84 research outputs found
Non-modal stability analysis and transient growth in a magnetized Vlasov plasma
Collisionless plasmas, such as those encountered in tokamaks, exhibit a rich
variety of instabilities. The physical origin, triggering mechanisms and
fundamental understanding of many plasma instabilities, however, are still open
problems. We investigate the stability properties of a collisionless Vlasov
plasma in a stationary homogeneous magnetic field. We narrow the scope of our
investigation to the case of Maxwellian plasma. For the first time using a
fully kinetic approach we show the emergence of the local instability, a
transient growth, followed by classical Landau damping in a stable magnetized
plasma. We show that the linearized Vlasov operator is non-normal leading to
the algebraic growth of the perturbations using non-modal stability theory. The
typical time scales of the obtained instabilities are of the order of several
plasma periods. The first-order distribution function and the corresponding
electric field are calculated and the dependence on the magnetic field and
perturbation parameters is studied. Our results offer a new scenario of the
emergence and development of plasma instabilities on the kinetic scale.Comment: 6 pages, 5 figure
Hypervelocity Richtmyer–Meshkov instability
The Richtmyer-Meshkov instability is numerically investigated for strong shocks, i.e., for hypervelocity cases. To model the interaction of the flow with non-equilibrium chemical effects typical of high-enthalpy flows, the Lighthill-Freeman ideal dissociating gas model is employed. Richtmyer's linear theory and the impulse model are extended to include equilibrium dissociation chemistry. Numerical simulations of the compressible Euler equations indicate no period of linear growth even for amplitude to wavelength ratios as small as one percent. For large Atwood numbers, dissociation causes significant changes in density and temperature, but the change in growth of the perturbations is small. A Mach number scaling for strong shocks is presented which holds for frozen chemistry at high Mach numbers. A local analysis is used to determine the initial baroclinic circulation generation for interfaces corresponding to both positive and negative Atwood ratios
On initial-value and self-similar solutions of the compressible Euler equations
We examine numerically the issue of convergence for initial-value solutions and similarity solutions of the compressible Euler equations in two dimensions in the presence of vortex sheets (slip lines). We consider the problem of a normal shock wave impacting an inclined density discontinuity in the presence of a solid boundary. Two solution techniques are examined: the first solves the Euler equations by a Godunov method as an initial-value problem and the second as a boundary value problem, after invoking self-similarity. Our results indicate nonconvergence of the initial-value calculation at fixed time, with increasing spatial-temporal resolution. The similarity solution appears to converge to the weak 'zero-temperature' solution of the Euler equations in the presence of the slip line. Some speculations on the geometric character of solutions of the initial-value problem are presented
Energy transfers and magnetic energy growth in small-scale dynamo
In this letter we investigate the dynamics of magnetic energy growth in
small-scale dynamo by studying energy transfers, mainly energy fluxes and
shell-to-shell energy transfers. We perform dynamo simulations for magnetic
Prandtl number on grid using pseudospectral method.
We demonstrate that the magnetic energy growth is caused by nonlocal energy
transfers from the large-scale or forcing-scale velocity field to small-scale
magnetic field. The peak of these energy transfers move towards lower
wavenumbers as dynamo evolves, which is the reason why the integral scale of
the magnetic field increases with time. The energy transfers (velocity to
velocity) and (magnetic to magnetic) are forward and local.Comment: 6 pages, 8 figure
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