{"id":{"repo_id":"columbia-diss","oai_identifier":"oai:academiccommons.columbia.edu:10.7916/D8C82HC3"},"canonical_url":"https://search.dev.ndltd.org/etd/columbia-diss/oai:academiccommons.columbia.edu:10.7916/D8C82HC3","repository":{"repo_id":"columbia-diss","name":"Columbia University","base_url":"https://academiccommons.columbia.edu/oai"},"display":{"title":"Multimode Structure of Resistive Wall Modes near the Ideal Wall Stability Limit","abstract":"This thesis presents the first systematic study of multimode external kink structure and dynamics in a tokamak using a high-resolution magnetic sensor set. Multimode effects are directly measured, rather than inferred from anomalies in single-mode behavior. In order to accomplish this, an extensive set of 216 poloidal and radial magnetic field sensors has been installed in the High Beta Tokamak -- Extended Pulse (HBT-EP) device for high-resolution measurements of three-dimensional mode activity. An analysis technique known as biorthogonal decomposition (BD) is described, and simulations are presented to justify its use for studying kink mode dynamics in HBT-EP data. Coherent activity of multiple simultaneous modes is observed using the BD without needing to define a mode structure basis beforehand. Poloidal mode numbers up to m=8 are observed via sensor arrays with full 360 degree coverage. Higher poloidal mode numbers are suggested by the data, but cannot be well-resolved with the available diagnostics. Toroidal mode numbers up to n=4 are observed. Non-rigid, multimode activity is observed for coexisting external kinks having m/n=3/1 and 6/2 structures. Despite sharing the same helicity and same resonant surface, rotation of 6/2 modes is independent of 3/1 mode rotation -- the n=2 mode does not simply rotate with double the frequency of the n=1 mode. During periods of 3/1-dominated activity, the 6/2 mode is observed to modulate the 3/1 amplitude, and in brief instances can overpower the 3/1. Statistical analysis over many shots reveals the multimode nature of the 3/1 kink to be more significant when the resonant q=3 surface begins internal, then is ejected from the plasma. This inference is based on the relative amplitudes of secondary modes during 3/1-dominated activity, as well as spectral content of the modes. Conformal conducting wall segments were also retracted away from the plasma surface using low-order poloidal and toroidal asymmetries to excite measurable differences in low m- and n-number modes. Kink mode amplitudes increase as the wall segments are withdrawn, and non-symmetric wall configurations modulate the amplitude and frequency of the rotating modes depending upon their toroidal orientation with respect to the non-symmetric wall. Modulations of mode amplitude and rotation are larger for the toroidal wall asymmetry than for the poloidal wall asymmetry.","abstract_html":"This thesis presents the first systematic study of multimode external kink structure and dynamics in a tokamak using a high-resolution magnetic sensor set. Multimode effects are directly measured, rather than inferred from anomalies in single-mode behavior. In order to accomplish this, an extensive set of 216 poloidal and radial magnetic field sensors has been installed in the High Beta Tokamak -- Extended Pulse (HBT-EP) device for high-resolution measurements of three-dimensional mode activity. An analysis technique known as biorthogonal decomposition (BD) is described, and simulations are presented to justify its use for studying kink mode dynamics in HBT-EP data. Coherent activity of multiple simultaneous modes is observed using the BD without needing to define a mode structure basis beforehand. Poloidal mode numbers up to m=8 are observed via sensor arrays with full 360 degree coverage. Higher poloidal mode numbers are suggested by the data, but cannot be well-resolved with the available diagnostics. Toroidal mode numbers up to n=4 are observed. Non-rigid, multimode activity is observed for coexisting external kinks having m/n=3/1 and 6/2 structures. Despite sharing the same helicity and same resonant surface, rotation of 6/2 modes is independent of 3/1 mode rotation -- the n=2 mode does not simply rotate with double the frequency of the n=1 mode. During periods of 3/1-dominated activity, the 6/2 mode is observed to modulate the 3/1 amplitude, and in brief instances can overpower the 3/1. Statistical analysis over many shots reveals the multimode nature of the 3/1 kink to be more significant when the resonant q=3 surface begins internal, then is ejected from the plasma. This inference is based on the relative amplitudes of secondary modes during 3/1-dominated activity, as well as spectral content of the modes. Conformal conducting wall segments were also retracted away from the plasma surface using low-order poloidal and toroidal asymmetries to excite measurable differences in low m- and n-number modes. Kink mode amplitudes increase as the wall segments are withdrawn, and non-symmetric wall configurations modulate the amplitude and frequency of the rotating modes depending upon their toroidal orientation with respect to the non-symmetric wall. Modulations of mode amplitude and rotation are larger for the toroidal wall asymmetry than for the poloidal wall asymmetry.","abstract_has_math":false,"creators":["Levesque, Jeffrey Peter"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2012,"date_issued":"2012","date_published":"2012","updated_at":"2026-07-24T01:44:20Z","subjects":["Plasma (Ionized gases)","Physics","Tokamaks"],"languages":["English"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.7916/D8C82HC3","outbound_label":"DOI","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Levesque, Jeffrey