Enhanced ICRF (ion cyclotron range of frequencies) mode conversion efficiency in plasmas with two mode conversion layers

Abstract

The ICRF (ion cyclotron range of frequencies) mode conversion regime efficiently provides local electron heating. The efficiency of mode conversion could be enhanced due to the interference between the reflected waves (Fuchs V et al 1995 Phys. Plasmas 2 1637-47). Plasmas of large-scale tokamaks can include multiple mode conversion layers which results in a complicated picture of mode conversion. The 1D theory of mode conversion in plasmas with two ion-ion hybrid resonance layers is presented. Using the phase-integral method the analytical expression for the conversion coefficient is derived within a cold plasma model. The possible enhancement of the mode conversion coefficient in such plasmas is shown. The developed theory is used to analyze the role of carbon ions in the ( 3 He)H scenario of ICRF heating. As hot plasma effects may decrease the amount of power ultimately ending up on mode converted waves, a brief discussion of numerically obtained results but relying on a hot plasma model is included.

An unconditionally stable time-domain discretization on cartesian meshes for the simulation of nonuniform magnetized cold plasma

“…Further remark that (10) features derivatives with respect to x, z and t and not with respect to y. The testing function (13) is chosen such that one of its factors is a rooftop function with respect to this y-coordinate, while for the other coordinates pulse functions are used.…”

“…Let us now return to (10). Representing E x , E z and B y by expansions of the form (11), we remark that at a given y = y 0 coordinate, we can factor out r(y, y 0 , ∆ y ), allowing to rewrite (10) as…”

“…There are in total 8 E x basisfunctions that overlap with any given test function (4 at t, 4 at t + ∆ t ) and the testing procedure averages their z−derivative (4 such derivatives, each containing an extra factor 1 4 ) at the center of a (x, z, t)-cube. There are also 8 basis-functions corresponding with each of the other two field components (E z and B y ) in (10) and their derivatives too, are interpolated to the cube center. This finally leads to a discretized version of (10) that is implicit both in space and in time.…”

“…Above, we have explained how the proposed spatial and temporal discretization works for the y-component of (10). Similarly, for all other components of Maxwell's equations a dedicated testing function similar to (13) must be constructed in such a way that derivatives w.r.t.…”

“…Explicit solutions have been proposed [7] and are stable provided the vacuum Courant condition is obeyed. This is problematic when simulating phenomena whose wavelength is much shorter than the vacuum wavelength λ vac = 2πc/ω, like the waves that occur in mode conversion layers [7,8,9,10]. In that case, to resolve the phenomena in space (i.e.…”