Thermal energy density of dust in dusty plasmas: Experiment and theory

A surprising observation in dusty plasma experiments is that the dust thermal energy density, $P_d\propto n_d{T}_d$, is typically much greater than $n_d{T}_n$ (where $n_d$ and $T_d$ are the dust density and temperature, and $T_n$ is the neutral temperature), even though the dust particles would be expected to be in thermal equilibrium with the neutrals. We show here, theoretically and experimentally, that the anomalously high dust thermal energy density can be accounted for if electrostatic interactions between the dust particles and the background plasma are taken into account. Thus, the dust pressure in dusty plasma is mostly of electrostatic origin.

Figure 1

A full camera frame view (color-inverted) of a dust cloud cross section in the 3DPX device.

Figure 2

Thermal energy density. Histogram showing the energy density values calculated throughout the cloud attributable to the width of the velocity distribution. The energy densities are shown on a logarithmic scale. The average approximate thermal energy densities of the ion ($u_i$), electron ($u_e$), and neutral ($u_n$) plasma populations, multiplied by the indicated scaling factor, are indicated on the histogram for scale. The scalar field plots show the spatial distribution of the energy density using the same color scheme that was used in the histogram.