Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Material Physics 1875.2.2.3 Electron inertia driven interchange mode and shearflow in electronmagnetohydrodynamicplasmaA numerical simulation of the nonlinear state of interchange instability associated with electroninertia in a magnetized plasma is studied. It is shown that a self consistent sheared transverseelectron flow, is generated due to nonlinear mechanisms. This shear flow can be reduce the growthrate of the magnetic interchange instability and reach to a steady state. The shear flow generationmechanisms are discussed by truncated Fourier mode representation. In truncated mode we considerthree mode equation which has exact analytic solution that matches well with the numericalsolution. Effect of different boundary conditions in such investigations are also discussed.Nikhil Chakrabarti, Ritoku Horiuchi†PP5.2.2.4 Nonlinear excitation of geodesic acoustic modes by drift wavesIn this paper, two mode-coupling analyses for the nonlinear excitation of the geodesic acousticmodes (GAMs) in tokamak plasmas by drift waves is presented. The first approach is a coherentparametric process, which leads to a three-wave resonant interaction. This investigation allows forthe drift waves and the GAMs to have comparable scales. The second approach uses the wavekineticequations for the drift waves, which then couples to the GAMs. This requires that the GAMscale length be large compared to the wave packet associated with the drift-waves. The relationshipof the two approaches is clearly established.Nikhil Chakrabarti, R Singh, PK Kaw†, PN Guzdar†PP5.2.2.5 Nonlinear electrostatic strunctures in the presence of correlationsThe Born-Bogolyubov-Green-Kirkwood-Yvon (BBGKY) hierarchy at the first order retaining theeffects of pair correlations is considered approriate for the study of a moderately coupled plasma. Inthermal equilibrium, the pair correlation function is shown to be the product of two single particleinhomogeneous distribution functions and the Debye-Hückel function. The equilibrium first orderkinetic equation is shown to be modified by a force term that is proportional to the density gradient.The steady state solutions for such first-order kinetic equation and Poisson’s equation represent akind of BGK mode. They are obtained as localized solitary wave-like structures with the amplitudeand width varying with the correlation parameter.Anirban Bose, Janaki Sita MylavarapuPP