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The analysis of parameters of radio pulsars with periods s has been carried out. It was found that there is no clear dependence of on on the diagram. The lack of dependence can be explained within the disk model. It is shown that the pulse width decreases with increasing period for the sample considered. It is the opposite of the dependence in the generally accepted pulsar model. It indicates that the distance from the surface of the neutron star to the radio emission generation region in the studied population depends on the period or that the magnetic field in the generation region has a non-dipolar structure. The possibility of explaining the longest intervals between successive pulses in pulsars J0901–4046 and J0250+5854 by the influence of drift waves at the periphery of the magnetosphere has been considered. Within the framework of the drift model, the calculated rotation periods in these pulsars turn out to be several times shorter than the observed intervals between successive pulses. [ABSTRACT FROM AUTHOR]

Turbulence and transport phenomena play a crucial role in the confinement and stability of tokamak plasmas. Turbulent fluctuations in certain physical quantities, such as density or temperature fluctuations, can have a wide range of spatial scales, and understanding their correlation length is important for predicting and controlling the behavior of the plasma. The correlation length in the radial direction is identified as the critical length in real space. The dynamics in real space are of significant interest because transport in configuration space is primarily focused on them. When investigating transport caused by the E×B drift, the correlation length in real space represents the size of E×B whirls. It was numerically discovered that in drift wave turbulence, this length is inversely proportional to the normalized mode number of the fastest growing mode relative to the drift frequency. Considerable time was required before a proper analytical derivation of this condition was accomplished. Therefore, a connection has been established between phenomena occurring in real space and those occurring in k-space. Although accompanied by a turbulent spectrum in k-space with a substantial width, transport in real space is uniquely determined by the correlation length, allowing for accurate transport calculations through the dynamics of a single mode. Naturally, the dynamics are subject to nonlinear effects, with resonance broadening in frequency being the most significant nonlinear effect. Thus, mode number space is once again involved. Resonance broadening leads to the detuning of waves from particles, permitting a fluid treatment. It should be emphasized that the consideration here involves the total electric field, including the induction part, which becomes particularly important at higher beta plasmas.

Wave processes in dusty plasma near the surface of Mercury are discussed. The near-surface layers of Mercury's exosphere have a number of common features with those of the exosphere of the Moon, e.g., there are dust particles above the illuminated side of both cosmic bodies that become positively charged due to the photoelectric effect. Mercury has its own magnetosphere that protects the surface from particles of the solar wind. However, the solar wind can reach the surface of the planet near the magnetic poles. Therefore, dust particles of the same size get different charges depending on their localization above the Mercury's surface. A drift wave turbulence can appear in dusty plasma in the magnetic field near the Mercury's surface in the presence of gradient of electron concentration. The solar wind that streams at speeds of about 400 km/s relative to plasma near the surface of the planet can induce longitudinal electrostatic oscillations with frequencies determined by the electron plasma frequency. We analyze wave processes taking into account the difference in parameters at aphelion and perihelion of the Mercury's orbit, along with the fact whether the dust particles are located near the magnetic poles or far from them. [ABSTRACT FROM AUTHOR]

A geometrical method for assessing stochastic processes in plasma turbulence is investigated in this study. The thermodynamic length methodology allows using a Riemannian metric on the phase space; thus, distances between thermodynamic states can be computed. It constitutes a geometric methodology to understand stochastic processes involved in, e.g., order–disorder transitions, where a sudden increase in distance is expected. We consider gyrokinetic simulations of ion-temperature-gradient (ITG)-mode-driven turbulence in the core region of the stellarator W7-X with realistic quasi-isodynamic topologies. In gyrokinetic plasma turbulence simulations, avalanches, e.g., of heat and particles, are often found, and in this work, a novel method for detection is investigated. This new method combines the singular spectrum analysis algorithm with a hierarchical clustering method such that the time series is decomposed into two parts: useful physical information and noise. The informative component of the time series is used for the calculation of the Hurst exponent, the information length, and the dynamic time. Based on these measures, the physical properties of the time series are revealed. [ABSTRACT FROM AUTHOR]

