Electrical and Computer Engineering ETDs

Publication Date

Spring 5-10-2018

Abstract

Helicon plasma sources are widely used in basic plasma science, as well as for materials processing. These plasmas typically operate at high gas fill pressure, and therefore have significant densities of neutral particles. However, the role of neutrals in the overall plasma dynamics, such as ion flows, remains poorly understood. There are at least two possible mechanisms for neutrals to influence ion flows. One is an FxB drift, where F is the force exerted on ions by neutrals through collisions. The second is through Pedersen conductivity which is dependent on the ratio of the ion cyclotron frequency, ωci, to the ion-neutral collision frequency, νin.

To investigate this interaction, a laser induced fluorescence (LIF) system has been developed for the Helicon-Cathode (HelCat) linear helicon plasma device at the University of New Mexico (UNM). The LIF system is based on a > 250 mW, tunable diode laser with a tuning range between 684 and 699 nm. One neutral and one ion metastable energy state can be excited. For neutral argon (ArI) LIF, the laser pumps the metastable (2P03/2)4s 2[3/2]02 level to the (2P01/2)4p 2[1/2]1 level using 696. 7352 nm light. The fluorescence radiation from decay to the (2P01/2)4s 2[1/2]00 level at 772. 6333 nm is observed. Two ion transitions are also explored, one of which yielded usable results.

The system design, measurements, and analysis for axial, radial and azimuthal velocity of ArI is presented. The neutral flow is found to be axially away from the source, radially outward from the center of the machine, and azimuthally in the electron diamagnetic direction. It is less than 50 m/s in all directions. The neutral temperature is ~ 0.05eV. A collisional-radiative (CR) model is used to estimate the neutral ground state density profile, which is used to calculate the neutral-driven FxB drift. Swept, compensated probe data are used to calculate ExB velocity, modified by the Pedersen conductivity, and diamagnetic drifts. A total drift is calculated and compared to Mach probe measurements of ion flow. Although the combined drifts fail to account for the measured ion flow, results indicate that the neutrals do influence the flow.

Keywords

Plasma Physics, laser induced fluorescence (LIF), neutral argon (ArI) motion in plasma, ion-neutral interaction, HelCat

Sponsors

National Science Foundation

Document Type

Dissertation

Language

English

Degree Name

Electrical Engineering

Level of Degree

Doctoral

Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Mark Gilmore

Second Committee Member

Edl Schamiloglu

Third Committee Member

Gary Cooper

Fourth Committee Member

Todd Pedersen

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