Explore the vast range of titles available.

In the present work, the effect of rotation and finite Larmor radius (FLR) correction of ions on gravitational instability in the context of anisotropic white dwarf situation is investigated. The propagation dynamics of the various modes has been discussed using general dispersion relation which is obtained by quantum magnetohydrodynamic and Chew-Goldberger-Low (CGL) set of equations. The properties of dispersion relation are discussed for four different cases. The Alfven mode is modified with rotation and FLR correction while the gravitational mode remains unaffected by both the parameter for the case when rotation and wave vector both are parallel to magnetic field. Moreover, rotation (when longitudinal to magnetic field) becomes effective on gravitational mode in the perpendicular direction of propagation, as it modifies the condition of gravitational instability. The obtained analytical results are also discussed numerically. The implication of the present work is described for dense white dwarfs where the electrons are in a degenerate state with a strong magnetic field. The estimated value of Jeans length and Jeans mass are L J 1 = 5.5 × 10 7 m and M J 1 = 3.5 M ⊙ respectively for rotating anisotropic plasma which corresponds to super Chandrashekhar white dwarfs while for non-rotating degenerate magnetized plasma, the Jeans length is L J 1 ′ = 4.7 × 10 7 m and Jeans mass is M J 1 ′ = 2.1 M ⊙ . The presence of rotation effectively increases the critical mass of white dwarf.

A novel method for solving wave equations with spatial dispersion is presented, suitable for applications to ion cyclotron resonance heating. The method splits the wave operator into a dispersive and a non-dispersive part. The latter can be inverted with e.g. finite element methods. The spatial dispersion is evaluated using a wavelet representation of the dielectric kernel and added by means of iteration. The method has been successfully tested on a low frequency kinetic Alfven wave with second order Larmor radius effects in a nonuniform plasma slab.

We analyze the undulator and gyro-synchrotron radiation of the devices by equating the number of periods of the helical trajectory of the gyrating motion to the number of undulator periods. The gyro radiation is characterized by cyclotron resonance maser interaction exhibits superior line width quality but higher sensitive to beam energy spread when operated at tera-hertz due to finite larmor radius effects.

Turbulence in plasmas is modeled by fluctuating electric fields that determine particle motion through the E × B drift velocity which can lead to chaotic behavior. When applied to an ensemble of plasma particles in the chaotic regime their transport is studied: the anomalous plasma transport. The fluctuations are modeled by a spectrum of traveling waves with a wide frequency span which converts the equations of motion into an iterative mapping. The statistical properties of transport are derived. When the waves amplitude is small the particle orbits are regular, but as it is increased the behavior becomes increasingly chaotic. The effect of finite Larmor radius and the presence of a background plasma flow is also studied. We show that when a thermal population of particles is considered, the transport becomes non-local, as evidenced by a non-Gaussian particle distribution function (PDF). We have analyzed two different kinds of sheared flows: (1) a monotonic velocity shear and (2) a non-monotonic shear. The presence of transport barriers associated with the sheared velocity is also studied. We also present the application of the same techniques to study the transport of energetic particles that are born with a monoenergetic distribution.

We investigate the problem of the tearing stability of a post-disruption weakly collisional plasma where the current is completely carried by runaway electrons. We adopt here a two fluid model which takes into account also ion sound Larmor radius and electron inertia effects in the description of the reconnection process. In the past, it has been demonstrated in [Helander et al. Phys. Plasmas 14 , 12, (2007)] that in the purely resistive regime the presence of runaway electrons in plasma has a significant effect on the saturated magnetic island width. In particular, runaway electrons generated during disruption can cause an increase of 50% in the saturated magnetic island width with respect to the case with no runaway electrons. These results were obtained adopting a periodic equilibrium magnetic field that limited the analysis to small size saturated magnetic islands. Here we present our results to overcome this limitation adopting a non-periodic Harris’ type equilibrium magnetic field. Preliminary results on the effects of the ion sound Larmor radius effects will also be presented.

High-order moment fluid equations for simulation of plasmas are presented. The ten-moment equations are a two-fluid model in which time dependent equations are used to advance the pressure tensor. With the inclusion of the full pressure tensor Finite Larmor Radius (FLR) effects are captured. Further, Hall-effects are captured correctly by including the full electron momentum equation. Hall and FLR effects are important to understand stability of compact toroids like Field Reversed Configurations (FRCs) and also to detailed understanding of small scale instabilities in current carrying plasmas. The effects of collisions are discussed. Solutions to a Riemann problem for the ten-moment equations are presented. The ten-moment equations show complex dispersive solutions which come about from the source terms. The model is validated with the GEM fast magnetic reconnection challenge problem.

