2026-09-20T19:40:31Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/868672026-06-17T14:44:09Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Dennis G. Whyte.
Ochoukov, Roman Igorevitch
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering.
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
2014-05-07T17:11:06Z
2014-05-07T17:11:06Z
2013
2013
http://hdl.handle.net/1721.1/86867
878533094
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 179-187).
ICRF-heated discharges on Alcator C-Mod are associated with enhanced sputtering of molybdenum plasma facing surfaces and increased levels of core impurity contents, which subsequently degrade the core plasma performance. RF sheath rectification on open magnetic field lines that intercept material surfaces is currently suspected of causing an enhancement of molybdenum impurity sources by increasing the energy with which incident plasma ions strike material surfaces. While it has previously been observed that plasma potentials on open magnetic field lines are enhanced in ICRF-heated discharges on Alcator C-Mod, a direct link between local RF wave fields and plasma potentials has yet to be established. Experimental measurements reveal that regions that directly magnetically map and do not map to the active antennas experience plasma potential enhancement. The "mapped" results are consistent with the slow wave rectification mechanism where the plasma potential enhancement is a result of rectification of the slow ICRF wave electric field launched directly by the antenna. This rectification mechanism is localized to regions directly magnetically mapped to the active antennas and occurs over a narrow plasma density range where the slow waves can propagate. The potential enhancement in the "unmapped" regions (inaccessible to directly launched slow waves) correlates well with the local fast wave fields and has multiple features that are consistent with the theory that involves fast waves coupling to a slow wave at a conducting surface, which then leads to rectification of the plasma potential. Cross field profile measurements reveal that the plasma density profile is also affected by ICRF power and it is suspected that the gradients in the plasma potential profile are responsible for the density profile changes through E x B plasma flows along equipotential surfaces. The implications are that the absolute plasma potentials and the plasma potential gradients are capable of affecting molybdenum sputtering and sources by modifying the sputtering yield and the incident ion flux, respectively.
by Roman Igorevitch Ochoukov.
Ph.D.
187 pages
eng
Massachusetts Institute of Technology
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
Nuclear Science and Engineering.
Investigation of plasma potential enhancement in the scrape-off layer of ion cyclotron range of frequencies heated discharges on Alcator C-Mod
Thesis
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<Abstract>ICRF-heated discharges on Alcator C-Mod are associated with enhanced sputtering of molybdenum plasma facing surfaces and increased levels of core impurity contents, which subsequently degrade the core plasma performance. RF sheath rectification on open magnetic field lines that intercept material surfaces is currently suspected of causing an enhancement of molybdenum impurity sources by increasing the energy with which incident plasma ions strike material surfaces. While it has previously been observed that plasma potentials on open magnetic field lines are enhanced in ICRF-heated discharges on Alcator C-Mod, a direct link between local RF wave fields and plasma potentials has yet to be established. Experimental measurements reveal that regions that directly magnetically map and do not map to the active antennas experience plasma potential enhancement. The "mapped" results are consistent with the slow wave rectification mechanism where the plasma potential enhancement is a result of rectification of the slow ICRF wave electric field launched directly by the antenna. This rectification mechanism is localized to regions directly magnetically mapped to the active antennas and occurs over a narrow plasma density range where the slow waves can propagate. The potential enhancement in the "unmapped" regions (inaccessible to directly launched slow waves) correlates well with the local fast wave fields and has multiple features that are consistent with the theory that involves fast waves coupling to a slow wave at a conducting surface, which then leads to rectification of the plasma potential. Cross field profile measurements reveal that the plasma density profile is also affected by ICRF power and it is suspected that the gradients in the plasma potential profile are responsible for the density profile changes through E x B plasma flows along equipotential surfaces. The implications are that the absolute plasma potentials and the plasma potential gradients are capable of affecting molybdenum sputtering and sources by modifying the sputtering yield and the incident ion flux, respectively.</Abstract>
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