Intermittent Convecting structures in Tokamak SOL plasma

Radial transport at the edge of magnetic confinement devices (such as a tokamak) has been found to be often dominated by intermittent convective-like transport in the form of meso-scale coherent structures that are extended along the magnetic field lines. Such filament-like structures can propagate in a ballistic way toward the wall, for the distance of ten centimeters or more, and can strongly enhance both plasma energy and particle transport and plasma-wall interactions. The apparent examples of such meso-scale structures in the edge and the SOL plasmas are ELMs and blobs, and pellet clouds in the core of fusion devices. In this work we show that the interplay of the interchange drive and nonlinear effects associated with drift wave turbulence (which is rather strong at the edge in L-mode) can lead to the blob formation.

Effect of density non-uniformity on convecting structures

In this work we look at the convective blob propagation in the Scrape-Off-Layer and/or limiter shadow region with emphasis on the effect of a gradient in the equilibrium plasma density. We consider the effect of the gradient of equilibrium plasma density beyond the Boussinesq approximation. We show that the vorticity modification due to the plasma density gradient leads to the acceleration for the blobs propagating into the region of lower density and deceleration for the blobs propagating toward the regions of higher density. Analytical estimates are corroborated by numerical simulations.

Anomalous transport model for kinetic codes

In this work we present an anomalous radial transport model for kinetic codes. The focus of this work is the application to continuum kinetic edge codes such as the (2-D, 2-V) transport versions of TEMPEST, NEO, and COGENT codes developed by the Edge Simulation Laboratory, though the model also has a wider application. The model is implemented in the kinetic code TEMPEST to illustrate that the velocity-dependent coefficients allow contact with typical 2-D fluid transport models (e.g., UEDGE). A goal is to combine the anomalous transport model and collisional transport (owing to ion drift orbits) for future simulations aimed at computing the relative magnitudes and possible synergistic effects of the two processes for typical tokamak device parameters.

LES of compressible mixing layers

The problem of adequate mixing of reactants is critical in the design of SCRAMJet engines for the proposed Hypersonic flying vehicles. The extremely high speeds of these vehicles imply a very small residence time for the atmospheric air inside the engine, and hence require much faster mixing compared to their low-speed counterparts. Additional complexity is introduced in such engine flow fields by the prominence of compressibility effects on the mixing phenomenon. Thus proper understanding of the phenomenon of 'compressible turbulent mixing' is needed for the design of high-speed propulsion systems. An understanding of 'compressible turbulent mixing' is also essential to ensure rapid mixing of jet exhausts with ambient fluid to reduce noise pollution, reducing the impact of the exhaust from V/STOL aircraft engines etc. This work, as a part of my Masters degree at Indian Institute of Science, was aimed at examining the applicability of Large Eddy Simulations (LES) to study supersonic mixing layers.