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Due to their cost, experiments for inertial confinement fusion (ICF) heavily rely on numerical simulations to guide design. As simulation technology progresses, so too can the fidelity of models used to plan for new experiments. However, these high-fidelity models are by themselves insufficient for optimal experimental design, because their computational cost remains too high to efficiently and effectively explore the numerous parameters required to describe a typical experiment. Therefore, traditionally, ICF design has relied on low-fidelity modeling to initially identify potentially interesting design regions, which are then subsequently explored via selected high-fidelity modeling. In this paper, we demonstrate that this two-step approach can be insufficient: even for simple design problems, a two-step optimization strategy can lead high-fidelity searching toward incorrect regions and consequently waste computational resources on parameter regimes far away from the true optimal solution. We reveal that a primary cause of this behavior in ICF design problems is the presence of low-fidelity optima in different regions of the parameter space far away from high-fidelity optima. To address this issue, we propose an iterative multifidelity Bayesian optimization method based on Gaussian Process Regression that leverages both low- and high-fidelity models simultaneously. We demonstrate, using both two- and eight-dimensional ICF test problems, that our algorithm can effectively utilize both low-fidelity and high-fidelity models to refine the designs. This approach proves to be more efficient than relying solely on high-fidelity modeling for optimization. [ABSTRACT FROM AUTHOR]

In direct-drive inertial confinement fusion, target offset from the target chamber center (or center of beam convergence) may lead to significant implosion asymmetry and fusion yield degradation. In addition, cross-beam energy transfer (CBET) has been shown to be a significant source of laser energy scattering and leads to a reduction in implosion velocity and yield. To improve energy coupling and implosion performance, several techniques for CBET mitigation have been proposed. Recent simulations, however, have shown that CBET also substantially mitigates the effect of target offset on implosion asymmetry and yield [Anderson et al., Phys. Plasmas 27, 112713 (2020)]. Furthermore, the inclusion of CBET models in radiation-hydrodynamics codes was shown to greatly improve agreement between simulations and experiments involving substantial target offset distances. This paper explores the intensity dependence of this CBET–offset effect. In addition, it is shown that enhanced sensitivity to target offset can be expected when CBET-mitigation techniques are used in direct-drive implosions. This is shown through simulations of two such CBET-mitigation techniques on the OMEGA laser: (1) decreased beam-to-target radius, and (2) beam-to-beam frequency detuning. For the typical target offset distances (<15 μm) observed in experiments on OMEGA, however, overall yield is still anticipated to be substantially higher when CBET-mitigation techniques are employed. [ABSTRACT FROM AUTHOR]

A large number of magnetohydrodynamic (MHD) equilibrium calculations are often required for uncertainty quantification, optimization, and real-time diagnostic information, making MHD equilibrium codes vital to the field of plasma physics. In this paper, we explore a method for solving the Grad–Shafranov equation by using physics-informed neural networks (PINNs). For PINNs, we optimize neural networks by directly minimizing the residual of the partial differential equation as a loss function. We show that PINNs can accurately and effectively solve the Grad–Shafranov equation with several different boundary conditions, making it more flexible than traditional solvers. This method is flexible as it does not require any mesh and basis choice, thereby streamlining the computational process. We also explore the parameter space by varying the size of the model, the learning rate, and boundary conditions to map various tradeoffs such as between reconstruction error and computational speed. Additionally, we introduce a parameterized PINN framework, expanding the input space to include variables such as pressure, aspect ratio, elongation, and triangularity in order to handle a broader range of plasma scenarios within a single network. Parameterized PINNs could be used in future work to solve inverse problems such as shape optimization. [ABSTRACT FROM AUTHOR]

In the context of KSTAR plasma research, the discovery of the fast ion regulated enhanced mode is noteworthy due to its remarkable ability to maintain ion temperatures exceeding up to 10 keV for a few tens of seconds, avoid impurity accumulation, and keep low loop voltages. This new plasma operating scenario is achieved in a diverted configuration plasma by avoiding the H-mode transitions with sufficient additional power for the transition. Keeping the density low is the primary method for the avoidance. Additionally, adjustments to other parameters (plasma shape, neutral beam injection, and toroidal magnetic field) associated with the H-mode threshold power are applied to inhibit the transition process. This paper includes an experimental analysis and discussion of these findings. [ABSTRACT FROM AUTHOR]

Nonlinear kinetic structures, called electron phase-space holes (EHs), are regularly observed in space and experimental magnetized plasmas. The existence of EHs is conditioned and varies according to the ambient magnetic field and the parameters of the electron beam(s) that may generate them. The objective of this paper is to extend the 3D Bernstein–Greene–Kruskal model with cylindrical geometry developed by L.-J. Chen et al. ["Bernstein–Greene–Kruskal solitary waves in three-dimensional magnetized plasma," Phys. Rev. E 69, 055401 (2004)] and L.-J. Chen et al., ["On the width-amplitude inequality of electron phase space holes," J. Geophys. Res. 110, A09211 (2005)] to include simultaneously finite effects due to (i) the strength of the ambient magnetic field B 0 , by modifying the Poisson equation with a term derived from the electron polarization current, and (ii) the drift velocity ue of the background plasma electrons with respect to the EH, by considering velocity-shifted Maxwellian distributions for the boundary conditions. This allows us to more realistically determine the distributions of trapped and passing particles forming the EHs, as well as the width-amplitude relationships for their existence. [ABSTRACT FROM AUTHOR]

The process of numerical thermalization in particle-in-cell (PIC) simulations has been studied extensively. It is analogous to Coulomb collisions in real plasmas, causing particle velocity distributions (VDFs) to evolve toward a Maxwellian as macroparticles experience polarization drag and resonantly interact with the fluctuation spectrum. This paper presents a practical tutorial on the effects of numerical thermalization in 2D PIC applications. Scenarios of interest include simulations, which must be run for many thousands of plasma periods and contain a population of cold electrons that leave the simulation space very slowly. This is particularly relevant to many low-temperature plasma discharges and materials processing applications. We present numerical drag and diffusion coefficients and their associated timescales for a variety of grid resolutions, discussing the circumstances under which the electron VDF is modified by numerical thermalization. Though the effects described here have been known for many decades, direct comparison of analytically derived, velocity-dependent numerical relaxation timescales to those of other relevant processes has not often been applied in practice due to complications that arise in calculating thermalization rates in 1D simulations. Using these comparisons, we estimate the impact of numerical thermalization in several examples of low-temperature plasma applications including capacitively coupled plasma discharges, inductively coupled plasma discharges, beam plasmas, and hollow cathode discharges. Finally, we discuss possible strategies for mitigating numerical relaxation effects in 2D PIC simulations. [ABSTRACT FROM AUTHOR]

