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.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/34459 |
| Date | January 2005 |
| Creators | Vetoʺ, Baʹlint |
| Contributors | James Terry., Massachusetts Institute of Technology. Dept. of Nuclear Engineering., Massachusetts Institute of Technology. Department of Nuclear Engineering, Massachusetts Institute of Technology. Department of Nuclear Science and Engineering |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | 88 leaves, 3787719 bytes, 3791333 bytes, application/pdf, application/pdf, application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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