  Three-dimensional structure of complex (dusty) plasmas was investigated under
long-term microgravity conditions in the International-Space-Station-based
Plasmakristall-4 facility. The microparticle suspensions were confined in a
polarity-switched dc discharge. The experimental results were compared to the
results of the molecular dynamics simulations with the interparticle
interaction potential represented as a superposition of isotropic Yukawa and
anisotropic quadrupole terms. Both simulated and experimental data exhibited
qualitatively similar structural features indicating the bulk liquid-like order
with the inclusion of solid-like strings aligned with the axial electric field.
Individual strings were identified and their size spectrum was calculated. The
decay rate of the size spectrum was found to decrease with the enhancement of
string-like structural features.