Zonal flows are known to diminish turbulent transport in magnetic fusion. Interestingly, there is an adiabatic invariant that implies the emergence of zonal flow. This paper shows that if this invariant is decreasing (due to some external factors), then the emerging zonal flow is better. It is also shown that the plasma inhomogeneity can lead to the decrease in the adiabatic invariant. A simple condition for such decrease is found. [ABSTRACT FROM AUTHOR]

The inclusion of drifts in plasma edge codes like SOLPS-ITER is required to match simulation data with experimental profiles. However, this remains numerically challenging. In this paper, the effect of some numerical factors on the final plasma solution is investigated. This study is performed on three EAST simulations in the upper single null configuration: an attached purely deuterium case, an attached case with limited Ne-seeding, and a detached Ne-seeded case. The effects of the anomalous conductivity and anomalous thermo-electric coefficient on the plasma potential are investigated. Next, the effect of the employed grids is shown. In order to investigate these effects, accurate drift simulations are needed. Therefore, the employed time step and numerical parameters are discussed for the three studied simulations. For all presented simulations, it is verified that the restriction of the grid to the first flux surface tangent to the main chamber wall is sufficient within the context of non-extended simulations. This means that the main power dissipation takes place inside the simulated domain, and only a small fraction of the power is leaving the B2.5 grid through the grid boundary closest to the first wall. Finally, the effect of drifts on the asymmetry between the inner and outer target for EAST simulations is demonstrated. [ABSTRACT FROM AUTHOR]

The numerical investigations into the acceleration of superheavy ions driven by a multi-PW, 30 fs laser pulse with a peak intensity from 5 × 1022 to 2 × 1023 W/cm2 were carried out using an advanced 2D3V particle-in-cell code. The properties of laser-accelerated Au, Pb, Bi, and U ion beams, such as ionization and ion energy spectra, ion beam energies, angular distributions of the beam fluence, the ion pulse shapes, and peak intensities, were examined and compared. It was found that for a laser intensity of 1023 W/cm2, a common feature of the Au, Pb, Bi, and U ion beams was the dominance in the beam of Ne-like ions that carry the vast majority (≥90%) of the energy of all accelerated ions and have by far the highest mean and maximum ion energy. The Ne-like ion beams for Au, Pb, Bi, and U have almost identical angular fluence distributions and ion pulse shapes, as well as peak fluencies and intensities. However, the dependence of the parameters of the Ne-like ion beam on the laser intensity is different for ions with different masses. In the considered laser intensity range, the heaviest ions (U ions) ensured the achievement of the highest beam parameters, such as the mean and maximum ion energy, the ion beam energy, or the laser-to-ions energy conversion efficiency. The mono-charge superheavy ion beams demonstrated in this paper open the prospect for novel applications of heavy ions in high energy-density physics, nuclear physics, and possibly in other fields. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) breakdown is one of the crucial factors limiting the power capacity of high-power microwave (HPM) generators. In this paper, a waveguide cavity has been designed to study quantitatively the influence of temperature on high-gradient RF breakdown. The two planes of the waveguide cavity are divided into a strong-field side and a weak-field side with the feeding of microwave signals. The temperature of the strong-field side of the waveguide cavity can be adjusted from ambient temperature (25 °C) to 435 °C by loading a resistive wire heater. The breakdown threshold of the waveguide cavity decreases apparently with the increase in the temperature. The breakdown threshold at 408 °C is 751 kV/cm, which is about 150 kV/cm lower than that at ambient temperature. In addition, the higher the temperature, the more pronounced the pulse shortening. Under the same microwave power injection, the averaged pulse width of HPM after passing through the waveguide cavity at 408 °C is equal to 17.6 ns, shortened by about 1/3 compared to that at ambient temperature. The quantitative study of the influence of temperature on the RF breakdown provides a new guideline for exploring breakdown suppression methods in HPM generators. [ABSTRACT FROM AUTHOR]

High-order spoof surface plasmon (SSP) mode on corrugated metallic surfaces can find many interesting applications, such as in imaging, sensing, transmission and enhanced radiation source, etc. In this paper, an efficient excitation method of the high-order SSP mode by using an injected electron beam on the uniform rectangular metallic grating is proposed and investigated numerically. Based on the matched wave momentum between the SSP mode and the electron beam, both the fundamental and high-order SSP modes can be excited on the structure by using a single injected electron beam. Numerical simulation results indicate that the maximum electric field intensity of the generated high-order SSP mode is about two orders higher than that of the fundamental SSP mode. In addition, the peak power of the excited high-order SSP mode is almost two times that of the fundamental SSP mode power by the same energy electron beam, which demonstrates the obvious advantage of the high-order SSP electronic excitation approach compared to the previous fundamental SSP mode excitation on the structure. The central working frequency of high-order SSP power spectrum is about three times that of the fundamental SSP power spectrum. Moreover, the influences of the injected electron beam energy on the excited SSP power spectrum are analyzed specifically. It is shown that the generated SSP power spectrum demonstrates a blue shift with the decreased working voltage of the electron beam simultaneously, with its peak power increasing. However, the working bandwidth is narrowed with decreased beam voltage, which further reveals its working mechanism of presented electronic excitation of the SSP mode. The presented studies provide a new method to excite a high-order SSP mode on the metallic grating, which can find some potential applications in high-sensitivity sensing, deep sub-wavelength waveguide, and many others in terahertz spectra. [ABSTRACT FROM AUTHOR]

Direct laser acceleration of electrons is an important energy deposition mechanism for laser-irradiated plasmas that is particularly effective at relativistic laser intensities in the presence of quasi-static laser-driven plasma electric and magnetic fields. These radial electric and azimuthal magnetic fields provide transverse electron confinement by inducing betatron oscillations of forward-moving electrons undergoing laser acceleration. Electrons are said to experience a betatron resonance when the frequency of betatron oscillations matches the average frequency of the laser field oscillations at the electron position. In this paper, we show that the modulation of the laser frequency as seen by an electron performing betatron oscillations can be another important mechanism for net energy gain that is qualitatively different from the betatron resonance. Specifically, we show that the frequency modulation experienced by the electron can lead to net energy gain in the regime where the laser field performs three oscillations per betatron oscillation. There is no net energy gain in this regime without the modulation because the energy gain is fully compensated by the energy loss. The modulation slows down the laser oscillation near transverse stopping points, increasing the time interval during which the electron gains energy and making it possible to achieve net energy gain. [ABSTRACT FROM AUTHOR]

