Date of Award:

5-2017

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Physics

Committee Chair(s)

Michael J. Taylor

Committee

Michael J. Taylor

Committee

Erik A. Syrstad

Committee

JR Dennison

Committee

Ludger Scherliess

Committee

Charles M. Swenson

Abstract

The mesosphere/lower thermosphere (MLT) is perhaps the least understood region of Earth's atmosphere. Too high for balloons and winged aircraft, yet too low for satellites, direct access to the MLT to make in-situ measurements is via high-speed sounding rockets for brief periods of at most a few minutes. Mass spectrometers have previously been used to make composition measurements in this region. But, mass spectrometry in the MLT is difficult, mainly due to the ambient pressures here and also the high speeds and short flight durations of sounding rocket missions. Time-of-flight mass spectrometers (TOF-MS) are capable of making fast, accurate measurements over a wide mass range. However, due to its dependence on microchannel plate (MCP) detectors and high acceleration voltages, this technique has rarely been applied in the MLT.

A new TOF-MS for making composition measurements of both charged and neutral particles in the upper atmosphere has been developed at the Space Dynamics Laboratory. This instrument employs modest acceleration potentials and a pressure-tolerant MCP detector. A prototype instrument was constructed and used to demonstrate TOF-MS technology under conditions relevant to in-situ MLT research. Laboratory experiments with this instrument also demonstrated its ability to resolve major atmospheric species of interest. A novel vacuum system for the new TOF-MS was evaluated. Results from these experiments were incorporated in a computer model to simulate instrument pressure during a sounding rocket flight. A computer model was also developed to evaluate the effects of critical operating parameters on instrument performance; the initial energy spread of sampled particles was found to have the greatest impact on mass resolution. Composition measurements made with the new TOF-MS will advance our understanding of the MLT.

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