The circumlunar environment is a dusty plasma consisting of small particles of lunar regolith, photoelectrons, electrons, and solar wind ions. When moving around the Earth, part of the trajectory of the Moon passes through the Earth's magnetosphere. In addition, the magnetic field is characteristic for some areas on the Moon, the so-called lunar magnetic anomalies. The magnetic field values above these areas can exceed the magnetic field values of the Earth's magnetosphere in the region of the Moon's trajectory by one or two orders of magnitude. The magnetic field and photoelectron density gradients can lead to the development of drift turbulence. The relevant conditions are discussed in this work. [ABSTRACT FROM AUTHOR]

The linear eigenmode characterizations and the nonlinear turbulence energy spreading of the drift waves in a tokamak plasma with strong pedestal gradient are numerically investigated based on an electromagnetic Landau fluid model. By the linear eigenmode analysis, it is found that the dominant instability in the low β regime is the ion-temperature-gradient (ITG ^c ) mode and the electron drift wave instability (eDWI ^p ) in the core and edge region with strong density gradient, respectively. Multiple eigenstates of the eDWI ^p with different peak locations in the poloidal direction can be obtained by the eigenvalue problem solver. The dominant one is the high order eDWI ^p corresponding to the unconventional ballooning mode structure with multiple peaks in the poloidal position, in contrast to the conventional modes that peak at the outboard mid-plane, and has been verified through initial value simulation. In the high β regime, the dominant eigenmodes in the core and edge region are the conventional and unconventional kinetic ballooning modes respectively. In the nonlinear simulation, an inward turbulence spreading phenomenon during the quasi-saturation phase of the edge turbulence is clearly observed. The inward speed of the turbulence energy front in the high β regime is much faster than that in the low β regime. It is interestingly found that the speed of the turbulence energy front increases with the increase of the plasma β in the low β regime, while it is almost unchanged in the high β regime. It is identified that the turbulence spreading in the low and high β regimes are determined by the nonlinear dynamics and the linear toroidal coupling respectively.

The derivation of an intermediate-scale gyrokinetic-electron theory in nonuniform tokamak plasmas (Chen et al 2021 Nucl. Fusion 61 https://doi.org/10.1088/1741-4326/abf81a ) has shown that a Navier–Stokes type nonlinearity couples electron-temperature-gradient (ETG) modes and zonal flow (ZF) modes with wavelengths much shorter than the ion gyroradius but much longer than the electron gyroradius. This intermediate-scale ETG-ZF coupling is typically stronger than the Hasegawa–Mima type nonlinearity characteristic of the fluid approximation and is predicted to lead to relevant ZF generation and ETG mode regulation. Electron-scale, continuum, gyrokinetic simulation results are presented here which include both single-mode ETG and full-spectrum ETG turbulence. The ZF generation due to single ETG modes is investigated and the single-mode intermediate-scale results are found to be in agreement with theory. The full-spectrum results are then presented and explained qualitatively in terms of the single-mode results. It is found that the ETG-driven ZFs regulate intermediate-scale electron heat flux transport to levels in the predicted range.

We present an analysis of the effect of entropy on ion temperature gradient ηi-mode driven solitary and shock waves in electron–positron–ion plasma having density and temperature inhomogeneities. Linear and nonlinear analysis having solutions in form of solitons and shocks shows that entropy influence changes the drift mode instability. Different limiting cases when (i) temperature fluctuations due to E × B only (ηi ≫ 2/3), (ii) in the absence of entropy and (iii) neglecting positron effect (β = 1) are discussed. The homotophy perturbation method (HPM) is applied on the derived Korteweg–de-Vries (KdV) and KdV–Burger equations under small time approximation. It is found that both results, those obtained analytically and by the HPM technique, strongly agree with each other. These investigations may be useful to study low frequency electrostatic modes in magnetized electron–positron–ion plasma. For illustration, the model has been applied to the nonlinear electrostatic excitations in interstellar medium and tokamak plasma. [ABSTRACT FROM AUTHOR]

