380 research outputs found
A Simple Method to Measure the Interaction Potential of Dielectric Grains in a Dusty Plasma
A simple minimally perturbative method is introduced which provides the
ability to experimentally measure both the radial confining potential and the
interaction potential between two individual dust particles, levitated in the
sheath of a radio-frequency (RF) argon discharge. In this technique, a single
dust particle is dropped into the plasma sheath to interact with a second
individual dust particle already situated at the system's equilibrium point,
without introducing any external perturbation. The resulting data is analyzed
using a method employing a polynomial fit to the particle displacement(s),
X(t), to reduce uncertainty in calculation. Employing this technique, the
horizontal confinement is shown to be parabolic over a wide range of pressures
and displacements from the equilibrium point. The interaction potential is also
measured and shown to be well-described by a screened Coulomb potential and to
decrease with increasing pressure. Finally, the charge on the particle and the
effective dust screening distance are calculated. It is shown for the first
time experimentally that the charge on a particle in the sheath of an RF plasma
decreases with increasing pressure, in agreement with theoretical predictions.
The screening distance also decreases with increasing pressure as expected.
This technique can be used for rapid determination of particle parameters in
dusty plasma
Glow and dust in plasma boundaries
The sheath region is probed in different complex plasma experiments using
dust particles in addition to measurement of the optical emission originating
from the plasma. The local maximum in optical emission coincides with the
breaking of quasi-neutrality at the sheath boundary as indicated by the
vertical force profile reconstructed from dust particle trajectories, as well
as by the local onset of dust density waves in high density dust clouds
suspended in a dielectric box
Vibrational Modes and Instabilities of a Dust Particle Pair in a Complex Plasma
Vibrational modes and instabilities of a dust particle pair in a terrestrial
laboratory complex plasma are investigated employing an analytical method
whereby the plasma wakefield induced by an external electric field is modeled
using an image charge method. It is found that for both horizontally and
vertically aligned dust particle pairs in equilibrium, four normal modes exist.
Variations of the confinement parameters cause a single type of instability in
the horizontal pair and two types of instabilities in the vertical pair
Determination of the levitation limits of dust particles within the sheath in complex plasma experiments
Experiments are performed in which dust particles are levitated at varying
heights above the powered electrode in a RF plasma discharge by changing the
discharge power. The trajectories of particles dropped from the top of the
discharge chamber are used to reconstruct the vertical electric force acting on
the particles. The resulting data, together with the results from a
selfconsistent fluid model, are used to determine the lower levitation limit
for dust particles in the discharge and the approximate height above the lower
electrode where quasineutrality is attained, locating the sheath edge. These
results are then compared with current sheath models. It is also shown that
particles levitated within a few electron Debye lengths of the sheath edge are
located outside the linearly increasing portion of the electric field
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