{"created":"2023-06-20T13:20:30.105759+00:00","id":528,"links":{},"metadata":{"_buckets":{"deposit":"20ce1091-8d9e-4816-bc15-b51d44ee3224"},"_deposit":{"created_by":1,"id":"528","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"528"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00000528","sets":["2:427:12"]},"author_link":["0","0","0"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"KHAN, RIAZ"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ハーン, リアズ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2006-09-29"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":" The ballooning mode is a magnetohydrodynamic (MHD) instability that is excited
in finite beta plasmas. The energy source of the ballooning mode originates
from the pressure gradient in a locally unfavorable magnetic curvature region, typically,
in the outboard of the torus. The proximity of the measured edge pressure gradient
in H-mode to the critical gradient for ideal ballooning instability has led to the
proposal that these instabilities might have a role in triggering edge localized modes
(ELMs). New nonlinear theoretical models describe ELMs in terms of filaments that
erupt from the plasma. This is supported by strong experimental evidence from the
MAST tokamak[1, 2, 3] that the ELM does indeed exhibit a mode structure predicted
by the nonlinear ballooning mode theory. This thesis presents the nonlinear dynamics
of the ballooning mode and its relation with ELMs by means of numerical simulations
in spherical tokamak (ST) devices in the framework of MHD model and the drift
model. Our simulation reproduces the characteristic features of ELM crash phase.
The nonlinear simulations using MHD model are executed in a three dimensional
full toroidal geometry. The initial MHD equilibrium for the simulation is given
as an axisymmetric numerical MHD equilibrium, which is obtained by solving the
Grad-Shafranov equation on the poloidal cross-section. The profiles are selected to be
moderately broad in the core region following the conventional experiments. During
the linear analysis, the intermediate-n modes (i.e., n = 5−9) have larger growth rates
than others, where n is the toroidal mode number. It is shown that these intermediate-n
modes have a ballooning mode nature in that the mode structures are poloidaly localized in the bad curvature region, and have a wide envelope consisting of several
poloidal components. In the nonlinear phase, the MHD ballooning modes evolve into
a nonlinear structure that results in the formation of a number of hot plasma filaments,
elongated along a magnetic field line, but localized about it. These filaments extend
out into the scrape-off layer on the outboard side but remain connected back into the
pedestal region on the inboard side. This filamentary structure is correspondent to the
convection motion of the plasma flows, which forms a twin-vortex flow pattern in such
a way that the plasma moves in outward direction, pushing the core plasma from inside
to outside of the torus. When the balloon structure is initially formed at the plasma
surface, the magnetic field lines on both sides of the separatrix are pushed against each
other by such perpendicular flows due to the spouting-out and the perfect conductor
conserving the poloidal flux. Under this situation, the reconnection of the field lines
can effectively occur by the driven reconnection mechanism. Once such reconnection
occur, the plasma rapidly flows out through the reconnected field lines due to the
parallel pressure gradient, leading to the filamentary structure. After the internal free
energy is partially lost by such convective processes, the system ceases to develop and
reaches a relaxed state. These results are compared qualitatively with the experimental
observation of the ELMs in MAST and NSTX experiments. Good agreement is
found in the following characteristics formation of filaments separating from the core,
non-uniform growth of filaments due to toroidal mode coupling, time scale of ELM
crash, triggering by the ideal ballooning mode, presence of intermediate-n precursors
and loss of plasma through convective process.
Moreover the finite Larmor radius (FLR) effect is also addressed using the simplified drift model, where the ion diamagnetic drift effect is included in the advection
term of the equation of motion. This modification has been found to suppress the
higher-n components linearly, since the mode growth is suppressed by the sheared rotation flows. However, it has been also found that the filament separation from the core
can take place universally for FLR as well as the MHD case.","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第984号","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"物理科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"10 核融合科学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2006"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"KHAN, Riaz","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲984_要旨.pdf","filesize":[{"value":"273.8 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨","url":"https://ir.soken.ac.jp/record/528/files/甲984_要旨.pdf"},"version_id":"e8ba8b68-a9d4-411b-8005-1c7621bf9534"},{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲984_本文.pdf","filesize":[{"value":"6.2 MB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"本文","url":"https://ir.soken.ac.jp/record/528/files/甲984_本文.pdf"},"version_id":"344f8044-c71e-41b4-8ad1-a823e5886e8e"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Simulation study on nonlinear dynamics of ballooning modes in a spherical tokamak","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Simulation study on nonlinear dynamics of ballooning modes in a spherical tokamak"},{"subitem_title":"Simulation study on nonlinear dynamics of ballooning modes in a spherical tokamak","subitem_title_language":"en"}]},"item_type_id":"1","owner":"1","path":["12"],"pubdate":{"attribute_name":"公開日","attribute_value":"2010-02-22"},"publish_date":"2010-02-22","publish_status":"0","recid":"528","relation_version_is_last":true,"title":["Simulation study on nonlinear dynamics of ballooning modes in a spherical tokamak"],"weko_creator_id":"1","weko_shared_id":1},"updated":"2023-06-20T16:01:33.433757+00:00"}