In this paper, the effect of generalized (r, q) distributed electrons on the linear and nonlinear coupling of drift and ion acoustic waves in a nonuniform plasma containing Hydrogen and Oxygen ions is investigated. In the linear regime, it is observed that increasing the percentage of flat-topped (i.e. r >0) electrons enhances the frequency of the coupled drift-ion acoustic waves, whereas the increasing values of the spectral index q mitigates it. In the nonlinear regime, one-and two-dimensional Korteweg de Vries-like and Kadomtsev-Petviashvili-like equations are derived and their solutions are plotted for different ratios of ion number densities and for different values of double spectral indices r and q of the generalized distribution of electrons. It is found that only rarefactive structures exist for two-dimensional solitons, however, both rarefactive and compressive structures are observed for the one-dimensional case. The limiting cases of kappa andMaxwellian distributions are also discussed and their comparison with the generalized (r, q) distribution is thoroughly investigated. Spatial scales for the formation of rarefactive and compressive solitary structures are also discussedwith reference to the changing electron distribution functions. The possible applications of the present study are also spelled out with special reference to space plasmas. [ABSTRACT FROM AUTHOR]

High power impulse magnetron sputtering (HiPIMS) plasmas produce a very energetic growth flux for the synthesis of thin films with superior properties. High power densities in the range of a few kW / cm 2 are applied to a metal target electrode in short pulses with a length of 10– 400 μ s and duty cycles of a few percent or less in an argon plasma gas. Fast camera and probe measurements revealed the formation of very characteristic plasma patterns that become visible as rotating localized ionization zones, so called spokes. The appearance of these spokes at high plasma powers is believed to be essential for the good performance of HiPIMS plasmas. The rotation direction of the spokes is in E → × B → direction at high plasma powers, but in retrograde E → × B → direction at low plasma powers. This characteristic behavior is explained by applying a simple drift wave model from literature and comparing the dispersion relation of those waves with measured data. The pronounced rotation reversal is explained by either a change in the governing density gradient in the plasma or by the change in the direction of the streaming ions during the transition from an argon dominated regime at low powers to a metal dominated regime at high powers. [ABSTRACT FROM AUTHOR]

Linear and nonlinear propagation characteristics of drift ion acoustic waves are analyzed in an inhomogeneous plasma comprising of warm ions having shear flow parallel to the magnetic field and electrons that are followed by a distribution which is dictated by spectral indices, r and q in low and high phase density regions. In the linear regime, the dispersion relation of the drift-ion acoustic wave is derived and the condition for the onset of shear flow instability is presented. It is found that condition for the emergence of shear flow instability gets modified by generalized (r , q) distribution and ion to electron temperature ratio. In the nonlinear regime, vortex formation with non-Maxwellian electron distribution is investigated and the effects of low and high energy electrons in this context are explored in detail. Interestingly, it is found that unlike the dipolar vortices, the electrons in the high phase space density regions do not significantly affect the Kelvin-Stuart's cat's eyes structures, however, the converse is true for the electrons belonging to the regions of low phase space density. Estimates of the size of these vortex structures in space plasmas are also given where the distribution function presented here is frequently encountered. [ABSTRACT FROM AUTHOR]

The control of spiral breakup due to Doppler instability is investigated. It is found that applying an alternating advective field with suitable amplitude and period can prevent the breakup of spiral waves. Further numerical simulations show that the growing meandering behavior of a spiral tip caused by decreasing the excitability of the medium can be efficiently suppressed by the alternating advective field, which inhibits the breakup of spiral waves eventually. [ABSTRACT FROM AUTHOR]

