Instability of Shear Waves in an Inhomogeneous Strongly Coupled Dusty Plasma

It is demonstrated that low frequency shear modes in a strongly coupled, inhomogeneous, dusty plasma can grow on account of an instability involving the dynamical charge fluctuations of the dust grains. The instability is driven by the gradient of the equilibrium dust charge density and is associated with the finite charging time of the dust grains. The present calculations, carried out in the generalized hydrodynamic viscoelastic formalism, also bring out important modifications in the threshold and growth rate of the instability due to collective effects associated with coupling to the compressional mode.Comment: 9 pages with 2 figure

Driven transverse shear waves in a strongly coupled dusty plasma

The linear dispersion properties of transverse shear waves in a strongly coupled dusty plasma are experimentally studied by exciting them in a controlled manner with a variable frequency external source. The dusty plasma is maintained in the strongly coupled fluid regime with (1 < Gamma << Gamma_c) where Gamma is the Coulomb coupling parameter and Gamma_c is the crystallization limit. A dispersion relation for the transverse waves is experimentally obtained over a frequency range of 0.1 Hz to 2 Hz and found to show good agreement with viscoelastic theoretical results.Comment: The manuscripts contains five pages and 6 figure

Phase Mixing of Nonlinear Plasma Oscillations in an Arbitrary Mass Ratio Cold Plasma

Nonlinear plasma oscillations in an arbitrary mass ratio cold plasma have been studied using 1-D particle-in-cell simulation. In contrast to earlier work for infinitely massive ion plasmas it has been found that the oscillations phase mix away at any amplitude and that the rate at which phase mixing occurs, depends on the mass ratio ($\Delta = m_{-}/m_{+}$) and the amplitude. A perturbation theoretic calculation carried upto third order predicts that the normalized phase mixing time $\omega_{p-} t_{mix}$ depends on the amplitude $A$ and the mass ratio $\Delta$ as $\sim [(A^{2}/24)(\Delta/\sqrt{1 + \Delta})]^{-1/3}$. We have confirmed this scaling in our simulations and conclude that stable non-linear oscillations which never phase mix, exist only for the ideal case with $\Delta = 0.0$ and $A < 0.5$. These cold plasma results may have direct relevance to recent experiments on superintense laser beam plasma interactions with applications to particle acceleration, fast ignitor concept etc.Comment: pp 10 and two figures in PS forma

Experimental study of nonlinear dust acoustic solitary waves in a dusty plasma

The excitation and propagation of finite amplitude low frequency solitary waves are investigated in an Argon plasma impregnated with kaolin dust particles. A nonlinear longitudinal dust acoustic solitary wave is excited by pulse modulating the discharge voltage with a negative potential. It is found that the velocity of the solitary wave increases and the width decreases with the increase of the modulating voltage, but the product of the solitary wave amplitude and the square of the width remains nearly constant. The experimental findings are compared with analytic soliton solutions of a model Kortweg-de Vries equation.Comment: The manuscripts includes six figure

Control of neoclassical tearing modes in large tokamaks

Some self-consistent effects pertaining to feedback control of neoclassical tearing modes in high temperature large tokamaks are investigated. For the ECRH scheme of local electron heating, it is shown that the self-consistent bootstrap currents created by the driven pressure gradients within the island are comparable to those due to the usually considered resistivity change mechanism. Similar self-consistent currents can also arise from pressure gradients created by density and energy deposition from neutral beams, thereby offering a new possibility for neoclassical mode control. The stabilizing current in such an application of neutral beams is estimated. It is further shown that such a feedback scheme can be made even more effective through appropriate modulation of the beam source to match the phase variation arising from the island rotation

Plasma rotation effects on Neoclassical tearing modes

The effect of an equilibrium sheared flow on the nonlinear evolution of a neoclassical tearing mode is investigated by estimating the influence it has on the inner and outer layer dynamics of the mode. Two complementary approaches are adopted. A generalized Rutherford model calculation is carried out to estimate the flow contributions to the polarization current term in the inner layer. For the outer layer,flow induced changes in the stability parameter Δ` are estimated with the help of a 3D initial value reduced MHD code (NEAR). For realistic parameters it is found that the outer layer modification is the dominant one and the scaling of Δ` with the flow shear parameter appears to agree with recent experimental observations