Simulation isolates confinement effects in dusty plasma experiments

Dusty plasma, also known as complex plasma, consists of nanometer- or micrometer-sized particles embedded in a background plasma of electrons and ions. Examples of dusty plasma found in nature include comets, planetary rings and interstellar clouds.

So far, theoretical values of dust pressures from simulations of such plasmas have failed to agree with experimental results. Some suspect this disparity can be explained by taking into account the external fields in experiments that confine the dust within the plasma. To answer this question, researchers investigated the role of confinement effects on dust pressure, reported in Physics of Plasmas.

The authors performed a large-scale molecular dynamics simulation using a parallelized 3-D molecular dynamics code. The 3-D trajectories of thousands of interacting dust particles are rigorously followed until the ensemble of particles arrived at statistical equilibrium. To simulate the effect of confinement, the dust particles were placed within a large cube with perfectly reflecting walls. In this way, the dominant interaction among particles in a dusty plasma is the Yukawa, or screened Coulomb, potential. They varied dust density, while keeping the dust temperature constant, to obtain the isothermal equation of state for a 3-D Yukawa gas in the low-density, weak-coupling regime.

According to Manish Shukla, one of the authors, they expected that the isothermal dust pressure would be linearly proportional to the dust density, since weakly coupled dusty plasma behaves similarly to how an ideal gas behaves. To their surprise, the pressure contained not only the linear kinetic pressure term, but also a nonlinear pressure term proportional to the square of the dust density as predicted earlier by Khare Avinash, another of the work’s authors.

Source: “Isothermal equation of state of three dimensional Yukawa gas,” by Manish K. Shukla, K. Avinash, Rupak Mukherjee, and R. Ganesh, Physics of Plasmas (2017). The article can be accessed at https://doi.org/10.1063/1.5000409 .