Magnetic reconnection at the subsolar magnetopause is persistently accompanied by strong fluctuations of the magnetic field (B), plasma density (n), and all components of the electric field (E) and current (J). The strongest fluctuations are at frequencies below the lower hybrid frequency and observed in a thin, intense current sheet adjacent to the electron diffusion region. In this current sheet, the background magnitudes of B and n are changing considerably, creating an inhomogeneous plasma environment. We show that the fluctuations in B and n are consistent with an oscillatory displacement of the current sheet in the surface normal direction. The displacement is propagating parallel to the magnetic reconnection X line. Wavelengths are on the order of or longer than the thickness of the current sheet to which they are confined, so we label these waves electromagnetic drift waves. E and J fluctuations are more complex than a simple displacement. They have significant variations in the component along B, which suggest that the drift waves also may be confined along B. The current sheet is supported by an electron drift driven by normal electric field, which, in turn, is balanced by an ion pressure gradient. We suggest that wave growth comes from an instability related to the drift between the electrons and ions. We discuss the possibility that drift waves can displace or penetrate into the electron diffusion region giving magnetic reconnection three‐dimensional structure. Drift waves may corrugate the X line, possibly breaking the X line and generating turbulence. Key Points: Electromagnetic drift waves are observed adjacent to the electron diffusion region of magnetic reconnectionElectromagnetic drift waves appear to corrugate the X‐line, possibly breaking the X‐line and generating turbulenceDrift waves reside inside of an intense current sheet adjacent to the electron diffusion region [ABSTRACT FROM AUTHOR]

We present a model of electromagnetic drift waves in the current sheet adjacent to magnetic reconnection at the subsolar magnetopause. These drift waves are potentially important in governing 3‐D structure of subsolar magnetic reconnection and in generating turbulence. The drift waves propagate nearly parallel to the X line and are confined to a thin current sheet. The scale size normal to the current sheet is significantly less than the ion gyroradius and can be less than or on the order of the wavelength. The waves also have a limited extent along the magnetic field (B), making them a three‐dimensional eigenmode structure. In the current sheet, the background magnitudes of B and plasma density change significantly, calling for a treatment that incorporates an inhomogeneous plasma environment. Using detailed examination of Magnetospheric Multiscale observations, we find that the waves are best represented by series of electron vortices, superimposed on a primary electron drift, that propagate along the current sheet (parallel to the X line). The waves displace or corrugate the current sheet, which also potentially displaces the electron diffusion region. The model is based on fluid behavior of electrons, but ion motion must be treated kinetically. The strong electron drift along the X line is likely responsible for wave growth, similar to a lower hybrid drift instability. Contrary to a classical lower hybrid drift instability, however, the strong changes in the background B and no, the normal confinement to the current sheet, and the confinement along B are critical to the wave description. Key Points: Drift waves are potentially important in governing 3D structure of subsolar magnetic reconnection and in generating turbulenceDrift waves displace or corrugate the current sheet and potentially displace the electron diffusion region of magnetic reconnectionParallel electric fields arise in the drift waves [ABSTRACT FROM AUTHOR]

Using a quantum magneto-hydrodynamic mathematical model, a set of governing equations is presented for electrostatic drift-type modes in an extremely dense plasma environment. In this regard, new local dispersion relations for coupled quantum drift modes in a magnetized plasma for two cases, (a) stationary ions and (b) mobile ions, are derived, considering the effects of exchange and correlation for electrons. The dispersion relations are then analyzed both analytically and numerically. It is found that the inclusion of exchange and correlation effects, which is the quantum effect of electrons, modifies the frequency of the quantum electron drift-acoustic mode. It is investigated that the newly found quantum drift mode exists only under low-temperature conditions. Furthermore, the results are estimated to be useful in the interpretation of electrostatic fluctuations in a dense magnetized plasma. [ABSTRACT FROM AUTHOR]

Investigates the influence of the initial energy modulation caused by the self-potential depression on the premodulated electron-beam propagation through a drift tube. Reduction of the beam's kinetic energy due to its potential depression; Debunching process of the initial current modulation; Modulation frequency.

Presents a study which examined the electrostatic flute and drift wave modes in the shared flux region of a magnetic quadrupole. Details of the eigenvalue equation; Analysis of dispersion relation; Numerical results and discussion.

