Abstract
A model is proposed which accounts for the modification in the electron cyclotron (EC) resonance condition for Gaussian beams injected in inhomogeneous plasmas, due to the finite width of the transversal spectrum caused by the paraxial character of the beams, within the framework of the complex geometrical optics. The resonance modification due to the non-uniformity of the equilibrium magnetic field is taken into account as well. This model, which is suitable for electron cyclotron resonance heating and current drive applications, has been implemented as an option in the beam-tracing code GRAY. Numerical examples of the application of this new tool to International Thermonuclear Experimental Reactor scenarios are given, with results that indicate a minor effect of the EC resonance broadening on the EC power deposition profiles for the considered cases.
Highlights
High power microwave focused beams with frequency of the order of the electron cyclotron (EC) frequency in the plasma are routinely adopted in most of the recent tokamaks in order to perform important tasks, ranging from plasma bulk heating to magnetohydrodynamic (MHD) instability control
A model is proposed which accounts for the modification in the electron cyclotron (EC) resonance condition for Gaussian beams injected in inhomogeneous plasmas, due to the finite width of the transversal spectrum caused by the paraxial character of the beams, within the framework of the complex geometrical optics
In real EC heating and current drive (H&CD) applications, finite width Gaussian beams propagate in finite, non-homogeneous plasmas, which are immersed in a nonuniform equilibrium magnetic field
Summary
High power microwave focused beams with frequency of the order of the electron cyclotron (EC) frequency in the plasma are routinely adopted in most of the recent tokamaks in order to perform important tasks, ranging from plasma bulk heating to magnetohydrodynamic (MHD) instability control. In most of the actual ray-tracing and beam-tracing codes, the EC resonance condition is locally approximated as the interaction of a monochromatic plane wave propagating in an infinite homogeneous plasma immersed in a uniform equilibrium magnetic field. In real EC H&CD applications, finite width Gaussian beams propagate in finite, non-homogeneous plasmas, which are immersed in a nonuniform equilibrium magnetic field. All these factors play a role in the resonance condition.. A revision and refinement of that model is proposed in this work, which includes the effects due to the astigmatism which, even in the case of a stigmatic beam at the antenna, is induced by the propagation in a non-uniform plasma and the non-uniformity of the equilibrium magnetic field.
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