Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003. / Includes bibliographical references. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / We attempted to measure the anisotropy in the electron distribution function in magnetized plasma by exploiting the adiabatic invariance of the electron's magnetic moment with a probe comprising a grid, a collector, and an inertially cooled electromagnet. The electric mirror force of the grid, which is located at the electromagnet throat, reduces the demand on the magnetic mirror force and thereby on the electromagnet current, which then allows for the construction of a compact probe that can be inserted inside the plasma chamber. An analysis of the effects of space charge inside the grid-collector cavity revealed that the size of the probe's entrance aperture, b, which gives the size of the plasma beam inside the probe, should be chosen to be within a factor of ten of the electron Debye-length [lambda][sub]De. In addition, an analysis of the discrete structure of the grid showed that the mesh wire spacing d should be chosen to be much less than [lambda][sub]De. Also, the wire thickness t should be chosen to be much less than d . We built a probe with a grid of tungsten wires with dimensions, t = 5,[mu]m and d = 200[mu]m . We then tested this probe in a hydrogen plasma immersed in a background magnetic field of B [approximately] 1kG. The plasma was heated by microwaves via the electron cyclotron resonance. It was characterized by a density and temperature equal to n[sub]e [approximately] 10¹⁰ cm⁻³ and T[sub]e [approximately] 10eV, respectively, which gave [lambda][sub]De [approximately] 300[mu]m. The collector's current-voltage characteristic demonstrated the interaction between the electric barrier at the collector and the hybrid electric-magnetic barrier at the grid, thereby establishing the basic principles of the probe. / (cont.) The characteristic also revealed the non-ideal behaviors associated with the electric hole in the mesh and the effects of space charge. These effects in conjunction with the poor signal-to-noise level of the data prevented the measurement of the distribution function. Still, we were able to extract the temperature anisotropy for an assumed two-temperature Maxwellian distribution. The value for this ratio was found to be greater than one (greater temperature for the perpendicular gyro-motion), which is plausible given the way in which the plasma is heated. / by Khashayar Shadman. / Ph.D.

Thesis (Nucl. E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 22-24). / by Mahmood A. Cheema. / Nucl.E.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 151-160). / by Leigh Scott Johnson. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 128-131). / by Jyh-Tzh-Tzong Hwang. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 87-90). / In recent history, nuclear engineers and the nuclear power industry have been primarily concerned with two things: safety and waste. In the past few years, a third concern has risen to join these two at the top: terrorism. This change occurred on September 11, 2001. Americans now realize that terrorists are willing and able to attack on their home soil and that terrorists have no qualms about attacking civilians. This thesis examines in detail why people are especially afraid of nuclear power, from the standpoint of both safety and terrorist threats, more so than the other risks that we face everyday. This thesis then explores the role of the press in influencing and being influenced by public perception. The conclusions of this thesis can be boiled down to these main points: (1) The publics fear of terrorism against a nuclear facility has the same roots as the fear caused by safety concerns over nuclear power, and the strongest of these roots is the association of all things "nuclear" with the threat of nuclear war. (2) Terrorism risk perception is largely influenced by proximity to a particular threat. That is, people see more risk in threats that are close to themselves or their loved ones. Likewise, authorities assume that the public perceives greater risk in their particular area of responsibility. / (cont.) (3) Since the purpose of terrorism is to incite terror, the public perception of nuclear power plants as tempting terrorist targets may be self-fulfilling. (4) Any public action by government or industry leads to increased media coverage, and any media coverage, positive or negative, increases public fear. Therefore, the nuclear establishment should take no action to lower terrorism risk with the hope that it will allay public concern. Instead, the establishment should take whatever reasonable actions it thinks will reduce the actual risk and make appropriate emergency response preparations, while avoiding additional media coverage. / by Mark Laughter. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (leaves 87-88). / The tokamak is so far the most promising magnetic confinement configuration to control fusion scale plasmas and to be a large scale source of electricity in the future. Built in the shape of a torus of major and minor radius R and r respectively, the charged particles are confined by the superposition of a toroidal and a poloidal magnetic field. In order to study the transport processes that lead to the removal of energetic particles from the hot plasma, two tangentially viewing optical diagnostics have been installed to look at the plasma edge region (0.9 < < 1.1) of the Alcator C-Mod diverted tokamak. The toroidally looking views are coupled to fast photodiode amplifier circuits that record the D, brightness at a rate of 1 MHz. Two plasma-directed gas puffs are employed at the inboard and outboard plasma edges to enhance the emission at the desired toroidal locations. The absolutely calibrated views yield the required data for building radial and poloidal profiles of the intrinsic D, plasma brightness. The Abel inverted radial D, emissivity profile typically peaks at 30 W/m3/ster at I cm outside the separatrix ( ... 