Structural transformation of dusty plasma crystal in DC discharge plasma by changing confinement ring bias

TL;DR

This study experimentally investigates how adjusting the confinement potential in a dusty plasma crystal causes a structural transition from a stable crystal to a phase coexistence, revealing the role of sheath structure and dust fluctuations.

Contribution

It demonstrates a novel method of inducing structural transitions in plasma crystals solely through confinement bias adjustments, without altering plasma parameters.

Findings

Structural transition observed with confinement bias change

Transition confirmed by pair correlation and bond order parameters

Dust fluctuations trigger melting in the core region

Abstract

We report the experimental study of the structural transition of a stable complex plasma crystal to a solid-liquid phase coexistence by the controlled adjustment of the confinement potential, while keeping all other parameters constant. The experiments are carried out in a tabletop Linear Dusty Plasma Experimental (LDPEx) device which consists of a circular powered electrode and an extended grounded cathode plate. A stationary crystal of melamine formaldehyde particles is formed in a background of Argon plasma inside a confining ring that is isolated to the cathode by a ceramic cover. The stable crystal structure breaks in the core region and transitions to a coexistent state by carefully changing the confining potential, thereby modifying the sheath structure. The transition is confirmed by evaluating the variation in different characteristic parameters such as the pair correlation function, local bond order parameter, and dust kinetic temperature as a function of confining bias potential. It is found that melting in the core is due to the onset of dust fluctuations in the layers beneath the topmost layer, which grow in amplitude as the confining bias potential is reduced below a threshold value. The present technique of changing confinement provides a unique feature to study structural transitions of plasma crystals without affecting the overall plasma parameters.