Dust-cloud spatial distribution and striated discharge structure in complex plasmas driven by dual-frequency discharges

Abstract Dust-plasma interactions in complex plasmas driven by dual-frequency capacitively coupled discharges have been investigated using a self-consistent two-dimensional fluid model. The effects of single-frequency driving voltages on dust-cloud spatial distribution are validated by comparing the void size with previous experiment and simulation, achieving a good qualitative consistency. Independent tuning of the high- (27 MHz) and low-frequency (2 MHz) driving voltages enables opposite control of dust-cloud spatial distribution: the high-frequency voltage expands the void by driving the cloud outward, whereas the low-frequency voltage compresses it, leading to void closure. This behavior reflects the balance among the electric-field force, ion-drag force, and self-diffusion of dust. Moreover, a quadrupole vortex pattern in the cloud with large central vortices and counter-rotating edge vortices has been observed and attributed to competition between curls of ion-drag and electric-field forces. Specially, dust-cloud spatial distribution markedly modifies plasma properties via collisional electron absorption, which lowers conductivity, strengthens the drift field, and produces both reversed and amplified ambipolar fields. These changes transform the spatio-temporal ionization pattern from tilted to nearly vertical, resulting in a striated discharge structure.