Confinement-driven structural transitions in a dusty plasma crystal

We present experimental results supported by numerical simulations of structural transitions in a strongly coupled dusty plasma crystal by controlled variations of the confinement potential. The experiments are carried out in the Capacitively Coupled Dusty Plasma Experimental (CCDPx) device, which provides for creation of various potential well configurations by systematically varying the channel width of its lower electrode. The dusty plasma is generated by introducing mono-dispersive melamine formaldehyde (MF) particles of 7.43 μm diameter in an Argon background plasma generated by a radio-frequency (RF) discharge. For a given discharge condition, a clear structural transition is observed as the channel width is varied, leading to a change in the dimensional configuration of a dusty plasma crystal. From the equation of state it is ensured that, the screening length and the dust charge remain constant while varying the channel width of the lower electrode. With increasing channel width, the average inter-particle spacing, the levitation height, and the dust temperature show a decreasing trend. Conversely, the structural ellipticity and effective coupling parameter increase. An emissive probe based potential profile measurements corresponding to different channel widths essentially confirm that the trapping potential is responsible for the structural transition. The experimental observations are compared with Molecular Dynamics (MD) simulations, which show a good qualitative agreement. Our work demonstrates a novel technique for structural phase transitions of complex plasma crystalline structures in a controlled manner that can prove useful in gaining valuable insights into their fundamental dynamics.