Computational modeling of electromagnetic waves and their interactions with microplasmas




Panneer Chelvam, Prem Kumar

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Development of a computational model to study the interaction of high frequency electromagnetic (EM) waves with plasmas is presented. The plasma is described using a fluid model which is a multi-species, multi-temperature continuum representation with nite rate chemistry. The governing equations in the plasma module comprise the conservation laws for species number densities, electron energy and heavy species energy. The EM waves are described using the classical Maxwell's equations. The plasma governing equations are discretized in space using the finite volume method and the backward Euler method is used for temporal discretization. Maxwell's equation are represented as a second order curl-curl equation for the electric fi eld which is discretized in space using the Nédélec finite elements of first type and discretized in time using the backward Euler method. Linear system of equations arising out of the discretization is solved using Krylov subspace methods, typically the GMRES algorithm. A preconditioner based on nodal auxiliary subspaces of H(curl) space and Multigrid algorithms is used for the curl-curl equation. This preconditioner accelerates the convergence of the Krylov method and provides a mesh and time-step independent convergence rate. Preconditioners for time-harmonic Maxwell's equations is also studied. A two-level preconditioner comprising the shifted Laplacian preconditioner and deflation preconditioner is developed and its performance for different problem sizes and frequencies is reported. The developed wave-plasma model is used to simulate the following physical problems. First is the simulation of gas breakdown and transient evolution of plasma in a direct current microdischarge. The study also simulates the effect of active external electron injection into the discharge from the electrode surfaces. The time scales of switching the plasma between the pre-injection and the post-injection steady state is found to be approximately 1 [mu]s. The second problem is the simulation of a microdischarge and its interaction with a high frequency EM wave propagating in a wave guide. This study is focused on understanding different regimes in wave-plasma interactions. The nature of wave propagation in an under-dense and over-dense plasma medium is reported. The over-dense plasma medium interacts strongly with the propagating wave and the epsilon-zero resonance is observed. The final problem considered is the simulation of plasma breakdown and evolution in a two cylindrical Dielectric Resonator (DR) structure. The spatial structure of the plasma at different instants of discharge evolution is examined. The evolving plasma medium acts as a lossy medium to the propagating wave and damps the resonance in the DR structure thereby providing a pathway for stable steady state operation.


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