(a) A schematic cross section of the discharge chamber. The powered electrode is located inside the grounded vacuum vessel. The dust particles are confined in a cubical glass box located on top of the electrode. (b) Top view of the video microscopy setup. A vertical laser sheet illuminates a thin slice of the dust cloud. Images are taken at right angle by a CCD camera with a macro lens.
(a) Vertical sections through the center of a trapped Coulomb ball at different electrode temperatures . With increasing temperature the shape of a trapped Coulomb ball merges from prolate to oblate. (b) Superposition of multiple video frames. Initially a spherical Coulomb ball with a radius is trapped at (, ). The rf voltage is then switched off, which leads the particles to fall down (white traces), affected only by gravity and the thermophoretic force.
(a) The superposition of gravity , thermophoretic force , electric field force , and ion-drag force , yields a stable confinement of the Coulomb ball inside the glass box. (b) Timing scheme illustrates relation of camera exposure and pulsed laser illumination for PIV measurements.
(a) Velocity field of falling tracer particles that are affected by only gravity and thermophoretic force. (b) Average horizontal component of acceleration derived by numerical differentiation from the measured velocity field.
(a) Temperature gradient field derived from the measured velocity field of the tracer particles. The contours show the corresponding temperature differences in kelvin with respect to the position (, ). (b) Sum of thermophoretic force and gravitational force . The contours show the vertical components in .
(a) SIGLO-2D simulation of the electron density inside the discharge chamber. (b) Detailed view of the electron density inside the glass box.
(a) Mach number and (b) linearized Debye length inside the glass box derived from SIGLO-2D simulations.
(a) Electric field force and (b) ion-drag force (Khrapak) acting on a negatively charged dust particle inside the glass box (SIGLO-2D simulation). The contours show the vertical components and .
(a) Superposition of all forces: . The contours show the potential energy of a sample particle in units of . (b) The horizontal section through the potential minimum yields a parabolic potential well (crosses: data values; solid curve: parabolic fit). The vertical lines mark the dimensions of a simulated cluster (, ) with pure Coulomb (solid line) and Yukawa (, dotted line) interaction.
A vertical section of a large dust cloud containing a few thousand particles. The triangular shape of the cloud is in good agreement with the topology of the trap potential.
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