Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The sintering of aluminum nitride in a microwave induced plasma was investigated. The plasma furnace consisted of a quartz tube inserted into a waveguide connected to a 2450 MHz microwave generator. After evacuating the tube to about 1.33 mbar, nitrogen gas was introduced, generating a steady plasma. Processing parameters such as gas pressure, power level, and time were optimized to yield maximum densification of aluminum nitride. Sintering of pure and doped AlN compacts was performed in the nitrogen plasma at temperatures up to 2000 S C. Undoped specimens reached densities of only 81% theoretical, while densities in excess of 95% theoretical were achieved for yttria doped specimens in less than 15 minutes. Microstructural investigations revealed a smaller grain size in the plasma sintered specimens (about 2μ) than are present in conventionally sintered AlN (about 8μ).

No description available.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains v, 127 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 94-98).

Electron Bernstein waves are a mode of oscillation in a plasma, thought a candidate for providing radiofrequency heating and non-inductive current drive in spherical tokamaks. Previous studies of these modes have relied on neglecting or simplifying the contribution made by relativistic effects. This work presents fully relativistic numerical results that show the mode's dispersion relation for a wide range of parameters. Relativistic effects are shown to shift the location of the resonance as in previous studies, but the effects beyond this are shown to matter only in high temperature (10-20keV) plasmas. At these higher temperatures however, the fully relativistic model differs markedly. The assumption that the mode is electrostatic is looked at, and found to be inadequate for describing fully the electron Bernstein modes dispersion relation. Simple estimates that neglect toroidal effects show current drive efficiency is expected to be an order of magnitude higher than that for conventional electron cyclotron current drive using the O or X modes. It is shown for a number of model tokamaks that heating the center of the plasma and driving current using EBWs is impossible launching from the outside due to strong damping of the wave at higher cyclotron harmonics. Results from a code based on a more complicated semi-analytic model of current drive, that includes toroidal effects and calculates the average current drive over the magnetic surface, confirm the higher expected current drive efficiency, and the code is shown to give good agreement with a Fokker-Planck code. The higher values of perpendicular refractive index associated with the EBWs are shown to mitigate the deleterious effects of trapping on current drive efficiency to a small extent. The details of the magnetic field are found to be unimportant to the calculation beyond determing where the wave is absorbed. The codes written to produce these results are outlined before each set of results. The last of these is considerably faster than conventional Fokker-Planck codes and a useful tool in studying electron cyclotron current drive in the future.

No description available.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / by Marcel P. J. Gaudreau. / Sc.D.

<p>High power fusion plasmas produced in the world’s largest facility for magnetic confinement experiments (JET), have been studied using the neutron emission measured with the magnetic proton recoil (MPR) spectrometer. The MPR has been used to observe plasmas since 1996 including those of deuterium-tritium leading to several fusion records and corresponding observational achievements of neutron emission spectroscopy. Noteworthy are novel studies of the complex states of fuel ions arising through plasma heating by neutral beam (NB) injection and radio frequency (RF) power.</p><p>This thesis concerns the analysis of MPR data on the neutron emission from NB heated discharges alone and in combination with RF. A main objective of these studies has been the effect of supra-thermal fuel ion reactions on the fusion power as compared to the basic thermal component. The analysis was based on dedicated models to describe the velocity distributions of the ion population under the influence of the NB and RF heating in a parametric form allowing trial neutron spectra to be calculated and fitted to the data to select the kinetic state of the fuel ions that best described the MPR observations.</p><p>Spectral signatures of different underlying plasma states and phenomena were identified and results from up to five different ion reaction contributions to the fusion power were demonstrated besides the global plasma features of toroidal rotation. Moreover, the thesis presents examples of derived detailed plasma information from MPR data such as the kinetic energy densities for the thermal and supra-thermal parts of the fuel ion population as well as the synergetic coupling of RF power to the fast ions from NB injection. The results constitute a stepping-stone for neutron emission spectroscopy as a main diagnostic for ITER and other future fusion experiments on thermonuclear ignition.</p>

High power fusion plasmas produced in the world’s largest facility for magnetic confinement experiments (JET), have been studied using the neutron emission measured with the magnetic proton recoil (MPR) spectrometer. The MPR has been used to observe plasmas since 1996 including those of deuterium-tritium leading to several fusion records and corresponding observational achievements of neutron emission spectroscopy. Noteworthy are novel studies of the complex states of fuel ions arising through plasma heating by neutral beam (NB) injection and radio frequency (RF) power. This thesis concerns the analysis of MPR data on the neutron emission from NB heated discharges alone and in combination with RF. A main objective of these studies has been the effect of supra-thermal fuel ion reactions on the fusion power as compared to the basic thermal component. The analysis was based on dedicated models to describe the velocity distributions of the ion population under the influence of the NB and RF heating in a parametric form allowing trial neutron spectra to be calculated and fitted to the data to select the kinetic state of the fuel ions that best described the MPR observations. Spectral signatures of different underlying plasma states and phenomena were identified and results from up to five different ion reaction contributions to the fusion power were demonstrated besides the global plasma features of toroidal rotation. Moreover, the thesis presents examples of derived detailed plasma information from MPR data such as the kinetic energy densities for the thermal and supra-thermal parts of the fuel ion population as well as the synergetic coupling of RF power to the fast ions from NB injection. The results constitute a stepping-stone for neutron emission spectroscopy as a main diagnostic for ITER and other future fusion experiments on thermonuclear ignition.

The neutron spectrometer TOFOR was installed at JET in 2005 for high-rate observation of neutrons from reactions between two deuterium (D) ions. Neutron spectrometry as a fusion plasma diagnostic technique is invoked to obtain information about the velocity states of fusion fuel ions. Based on neutron spectrometry data, conclusions can be drawn on the efficiency of plasma heating schemes as well as optimization of fuel ion confinement. The quality of TOFOR analysis is found to depend on how well the instrument response function is known; discriminator threshold levels, detector time alignment and electronics broadening are identified as crucial issues. About 19 percent of the neutrons observed with TOFOR have scattered off the JET vessel wall or other structures in the line-of-sight before reaching the instrument, as established through simulations and measurements. A method has been developed to take these neutrons into account in the analysis. TOFOR measurements of fast deuterium distributions are seen to agree with distributions deduced from NPA data, obtained based on an entirely different principle. This serves as validation of the modeling and analysis. Extraordinary statistics in the TOFOR measurements from JET pulses heated with 3rd harmonic RF heating on D beams allow for study of instabilities using neutron emission spectrometry. At ITER, similar studies should be possible on a more regular basis due to higher neutron rates. Observations of neutrons from Be+3He reactions in the TOFOR spectrum from D plasmas heated with fundamental RF tuned to minority 3He raise the question of beryllium neutrons at JET after installation of the ITER-like wall, and at ITER, with beryllium as the plasma facing component. This is especially important for the first few years of ITER operation, where the machine will not yet have been certified as a nuclear facility and should be run in zero-activation mode.