Scattering of radio frequency waves by cylindrical blobs in the plasma edge in tokamaks

TL;DR

This paper investigates how radio frequency waves scatter when passing through cylindrical plasma blobs in tokamak edge regions, affecting plasma heating and diagnostics in fusion devices.

Contribution

It provides a detailed analysis of RF wave scattering by cylindrical plasma blobs with various density contrasts and sizes, considering different wave frequencies and tokamak configurations.

Findings

Scattering depends on blob density contrast and size.

Different wave frequencies exhibit distinct scattering behaviors.

Results inform RF wave propagation models in turbulent tokamak edges.

Abstract

Radio frequency waves are routinely used in tokamak fusion plasmas for plasma heating, current control, and as well as in diagnostics. These waves are excited by antenna structures placed near the tokamak's wall and they have to propagate through a turbulent layer known as scrape-off layer, before reaching the core plasma (which is their target). This layer exhibits coherent density fluctuations in the form of blobs and filaments. The scattering processes of RF plane waves by single blob is studied, with the assumption that the blob has cylindrical shape and infinite length. The axis of the blob is not necessarily aligned with the externally applied magnetic field in the case of plane waves. The investigation concerns the case of Electron Cyclotron (EC) waves ($f_0$=170 $GHz$) for ITER-like and Medium Size Tokamak applications (such as TCV, ASDEX-U, DIII-D, etc) as well as the case of Low Hybrid (LH) waves ($f_0$=4.6 $GHz$) for ALCATOR C-MOD Tokamak device. The study covers for a variety of density contrasts between the blobs and the ambient plasma and a wide range of blob radii.