Since the research toward high-power millimeter-wave generator becomes a tendency in high-power microwave, overmoded structure with the high-order mode has been a considerable interest because of its potential to increase power handling capacity (PHC). To expand the PHC of V-band transit-time oscillator and excite higher mode TM03, a dual annular multiple-beam cathode has been proposed. In the geometric structure of the dual annular multiple-beam diode, cathode rods around two concentric circles are uniformly placed on cathode base, and each circle has several graphite rods. Because of space charge shielding effect and fluctuation of electron beam, explosive emission current of inner and outer cathode circles is difficult to be balanced, and the electron beam transmission rate is not very high. To solve those two problems, the relative length (ΔL) and the relative radius (Δr) between the inner and outer cathode circles are optimized to obtain balanced currents of inner and outer beams and a good transmission rate. In this paper, the preliminary study of a dual annular multiple-beam cathode is carried out by optimizing the cathode structure. When ΔL and Δr are equal to 2.5 and 4 mm, respectively, the dual annular multiple-beams cathode can provide 2.71 kA uniform intense relativistic electron beams under 421 kV, and the magnetic field is 1.2T. As a simulation result, explosively emitted and the 95.2% of total beam current transmission rate can be reached. [ABSTRACT FROM AUTHOR]

A cascaded relativistic magnetron array with symmetric feeder structure was first proposed as a multi-port phase-coherent high-power microwave source, which is intrinsically equipped with high structural symmetry. Two symmetrically positioned slow-wave structures surround the feeder structure, which reduces axial electron drifting in each resonant system and ensures the phase-locking process. In this paper, a theory of structure-provided coupling coefficient and oscillator-required coupling coefficient is proposed as the phase-locking prerequisites. The method is evaluated by adopting two A6-type resonant systems. The symmetrically driven cascaded relativistic magnetron array employs a typical π-mode with an anode voltage of 450 kV and an axial magnetic field of 0.47 T. The phase-locked state was achieved in 17 ns with a jitter less than 5 deg. The total output power exceeds 2.3 GW at a frequency of 2.15 GHz, and the power flow in each output port exceeds 350 MW. The transversely opposed driven scheme can be combined with other phase-locking patterns for additional uses, and further optimization of resonant system could be applied for enhancing device performance. The theory of coupling prerequisites is also sufficient for analyzing other cascaded relativistic magnetrons. [ABSTRACT FROM AUTHOR]

This paper is concerned with the condition for the development of ballooning instability in the dipole Earth's magnetosphere. Under investigation is the dependence of the ratio of the radial and azimuthal wave vector components squared on the wave frequency squared ω 2 . It is shown that this dependence is depicted by continuous curve (the dispersion curve). The part of the dispersion curve with ω 2 > 0 corresponds to the slow magnetosonic mode modified by the coupling with the Alfvén mode, while the part with ω 2 < 0 corresponds to the ballooning instability. The instability appears at some critical ratio of the radial and azimuthal wave vector components, the growth rate reaches the maximum value where this ratio is zero. The instability threshold is determined depending on the β parameter and the pressure gradient when the coupling of the slow and Alfvén modes is taken into account. On a given magnetic shell, at a given β value, large pressure gradient favors the instability, and vice versa, at a given pressure gradient, a large β favors instability. It is shown that in the unstable mode, the compressional magnetic field component has a phase shift with respect to the radial component. This can be used to detect unstable ballooning modes during observations in the Earth's magnetosphere. [ABSTRACT FROM AUTHOR]

The Helically Symmetric Experiment (HSX) is a quasisymmetric stellarator with minimal parallel viscous damping in a helical direction. The parallel flow (Vǁ) along the magnetic field is similarly weakly damped by viscosity. In this paper, the self-consistent steady-state parallel and poloidal momentum balance equations are used to show that a large Vǁ on the order of the ion thermal velocity can increase the ion resonant radial electric field (Er) beyond the value calculated using the typical approximation that Vǁ is zero. By altering the damping of Vǁ, either by degrading the quasisymmetry or varying the neutral density, the ion resonant Er can shift in a controllable fashion. It is shown explicitly that there exist stable and unstable steady-state solutions in the two-dimensional space of Vǁ and Er. A stability analysis of each solution is performed by calculating the eigenvalues and eigenvectors of the Jacobian. The unstable solution corresponds to a saddle point in which the eigenvalues have opposite signs. The analysis leads to the conclusion that unstable solutions occur when the derivative of the total poloidal damping with respect to Er is positive. A hysteresis in Er and Vǁ is observed when the radial current density is linearly increased to a maximum and then decreased back to zero. Jumps in the radial electric field and the parallel flow are observed as the radial current density drives the evolution from one stable point to the next. This result is similar to experimental data observed on several devices. [ABSTRACT FROM AUTHOR]

Branched flow is a universal phenomenon in which treebranch-like filaments form through traveling waves or particle flows in irregular mediums. Branched flow of high-current relativistic electron beams (REBs) in porous materials has been recently discovered [Jiang et al., Phys. Rev. Lett. 130, 185001 (2023)]. REB branching is accompanied by extreme beam focusing, up to a hundred times the initial value, at predictable caustic locations. The energy coupling efficiency between the beam and porous material surpasses that in homogeneous targets by two orders of magnitude. This paper examines REB branching, focusing on how beam parameters (e.g., Lorentz factor and density) and characteristics of the porous materials (e.g., pore size, skeleton thickness, and density) influence branching patterns. Analyses of the dynamics of individual beam electrons are also provided. The findings pave the way for further understanding REB branching and its potential applications in the future. [ABSTRACT FROM AUTHOR]

Darwin approximation, a non-relativistic submodel of the Maxwell's equations, has been used for theoretical and computational investigations of magnetized plasmas. In this short paper, an improved Darwin approximation is proposed, which is applicable not only to the Coulomb gauge but also to the Lorenz counterpart. The proposed approximation exactly satisfies the conservation of charge, momentum, and energy under the use of the Lorenz and Coulomb gauges. [ABSTRACT FROM AUTHOR]

