Physics & Astronomy ETDs

Tiffany Hayes

Publication Date

2-8-2011

Abstract

Sheared Flows have been studied extensively in devices such as tokomaks, and Q-machines. The study of flows has multiple purposes; it is observed that plasmas in space, and in the ionosphere, tend to have sheared flows, and to be able to better understand these, it is desired to perform experiments in the laboratory. As well, flows have been studied extensively for the purposes of fusion. It has been observed that sheared flows may excite certain instabilities such as the Kelvin-Helmholtz instability; sheared flows also have the ability to suppress gradient-drive instabilities, such as drift-waves. Being able to change and control the flow, and flow shear in a plasma is an important region of experimental study. The Helicon-Cathode device at the University of New Mexico is a linear device that can produce a plasma via an rf-antenna, or via a cathode discharge. Using the helicon source, it is possible to create a dense lab plasma ~ 10^19 m^-3, and an electron temperature around 5eV. Using this device, electrodes were placed into the plasma, and biased. In order to characterize if any changes occurred in the plasma, electrostatic probes were used to measure the (floating) potential, and the density profile, in addition to mach probe measurements, which were used to measure axial flow (flow along the magnetic field), and azimuthal flow (flow perpendicular to the magnetic field). Experimental were completed with two goals. The first goal of the project was to compare estimated flow values, found from the measured density and potential measurements, with the measured flow values. The second goal of the project was to have an empirical analysis of the electrode affects on the plasma. It is hoped that this analysis will make it possible for other groups to re-create specific shear profiles, and flow speeds in a similar device. It is observed that measured flow values do not match estimated flow values, and reasonable explanations may be the lack of temperature and plasma potential measurements, or the failure of mach probe theory due to an insufficiently magnetized plasma. It may also be possible that more complicated physics is occurring due to drift-waves, and zonal flows in the system. It is also observed that it is possible to affect the (floating) potential of the system, along with the azimuthal and axial flows of the system. Different sheared profiles are exhibited for different grid biases; the results provide a frame-work for better controlling flows using multiple electrodes, and for creating specific flow values in a similar device.

Degree Name

Physics

Level of Degree

Masters

Department Name

Physics & Astronomy

First Committee Member (Chair)

Gilmore, Mark

Second Committee Member

Lynn, Alan

Third Committee Member

Pihlstrom, Ylva

Language

English

Keywords

Shear flow, Plasma (Ionized gases), Helicons (Electromagnetism)

Document Type

Thesis

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