Peter"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2012"]},{"key":"dc:type","label":"Dc Type","values":["Theses"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Plasma (Ionized gases)","Physics","Tokamaks"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.7916/D8C82HC3"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["This thesis presents the first systematic study of multimode external kink structure and dynamics in a tokamak using a high-resolution magnetic sensor set. Multimode effects are directly measured, rather than inferred from anomalies in single-mode behavior. In order to accomplish this, an extensive set of 216 poloidal and radial magnetic field sensors has been installed in the High Beta Tokamak -- Extended Pulse (HBT-EP) device for high-resolution measurements of three-dimensional mode activity. An analysis technique known as biorthogonal decomposition (BD) is described, and simulations are presented to justify its use for studying kink mode dynamics in HBT-EP data. Coherent activity of multiple simultaneous modes is observed using the BD without needing to define a mode structure basis beforehand. Poloidal mode numbers up to m=8 are observed via sensor arrays with full 360 degree coverage. Higher poloidal mode numbers are suggested by the data, but cannot be well-resolved with the available diagnostics. Toroidal mode numbers up to n=4 are observed. Non-rigid, multimode activity is observed for coexisting external kinks having m/n=3/1 and 6/2 structures. Despite sharing the same helicity and same resonant surface, rotation of 6/2 modes is independent of 3/1 mode rotation -- the n=2 mode does not simply rotate with double the frequency of the n=1 mode. During periods of 3/1-dominated activity, the 6/2 mode is observed to modulate the 3/1 amplitude, and in brief instances can overpower the 3/1. Statistical analysis over many shots reveals the multimode nature of the 3/1 kink to be more significant when the resonant q=3 surface begins internal, then is ejected from the plasma. This inference is based on the relative amplitudes of secondary modes during 3/1-dominated activity, as well as spectral content of the modes. Conformal conducting wall segments were also retracted away from the plasma surface using low-order poloidal and toroidal asymmetries to excite measurable differences in low m- and n-number modes. Kink mode amplitudes increase as the wall segments are withdrawn, and non-symmetric wall configurations modulate the amplitude and frequency of the rotating modes depending upon their toroidal orientation with respect to the non-symmetric wall. Modulations of mode amplitude and rotation are larger for the toroidal wall asymmetry than for the poloidal wall asymmetry."]},{"key":"dc:title","label":"Title","values":["Multimode Structure of Resistive Wall Modes near the Ideal Wall Stability Limit"]}]}],"canonical_facts":{"dc:creator":["Levesque, Jeffrey Peter"],"dc:date":["2012"],"dc:description":["This thesis presents the first systematic study of multimode external kink structure and dynamics in a tokamak using a high-resolution magnetic sensor set. Multimode effects are directly measured, rather than inferred from anomalies in single-mode behavior. In order to accomplish this, an extensive set of 216 poloidal and radial magnetic field sensors has been installed in the High Beta Tokamak -- Extended Pulse (HBT-EP) device for high-resolution measurements of three-dimensional mode activity. An analysis technique known as biorthogonal decomposition (BD) is described, and simulations are presented to justify its use for studying kink mode dynamics in HBT-EP data. Coherent activity of multiple simultaneous modes is observed using the BD without needing to define a mode structure basis beforehand. Poloidal mode numbers up to m=8 are observed via sensor arrays with full 360 degree coverage. Higher poloidal mode numbers are suggested by the data, but cannot be well-resolved with the available diagnostics. Toroidal mode numbers up to n=4 are observed. Non-rigid, multimode activity is observed for coexisting external kinks having m/n=3/1 and 6/2 structures. Despite sharing the same helicity and same resonant surface, rotation of 6/2 modes is independent of 3/1 mode rotation -- the n=2 mode does not simply rotate with double the frequency of the n=1 mode. During periods of 3/1-dominated activity, the 6/2 mode is observed to modulate the 3/1 amplitude, and in brief instances can overpower the 3/1. Statistical analysis over many shots reveals the multimode nature of the 3/1 kink to be more significant when the resonant q=3 surface begins internal, then is ejected from the plasma. This inference is based on the relative amplitudes of secondary modes during 3/1-dominated activity, as well as spectral content of the modes. Conformal conducting wall segments were also retracted away from the plasma surface using low-order poloidal and toroidal asymmetries to excite measurable differences in low m- and n-number modes. Kink mode amplitudes increase as the wall segments are withdrawn, and non-symmetric wall configurations modulate the amplitude and frequency of the rotating modes depending upon their toroidal orientation with respect to the non-symmetric wall. Modulations of mode amplitude and rotation are larger for the toroidal wall asymmetry than for the poloidal wall asymmetry."],"dc:identifier":["https://doi.org/10.7916/D8C82HC3"],"dc:language":["English"],"dc:subject":["Plasma (Ionized gases)","Physics","Tokamaks"],"dc:title":["Multimode Structure of Resistive Wall Modes near the Ideal Wall Stability Limit"],"dc:type":["Theses"]},"updated_at":"2026-07-24T01:44:20Z"}