Abstract We present a novel nonlinear adaptive path following controller that compensates for drift forces though time-varying sideslip for amphibious hovercrafts. The sideslip arises and changes with time during path following when the hovercraft is subject to drift forces caused by ocean disturbances or control forces. The time-varying sideslip of hovercraft is estimated online and independent of the tracking error by a bounded-gain-forgetting (BGF) adaptive estimator. Then, a line-of-sight (LOS) guidance law based on BGF is designed to follow the desired path accurately in the presence of ocean disturbances, in which the parameter estimation and the tracking errors are both proven to be bounded. Furthermore, the closed-loop cascade BGF-LOS guidance system, which is composed of tracking subsystem and sideslip parameter estimation subsystem, is proven to be input-to-state stable (ISS) according to the stability theory of cascaded system. The proposed guidance law is intended for maneuvering of an amphibious hovercraft in the horizontal-plane to follow a predefined parametrized curve without time constraints. The theoretical results are supported by two cases studies of an amphibious hovercraft. [ABSTRACT FROM AUTHOR]

Abstract The paper discusses high-order finite-volume numerical modeling of drift waves, which is an ubiquitous phenomenon in magnetized plasmas. It is found that some standard discretization methods applied to the conservative form of the governing equations can lead to a numerical instability. A method to stabilize high-order discretization is proposed and demonstrated to work in numerical simulations performed with the fourth-order finite-volume code COGENT. As practical examples, a stable drift-wave solution with adiabatic electrons and the collisionless (universal) drift-wave instability driven by electron kinetic effects are considered. Application of the present analysis to a broader range of computational fluid dynamics systems is discussed. Highlights • High-order finite-volume numerical modeling of drift waves and other incompressible flow systems is discussed. • It is shown that some standard high-order finite-volume discretization methods can lead to a numerical instability. • A method to stabilize a high-order discretization is proposed and is demonstrated to work in COGENT simulations. [ABSTRACT FROM AUTHOR]

The role of density modulation in driving streamer flows in drift wave turbulence is discussed. In contrast to the conventional shearing mechanism, we emphasize the impact of frequency modulation by meso-scale density perturbation. This mechanism is more effective for streamers than for zonal flows. The Reynolds stress and nonlinear growth rate are calculated. The result indicates that the streamer growth is enhanced due to the density modulation. Implications on the selection of streamers and zonal flows are discussed as well. [ABSTRACT FROM AUTHOR]

The impact of electron exchange-correlation term on the linear and nonlinear quantum ion (QIA) acoustic drift waves in a highly degenerate plasma is investigated. An analytical approach is employed to derive the differential equation which is later on turned into Sagdeev energy integral equation that can be utilized to get drift solitons under existence conditions. It is noted that phase speed/frequency of the linear drift quantum ion acoustic (QIA) waves increases with electron exchange-correlation effect, but the amplitude of the corresponding solitons decreases with inclusion of these effects. Present study is carried out with reference to highly dense plasma environments like fast ignition inertial confinement fusion and white dwarfs etc. [ABSTRACT FROM AUTHOR]

The motions of a small-freeboard tunnel element are prone to strongly nonlinear wave-body interaction as a result of significant water-on-deck occurrence. To obtain a better prediction for the accurate and safe handling of a tunnel element in severe weather, 3D physical model tests were conducted under regular and irregular waves with long period to estimate the motions of three floating bodies (single tunnel element, pontoon and the tunnel-pontoons assembly) and predict possible resonance. The experimental results demonstrate that, due to the green water loadings, the non-zero mean heave of the tunnel and tunnel-pontoons assembly is significantly affected by roll resonant motion and has a similar dependence on the wave period as the roll in long wave regime. For wave period smaller than the roll period, the mean drift forces have substantial influence on the mean sway of all the three floating bodies, provoking greater offshore mooring tensions. Wave excitation at periods close to resonance of the heave, roll and pitch results in large local peaks in RAOs of the three floating bodies. [ABSTRACT FROM AUTHOR]

