The lower hybrid wave cutoff: A case study in eikonal methods

TL;DR

This paper compares traditional eikonal ray tracing and wave packet methods for estimating radio frequency fields in plasmas, demonstrating that wave packet methods handle caustics more effectively near reflection points.

Contribution

It introduces a wave packet-based approach for field approximation that naturally manages caustics, improving upon standard eikonal methods in plasma wave propagation analysis.

Findings

Wave packet method accurately handles caustics without special treatment.

Comparison shows wave packet approach aligns closely with analytical solutions.

Standard eikonal method struggles near reflection and focusing regions.

Abstract

Eikonal, or ray tracing, methods are commonly used to estimate the propagation of radio frequency fields in plasmas. While the information gained from the rays is quite useful, an approximate solution for the fields would also be valuable, e.g., for comparison to full wave simulations. Such approximations are often difficult to perform numerically because of the special care which must be taken to correctly reconstruct the fields near reflection and focusing caustics. In this paper, we compare the standard eikonal method for approximating fields to a method based on the dynamics of wave packets. We compare the approximations resulting from these two methods to the analytical solution for a lower hybrid wave reflecting from a cutoff. The algorithm based on wave packets has the advantage that it can correctly deal with caustics, without any special treatment.