Ross Fisher

Observations of dust acoustic waves driven at high frequencies: Finite dust temperature effects and wave interference

An experiment has been performed to study the behavior of dust acoustic waves driven at high frequencies (f>100Hz), extending the range of previous work. In this study, two previously unreported phenomena are observed—interference effects between naturally excited dust acoustic waves and driven dust acoustic waves, and the observation of finite dust temperature effects on the dispersion relation.

Measurement of the ion drag force in a collisionless plasma with strong ion-grain coupling

The ion drag force acting on dust grains was measured experimentally in a low-pressure Ar plasma in the regime of strong ion-grain coupling. Argon ions were drifting in the axial ambipolar electric field naturally present in a hot-filament dc discharge plasma. Following the method of Hirt et al. [Phys. Plasmas 11, 5690 (2004)], hollow glass microspheres were dropped into the plasma and allowed to fall due to gravity. The ion drag force was derived from the particle trajectory deflection from the vertical direction. The result is in reasonable agreement with a theoretical model that takes strong ion-grain coupling into account.

Preliminary characteristics of magnetic field and plasma performance in the Magnetized Dusty Plasma Experiment (MDPX)

The Magnetized Dusty Plasma Experiment (MDPX) device is a newly constructed research instrument for the study of dusty (complex) plasmas. The MDPX device is envisioned as an experimental platform in which the dynamical behavior of all three charged plasma components, the electrons, ions, and charged microparticles (i.e., the ‘dust’) will be significantly influenced by the magnetic force. This brief paper will provide a short overview of the design, magnetic performance, and initial plasma measurements in the MDPX device.

Thermal Properties of a Dusty Plasma in the Presence of Driven Dust Acoustic Waves

In this paper, the thermal properties of a weakly coupled dc glow discharge dusty plasma with driven dust acoustic waves are investigated. Here, the waves are driven using a current modulation at a fixed frequency with varying amplitudes. Stereoscopic particle image velocimetry is used to measure the velocity space distribution of the dusty plasma. It is shown that, with increasing amplitude of the modulation, there is a corresponding increase in the measured kinetic temperature. In addition, there is an evidence of non-Maxwellian features in the velocity distribution.

Observation and model of an ellipsoidally symmetric velocity space distribution in a weakly-coupled dusty plasma

The spatially resolved phase space distribution was measured for a dusty plasma system. Analysis of the velocity space component of the distributions revealed that the standard assumption of a spherically symmetric velocity space is not applicable to the observed system. The more general, ellipsoidally symmetric, multi-normal distribution function was applied to model the velocity space and is compared to the canonical spherically symmetric model.

Weakly Coupled Dusty Plasma With a High Dust Temperature and Low Thermal Energy Density

Relatively large values of the temperature for the dust component of plasma systems are an area of concern in the understanding of such systems. Dust temperatures are regularly observed to be several orders of magnitude higher than the temperatures of the other plasma components, leading to questions of the validity of the measurements. In order to address such concerns, the phase space distribution was measured for a weakly coupled dusty plasma system. The measurements are used to illustrate the differences between two metrics of the thermal motion of the dust component, namely, the temperature and the thermal energy density. It is shown that, by considering the thermal energy density, instead of the temperature, the energy associated with the random motion of the dust component is comparable to that of the other plasma species.

The Magnetized Dusty Plasma Experiment (MDPX) device: First observations

Summary form only given. A dusty (or complex) plasma is a four-component plasma system consisting of electrons, ions, neutral atoms, and charged, nanometer to micrometer-sized particles (i.e., the “dust”). Because these dust grains are charged, they fully participate in the plasma dynamics and can be used to reveal details about transport, instabilities, and charging properties of plasmas. However, one important area that has not been studied extensively is the area of magnetized dusty plasmas. Even though the charged dust grains in a typical laboratory experiment can acquire several thousand elementary charges, the large mass of the grains ensures that the charge-to-mass ratio is quite low. As a result, it is technically challenging to design an experiment that can achieve full magnetization of ions, electrons, and the charged dust grains. The Magnetized Dusty Plasma Experiment (MDPX) device is a flexible, multiuser research instrument that is being used to study the physics of highly magnetized plasmas and magnetized dusty plasmas. The MDPX device uses four independent superconducting coils to produce a variety of magnetic field configurations: from a uniform field mode at greater than 4 Tesla to a linear gradient mode at up to 2 T/m. Plasmas are produced in a large octagonal chamber that has a 35 cm inner diameter and an axial length of 19 cm. With the addition of two, 15 cm diameter, 76 cm long cylindrical extensions, the vacuum vessel can have a length of over 170 cm. A broad range of probe and optical diagnostics (e.g., particle image velocimetry, high speed imaging, laser induced fluorescence, etc.) are used for plasma measurements. Initial operation of the MDPX device will begin in late Fall, 2013. This presentation will report on the construction, assembly, and initial plasma operations of the MDPX device.

New Developments In Particle Image Velocimetry (PIV) For The Study Of Complex Plasmas

Particle Image Velocimetry (PIV) is a fluid measurement technique in which the average displacement of small groups of particles is made by comparing a pair of images that are separated in time by an interval Δt. For over a decade, a several variations of the PIV technique, e.g., two‐dimensional, stereoscopic, and tomographic PIV, have been used to characterize particle transport, instabilities, and the thermal properties of complex plasmas. This paper describes the basic principles involved in the PIV analysis technique and discusses potential future applications of PIV to the study of complex plasmas.