The importance of realistic plasma filament waveforms for the study of resonant wave-filament interactions in tokamak edge plasmas

Abstract

Recently, an analytical solution for plane wave scattering at density filaments in magnetized plasma was derived 1 , from which conclusions were drawn regarding the possibility of resonant wave-filament interactions 2 between electromagnetic waves in the Ion Cyclotron Range of Frequencies and density filaments in tokamak edge plasmas. This analytical solution relies on several strongly simplified assumptions, such as a constant background density and a discontinuous density step at the filament surface. In this work we numerically investigate to what extent conclusions based on this analytical solution remain qualitatively true in more realistic scenarios.

Slab-geometry surface waves on steep gradients and the origin of related numerical issues in a variety of ICRF codes

“…Due to the finite steepness correction, there is a new root whose increases with increasing steepness, which may provide a qualitative explanation for numerical observations under similar conditions such as those reported in Tierens et al. (2020 a ), where surface waves on filaments have azimuthal wavelengths that decrease with increasing steepness, as shown in the right-hand panels for a filament with a radius of 1 cm.…”

“…2020; Tierens et al. 2020 a , b ). Messiaen & Weynants (2011) show that they are also of numerical interest, since they may occur in slab-geometry approximations.…”

“…2020; Tierens et al. 2020 a , b ). Here, there is no sign change, no role of the lower hybrid resonance and no reason to expect warm plasma effects to come into play.…”

“…Physically, in the context of electromagnetic waves in magnetized plasmas in the ion cyclotron range of frequencies (ICRF), surface waves may cause parasitic heating (Messiaen & Maquet 2020), play a role in interactions between electromagnetic waves and filaments in the edge plasma (Lau et al. 2020; Tierens, Zhang & Manz 2020 a ; Tierens, Zhang & Myra 2020 b ) or occur as ‘sheath–plasma waves’ (Myra et al. 1991; Myra & D'Ippolito 2009) on the ‘interface’ formed by the sudden and steep plasma density decrease in the plasma sheath.…”

A hybrid full-wave Markov chain approach to calculating radio-frequency wave scattering from scrape-off layer filaments

“…In reality, filaments usually develop a shock front as they convect outward (Krasheninnikov et al. 2008), and the resulting crescent-like filament shape can lead to significantly modified scattering behaviour, at least for ion cyclotron waves (Tierens, Zhang & Manz 2020 a ). Furthermore, the filament in the SAS model is assumed to be aligned with the magnetic field, so that .…”