The anisotropy in the electron velocity distribution (EVD) was measured using the polarization of two helium atom emission lines, 21P–31D (668 nm) and 23P–33D (588 nm), in a helium electron cyclotron resonance (ECR) discharge plasma. A small polarization degree of less than 4% was measured by adopting a temporal modulation technique. It was found that the polarization originated locally from around the ECR layer and that the anisotropic component of the EVD produced by ECR heating had an average kinetic energy of approximately 40 eV. [ABSTRACT FROM AUTHOR]

We show that shear is not the exclusive parameter that represents all aspects of flow structure effects on turbulence. Rather, wave-flow resonance enters turbulence regulation, both linearly and nonlinearly. Resonance suppresses the linear instability by wave absorption. Flow shear can weaken the resonance, and thus destabilize drift waves, in contrast to the near-universal conventional shear suppression paradigm. Furthermore, consideration of wave-flow resonance resolves the long-standing problem of how zonal flows (ZFs) saturate in the limit of weak or zero frictional drag, and also determines the ZF scale. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF saturation in the absence of drag, and so is effective at regulating the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator-prey model of drift-ZF turbulence. This analysis determines the saturated ZF shear and shows that the mesoscopic ZF width scales as L Z F ∼ f 3 / 16 ( 1 − f ) 1 / 8 ρ s 5 / 8 l 0 3 / 8 in the (relevant) adiabatic limit (i.e., τ c k k ‖ 2 D ‖ ≫ 1 ). f is the fraction of turbulence energy coupled to ZF and l0 is the base state mixing length, absent ZF shears. We calculate and compare the stationary flow and turbulence level in frictionless, weakly frictional, and strongly frictional regimes. In the frictionless limit, the results differ significantly from conventionally quoted scalings derived for frictional regimes. To leading order, the flow is independent of turbulence intensity. The turbulence level scales as E ∼ ( γ L / ε c ) 2 , which indicates the extent of the “near-marginal” regime to be γ L < ε c , for the case of avalanche-induced profile variability. Here, ε c is the rate of dissipation of potential enstrophy and γL is the characteristic linear growth rate of fluctuations. The implications for dynamics near marginality of the strong scaling of saturated E with γL are discussed. [ABSTRACT FROM AUTHOR]

The finding of connection of plasma density and temperature with entropy gives an incitement to study different plasma models with respect to entropy. Nonlinear dissipative one- and two-dimensional structures (shocks) are investigated in nonuniform magnetized plasma with respect to entropy. The dissipation comes in the medium through ion-neutral collisions. The linear dispersion relation is derived. The Korteweg–deVries-Burgers and Kadomtsev-Petviashvili-Burgers equations are derived for nonlinear drift waves in 1-D and 2-D by employing the drift approximation. It is found that v d / u ( v d is the diamagnetic drift velocity and u is the velocity of nonlinear structure) plays a significant role in the shock formation. It is also found that entropy has a significant effect on the strength of shocks. It is noticed that v d / u determines the rarefactive and compressive nature of the shocks. It is observed that upper and lower bounds exist for the shock velocity. It is also observed that the existing regimes for both one- and two-dimensional shocks for kappa distributed electrons are different from shocks with Cairns distributed electrons. Both rarefactive and compressive shocks are found for the 1-D drift waves with kappa distributed electrons. Interestingly, it is noticed that entropy enhances the strength of one- and two-dimensional shocks. [ABSTRACT FROM AUTHOR]

