Engineering topics

Dasgupta, B

Publications and source records attributed to Dasgupta, B.

3 records

DOE OSTI2011

Heliopause Instabilities Driven by Plasma-Neutral Interaction: Linear Analysis from Fluid Model

The heliopause (HP) is the outer edge of the heliosphere that separates the tenuous and hot heliosheath plasma from the relatively dense and cool magnetized plasma of the local interstellar medium (LISM). As a surface of tangential discontinuity, the HP is subject to both Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities. The coupling between plasma ions and neutral atoms through charge exchange provides an ''effective gravity'' for RT, while shear flows due to the velocity difference between the heliosheath and the interstellar flows can drive KH modes. We derive the linearized dispersion relations for waves propagating along the surface of this discontinuity using a fluid picture, to study the possibility for both RT and KH instabilities, including a second population of energetic neutrals produced by charge exchange interactions between the hot solar wind plasma in the heliosheath with interstellar hydrogen. We show that due to charge exchange interactions, the HP is unconditionally unstable to all perturbations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Modified Burgers' equation resulting from a hydrodynamic model of shock waves with reflected particles

Ion reflection at perpendicular, collisionless shock waves is treated in a simple gas dynamical context. The effect of pickup ions reflected by the cross-shock potential and their subsequent energization in the motional electric field is included through the introduction of source terms in the basic inviscid fluid equations. From a weak source description, a Burgers' equation is derived modified by the addition of a quadratically nonlinear term. The construction of Burgers' equation demonstrates explicitly that particle reflection is a dissipation mechanism for collisionless shocks. Numerical solutions for the modified Burgers' equation (MBE) are presented. From these solutions it is implied that the dissipative term of the MBE is associated with the length scale of the shock foot, while the additional term is associated with the shock ramp. The general physical model is discussed in terms of the reflection and energization of pickup ions at outer heliospheric perpendicular shocks.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

ALFVEN SIMPLE WAVES: EULER POTENTIALS AND MAGNETIC HELICITY

The magnetic helicity characteristics of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulae. Two basic Alfven modes are identified: (1) the plane one-dimensional Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis with wave phase {psi} = k{sub 0}(z - {lambda}t), where k{sub 0} is the wave number and {lambda} is the group velocity of the wave and (2) the generalized Barnes simple Alfven wave in which the wave normal n moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (1) is analogous to the slab Alfven mode and the generalized Barnes solution (2) is analogous to the two-dimensional mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Alfvenic fluctuations and structures observed in the solar wind are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