Impact of Electron Temperature Control on Complex Plasmas

Complex plasmas consist of micron-sized particles immersed in a low-temperature plasma. The particles acquire a high negative charge in the plasma and interact via a screened Coulomb potential. Direct optical observation of the particle motion allows the study of fundamental properties of the particle dynamics on the kinetic level. The electron temperature in the surrounding plasma is an important factor in defining the particle charge and interaction. One possible way to control the electron temperature is a biased grid inserted into the plasma chamber, separating the plasma source (e.g. an rf-electrode) from the rest of the chamber volume. Depending on their initial temperature, electrons and ions selectively pass through the grid. The electron temperature behind the grid can be controlled by varying the DC bias of the grid, or the mesh size [1]. To investigate the possibility to manipulate particle behavior by changing the electron temperature, experiments were performed in the “Zyflex” chamber — a cylindrical plasma chamber with parallel, rf-driven electrodes. The chamber is build as part of the PlasmaLab project, a proposed follow-up experiment for complex plasmas aboard the International Space Station (ISS) to study fundamental properties of complex plasmas in large 3D systems in microgravity. Electrode bodies were designed for the Zyflex chamber, with a grid mounted parallel to a driven electrode. The grid separates the electrode (and therefore the region of plasma production) from the main chamber volume, and can be either grounded, floating or set to an adjustable voltage. It can be observed that there is no visible glow in the main chamber volume, but particles which are inserted into the chamber can be levitated in that region. First experimental results of the influence of different grid voltages (different electron temperatures) on the behavior and distribution of the particles are presented, as well as accompanying measurements of the plasma parameters behind the grid.