In this paper, the effects of pulse voltage rise time on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are analyzed. Based on the assumption of initial electrons generation due to the field emission, the simulations are performed using a three-dimensional particle-in-cell, Monte Carlo-collision model for the pulse voltage with a rise time of 40, 60, and 100 ns, respectively. The breakdown experiments of the nitrogen spark switch are carried out for three different rise times. The results obtained are as follows. First, the nanosecond pulsed breakdown of the switch includes the formation and fast propagation of the streamer, which depend on the multiplication of the electron avalanche, and the intense ionization due to photoelectrons and energetic electrons, respectively. Second, with the rise time of pulse voltage increasing, the generation of runaway electrons becomes more difficult and the streamer branches, which are mainly caused by photoionization and captured energetic electrons, become more obvious. Finally, the breakdown time delay of the switch becomes shorter and the breakdown voltage becomes higher at the same pressure for the decreasing rise time of pulse voltage, which is consistent with the measurement results. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental observation of the transition of a 2D dust crystal to a non-equilibrium solid–liquid phase coexistence state. The experiments have been carried out in an L-shaped dusty plasma experimental device in a DC glow discharge argon plasma environment. Initially, a monolayer crystalline structure is formed, which is later transformed to a two-phase coexistence state using the background neutral pressure as a control parameter. Self-excited horizontal oscillations are found in the center of the monolayer prior to the appearance of the coexistence state. It is observed that a molten center coexists with a solid periphery. Various structural, thermodynamic, and dynamical quantities are used to characterize the phase state. The surface tension at the solid–liquid circular interface is also determined. A detailed parametric study is made to delineate the existence region of such a state. It is found that melting caused at the core is due to the onset of a localized Schweigert instability in the presence of a few stray particles beneath the top layer in that region. [ABSTRACT FROM AUTHOR]

In this paper, the mechanisms of the period-doubling bifurcation in pulsed Dielectric Barrier Discharges (DBDs) are numerically investigated at atmospheric pressure. Under the given discharge conditions, the pulsed DBDs could maintain a normal period-1 (P1) state at relatively larger repetition frequencies over 40 kHz, by decreasing the repetition frequency, namely, keeping the duration of the power-on phase unchanged but increasing the duration of the power-off phase, the simulation shows that the discharge bifurcates into a period-2 (P2) state after a transient period of instability. Although the charged particles can diffuse to the surface of dielectric plates more fully at a lower repetition frequency, the large quantities of ions in the sheath region produced by the relatively larger discharge current that have not yet dissipated completely before the next discharge event are proposed to play an important role in the discharge bifurcation process, and the spatial profiles of the charged particle density, electric field, and space charge density in the sheath region before the discharge ignition are examined deeply to further explore the corresponding underpinning physics. The large density of residual ions in the sheath region with the enhanced electric field can weaken the subsequent discharge event and induce the discharge to enter the period-doubling state. Moreover, the computational data indicate that the discharge evolves into the period-4 (P4) and period-8 (P8) state when the repetition frequency approaches 30 and 26 kHz at the given discharge conditions. The simulation data can effectively facilitate the understanding of the temporal nonlinear behaviors in pulsed DBDs and propose ways to further control the plasma stability in applications. [ABSTRACT FROM AUTHOR]

The effects of pulse rise time on the temporal evolution of electron energy and density under repetitive nanosecond pulses in atmospheric nitrogen with 100 ppm oxygen impurities are investigated in this paper by a two-dimensional particle-in-cell/Monte Carlo collision model. It is found that the peak value of mean electron energy increases with decreasing pulse rise time in the single pulsed discharge. However, in the repetitive pulsed discharge approximated by pre-ionization, the peak value of mean electron energy no longer varies with the pulse rise time, showing a saturation trend with decreasing pulse rise time. Whether or not pre-ionization is present, the time required for the mean electron energy to reach its peak is approximately equal to the pulse rise time. It is worth noting that the presence of pre-ionization enhances the tracking ability of the mean electron energy to the pulse waveform during the pulse rise edge. Although after the peak of the pulse, the mean electron energy terminates the tracking process to pulse waveform due to the formation of high-density avalanches and even streamers, its energy decay rate gradually decreases with the increase in the pre-ionization density. Therefore, when the pulse repetitive frequency is greatly increased or the pre-ionization density is increased by other means, it is possible to achieve the complete control of the mean electron energy by pulse waveform modulation. [ABSTRACT FROM AUTHOR]

This paper presents the results of theoretical and experimental studies of a surface-wave oscillator (SWO) of planar geometry excited by a ribbon high-current relativistic electron beam. Within the framework of the quasi-optical approach and direct three-dimensional particle-in-cell modeling, we demonstrate the advantages of open transverse edged configuration against the closed one for effective mode selection at a fairly large oversize factor. In the experiments carried out on the basis of the SINUKI accelerator (Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, 1 kA/650 keV/17 ns), we form a magnetically guided ribbon electron beam with a cross-section of 0.3 × 20 mm2, which moves parallel to a slow-wave structure with a period of 1.75 mm. A planar W-band SWO both of open and closed edged configuration has been experimentally tested. In full agreement with modeling, the open configuration exhibits much more stable operation, where at a frequency of 75 GHz, we observe pulse generation with duration of about 7 ns. The output power measured by the calorimetric method reaches 25 MW. [ABSTRACT FROM AUTHOR]

Space propulsion is unique among many proposed applications of the dense plasma focus in being critically dependent on the availability of a scaling theory that is well-grounded in physics, in conformity with existing experimental knowledge and applicable to experimentally untested configurations. This paper derives such a first-principles-based scaling theory and illustrates its application to a novel space propulsion concept, where the plasma focus sheath is employed as a power density amplifying mechanism to transport electric energy from a capacitive storage to a current-driven fusion load. For this purpose, a Generalized Plasma Focus problem is introduced and formulated. It concerns a finite, axisymmetric plasma, driven through a neutral gas at supersonic speed over distances much larger than its typical gradient scale length by its azimuthal magnetic field while remaining connected with its pulse power source through suitable boundaries. The Gratton-Vargas equation is rederived from the scaling properties of the equations governing plasma dynamics and solved for algebraically defined initial (insulator) and boundary (anode) surfaces. Scaling relations for a new space propulsion concept are derived. This consists of a modified plasma focus with a tapered anode that transports current from a pulsed power source to a consumable portion of the anode in the form of a hypodermic needle tube continuously extruded along the axis of the device. When the tube is filled with deuterium, the device may serve as a small-scale version of magnetized liner inertial fusion (MAGLIF) that could avoid failure of neutron yield scaling in a conventional plasma focus. [ABSTRACT FROM AUTHOR]

