Fluid-solid phase transitions in three-dimensional complex plasmas under microgravity conditions

Abstract

Phase behavior of large three-dimensional (3D) complex plasma systems under microgravity conditions onboard the International Space Station is investigated. The neutral gas pressure is used as a control parameter to trigger phase changes. Detailed analysis of structural properties and evaluation of three different melting-freezing indicators reveal that complex plasmas can exhibit melting by increasing the gas pressure. Theoretical estimates of complex plasma parameters allow us to identify main factors responsible for the observed behavior. The location of phase states of the investigated systems on a relevant equilibrium phase diagram is estimated. Important differences between the melting process of 3D complex plasmas under microgravity conditions and that of flat 2D complex plasma crystals in ground based experiments are discussed.

Complex Plasma Research under Microgravity Conditions: PK‐3 Plus Laboratory on the International Space Station

“…Applying the threshold condition R 0.2 would imply that the system of small particles melts upon an increase in the neutral gas pressure (second half of the observation sequence), while the system of large particles remains in the solid state. This is consistent with the results of more detailed structural analysis [12]. Concerning the structural properties of the observed clouds of particles it should be noted that they are not very homogeneous.…”

Particle flows in a dc discharge in laboratory and microgravity conditions

“…For the Debye-Hückel (Yukawa) potential a simple formula of the type R 0 ≃ λ ln(1 + R C /λ), where λ is the plasma screening length and R C = |Q|e/T i is the (ion) Coulomb radius, would describe adequately the respective limits of weak and strong ion-particle coupling and provide a smooth transition between them [42]. The remaining step is to estimate how the presence of the ion flow modifies this collisional contribution.…”

Simulating the dynamics of complex plasmas

“…The sheath width is fixed during the run of one simulation. This means that effects that depend on a changing sheath width, such as melting a plasma crystal by increasing the gas pressure [78], cannot be modelled accurately without extending the model. Also, we do not include the feedback from the microparticles to the plasma in this version of the model.…”