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Author: alessandro Cardinali
Requested Type: Poster
Submitted: 2016-02-15 16:07:20


Contact Info:
Via E Fermi 45
frascati, rome   00044

Abstract Text:
The propagation of the electromagnetic modes from low (Radio Waves) to high frequencies (TeraHertz) in magnetized plasma is described by means of the Maxwell’s equation system coupled to the plasma dynamics that can be modeled by means of the fluid theory. In some relevant conditions, after linearizing the fluid equations for both plasma species, an asymptotic treatment of the problem can be given in terms WKB [1] expansion of the fields. At the lowest order a non linear first-order partial differential equation for the Phase Integral, formally equivalent to the Hamilton-Jacobi equation in classical mechanics, can be obtained and solved in terms of the ray trajectories, while at the next order a transport equation for the slowly varying wave energy density can be obtained and solved, that allows to reconstruct the electric field inside the plasma. The absorption of the propagating wave is studied by coupling the energy density transport equation to a quasilinear model, based on the solution of the Fokker-Planck equation for the electron distribution function. The effect of wave energy on the plasma (e.g. formation of the tail at high energy) is taken into account by the quasilinear diffusion operator, which, in turn, can be constructed using the wave energy transport equation. The combined analytical solution of ray tracing, amplitude transport equations and time dependent 1D Fokker Planck equation, in fact, illuminates and explains features of the quasilinear approach and the key role of the wave spectrum, for example, in the case of LH power deposition profiles. Examples of solution for the propagation of the Lower Hybrid Waves for heating and current drive (H&CD) in reactor-relevant tokamak plasma are shown and discussed.

[1] N. Fröman, P.O. Fröman, JWBK Approximation, North-Holland 1965.