Experimental measurement of velocity correlations for two microparticles in a plasma with ion flow

Abstract

Velocity correlations are measured in a dusty plasma with only two microparticles. These correlations allow a characterization of the oscillatory modes and an identification of the effects of ion wakes. Ion wake effects are isolated by comparing two experiments with the microparticles aligned parallel vs perpendicular to the ion flow. From records of microparticle velocities, the one- and two-particle distribution functions f(1) and f(2) are obtained, and the two-particle correlation function g(2) ≡ f(2)-f(1)f(1) is calculated. Comparing the two experiments, we find that motion is much more correlated when the microparticles are aligned with the ion flow and the character of the oscillatory modes depends on the ion flow direction due to the ion wake.

Noise-induced standing waves in oscillatory systems with time-delayed feedback

“…The key construct here is the segregation of the mean and fluctuating components of a dynamical field, in line with the DeDominicis-Martin scheme [27]. The methodology has recently been successfully used in fluid and magnetohydrodynamic models as well [28,31,32]. In this approach, each vector field φ will be split into a mean component φ 0 and a stochastic random part δφ representing the (often) nonlinear flow close to the boundary layer as follows: φ = φ 0 + δφ.…”

Statistics for motion of microparticles in a plasma

“…38 4.1 Sequence of video images of two microparticles in (a) an experiment where they were aligned vertically, i.e., parallel to the ion flow [120] and (b) horizontally. These images are reprinted from [120] and [121] [120] by assuming k x = 1.40×10 −11 kg/s 2 , k y = 5.62×10 −11 kg/s 2 and k z = 8.78×10 −11 kg/s 2 . In (b) I simulate the experiment of [121] assuming k x = k y = 4.68 × 10 −11 kg/s 2 , and k z = 8.99 × 10 −10 kg/s 2 .…”

“…These images are reprinted from [120] and [121] [120] by assuming k x = 1.40×10 −11 kg/s 2 , k y = 5.62×10 −11 kg/s 2 and k z = 8.78×10 −11 kg/s 2 . In (b) I simulate the experiment of [121] assuming k x = k y = 4.68 × 10 −11 kg/s 2 , and k z = 8.99 × 10 −10 kg/s 2 . These results can be compared to panels (a) and (b) of Fig.…”

“…The forces acting on the microparticles that I take into account are gravity, gas friction, Markovian forces from gas atom impacts, electrical force due to confining potentials due to the sheath, and electrical forces for the interaction of the two microparticles. Results from this simulation are compared to two recent experiments that were performed under similar conditions, but with plasma sheaths that were curved differently so that in the experiment of [120] the two microparticles were horizontally aligned while in the experiment of [121] they were vertically aligned.…”

“…Fewer simulations have been reported [cite] for only two microparticles, as I do here. My simulations are motivated by two recent experiments [120,121] which allow a qualitative comparison to a model.…”