Thermodynamic instability and the critical point of fine particle (dusty) plasmas: enhancement of density fluctuations and experimental conditions for observation

We analyze thermodynamics of fine particle (dusty) plasmas, regarding them as systems composed of charged particles with hard cores interacting via the repulsive Yukawa potential and the ambient plasma (of ions and electrons), taking the contribution of the latter properly into account. When the Coulomb coupling between fine particles becomes sufficiently strong, the isothermal compressibility of the whole system diverges and we have a phase separation and an associated critical point. The enhancement of long-wavelength density fluctuations near the critical point is shown. Experimental conditions of fine particle plasmas, densities and temperatures of components and the fine particle size are obtained corresponding to characteristic parameters around the critical point and the dependence on ion species and other factors is discussed. These phenomena will be observed in the bulk three-dimensional system which may be realized on the ground by somehow canceling the effect of gravity on fine particles. Experiments under the microgravity environment are naturally expected to provide a chance of observation.