Date of Award

Winter 2019

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Harald Kucharek

Second Advisor

Karsten Pohl

Third Advisor

James Ryan

Abstract

Earth's magnetosphere contains plasma originating both from the solar wind and from

the ionosphere. While H+ is the dominant ion from both sources, the solar wind contains

high charge state ions such as He++, and O6+, while the ionosphere contributes singly ionized

heavy ions including He+, N+ and O+. Measuring the composition gives information on

the source and mass dependent entry, heating and acceleration mechanisms. However, most

ion composition instruments are not able to clearly distinguish between some of the heavy

ions involved in these processes, particularly N+ and O+. This thesis aims to test a new

design of a Time-of-Flight mass spectrometer that should improve the mass resolution by

reducing scattering. In this new design, the carbon foil that is normally used to generate

a "Start" signal is replaced by a single straight-channel Microchannel Plate (MCP). These

changes are implemented in the engineering copy of the Ion Composition and Distribution

Function analyzer (CODIF) instrument, allowing us to investigate the eects of the change

on spectra and flux for different MCP geometries as well as different thin film coatings. We

demonstrate that all tested MCP geometries with or without coatings significantly reduce

the energy lost from the ion when compared against the carbon foil, but only for ions heavier

than carbon; this improves separation of the heavier ion species close in mass, characterized

by the transit time of the Gaussian-distributed centroid in time and the Full Width Half

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Max of the spectra. Geometry effects are the most significant, with the narrower pores

having the largest reduction in energy transferred from the ion. However, MCP response

is heavily dependent on impinging angle and comes at the cost of severely decreased ion

flux for the narrower pore sizes. Thin film coatings of Al2O3 on the MCPs result in smooth

surfaces that increase the probabilities of specular reflection occurring and reduce the energy

required to emit an electron, resulting in slightly increased scattering while improving the

detection efficiency. Additionally, the instrument using MCPs can accurately determine mass

at energies far lower than where the carbon foil's energy losses cause the spectra to be too

broad to be distinguished. This demonstrates that an MCP-based instrument would not

require a Post Acceleration voltage (PAC). Results from this work culminate in a future

detector design, capitalizing on the advantages offered by the MCP and carbon foils.

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