Measurement of the electric charge on particulates forming Coulomb crystals in the sheath of a radiofrequency plasma

Abstract

Monodisperse electrically charged particulates (9.4 p m diameter) are trapped in the sheath of an argon RF parallel plate discharge. The particulates form Coulomb crystals consisting of horizontal hexagonal layers. A method for the determination of the charge on the particles is demonstrated that uses the response to a modulation of the electrode bias. Charges about three to five thousand elementary units are measured. The commonly applied orbital motion limited (OML) charging model leads to charges higher than the measured values. The strong coupling system is compared to the one component plasma (OCP model) and to a model with Yukawa potentials.

Size and density evolution of a single microparticle embedded in a plasma

“…When analyzing plasma inherent processes like stochastic heating through charge fluctuations 3,4 , the dust radius is important for interpreting the charging mechanism. Other experiments, like the resonance method [5][6][7][8] , investigate the resonant response of the particle to small external forces. The resulting damped oscillation of the particle enables us to determine the coefficient of friction with the neutral gas as well as the particle charge with high accuracy.…”

Dynamic Light Scattering on Complex Plasmas

“…In contrast to the prediction of the Debye-Hückel theory, the dust grains can also order into a hexagonal close-packaged (hcp) structure [1,58]. The bcc and fcc structure is only observed under certain experimental conditions, albeit they are configurations with the lower Madelung energy 8 …”

“…The one-dimensional average velocity-squared can be obtained from the width of the Gaussian ω q via 58) where in the last expression 2σ = ω q is used. Assuming an isotropic two-dimensional system, the average velocity-squared is expressed by…”

“…The dust grain potential is not spherical anymore and shows an oscillating wake field with an area of enhanced ion density downstream to the dust grain. This ion focus is responsible for fundamental ordering phenomena observed in several complex plasma experiments [1,58].…”

Mechanism of particle transport in magnetized silane plasmas

“…Because the particles are isolated, they behave like floating probes resulting in a negative potential. The electron and ion currents are well known for spherical probes in a Maxwellian plasma [14] :…”