Experimental investigation of the melting transition of the plasma crystal

Measurements of the melting transition of a Coulomb crystal consisting of dust particles immersed in a rf parallel plate discharge in helium were performed. The dust crystal is shown to be solid at higher gas pressure (120 Pa) and low discharge power (10-20 W). Reducing the gas pressure or increasing the discharge power leads to fluid states of the dust ensemble. Even gaslike states are observed at low pressures of about 40 Pa. The transition is attributed to an increasing effective particle temperature. The phase transition is compared with one-component-plasma and Yukawa models and with basic predictions of theories for two-dimensional melting.