Schematic view of the experimental setup for the parabolic flights. (a) Top view and (b) side view with the rf electrodes and generators. See text for details.
(Top panel) A single frame from the high-speed camera showing a side view of the dust cloud and the void. The visible dimensions of the dust cloud are in height and in width. (Middle panel) Examples of trajectories of the particles in the dust cloud (region “a”) over about . The particles are pushed by the laser from left to right. (Lower panel) Trajectories of the particles at the void edge (region “b”). See text for details.
Manipulation of particles in the bulk of the dust cloud. Particle excursion during the time the manipulation laser is swept past the observed particles. Gray curves denote examples of measured data. The black solid line is the model trajectory according to Eq. (2). Here the gas pressure is .
Histogram of the measured total particle displacements in the plasma bulk.
Manipulation of particles at the void edge. Displacement from the void edge during the time the manipulation laser is swept past the observed particles. Three examples from different parabolas under the same gas pressure are shown (symbols). The black solid line is the model trajectory according to Eq. (6). The fit parameters, laser force , and force constant are indicated.
Spatially resolved Langmuir probe measurements of the (a) ion density, (b) electron temperature, and (c) plasma potential. The quantities are obtained from a radial scan at the midplane between the electrodes; corresponds to the discharge center and is at the outer electrode radius. The shaded area corresponds to the region with the dust cloud; the unshaded region is the void region.
Ion drag force after Barnes et al., Khrapak et al., and Hutchinson in relation to the electric field force as a function of dust charge number . From the Langmuir probe measurement, the electric field is and the ion density is .
Dust charge at the void boundary from the force balance for the three ion drag models (left panel). Value of the force constant derived from the ion drag models (right panel). In the left panel, the dust charges from quasineutrality, from OML and the collision-reduced charge (Ref. 51), are indicated. In the right panel, the shaded region is the experimental range of the force constant derived from the laser manipulation. The error bars are due to uncertainties in the electric field.
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