Excitation and dynamics of spiral structures (wave) in strongly coupled dusty plasmas

Spiral waves are ubiquitous structures observed in variety of natural and laboratory scenarios including Saturn ring, spiral galaxy, Belousov-Zabotinsky reaction, coupled oscillators, liquid crystal and cardiac tissue. Strongly coupled dusty plasma offers a model system to study generic phenomena such as self-organization and transport at individual particle level. For the first time in the dusty plasma medium, we have excited spiral waves using rotating electric fields (REFs). Both fluid and molecular-dynamics (MD) simulations have been carried out to study these waves. Characteristics of spiral waves with varying strength and frequency of REFs and strong coupling of the medium have been studied. It is found that the spiral structure gets determined by an interplay between the frequency of REF and acoustic speed of the dust medium. Comparative study of fluid and MD simulations reveal that single particle dynamical effects also play a crucial role in the formation of spiral pattern. Interestingly in the crystalline state of dusty plasma, the spiral wavefront becomes hexagonal in shape which is understood by the difference in the phase velocity in directions associated with the crystal lattice (viz., lattice axis and lattice diagonal). (author)