Thermally Excited Dust Lattice Waves in PK-4 Complex Plasmas*

In the PK-4 experiment onboard the International Space Station, the dust cloud can form systems of multiple chains within the DC trap. The study of the dispersion relations of the Dust Lattice Waves (DLWs) along and perpendicular to the chain direction can potentially reveal important information on intra- and inter-chain interactions. In this research, the phonon spectra for thermally excited DLWs are obtained from the spontaneous motion of particles in a single chain within a multi-chain system. Direct fitting of the experimental spectra to previous theoretical dispersion relations [1] gives a general scale of the intrachain interaction strength between particles. Using the measured particle charge and Debye length [2], the thermal Mach numbers found from fitting the dispersion relations are in agreement with prediction from kinetic theory for the ions [3]. These results are compared to simulations of dust chains in this environment, and the potential of using dispersion relations to determine interchain interactions discussed.