We present a nonlocal gyrokinetic theory for the drift‐mirror mode in high‐β$\\beta $anisotropic plasmas. Here, β$\\beta $represents the ratio of plasma pressure to magnetic pressure. The equilibrium distribution is established self‐consistently via guiding‐center Hamiltonian theory. To keep the nonuniformity and finite Larmor radius (FLR) effects on an equal footing, we derive the three‐field nonlocal eigenmode equations in Fourier space under the assumption of weak nonuniformity. It is found that the drift‐mirror mode is essentially a dissipative instability confined within the potential well due to the FLR effect. Numerical analyses demonstrate that the drift‐mirror mode originates from the coupling between shear Alfvén and mirror branch, where the ion‐sound wave component is negligible. Furthermore, the β$\\beta $threshold of this nonlocal drift‐mirror mode is significantly lower than that of the conventional drift‐mirror mode. Plain Language Summary The drift‐mirror instability has been intensively investigated in space physics. It can be destabilized by pressure anisotropy in magnetized plasmas and result in the formation of the cavity across the field lines where the mode is confined. In this study, we investigate the linear properties of the nonlocal drift‐mirror mode by employing the electromagnetic gyrokinetic theory. The nonuniform equilibrium is self‐consistently established, with both magnetic and plasma inhomogeneities taken into account on the equal footing. An eigenmode system describing the nonlocal drift‐mirror mode is then derived in Fourier space. It is found that the drift‐mirror mode arises from the coupling between the shear Alfvén branch and the mirror branch. The ion‐sound wave branch, however, is negligible. Additionally, further numerical analyses demonstrate that the kinetic drift‐mirror mode is more easily excited than the mirror mode in uniform and fluid limits. These results provide a deeper understanding of the drift‐mirror mode. Key Points By employing the nonlocal electromagnetic gyrokinetic theory, we present a self‐consistent description of the drift‐mirror mode It is showed that the drift‐mirror mode is a dissipative instability confined within the potential well arising from the FLR effect The drift‐mirror mode originates from the coupling between shear Alfvén and mirror branch, where the ion‐sound wave component is subdominant

Diffusion tensor coefficients play a central role in describing cosmic ray transport in various astrophysical environments permeated with magnetic fields, which are usually modeled as a fluctuating field on top of a mean field. In this contribution to CRIS-MAC 2024, a formal derivation of these coefficients is presented by means of the calculation of velocity decorrelation functions of particles. It relies mainly on expanding the 2-pt correlation function of the (fluctuating) magnetic field experienced by the particles between two successive times in the form of an infinite Dyson series and retaining a class of terms that converge to a physical solution. Subsequently, the velocity decorrelation functions, themselves expressed as Dyson series, are deduced from an iteration procedure that improves on the partial summation scheme. The results are shown to provide approximate solutions compared to those obtained by Monte-Carlo simulations as long as the Larmor radius of the particles is larger than at least one tenth of the largest scale of the turbulence.

A collisional gyro-fluid model is presented. The goal of the model is edge and scrape-off layer turbulence. The emphasize in the model derivation heavily lies on ”implementability” with today’s numerical methods. This translates to an avoidance of infinite sums, strongly coupled equations in time and intricate elliptic operator functions. The resulting model contains the four moments density, parallel momentum, perpendicular pressure and parallel energy and is closed by a polarisation equation and parallel Ampere law. The central ingredient is a collisional long-wavelength closure that relies on a drift-fluid gyro-fluid correspondence principle. In this way the extensive literature on fluid collisions can be incorporated into the model including sources, plasma-neutral interactions and scattering collisions. Even though this disregards the characteristic finite Larmor radius terms in the collisional terms the resulting model is at least as accurate as the corresponding drift-fluid model in these terms. Furthermore, the model does enjoy the benefits of an underlying variational principle in an energy-momentum theorem and an inherent symmetry in moment equations with regards to multiple ion species. Consistent particle drifts as well as finite Larmor radius corrections and high amplitude effects in the advection and polarization terms are further characteristics of the model. Extensions and improvements like short-wavelength expressions, a trans-collisional closure scheme for the low-collisionality regime or zeroth order potential must be added at a later stage.

We construct a description of ion-temperature-gradient (ITG)-driven localised linear modes which retains both wave–particle and magnetic drift resonant effects while capturing the field-line dependence of the electrostatic potential. We exploit the smallness of the magnetic drift and the strong localisation of the mode to resolve the problem with a polynomial–Gaussian expansion in the field-following coordinate. A simple semianalytical formula for the spectrum of the mode is shown to capture long wavelength Landau damping, ion-scale Larmor radius stabilisation, weakening of Larmor radius effects at short wavelengths and magnetic-drift resonant stabilisation. These elements lead to linear spectra with multiple maxima as observed in gyrokinetic simulations in stellarators. Connections to the transition to extended eigenfunctions and those localised by less unfavourable curvature regions (hopping solutions) are also made. The model provides a clear qualitative framework with which to interpret numerically simulated ITG modes’ linear spectra with realistic geometries, despite its limitations for exact quantitative predictions.