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The detection and analysis of VLF triggered emissions.

Morgan, David (1977) The detection and analysis of VLF triggered emissions. PhD thesis, University of Sheffield.

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The work described in this thesis consists essentially of two parts. The first is the design and development of/ ä rocket-borne V. L. P. receiver for the observation of the magnetic field component of electromagnetic waves in the frequency range 100 to 20,000 Hz. The author's particular contribution was/ the optimisation of the design of a smallμ-metal rod aerial. The approach was necessarily partly empirical, partly theoretical. The former involved the systematic adjustment of the number of turns, coil geometry, dimensions and type of wire, etc. for the particular rod length small enough to be flown in the space available in the rocket nose-cone. This was complemented by a theoretical approach involving the rod and equivalent circuits which satisfactorily reproduced the measured frequency response and signal/noise properties of the aerial and preamplifier. The second part of the thesis is concerned with the analysis and interpretation of discrete V. L. F. emissions using the phenomenological theory of Helliwell. Both medium and high latitude emissions were analysed in detail. Significant advances were made in the computer iteration techniques applied to the analysis of these emissions and limitations in the analytical methods used were investigated in great detail. Particularly interesting were several "slow risers" recorded at Andoya (L = 6.6) in northern Norway. The analysis determined the time varying energy spectrum of the phase-bunched electrons giving rise to the emission in the vicinity of the earth's equator (- 6.6 earth radii) for a rangeof possible equatorial ambient electron densities. It was possible to determine an upper limit to the electron density at the equator which, since it was in excellent agreement with that (2 to 5 electrons/ cc) determined by more direct measurements, provided new experimental support for the theory. The limitations in the theory were examined and a small error in the original formula of Helliwell corrected.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Physics and Astronomy (Sheffield)
Identification Number/EthosID: uk.bl.ethos.547849
Depositing User: EThOS Import Sheffield
Date Deposited: 31 May 2016 15:54
Last Modified: 31 May 2016 15:54
URI: http://etheses.whiterose.ac.uk/id/eprint/12822

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