Energy-frontier TeV colliders based on plasma accelerators are attracting much attention due to the recent achievements in multi-stage laser acceleration as well as the remarkable advances in electron- and proton-driven plasma accelerators. Such colliders may suffer a fundamental energy loss due to the radiation reaction (RR) effect, as the electrons lose energy through betatron radiation emission. Although the RR may not be critical for low-energy accelerators, it will exert limitations on TeV-class plasma-based colliders that need to be considered. In this paper, we have provided an extensive study of the RR effect in all pathways toward such colliders, including multi-stage plasma acceleration driven by the state-of-the-art lasers and the relativistic electron beam as well as the single-stage plasma acceleration with the energetic proton beams available at the CERN accelerator complex. A single-particle Landau–Lifschitz approach is used to consider the RR effect on an electron accelerating in the plasma blow-out regime. The model determines the boundaries where RR plays an energy limiting role on such colliders. The energy gain, the radiation loss, and the validity of the model are numerically explored. [ABSTRACT FROM AUTHOR]

Inertial confined fusion experiments at the National Ignition Facility have recently entered a new regime approaching ignition. Improved modeling and exploration of the experimental parameter space were essential to deepening our understanding of the mechanisms that degrade and amplify the neutron yield. The growing prevalence of machine learning in fusion studies opens a new avenue for investigation. In this paper, we have applied the Gradient-Boosted Decision Tree machine-learning architecture to further explore the parameter space and find correlations with the neutron yield, a key performance indicator. We find reasonable agreement between the measured and predicted yield, with a mean absolute percentage error on a randomly assigned test set of 35.5%. This model finds the characteristics of the laser pulse to be the most influential in prediction, as well as the hohlraum laser entrance hole diameter and an enhanced capsule fabrication technique. We used the trained model to scan over the design space of experiments from three different campaigns to evaluate the potential of this technique to provide design changes that could improve the resulting neutron yield. While these data-driven model cannot predict ignition without examples of ignited shots in the training set, it can be used to indicate that an unseen shot design will at least be in the upper range of previously observed neutron yields. [ABSTRACT FROM AUTHOR]

This paper considers the instabilities of imploding aluminum metal-puff Z-pinches with an outer plasma shell. An experiment was performed on the GIT-12 generator (3.2–3.6 MA, ∼1 μs implosion times, and ∼15 cm initial Z-pinch radius). It was shown that the density profile of the Z-pinch material had the dominant effect on the growth and suppression of instabilities. Two Z-pinch load configurations were used. The first configuration provided a tailored density profile (TDP) [A. L. Velikovich et al., Phys. Rev. Lett. 77, 853 (1996)], which ensured the suppression of the magneto-Rayleigh–Taylor (MRT) instability in the Z-pinch. For the second configuration, the density profile was changed in such a way that a density notch from 10 to 0.5 μg/cm3 occurred at a radius of about 3 cm from the Z-pinch axis. The notch in the density profile and the nonmonotonic increase in density resulted in a completely unstable compression of the Z-pinch. This gave rise to large-scale instabilities, which were detected by optical diagnostics. The instabilities grew and were not suppressed even in the stagnation phase, despite a sharp increase in the density of the Z-pinch material near the axis. The results were interpreted using the model proposed by Curzon et al. [Proc. R. Soc. London A 257, 386 (1960)]. The total instability amplitude is the sum of the amplitudes of MRT and magneto-hydrodynamic (MHD) instabilities. The growth of the total instability in the density notch region is due to the development of MRT instability. Thus, if the density profile has a notch, the Z-pinch compression in the stagnation phase occurs under strong perturbations at the magnetic field/plasma interface. This results in a dramatic growth of MHD instabilities. Hence, a stable implosion of a Z-pinch with TDP is possible only if the density increases monotonically toward the axis. [ABSTRACT FROM AUTHOR]

The prediction of power fluxes and plasma-wall interactions impacted by MHD processes during ITER operation [disruption, Edge Localized Modes (ELMs), 3D magnetic fields applied for ELM control, etc.] requires models that include an accurate description of the MHD processes themselves, as well as of the edge plasma and plasma-wall interaction processes. In this paper, we report progress on improving the edge plasma physics models in the nonlinear extended MHD code JOREK, which has capabilities to simulate the MHD response of the plasma to the applied external 3D fields, disruptions and ELMs. The extended MHD model includes E × B drifts, diamagnetic drifts, and neoclassical flows. These drifts can have large influences, on e.g., divertor asymmetries. Realistic divertor conditions are important for impurity sputtering, transport, and their effect on the plasma. In this work, we implemented kinetic and fluid neutral physics modules, investigated the influence of poloidal flows under divertor conditions in the ITER PFPO-1 (1.8T/5MA) H-mode plasma scenario, and compared the divertor plasma conditions and heat flux to the wall for both the fluid and kinetic neutral model (in JOREK) to the well-established 2D boundary plasma simulation code suite SOLPS-ITER. As an application of the newly developed model, we investigated time-dependent divertor solutions and the transition from attached to partially detached plasmas. We present the formation of a high-field-side high-density-region and how it is driven by poloidal E × B drifts. [ABSTRACT FROM AUTHOR]

Asymmetric halo currents (HCs) can exert large net forces on the vacuum vessel and other components during disruptions on tokamaks. The displacements caused by these forces can then be amplified if these asymmetric forces rotate at frequencies resonant with the vessel. This paper reports on the investigation of a recently proposed scaling law for the disruption HC rotation frequency [Saperstein et al., "Halo current rotation scaling in post-disruption plasmas," Nucl. Fusion 62, 026044 (2022)] that combines measurements on Alcator C-Mod with those on HBT-EP. We find that a new non-circular version of the scaling law [ ⟨ f rot ⟩ m / ⟨ m ⟩ ∝ 1 B T (S / π) ] takes into consideration the dependence of frot on the poloidal structure of the MHD instability (m) driving the asymmetry and describes the disruption-averaged rotation frequency on C-Mod. Disruption rotation is also found to be insensitive to the vertical position and impurity content of the plasma at the onset of the disruption. However, a stagnation in the time evolution of frot is occasionally observed. Observations are consistent with the dominance of poloidal rotation during the disruption, which is motivated by the poloidal drift nature of the scaling law. [ABSTRACT FROM AUTHOR]

