparable in magnitude) absorptivity, on ion acoustic wave and Langmuir wave damping, laser power, electron density, and temperature is studied. There are regimes in which the ponderomotive potential (as well as the Ohmic dissipation) of the induced Langmuir turbulence exceeds that of the localized laser pump. The results support the conclusion that the Langmuir wave Landau damping must be determined by an electron velocity distribution modified by quasilinear and Ohmic heating to account for SRS observed at low densities and high temperatures.

Existence regions of regimes with anomalously high rates of plasma generation in grid plasma switch elements

Results are presented from a systematic investigation of the conditions under which anomalously high rates of plasma generation are observed in the anode region of a low-voltage Knudsen arc in grid plasma switch elements. The phenomenon develops over a wide range of currents and switched voltages under conditions for which the plasma density in the cathode-grid region is noticeably higher than the density in the anode region. and its onset is characterized by a pronounced pressure threshold of ∼2×10−2 Torr. The results are analyzed from the standpoint of the possible mechanisms for anomalous plasma generation — collisional nonresonance diffusion of electrons in velocity space, leading to enrichment of the distribution function in fast particles, and the collapse of Langmuir waves in the gap at the high energies of the beam produced when the wires of the grid are bridged by the quenching pulse and and the current is blocked.

On the amplitude of intense Langmuir waves in the terrestrial electron foreshock

Waveforms of large‐amplitude Langmuir oscillations were recorded by the Wind spacecraft in the Earth's upstream electron foreshock region. We present some statistics of the waveforms and discuss them in the context of various saturation mechanisms. In particular, it is found that the value of Epeak/Erms is not large, as previously suggested, and that the largest‐amplitude Langmuir waveforms are generally somewhat sinusoidal and lack structure on small spatial scales. The measured probability distribution of electric field amplitude and dimensionless energy suggest that some stochastic process may play a role in wave generation. The values of dimensionless energy needed to arrest Langmuir wave collapse occur with very small probability and the value of Epeak/Erms for large fields suggests that, statistically, Langmuir wave collapse is not an important process in the terrestrial foreshock.

Nonlinear wave collapse and strong turbulence

The theory and applications of wave self-focusing, collapse, and strongly nonlinear wave turbulence are reviewed. In the last decade, the theory of these phenomena and experimental realizations have progressed rapidly. Various nonlinear wave systems are discussed, but the simplest case of collapse and strong turbulence of Langmuir waves in an unmagnetized plasma is primarily used in explaining the theory and illustrating the main ideas. First, an overview of the basic physics of linear waves and nonlinear wave-wave interactions is given from an introductory perspective. Wave-wave processes are then considered in more detail. Next, an introductory overview of the physics of wave collapse and strong turbulence is provided, followed by a more detailed theoretical treatment. Later sections cover numerical simulations of Langmuir collapse and strong turbulence and experimental applications to space, ionospheric, and laboratory plasmas, including laser-plasma and beam-plasma interactions. Generalizations to self-focusing, collapse, and strong turbulence of waves in other systems are also discussed, including nonlinear optics, solid-state systems, magnetized auroral and astrophysical plasmas, and deep-water waves. The review ends with a summary of the main ideas of wave collapse and strong-turbulence theory, a collection of open questions in the field, and a brief discussion of possible future research directions.