Phonon Spectrum in a Plasma Crystal

Abstract

The Fourier spectra of longitudinal and transverse waves corresponding to random particle motion were measured in a two-dimensional plasma crystal. The crystal was composed of negatively charged microspheres immersed in a plasma at a low gas pressure. The phonons were found to obey a dispersion relation that assumes a Yukawa interparticle potential. The crystal was in a nonthermal equilibrium, nevertheless phonon energies were almost equally distributed with respect to wave number over the entire first Brillouin zone.

Dusty plasma (Yukawa) rings

“…The velocity distribution functions indicate a minimum measurable velocity of ≈ 0.06 mm/s, where a velocity of 1 pixel/frame corresponds to v = 0.238 mm/s. Except for a small neighborhood around v = 0, the distributions in both directions are well fitted by a Maxwellian with a temperature T = 410 K, somewhat below 530 K reported for a 2D lattice [23]. This temperature indicates that the ring is stable and in equilibrium with the neutral gas.…”

“…For the 1-ring [ Fig. 2(a)], velocity distributions in the longitudinal (azimuthal) and transverse (radial) directions were computed from the time histories of the measured particle positions [23]. The velocity distribution functions indicate a minimum measurable velocity of ≈ 0.06 mm/s, where a velocity of 1 pixel/frame corresponds to v = 0.238 mm/s.…”

Observation of Temperature Peaks due to Strong Viscous Heating in a Dusty Plasma Flow

“…About 10 4 dust particles, which were 8.09 µm diameter melamineformaldehyde microspheres with a mass of m d = 4.18 × 10 −13 kg, were introduced into the plasma. They gained a large negative charge of −9700 e where e is the elementary charge as determined by a wave-spectra method [25] which has an accuracy of about ±10%. They became electrically levitated by a vertical dc electric field above a horizontal electrode due to its dc self-bias of −138 V. A weaker radial dc electric field in the plasma prevented the charged dust particles from escaping in the horizontal direction.…”

Observation of particle pairing in a two-dimensional plasma crystal

“…Therefore, the particle motion is not overdamped and studying of the naturally occurring waves (fluctuations) can give reliable information about the lattice layer. The values of the particle charge Q, interaction range κ = a/λ D (where λ D is the screening length), and the vertical confinement parameter f v were estimated from the fluctuation spectra of particle velocity [33,35,36]. These parameters are collected in Table I along with the parameter set adopted for numerical calculations performed for comparison reasons.…”