Dense stars (e.g., white dwarfs) are composed of mainly ultra-relativistic degenerate electrons and strongly coupled ions subjected to a gravitational field. Considering the physical conditions of such systems, in this paper, we investigate the linear Rayleigh–Taylor (R–T) instability in a compressible ultra-relativistic degenerate strongly coupled plasma (SCP) using the generalized hydrodynamic fluid model. The electron fluid is assumed to be inertialess, ultra-relativistic degenerate, and weakly coupled, while the ion fluid is treated as non-degenerate and strongly coupled. The compressibility effects are considered for the ion fluid in terms of the Coulomb coupling parameter and internal energy. The dispersion properties of the R–T instability have been analyzed using the normal mode analysis. For short wavelength perturbations, the R–T instability excites in the presence of compressibility and degeneracy of ultra-relativistic electrons; otherwise, the characteristic internal wave propagates in the plasma medium. The compressibility and strong coupling effects play a decisive role in suppressing the R–T modes in dense degenerate SCP. In the high-frequency kinetic limit, the instability region is observed to be shorter than the low-frequency hydrodynamic limit. The effects of ultra-relativistic degenerate electrons are almost negligible on the growth rates. However, they significantly modify the dispersion properties and R–T instability criterion. The astrophysical applications of the present work have been discussed in the high-density ultra-relativistic plasmas in the finite flame thickness near the center of white dwarfs. [ABSTRACT FROM AUTHOR]

It is believed that isolated defects within the capsule (e.g., void, high-density inclusion) can be one of the essential factors for implosion performance degradation by seeding hydrodynamic instabilities in implosions. Nonetheless, a systematic study on how the isolated defects evolve and why they are not stabilized by ablation given the length scale comparable with the typical cutoff wavelength is still lacking. This paper addresses the above concerns by looking into a simplified model where a planar shell (without convergent geometry) is driven by laser direct-drive, with a single defect (low/high density) of micrometer or sub-micrometer scale residing at different locations inside. The underlying dynamics of two key physical processes are analyzed, i.e., the shock–bubble interactions as well as the subsequent nonlinear evolution of ablative hydrodynamic instabilities initiated by the direct interaction of the deformed defect and ablation front, revealing that compressibility and baroclinic effects drive vorticity production during the interactions between the shock wave and the isolated defect. In the "light-bubble" case, the vortex pair generated in the first process is further strengthened by the laser ablation. Hence, a directed flow is formed in companion with the persistent flow entering the bubble of the surrounding ablator. The bubble exhibits a remarkable growth both laterally and deeply, seriously threatening the shell's integrity. The positive feedback mechanism of the vortex pair is absent in the "heavy-bubble" counterpart, and the ablation stabilization manifested itself in the reduction of spike amplitude. A systematic study of localized perturbation growth as a function of defect placement, size, and preheating intensity is presented. [ABSTRACT FROM AUTHOR]

NASA's Magnetospheric Multiscale (MMS) mission is a four-spacecraft formation of Earth orbiting satellites that have been providing unparalleled measurements of the local kinetic-scale plasma dynamics in near-Earth space for the past 8 years. The spacecraft carry a full complement of space plasma instrumentation capable of measuring the 3D electromagnetic fields and particle distribution functions at cadences up to 100 times faster than previous missions and with interspacecraft separations as small as ∼ 5 km, approaching the characteristic electron scales in many of the plasmas that MMS samples. In this Special Topic, we bring together 26 papers covering a broad range of topics—from magnetic reconnection, shocks, and turbulence to some of the basic nuances of collisionless dynamics—highlighting the many ways in which MMS is helping us to better understand both the dynamics of Earth's magnetosphere and the fundamental physics of plasmas. [ABSTRACT FROM AUTHOR]

Electron cyclotron drift instability (ECDI) and ion–ion two stream instability (IITSI) are both kinetic instabilities that can be present in low-temperature, partially magnetized plasmas. The coupling of instabilities in a three-dimensional configuration leads to the existence of more than one unstable roots to the kinetic dispersion relation. In this paper, a generalized method has been developed for numerically evaluating solutions to the three-dimensional dispersion relation for coupled ECDI and IITSI, assuming cold singly and doubly charged ions and a Maxwellian velocity distribution function for the electrons. The present study demonstrates the coupling between ECDI and IITSI that affects the most unstable mode as a function of the wavenumbers in three dimensions and various plasma properties, including the applied electric field, magnetic field, electron temperature, ion velocities, and plasma density. One of the most notable results is that, while the most unstable mode with the largest growth rate is in the direction of the E × B drift in the two-dimensional cases, the most unstable mode for the three-dimensional configuration occurs in the oblique direction between the applied electric field and the E × B drift. This agrees with experimental observations in cross field plasma sources using coherent Thomson scattering. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the gas inlet orientation on the discharge characteristics of the coaxial dual-channel cross-field plasma jet is investigated. A working gas helium is separately flowed into the annular space between the hollow needle tube and the quartz tube (called Q-Jet), as well as the hollow needle tube (called N-Jet). With the same discharge parameters, the results show that the radial and axial dimensions of Q-Jet plasma jet are larger than that of N-Jet. Compared with the latter, the discharge current amplitude of the former increases by about 3.8-fold, the net charge transferred increases by about 8.8-fold, and the variety and density of reactive species produced are remarkably increased. For Q-Jet, the 706-nm spectral band is distributed inside and outside the quartz tube, while the 391-nm spectral band is mainly distributed outside the quartz tube, and the plasma jet forms a conical luminous pattern in the quartz tube during the positive half cycle of the voltage, due to the influence of helium viscosity. For N-Jet, 706- and 391-nm spectral bands are only just distributed in the axis of the quartz tube, and the charges left by the first discharge in the axial position of the quartz tube remarkably amplify the intensity of the second discharge in the positive half cycle. [ABSTRACT FROM AUTHOR]

Recently, we developed a crossing frequency method using the cutoff probe, which is believed as applicable for measuring electron density regardless of chamber pressures. Although computational and experimental studies demonstrated its operation, the analytic formula for the crossing frequency ( f cross ) has yet to be investigated. In this paper, we derive the analytic formula based on a circuit model for the cutoff probe. As a result, the analytic formula explains the behavior of the f cross . Based on this formula, the meaning of the f cross is analyzed and it is proved that the f cross is independent of the chamber pressure. [ABSTRACT FROM AUTHOR]

