Document Type

Dissertation

Date of Degree

Spring 2015

Degree Name

PhD (Doctor of Philosophy)

Degree In

Physics

First Advisor

Robert Merlino

Abstract

I study a dusty plasma produced in a DC glow discharge device. The chamber is a stainless steel cylinder 0.6 m in diameter and 0.9 m long. A stainless steel disk 3.2 cm in diameter acts as the anode and the walls act as the cathode. The discharge current is set between 1 - 10 mA and the voltage at the anode between 250 - 300 V. Dust is initially on a tray beneath the anode, and becomes trapped in the anode glow naturally with high discharge current. A secondary cloud can be made at a different location using a biased mesh. I make experimental observations of the dynamics of the secondary cloud as well as the unique interaction of the dust with a wire loop near the anode.

First, I describe the interaction of the secondary cloud with a wire when it the cloud is released to flow back to the primary cloud. A detached bow shock is observed as the cloud encounters an obstacle, and an elongated teardrop shaped void is formed downstream of the obstacle.

Second, a continuous flow is set up using at biased ring. The potentials of the ring and anode create a converging-diverging electrostatic potential structure which accelerates dust particles into a thin stream in the diverging section. The interaction of this stream and a wire obstacle is described.

Finally, the potentials of the mesh and anode are suddenly switched to float simultaneously to observe the secondary cloud expansion in the afterglow plasma. The rate of expansion is shown to depend inversely on the background pressure in the range of 100-200mTorr. The expansion shows a separation in the cloud and possible Yukawa-like expansion where the center of the cloud does not respond initially to the removal of confinement.

Public Abstract

Plasma is described as the forth state of matter, and accounts for most of matter in the universe. A plasma is an ionized gas, in which one or more electrons has been stripped from the atoms or molecules, and thus is an electrically conducting medium. On Earth plasma is found in fluorescent light bulbs, plasma TVs, and arc welders. Natural plasmas occur in lightning, the aurora, and the Earth’s ionosphere. Plasmas are used to etch semiconductors used in computer chips. Laboratory dusty plasmas were discovered to be the source of defects during etching of substrates. Dusty plasmas also exist in space, particularly in Saturn’s rings. Our Sun is a glowing ball of plasma. An international program is presently planning to use plasma as a source of energy, to power electricity, from the nuclear fusion of hydrogen.

My work has concentrated on flowing dusty plasmas. My experiment shows a detached bow shock when the dust fluid passes around a blunt obstacle at a speed faster than density waves travel in it. This is similar to the sonic boom of an airplane travelling faster than the speed of sound. My experiment here is more similar to the solar wind impinging on the moon or potentially the sun into the interstellar medium.

I also study the expansion of dust clouds when its confinement is removed. I determine whether the expansion happens uniformly or evolves more like a wave phenomenon. I compare the experimental results with theoretical and numerical models that have been developed.

Keywords

publicabstract, Dust, Fluid, Plasma, Shock

Pages

ix, 45 pages

Bibliography

Includes bibliographical references (pages 43-45).

Copyright

Copyright 2015 John Kenneth Meyer

Included in

Physics Commons

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