The Stokes drift is an important component in the surface drift. We used the wave model WAM to evaluate the mean values and exceedance probabilities of the surface Stokes drift in the Baltic Sea. As there is no direct way to verify the accuracy of the modelled Stokes drift, we compared the bulk parameters calculated by the wave model against buoy measurements to ensure the quality of the wave hindcast. Furthermore, we evaluated the surface Stokes drift from measured wave spectra to assess the accuracy of the modelled surface Stokes drift. The importance of the Stokes drift as a component of the total surface drift was evaluated by calculating the hindcast mean values and percentiles of the surface Stokes drift. The mean values were between 0.08 and 0.10 ms in the open sea areas, thus being of the same order of magnitude as the mean wind shear currents. The highest values of the surface Stokes drift were slightly larger than 0.6 ms. The comparison of modelled Stokes drift values to estimates obtained from measured spectra suggests that the mean values are well represented by the model. However, the higher modelled values are most likely slightly too large because the wave energy was overestimated during high wind situations in some of the sub-basins, such as the Gulf of Finland. A comparison to a drifter experiment showed that use of the Stokes drift improves the estimate of both the drift speed and the direction in the Gulf of Finland. Parameterised methods to evaluate the Stokes drift that are used, e.g. in currently available Baltic Sea drift models, overestimate the smaller values (under 0.3 ms) and underestimate the larger values of the Stokes drift compared to the values calculated by the wave model. The modelled surface Stokes drift direction mostly followed the forcing wind direction. This was the case even in the Gulf of Finland, where the direction of the wind and the waves can differ considerably. [ABSTRACT FROM AUTHOR]

A coupled model of transport, turbulence, and mesoscale flows is proposed, including turbulence spreading. The model consists of transport equations for plasma density and pressure coupled to a shell model of drift wave turbulence, which incorporates coupling to mesoscale flows via disparate scale interactions. The model can describe the turbulent cascade and its dynamical interplay with zonal and mean shear flows as well as the profile evolution (including the profiles of turbulence intensity itself) due to these self-consistent turbulent fluxes. This simple system of equations is shown to capture the low to high confinement (L-H) transition. It is also observed that as the heating is increased, the system goes through an intermediate phase that displays oscillations between zonal flows and turbulence. The transition towards the H mode, which is characterized by the presence of a strong mean shear flow at the edge, is triggered by the mesoscale dynamics due to the action of zonal flows, with turbulence spreading playing an important role in the H to L back transition. [ABSTRACT FROM AUTHOR]

The role of parallel shear flow in the pattern selection problem in drift wave turbulence is discussed. Patterns of interest here are E×B convective cells, which include poloidally symmetric zonal flows and radially elongated streamers. The competition between zonal flow formation and streamer formation is analyzed in the context of modulational instability analysis, with the parallel flow shear as a parameter. For drift wave turbulence with k⊥ρs≲O(1) and without parallel flow coupling, zonal flows are preferred structures. While increasing the magnitude of parallel flow shear, streamer growth overcomes zonal flow growth. This is because the self-focusing effect of the modulational instability becomes more effective for streamers through density and parallel velocity modulation. As a consequence, the bursty release of free energy may result as the parallel flow shear increases. [ABSTRACT FROM AUTHOR]

Linear and nonlinear coupling of drift and ion acoustic waves are studied in a nonuniform magnetized plasma comprising of Oxygen and Hydrogen ions with nonthermal distribution of electrons. It has been observed that different ratios of ion number densities and kappa and Cairns distributed electrons significantly modify the linear dispersion characteristics of coupled drift-ion acoustic waves. In the nonlinear regime, KdV (for pure drift waves) and KP (for coupled drift-ion acoustic waves) like equations have been derived to study the nonlinear evolution of drift solitary waves in one and two dimensions. The dependence of drift solitary structures on different ratios of ion number densities and nonthermal distribution of electrons has also been explored in detail. It has been found that the ratio of the diamagnetic drift velocity to the velocity of the nonlinear structure determines the existence regimes for the drift solitary waves. The present investigation may be beneficial to understand the formation of solitons in the ionospheric F-region. [ABSTRACT FROM AUTHOR]

In magnetized toroidal plasmas, neoclassical effects and turbulent drift waves can induce the geodesic acoustic mode (GAM). We simulate the GAM using the gyro-kinetic code GTS for typical tokamak parameters and investigate its properties, especially its frequency continuum, evolution of its radial wave number, and propagation characteristics. The simulation results are compared with those of the relevant theory and experiment. It is found that the radial phase velocity of the GAM is roughly proportional to the ion thermal speed. [ABSTRACT FROM AUTHOR]