In this paper, a novel high-efficiency L-band Metamaterial Relativistic Oscillator (MRO) with high input and output power under relatively low guiding magnetic field has been proposed. In order to increase the power level while decreasing the guiding magnetic field, through our theoretical and simulation investigations on previously designed metamaterial (MTM) structure, we found that the thickness of the ring and the length of the drift tube are the two key factors that can improve the power handling capacity of the MTM structure and field uniformity. Through transmission analysis and electron conductance calculation of the novel MRO based on the improved MTM structure, preliminary MRO design is done. Within CST particle simulation of the proposed MRO and after optimizations, we computationally got a pure 718 MW TE10 output signal at 1.49 GHz using a pulsed electron beam with energy of 700 keV and current of 2 kA under 1 T guiding magnetic field, and the corresponding conversion efficiency is 51.3%. Relevant results of particle simulation verified the previous high frequency analysis. A comparison between our proposed MRO and the previous one reveals that while keeping the high efficiency and miniaturization merits of MRO, the power handling capacity has been increased and the novel MRO works more stable under low guiding magnetic field. [ABSTRACT FROM AUTHOR]

Traditional tapered waveguide devices are limited by their power efficiency and produce unstable plasmas and small reaction zones. To overcome these drawbacks, a multi-ridge field compressed reactor operating at a frequency of 2.45 GHz is designed in this paper. The finite element method is applied to numerically compute its properties. A coupling model for the multiple physical fields is introduced to simulate the transient processes of a microwave argon plasma. Experiments with different flow rates and power settings are performed. This novel device can both sustain a long-length plasma and increase the power transfer efficiency from microwave to air and to the argon plasma, respectively, to 97.4% and 95.2%. Moreover, both devices are used to process the degradation of ethanol and benzene. The removal efficiencies are increased by 38.8% and 73.8% for ethanol and benzene, respectively, in the novel waveguide compared with the tapered waveguide. [ABSTRACT FROM AUTHOR]

Coherent bipolar electric field structures with negative unipolar potentials are widely observed in space plasmas. These bipolar structures are often found to be ion Bernstein Greene Kruskal (BGK) modes or ion holes. Most theoretical models of ion holes assume them to be stationary with respect to the background plasma that follows either Maxwellian or kappa-type distribution. In this paper, we present a new theoretical model of ion holes where the structures are non-stationary, and electrons follow flat-topped distribution. We use the classical BGK approach to derive the inequality separating allowed and forbidden simultaneous values of amplitude and spatial width of ion holes. The model reveals that the parametric space for the existence of ion holes decreases with their speed. We applied the developed model to the largest available dataset of ion holes obtained from the magnetospheric multiscale spacecraft observations in the Earth's bow shock region. [ABSTRACT FROM AUTHOR]

We present the modeling of a quantum regime for surface plasmon polaritons (SPPs) excited by an electron beam skimming parallel to the surface of a metallic structure. The theoretical approach resembles that used to describe the quantum Cherenkov radiation in which the quantized free electrons interact with a classical radiation field. In this paper, we rephrase the model in a more rigorous way, considering the detrimental effects of losses on coherent light. In the quantum regime of SPPs, each electron emits a single photon due to the transition between two successive momentum states. It is shown that the quantum nature of SPPs is realized in the low beam current limit where the radiation (gain in the field strength) operates in discrete frequency bands with a remarkably narrow linewidth. When losses are negligible, the photon emission occurs in periodic bursts along the interaction length. We show also that the Ohmic loss effects in the SPP process set an intrinsic limit on the coherent production of photons and also have severe detrimental effects on the radiation intensity. The findings of this study can describe recent experimental observations of the surface plasmonic near-field based on the photon-induced near-field electron microscopy. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) magnetic nulls are preferential sites for triggering solar coronal transients. Although these nulls are abundant in the solar atmosphere, their generation is yet to be thoroughly explored. This paper explores the mechanism of null generation as well as annihilation in detail by means of implicit large eddy simulations where magnetohydrodynamic equations are solved in the absence of an explicit magnetic diffusivity. The magnetofluid is idealized to be thermodynamically inactive, incompressible, and have perfect explicit electrical conductivity. The simulated dynamics is initiated by a prescribed flow in a magnetic configuration having an isolated current-free 3D null. The flow facilitates reconnections, which lead to the generation of primary null pairs in a way that preserves the topological degree. The formation process of these null pairs is novel and different from the standard pitchfork bifurcation. Contrarily, here we found creation of null pairs away from the central null, which we hypothesize is due to the interaction of the imposed flow and the reconnection outflow from the central current layer. Intriguingly, further evolution spontaneously generates new null pairs, which have a novelty by itself. As theorized, these spontaneously generated null pairs also preserve the net topological degree—adding credibility to the simulation. The simulation also shows null pair annihilation. Magnetic reconnections are identified to be responsible for the generation and annihilation of the nulls—opening up the possibility for the nulls to be self-organized structures. Furthermore, the reconnection being ubiquitous in the corona, it can explain the coronal abundance of magnetic nulls. [ABSTRACT FROM AUTHOR]

Following the 3.15 MJ fusion milestone at the National Ignition Facility, the further development of inertial confinement fusion, both as a source for future electricity generation and for high-energy-density physics applications, requires the development of more robust ignition concepts at current laser facility energy scales. This can potentially be achieved by auxiliary heating the hotspot of low convergence wetted foam implosions where hydrodynamic and parametric instabilities are minimized. This paper presents the first multi-dimensional Vlasov–Maxwell and particle-in-cell simulations to model this collisionless interaction, only recently made possible by access to the largest modern supercomputers. The key parameter of interest is the maximum fraction of energy that can be extracted from the electron beams into the hotspot plasma. The simulations indicate that significant coupling efficiencies are achieved over a wide range of beam parameters and spatial configurations. The implications for experimental tests on the National Ignition Facility are discussed. [ABSTRACT FROM AUTHOR]

In 2021, the fusion yield of 1.35 MJ was produced at NIF by using indirect drive inertial confinement fusion (ICF), indicating that indirect drive ICF has reached ignition. However, the driving radiation flux on capsule inside Hohlraums is still a puzzle in indirect drive ICF studies. The energy deficit at NIF is still neither well understood nor solved. In this paper, we proposed a scheme to determine the driving radiation flux on the capsule by using the combination of the shock wave technique and the reemitted radiation flux measurement. In this scheme, a witness sample is placed in the Hohlraum center as the surrogate of the capsule. The shock velocity in the witness sample is measured by a streaked optical pyrometer from one side, and the temporal reemitted radiation flux is measured by a space-resolved flat response x-ray detector. Then, the peak of the radiation flux is determined by the shock velocity, and the time behavior of the radiation flux is determined by the reemitted flux through the numerical simulation of radiation hydrodynamic code. The rules for designing the witness sample and an example of applying this scheme to determine the driving radiation flux on capsule inside the octahedral spherical Hohlraum are presented in detail. [ABSTRACT FROM AUTHOR]