1.05) and drops on both sides of the separatrix. / (cont.) For the first time, the poloidal measurements of the plasma edge brightness with and without the D2 neutral gas puff yielded an estimate for the vertical extent of the neutral gas puff. The steady state inboard and outboard D, brightness profiles are also compared during two consecutive periods of L and H mode operation. The time lagged cross correlation calculated for neighboring views revealed quickly propagating local brightness maxima (blobs). The phase velocity of these systematically moving brightness perturbations ranges from -1 to 1 km/s inside the separatrix and becomes uniform outside the separatrix at 0.5 km/s where the positive velocity indicates radially outward motion. Downward propagating perturbations are also observed in the outboard SOL. / In French: Le tokamak est de loin la configuration la plus prometeuse pour confiner par champs magnetique des plasmas dedies h la fusion et constituer ainsi une source d'energie grande echelle pour le futur. Les particules chargees sont confinees dans un tore de grand et petit rayons R and r par la superposition de champs toroidal et poloidal. Afin de mieux comprendre les processus de transport qui conduisent h une perte d'energie pour le plasma chaud, un dtecteur en forme de croix a te installe sur le tokamak Alcator C-Mod pour observer le bord du plasma (0.9 < x < 1.1). Chaque vue toroidale est couple avec un circuit d'amplification des photodiodes rapides qui enregistre des fluctuations de brillance du plasma a la longeur d'onde D, avec une frequence de 1 MHz. Le dispositif utilise une injection de gaz neutre dirigee radialement vers l'interieur afin d'augmenter l'emission h un angle toroidal predetermine. Les vues sont calibrees de maniere absolue et permettent de construire le profil de la brillance radial et poloidal. Le profil radial culmine juste a l'exterieur de la sparatrix a une valeur de 30 WV/m3/ster et diminue vers zro des deux c6tes. / (cont.) La difference entre les profils poloidals avant et apres l'injection de gaz neutre estime la taille verticale de l'injection de gaz 5 cm. La correlation retardee est calcul6e pour les vues voisines et perinet d'observer la propagation de structures caractere d'ondes appelees blobs. La vitesse de phase de ces blobs est de -1 h 1 km/s l'interieur de la sparatrix et devient uniforme h l'exterieur avec une valeur moyenne 0.5 km/s, les vitesses positives indiquant un mouvement vers l'exterieur. / by Baʹlint Vetoʺ. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 276-279). / Eight heats of material with base alloy chemistries of Alloys 800 HT or 617 with platinum additions of 2, 5, 15, or 30 wt% have been characterized according to their microstructural features. The goals of characterization were to determine metallurgical stability for service as self-catalytic structural materials. The results presented herein will be useful to the development of a material for the construction of a heat exchanger designed for sulfuric acid decomposition. This type of heat exchanger is a key component to hydrogen generation by the thermochemical sulfur-iodine water-splitting process, a future technology that promises efficient hydrogen production if coupled to a Generation IV nuclear reactor heat source. Characterization of each material was carried out in the cast and wrought conditions with optical and SE microscopy, electron dispersive spectrometry, chemical composition analysis, and thermodynamic modeling. Materials have been characterized according to grain size and morphology, precipitate features, twinning characteristics, and platinum composition effects. Results indicate that platinum and carbon compositions have the greatest effect on the development of microstructural features. / (cont.) Increasing platinum compositions in both base alloy chemistries fosters the presence of annealing twins, which indicates that platinum additions reduce stacking fault energy within the alloy systems. Platinum additions appear to cause the development of larger grain structures as well as increase corrosion resistance. With the exception of the Alloy 800 HT - 30 wt% Pt system, the alloy systems characterized herein were melted with carbon contents between 1.2 - 3.6 times higher than the maximum specified compositions for the base chemistries. Excessive inter and intra-granular carbide precipitation resulted, which leads to compromised corrosion resistance and mechanical properties. Inter-granular attack due to sensitization is observed in the Alloy 800 HT - 2, 5 wt% Pt systems. SEM micrographs of the Alloy 617 - Pt systems show that these systems are less prone to inter-granular attack. The grain structures of each base alloy - Pt system are much finer than those of the respective base alloy systems included for comparison. Fine grain structures are detrimental to overall ductility and high temperature creep strength. On average, the Alloy 800 HT - Pt systems developed larger grains than the Alloy 617 - Pt systems. / (cont.) A two phase microstructure that resembles pearlite developed in the Alloy 617 - 30 wt% Pt system. This alloy system will be excluded from further characterization for self catalytic structural application due to expected poor mechanical and corrosion resistance properties. The most important microstructural improvements for the development of a self-catalytic structural material include a reduction of carbon content and an increase in grain size. Further characterization of catalytic, corrosion resistance, and mechanical properties are required for selection of the optimum platinum addition to the base chemistries of Alloys 800 HT and 617 for sulfuric acid decomposition service. / by David Andrés Rigual. / S.M.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1996. / Includes bibliographical references (leaves 114-123). / by Chandrasekhar Ramanathan. / Sc.D.

Thesis (Nucl. E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1996. / Includes bibliographical references. / by Bruce W. Brisson. / Nucl.E.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1997. / Includes bibliographical references (leaves [100]-[102]). / by Brandon William Blackburn. / M.S.