Jeremiah Williams

Application of stereoscopic particle image velocimetry to studies of transport in a dusty (complex) plasma

Over the past 5 years, two-dimensional particle image velocimetry (PIV) techniques [E. Thomas, Jr., Phys. Plasmas 6, 2672 (1999)] have been used to obtain detailed measurements of microparticle transport in dusty plasmas. This Letter reports on an extension of these techniques to a three-dimensional velocity vector measurement approach using stereoscopic PIV. Initial measurements using the stereoscopic PIV diagnostic are presented.

Measurement of the kinetic dust temperature of a weakly coupled dusty plasma

Measurements of the velocity space distribution function of 1.2-mum-diameter alumina particles in an argon direct-current glow discharge dusty plasma are made using stereoscopic particle image velocimetry. These distribution functions are then used to determine the kinetic temperature of the dust component. These measurements show that the kinetic temperature of the dust component is significantly larger than the other plasma components, such as electrons, ions, and background neutrals

Observations of vertically propagating driven dust acoustic waves: Finite temperature effects

In this study, the first measurement of the dispersion relationship for a vertically propagating (i.e., parallel to gravity), driven dust acoustic wave is reported. Finite dust temperature effects were observed in the dispersion relation of the dust acoustic wave.

Initial measurement of the kinetic dust temperature of a weakly coupled dusty plasma

Measurements of the velocity space distribution function of 2.9μm diameter silica particles in an argon dc glow discharge dusty plasma are made through the use of stereoscopic particle image velocimetry (stereo-PIV). These distribution functions are then used to determine the kinetic temperature of the dust component. These measurements show that the kinetic temperature of the dust component is significantly larger than the other plasma components (electrons, ions, and background neutrals).

Application of tomographic particle image velocimetry to studies of transport in complex (dusty) plasma

Over the past twelve years, two-dimensional and stereoscopic particle image velocimetry (PIV) techniques have been used to obtain detailed measurements of the thermal and transport properties of the microparticle component of dusty plasma systems. This letter reports on an extension of these techniques to obtain a volumetric, three-dimensional velocity vector measurement using tomographic PIV. Initial measurements using the tomographic PIV diagnostic are presented.

Applications of stereoscopic particle image velocimetry: Dust acoustic waves and velocity space distribution functions

Two-dimensional particle image velocimetry (2D-PIV) techniques have been applied to dusty plasmas for the past 5 years. During that time, 2D-PIV has been used to provide detailed measurements of microparticle transport in dusty plasmas. However, a measurement of the third velocity vector direction is necessary to fully understand the microparticle transport. In this paper, stereoscopic particle image velocimetry (stereo-PIV) is used as a technique for obtaining all three-velocity vector components. This paper discusses the application of stereo-PIV techniques to measurements of dust acoustic waves and velocity space distribution functions in dusty plasmas.

Measurements of the Dust Temperature in the Dispersion Relation of the Dust Acoustic Wave

Over the past 15 years, the dust acoustic wave has been a subject of intense study, and, in recent years, thermal effects in the dust acoustic wave have emerged as a new area of investigation. This paper presents preliminary measurements of the kinetic dust temperature using the dispersion relation of this wave mode as a function of the neutral gas pressure. It is found that dust temperature is significantly larger than the other plasma components and decreases with increasing neutral gas pressure.

Observation of the coupling of the driven dust acoustic wave

In this study, the coupling between the naturally occurring dust acoustic wave (DAW) and the discharge current modulation is examined. It is confirmed that, when the wave is driven by modulating the discharge current, the DAW is driven at the same frequency as the current modulation.

Volumetric measurements of a spatially growing dust acoustic wave

In this study, tomographic particle image velocimetry (tomo-PIV) techniques are used to make volumetric measurements of the dust acoustic wave (DAW) in a weakly coupled dusty plasma system in an argon, dc glow discharge plasma. These tomo-PIV measurements provide the first instantaneous volumetric measurement of a naturally occurring propagating DAW. These measurements reveal over the measured volume that the measured wave mode propagates in all three spatial dimensional and exhibits the same spatial growth rate and wavelength in each spatial direction.

Microparticle injection effects on microwave transmission through an overly dense plasma layer

Summary form only given. Vehicles traveling at hypersonic velocities within the Earths atmosphere, such as spacecraft during reentry and other hypersonic vehicles, are enveloped by a dense plasma layer. This plasma layer reflects and significantly attenuates GPS and S-band signals for vehicle navigation, telemetry, and voice communications, resulting in radio blackout.Injecting microparticles into a plasma discharge will reduce the free electron density via electron attachment to particles. Reducing the free electron density lowers the plasma cutoff frequency, and may allow lower frequency bands of electromagnetic signals to penetrate the plasma layer. In these studies, a linear hollow cathode produces an electron beam that is accelerated into a low pressure (50 to 150 mTorr) background of Argon gas, producing an electron beam discharge. A 170 Gauss axial magnetic field produced by two electromagnet coils in a Helmholtz configuration results in a well-collimated electron beam, producing a 2dimensional Argon plasma discharge. This discharge sheet is approximately 100 cm long by 30 cm wide by 2 cm thick, at densities as high as 1012 cm-3. The plasma sheet is intended to mimic the intense plasma layer produced and experienced by vehicles traveling at hypersonic velocities. A shaker device with fine mesh on the bottom is filled with alumina powder and fitted with a vibrating motor. When supplied with a modest voltage, the vibration drops alumina microparticles from the mesh openings, into the plasma sheet discharge, creating a dusty plasma. Varying the voltage supplied to the vibrating motor varies the flux rate and density of powder dropped into the plasma. A transmitting microwave horn is oriented normal to the dense plasma sheet while the receiving horn is mounted on a stage that can be rotated up to 180 degrees azimuthally. Results from these experiments measuring the cutoff and transmission of S-band microwaves incident on a dusty plasma layer, as well as Langmuir probe measurements assessing microparticle effects on plasma density and transparency are reported.