Anomalous diffusion in microgravity complex plasma cloud*

Diffusion is a persistent random walk characteristic of various physical systems, including amorphous semiconductors, porous media, glasses, granular matter, ionic liquids, polymers, and plasmas. In the normal diffusion regime, the mean square displacement (MSD) of an ensemble of moving particles increases linearly in time, i.e. 〈x²〉∼t^α, where α=1. However, exponents α≠1 are also possible, yielding two distinct examples of anomalous transport: subdiffusion when α<1 and superdiffusion when α>1. Here we present a study of anomalous diffusion in strongly coupled systems where both structural defects and long-distance interactions are present. Our innovative numerical technique combines results from spectral theory and fractional calculus to model transport characterized by an Anderson-type Hamiltonian with a fractional Laplacian operator. The numerical results are compared against video data from complex plasma experiments performed in the Plasmakristal-4 facility on board the International Space Station.