Ruhr University Bochum, Germany.
Phys Rev Lett. 2011 Sep 23;107(13):135002. doi: 10.1103/PhysRevLett.107.135002. Epub 2011 Sep 21.
We show the existence of the liquid-vapor phase coexistence and a critical point for strongly coupled ions in ultracold neutral (UCN) plasmas. Expressions for the free energy of UCN plasmas and an equation of state for the ions are obtained in the mean field approximation. A van der Waals-like isotherm shows the existence of a critical point in UCN plasmas. Depending on the ion temperature, the ions are shown to exist in a mixed vapor-liquid phase for a range of the ion Coulomb coupling parameter Γ(i) (defined by the ratio between the ion interaction and the ion kinetic energies), and in a strongly coupled liquid state for values of Γ(i) above this range. The estimates of critical constants show that it may be possible to observe these phenomena in the present day UCN plasmas.
我们证明了强耦合离子在超冷中性（UCN）等离子体中存在液-气相共存和临界点。在平均场近似下，得到了 UCN 等离子体的自由能表达式和离子的状态方程。范德瓦尔斯型等温线表明 UCN 等离子体中存在临界点。根据离子温度，离子在离子库仑耦合参数 Γ(i)（由离子相互作用与离子动能之比定义）的一定范围内，以混合的汽-液相存在，在该范围以上的 Γ(i)值时，以强耦合液相存在。临界点的估算表明，目前可能在 UCN 等离子体中观察到这些现象。
