Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. Includes bibliographical references (leaves 209-216).

This thesis examines theoretically the potential of the plasma confinement device known as a Stellarator as a fusion reactor. Chapter one contains a survey of the requirements for nuclear fusion to take place in a device employing magnetic confincment. The range of reactor parameters which are appropriate is- derived, both from the point of view of plasma physics and on the basis of a rather crude economic model. Chapter two begins with a discussion of the equilibrium of plasma in Stellarators. Solutions of the equilibrium equations are obtained, employing an Inverse aspect ratio axpansicn of the field quantities. Chapter three Indicates which macroscopic" instabilities are cause for concern in Stellarators without net longitudinal currant. A. stability criterion appropriate to Stellarators is evaluated, using the equilibrium fields found in the proceeding chapter. Chapter four is devoted to the study of the effects of particles which are localised in the ripple of the Stellarator masnetic field on transport. A random walk theory of their contribution to diffusion is given. Chapter five contains a description of the coil systems capable of generating fitellarator fields, and their properties. Specialising to "twisted" coils, geometrical scaling laws are sought, which describe the properties of the fields they produce. Chapter six is a brief indication as to how such coils may be incorporated into a reactor. Chapter seven considers the parameters of a Stellarator reactor based on "twisted" coils, and shows how they may be written in terms of the raajor and minor radii of the device. An economic model of the reactor is given, which allows us to optimise the reactor, to obtain the cheapest system at fixed total power output and wall loading. The result is shown Co be considerably less expensive than similar Tokamak designs.

Thesis (Ph.D.) -- Australian National University, 2007.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 404-410).

This thesis describes physics research carried out at the Columbia Neutral Torus (CNT) stellarator after its adaptation from a non-neutral plasma experiment to a device relevant to magnetic fusion energy research. Results are presented in the areas of plasma heating and related topics (microwave-assisted plasma start-up, overdense heating, inversion of stellarator images), as well as to stellarator stability and related topics (high β, error fields). This thesis also describes the engineering improvements which enabled the said adaptation of CNT. The first step of that process involved the installation of a low-power, pulsed 2.45 GHz magnetron. In those initial experiments it was found that the simultaneous use of microwave start-up and of an emissive hot cathode resulted in non-linearly increased electron densities, implying a synergy between the two start-up methods. Then, a 10 kW, 2.45 GHz heating system was commissioned including a custom-designed transmission line and launch antenna. Highly overdense plasmas (a factor of 4 above the cutoff density) were obtained with this system, both for O-mode and X-mode polarization. The analysis of Langmuir probe profiles of density and temperature required the accurate mapping of the minor radius in the plasma, which motivated a study of CNT error fields. This resulted in a new numerical method for inferring coil misalignments from flux surface measurements. The improved knowledge of the actual magnetic field geometry of CNT permitted to develop and successfully apply an inversion technique to experimental plasma images. This technique (“onion peeling”) reconstructs radial emissivity profiles, and can be considered a 3D generalization of Abel inversion. Finally, simulations of high-β plasma equilibria in different CNT magnetic configurations indicate that (1) ballooning stability limits should be accessible at volume-averaged β as low as 0.9% and (2) ballooning-stable β values as high as 3.0% should be attainable with heating powers as low as 40-100 kW and 1-3 MW respectively, according to stellarator energy confinement scaling laws.

Dissertation (Ph.D.)--Auburn University, 2008. / Abstract.

This thesis is a work divided into two parts on aspects of three-dimensional (3D) magnetic fields: (I) magnetic reconnection treated from a strictly 3D viewpoint and (II) the design of coils for producing the 3D magnetic fields of optimized stellarators. In astrophysical settings, magnetic fields are generically 3D. 3D divergence-free fields have rich topological structures such as magnetic nulls and chaotic field line structures. Standard reconnection literature identifies magnetic nulls as locations of magnetic reconnection, and that intense currents will build up around them. This idea is explored with a key realization that by placing a vanishingly small sphere around the null, boundary conditions on field lines passing through the sphere may be sorted out. The main result here is (1) the dismissal of the notion that nulls are crucial places for magnetic reconnection and current accumulation, instead identifying separatrices of topological type on the boundaries of null-passing field lines to be crucial. Standard reconnection literature dismisses chaotic flows yet 3D fields generically have chaotic flows. An inherent property of chaotic flows is exponentiation. The main result here is (2) the identification of exponentiation as a natural mechanism for magnetic reconnection and that the associated current builds up linearly in time in contradiction to standard results requiring the formation of high-density current sheets. The magnetic fields of optimized stellarators are intricate, producing complex 3D magnetic surfaces. These fields are conventionally generated by non-planar electromagnetic coils, though these coils are costly to manufacture, slow device assembly, and hinder stellarator maintenance. Part II of this thesis explores methods of stellarator coil simplification that do not involve modular coils. All of this work uses current potentials, which are stream functions of the current sheets that produce magnetic surfaces. We begin with a result found using analytic methods on current potentials that (1) there may be an inherent limitation in the ability of modular coils to produce fields at a distance. This result is not surprising, though further analysis is necessary to work out some complexities of the result. Next, (2) a novel method to produce localized patches of current potential, representative of patches of current sheets, is developed and used to identify crucial locations of current placement for shaping magnetic surfaces. Most notably, these current sheet patches are able to produce much of the surface shaping while occupying a small fraction of the winding surface, resulting in good open-access stellarator coil configurations. Continuing the trend away from modular coils, (3) helical coils are optimized to support stellarator magnetic fields. This work agrees with related work on the optimization of helical coils, finding them unsuitable to the precise production of equilibria generated by modular coils. To improve this result, we use coil sets of mixed-type: helical coils with windowpane coils or permanent magnets, to mitigate field error left behind by the helical coils. Finally, (4) the development of a generalized method to cut modular, helical, and windowpane coils out of current potentials and to identify the associated coil currents is developed and used in coil optimization.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1980. / Vita. / Includes bibliographical references. / by Alan Charles Janos. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1980.