Single-file diffusion in a dusty plasma

Summary form only given. Single-file diffusion (sfd) refers to diffusion in a one-dimensional (1D) system. Even though the particles cannot pass each other, their mean-squared displacements (msd) from the initial positions will increase with time t. For diffusion in higher-dimensions, Fick´s law predicts that the msd increases linearly with t. However, single-file diffusion is predicted to be sub-Fickean, where the msd increases as t^1/2. To test this prediction, a 1D dusty plasma ring has been created in the Dusty ONU experimenT (DONUT). The ring consisted of 29 melamine microspheres, had a radius of 10.2 mm and an average lattice constant of 2.2 mm. The neutral Ar pressure was 8.0 mtorr, giving a damping rate of 0.4 s^-1. As shown in the figure, for short times t <; 1 s, we find the msd is proportional to the t, indicating ballistic behavior, while for t >; 1 s, the msd increases approximately as t^1/2, confirming the theoretical prediction.