HEATING AND PHASE-TRANSITIONS OF DUST-PLASMA CRYSTALS IN A FLOWING PLASMA

A three dimensional particle simulation is used to study hexagonal dus t crystals in Bowing plasmas. The flowing velocity upsilon(0) is mesot hermal (upsilon(Ti)<upsilon(0)<upsilon(Te)), which is a typical situat ion for dust particles confined in industrial plasmas and plasma exper iments. Unlike for the Yukawa system (Debye-Huckel shielded dust), we find parameter regimes where a hexagonal dust crystal is stable. This is due to the wakefield generated around the individual particles whic h causes attractive interparticle forces along the axis of the plasma flow. These attractive forces cause a rather strong binding of the cry stal since the simulation shows that solid-fluid transitions occur at a much lower Gamma value (higher dust temperature) than for the Yukawa system. Stability of a hexagonal dust crystal is found to depend stro ngly upon the gas neutral pressure since stable crystal structure is o btained for dust-neutral collision frequencies gamma(d) above some thr eshold value gamma(d0). For gamma(d)<gamma(d0) the ion flow will excit e crystal waves (phonons) where the amplitude of these waves grows as a function of time. This instability will either saturate due to nonli near lattice waves or continue until the dust crystal structure eventu ally melts.