Diffusion of electrons in the solar corona
Başlık:
Diffusion of electrons in the solar corona
Yazar:
Galloway, Ross K., author.
ISBN:
9780438059337
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (171 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: Alec MacKinnon.
Özet:
This thesis explores aspects of electron transport in the solar corona, with emphasis on the contribution made by diffusive physical processes, both in real space and in velocity space. Chapter 1 gives a general introduction to the characteristics of the solar atmosphere, and in particular of coronal magnetic structures and solar flares. Chapter 2 discusses the design and performance of the RHESSI and TRACE spacecraft, whose data are extensively used for observational comparison in later chapters. Detailed background theory and observations are introduced in these later chapters as they become relevant to the discussion. Chapter 3 concerns the effects of velocity diffusion on a fast electron population injected into a high temperature region. Chapter 4 details the development of an approximate analytical solution for the thermalisation due to self-interactions of an electron population with an initially power-law distribution in energy. We study the temporal evolution of an isolated electron population relaxing towards a Maxwellian state, employing an idealised treatment in which the growth of the Maxwellian is governed by the conservation of particle number and energy. Chapter 5 discusses a code for simulating TRACE images of coronal plasma, which can be used to explore the observational consequences of various plasma temperature distributions. The design and features of the code are described, and some examples given to illustrate the effects of differing internal temperature profiles on the appearance of coronal plasma structures. The code can be used to simulate images in each of the three TRACE extreme ultra-violet pass- bands, and supports both straight and elliptical loop structures with a variety of cross-sectional and longitudinal plasma temperature profiles. Some limits on the temperature distribution within the coronal plasma are inferred from the simulated images: in particular, coronal loops are likely to be homogeneous in temperature to within less than 1 MK over their visible cross-sectional extent; and simple configurations of only thermal plasma are inconsistent with the observation that coronal structures frequently appear less spatially confined in transition lines characteristic of higher temperature plasma. Chapter 6 examines the implications of tangled magnetic fields in coronal loops for the transport of particles across the field. The theory of cross-field transport in a disordered magnetic field is reviewed, and examined in typical coronal conditions, where it is found to exceed other mechanisms of cross-field transport for moderately tangled fields, such as would be produced by random convective foot- point motion. Cross-sectional and longitudinal temperature profiles are generated for coronal loops with heat distributions governed by cross-field transport due to diffusion in a tangled magnetic field. These are combined with the TRACE image simulator introduced in the previous chapter to generate synthetic loop images, which are compared with observational data. Cross-field diffusion in a tangled magnetic field is found to generate loop widths consistent with observations for magnitudes of field line perpendicular stochastic wandering of up to a few tens of percent, and frequently less. Cross-sectional temperature profiles for loops cooled principally by conduction or radiation are compared: radiatively-cooled loops are found to generally show greater longitudinal uniformity in temperature and be visible over a larger cross-sectional radius than equivalent conductively-cooled loops. Approaches to independently determining the degree of magnetic disorder in the corona are discussed, including a method employing the cross-field diffusion of highly energetic, supra-thermal electrons. Chapter 7 summarises the conclusions of the previous chapters, and discusses some possible avenues of related future research.
Notlar:
School code: 0547
Konu Başlığı:
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684710.1) | 684710-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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