To obtain the radial profile of the ion velocity u i( r) of a pure ion cloud, for the first time, we successfully captured images of the shadow of a thin rotating metal wire by scanning the pure ion cloud using a combination of a micro-channel plate attached to a phosphor screen and a high-speed camera. It appears that the rotation angle of the measured metal wire agrees with the estimated value based on the theory of two-dimensional equilibria of non-neutral plasmas, rather than the magnetron motion of a single ion confined in a Penning trap. This method may be utilized as a tool to experimentally investigate u i( r, t) in electrically non-neutral two-fluid plasmas, which is an unexplored topic in advanced plasma physics.

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This research aimed to clarify the physical effects of plasma on microorganisms levitated in radio-frequency (RF) plasma and to develop a technology for classifying and confining microorganisms by controlling their behavior when levitated. In the experiment, multiple types of microorganisms were injected into the RF plasma one by one, and their behavior was analyzed. An external electric field was applied to the plasma. The experimental results revealed that the behavior of the levitated microorganisms differs depending on the species and the magnitude of RF discharge power.