Recent experimental and numerical results demonstrates that the interfacial motion of a liner Z-pinch during the early stage of implosion may be controlled by the coupled effects of magneto-Rayleigh–Taylor (MRT), sausage, and kink instabilities. However, previous treatments of sausage instability have not considered the mechanical properties of the liner material. In this paper, we present an analytical model that allows us to study the effects of liner viscosity and elasticity on the coupling effects of MRT and sausage instabilities, and we further assume that the wavelengths are much smaller than the liner thickness by neglecting the feedthrough effect. The dispersion relations are analyzed. It is found that viscosity suppresses short-wavelength perturbations, and longer wavelengths are needed to achieve the fastest growing mode as the viscosity grows. Elasticity also strongly suppresses short-wavelength perturbations and eventually leads to the appearance of a cutoff wavenumber beyond which the interface always remains stable. In particular, the present approach provides the basis for the development of a more general theory that would also include magnetohydrodynamic instabilities and would allow a more accurate description of liner motion. [ABSTRACT FROM AUTHOR]

In laser-driven inertial confinement fusion (ICF) specifically with high laser intensities, energetic (hot) electrons (HEs) can be generated via laser-plasma instabilities. HEs can significantly impact the target performance by modifying the implosion hydrodynamics. In this paper, the effects of moderate-energy (about 20 to 40 keV) HEs on the evolution of two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) are studied through numerical simulations with a multigroup diffusion model in which the HE population is treated as a high-energy group launched from the boundary. With HEs present, it is found that ARTI linear growth rates are reduced even though the acceleration of the implosion shell is enhanced by HEs. The reduction in the linear growth rate is owing to the increase in the ablation velocity and the density scale length, and this stabilization effect is greater in the shorter-wavelength modes and/or higher-energy HE cases. The ARTI linear growth does not get mitigated monotonically as the HE number density increases for a given fixed HE kinetic energy. The HE number density minimizing the ARTI growth rate is found, likely due to the competition of the stabilizing and destabilizing hydrodynamic-parameter variations caused by HEs. [ABSTRACT FROM AUTHOR]

A foreword to papers from the 49th Annual Meeting of the APS Division of Plasma Physics held in Orlando, Florida in 2007, published in this issue of the journal is presented.

The wandering of magnetic field lines is an important topic in theoretical plasma physics and astrophysics. Previous analytical work, as well as computer simulations, is based on magnetostatic models to warrant mathematical and numerical tractability. Recently, we have studied the first time field line random walk in dynamical turbulence by using a field line tracing method. These calculations were performed for a slab model of the turbulence. It is the purpose of the present paper to use the latter method to compute the field line diffusion coefficient for dynamical two-dimensional turbulence. Two models for the dynamical correlation function are used, namely the damping model of dynamical turbulence and the nonlinear anisotropic dynamical turbulence model. It is shown that the largest scales of the turbulence and the choice of the dynamical turbulence model have a strong influence on the diffusivity of the field lines and the absolute value of the diffusion coefficient. [ABSTRACT FROM AUTHOR]

An analytic model is derived for electromagnetic radio-frequency (rf) wave propagation in a plasma-filled waveguide with rf sheath boundary conditions. The model gives a simplified description of the rf fields and sheath potentials near an ion cyclotron range of frequencies antenna under certain conditions. The present work lifts the restriction to a low density plasma (“tenuous plasma model”) described in a previous paper [D. A. D’Ippolito and J. R. Myra, Phys. Plasmas 16, 022506 (2009)] to include the full plasma dielectric tensor with the ordering [variant_greek_epsilon]⊥∼[variant_greek_epsilon]×∼1, [variant_greek_epsilon]∥>1 for the case where the magnetic field is well aligned with the antenna. It is shown that retaining [variant_greek_epsilon]×∼1 provides an additional drive term for the rf sheath. This effect is shown to be negligible in most practical situations suggesting that the tenuous plasma model does not miss any essential finite-density effects. The condition to recover the tenuous plasma result is derived. Expressions for the sheath voltage and sheath power dissipation are given in the arbitrary density limit, and a comparison of several mechanisms for dissipating power in rf sheaths is discussed. [ABSTRACT FROM AUTHOR]

Electromagnetic waves are examined for a single isolated nanoparticle, which is composed of lossy plasmonic components and immersed in an unbounded homogeneous dielectric host medium. Wave characteristics thus obtained on resonance play crucial roles as the zero-order solution for periodic structures such as linear particle chains. The dispersion relation with cubic nonlinearity in frequency accounts for radiation damping in addition to dynamic depolarization. It is theoretically analyzed on the parameter plane spanned by the material loss and the plasma frequency. As in the preceding companion paper of Paper I, analysis shows two types of solutions: propagating waves and stationary states. In addition, the temporal attenuation rate exhibits a maximum feature at a certain material loss in confirmation of experimental results. However, physical behaviors of a nanoparticle turn out quite distinct from those illustrated in Paper I. The reasons are that the different mathematical structures are involved, and different geometries require different underlying assumptions. In special, the issue of series convergence in choosing proper solutions will be addressed. In addition, solutions to nanoparticles made of polarizable dielectric materials are found not to exist. [ABSTRACT FROM AUTHOR]

The present paper augments the previous paper [P. H. Yoon, Phys. Plasmas 14, 102302 (2007)] in which a formal kinetic theory of hydromagnetic turbulence propagating back-and-forth along the ambient magnetic field was developed. In the present paper, linear wave properties are discussed in detail, various symmetry properties associated with response functions are derived, alternative forms of the response functions are presented, and limiting and approximate forms of nonlinear susceptibilities are discussed. [ABSTRACT FROM AUTHOR]

Electrostatic waves with frequencies that are integer multiples of the electron plasma frequency have been observed since the early days of laboratory experiments on beam–plasma interactions, and also in experiments made in the space environment. These waves have also appeared in numerical experiments, and can be explained in the context of weak turbulence theory. This paper presents results obtained by numerical solution of the equations of weak turbulence theory, which show the coupled time evolution of the amplitudes of harmonic waves and of the amplitudes of Langmuir and ion acoustic waves, and the time evolution of the electron distribution function. The results are obtained considering a two-dimensional geometry, considering harmonics up to n = 5, and are consistent with earlier results obtained by one-dimensional analyses. [ABSTRACT FROM AUTHOR]