The extended magnetohydrodynamic stability of interchange modes is studied in two configurations. In slab geometry, a local dispersion relation for the gravitational interchange mode (g-mode) with three different extensions of the MHD model [Zhu et al., Phys. Rev. Lett. 101, 085005 (2008)] is analyzed. Our results delineate where drifts stablize the g-mode with gyroviscosity alone and with a two-fluid Ohm's law alone. The two-fluid Ohm's law produces an ion drift wave that interacts with the g-mode. This interaction gives rise to a second instability at finite ky. A second instability is also observed in numerical extended MHD computations of linear interchange in cylindrical screw-pinch equilibria, the second configuration. Particularly with incomplete models, this mode limits the regions of stability for physically realistic conditions. However, applying a consistent two-temperature extended MHD model that includes the diamagnetic heat flux density (...) makes the onset of the second mode occur at a larger Hall parameter. For conditions relevant to the SSPX experiment [E. B. Hooper, Plasma Phys. Controlled Fusion 54, 113001 (2012)], significant stabilization is observed for Suydam parameters as large as unity (Ds ≲ 1). [ABSTRACT FROM AUTHOR]

Gyrokinetic simulations of C-2-like field-reversed configuration (FRC) find that electrostatic driftwaves are locally stable in the core. The stabilization mechanisms include finite Larmor radius effects, magnetic well (negative grad-B), and fast electron short circuit effects. In the scrape-off layer (SOL), collisionless electrostatic drift-waves in the ion-to-electron-scale are destabilized by electron temperature gradients due to the resonance with locally barely trapped electrons. Collisions can suppress this instability, but a collisional drift-wave instability still exists at realistic pressure gradients. Simulation results are in qualitative agreement with C-2 FRC experiments. In particular, the lack of ion-scale instability in the core is not inconsistent with experimental measurements of a fluctuation spectrum showing a depression at ion-scales. The pressure gradient thresholds for the SOL instability from simulations are also consistent with the critical gradient behavior observed in experiments. [ABSTRACT FROM AUTHOR]

The reduction of turbulent transport across sheared flow regions has been known for a long time in magnetically confined toroidal plasmas. However, details of the dynamics are still unclear, in particular, in what refers to the changes caused by the flow on the nature of radial transport itself. In Paper II, we have shown in a simplified model of drift wave turbulence that, when the background profile is allowed to evolve self-consistently with fluctuations, a variety of transport regimes ranging from superdiffusive to subdiffusive open up depending on the properties of the underlying turbulence [D. Ogata et al., Phys. Plasmas 24, 052307 (2017)]. In this paper, we show that externally applied sheared flows can, under the proper conditions, cause the transport dynamics to be diffusive or subdiffusive. [ABSTRACT FROM AUTHOR]

From theoretical and modeling points of view, following Lagrangian trajectories is the most straightforward way to characterize the transport dynamics. In real plasmas, following Lagrangian trajectories is difficult or impossible. Using a blob of passive scalar (a tracer blob) allows a quasi- Lagrangian view of the dynamics. Using a simple two-dimensional electrostatic plasma turbulence model, this work demonstrates that the evolution of the tracers and the passive scalar field is equivalent between these two fluid transport viewpoints. When both the tracers and the passive scalar evolve in tandem and closely resemble stable distributions, namely, Gaussian distributions, the underlying turbulent transport character can be recovered from the temporal scaling of the second moments of both. This local transport approach corroborates the use of passive scalar as a turbulent transport measurement. The correspondence between the local transport character and the underlying transport is quantified for different transport regimes ranging from subdiffusive to superdiffusive. This correspondence is limited to the initial time periods of the spread of both the tracers and the passive scalar in the given transport regimes. [ABSTRACT FROM AUTHOR]