Experimental observation of drift acoustic cnoidal waves in a magnetized plasma

TL;DR

This paper reports the first controlled experimental observation of cnoidal wave trains, a type of nonlinear wave structure, in a highly collisional magnetized plasma with density gradients and shear.

Contribution

It provides the first experimental evidence of drift acoustic cnoidal waves in a collisional plasma, expanding understanding of nonlinear wave phenomena.

Findings

Observed large density fluctuations up to 10%

Waveforms match cnoidal functions, indicating nonlinear wave trains

Systematic variation of profile gradients confirms wave nature

Abstract

We report the experimental observation of highly nonlinear coherent structures in a linear magnettized plasma characterized by a strong background density gradient and significant ExB velocity shear under high ion-neutral collisionality. These structures, identified as drift acoustic waves, exhibit large normalized density fluctuations reaching amplitudes of up to ~10% and show periodic sawtooth-like waveforms. These observed waveforms are well described by cnoidal functions, corresponding to stationary nonlinear wave trains. Cnoidal waves are exact solutions of the Korteweg-de Vries (KdV)-type equations, alongside the more commonly studied soliton solutions. To the best of our knowledge, this work presents the first controlled experimental observation of cnoidal wave trains in a highly collisional magnetized plasma through systematic variation of profile gradients. These findings provide important new insights into the nonlinear evolution and saturation of drift acoustic waves in inhomogeneous, sheared, and collisional magnetized plasmas.