Date of Award

Winter 2004

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Kristina Lynch

Abstract

On January 14th 2002 the SIERRA sounding rocket was launched from Poker Flat Research Range, Alaska into active substorm expansion aurora and reached 735 km. For the first time, direct measurements of the cold ionospheric population in darkness were made by the UNH Thermal Electron Detector (TED). At these middle altitudes, understanding this population is important because the thermal electrons can carry currents coupling the lower ionosphere and the magnetospheric auroral source. This thesis, focusing on the development and analysis of this new instrument, incorporates the study of two distinct areas. One area is the direct measurement of the ambient thermal electrons which both form the background of the dynamic high latitude ionosphere and contribute directly to its behavior by modifying the plasma environment for other constituents. The second focus area is the concept that any attempt to measure thermal electrons must also be a careful study of potentials forming near conducting bodies in a plasma, a still poorly understood subject. The TED instrument response shows that a non-monotonic potential barrier can form in the sheath around the detector and prevent access to the core of the thermal electrons. A technique has been developed for reconstructing the plasma distribution which enables key measurements of temperature, density, and flow. Thermal electron core temperatures are seen to vary greatly, from as low as ∼0.1 eV in the polar cap to a maximum of ∼0.8 eV in auroral arcs. Outside active precipitation the density agrees with an independent calculation from the HF wave receiver. This verifies the method used for estimating the payload potential. In the "inverted V" and Alfvenic regions the HF measure of density was used to normalize our results for the changing payload potential. The thermal data indicate that in the dark, the non-negligible auroral and secondary emission currents must be accounted for in order to understand what controls the spacecraft potential. Finally, it is shown that, given this understanding of the potential structure and a quantitative measure of the payload potential, the critical thermal electron drift should be measurable with this new instrument.

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