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Still, some\u003cbr /\u003eproblems remain unsolved. The typical one is the onset problem, namely, how fast\u003cbr /\u003ereconnection is initiated. Another important issue is how huge magnetic energy is\u003cbr /\u003econverted to plasma energies in a short time scale. \u003cbr /\u003e Collisionless reconnection sets in when the current sheet is compressed as thin as\u003cbr /\u003eion kinetic scale by the external driving sources. After experiencing some transient\u003cbr /\u003ephase the system can relax to a steady state in which reconnection rate balances the\u003cbr /\u003einflow rate of magnetic flux from the external region, and then a new equilibrium\u003cbr /\u003estate is realized there through kinetic processes. Accordingly, driven reconnection\u003cbr /\u003emodel is applied to study physical processes of collisionless reconnection in a steady\u003cbr /\u003estate in this thesis. \u003cbr /\u003e The research focus of this thesis is on the electron force balance in the electron\u003cbr /\u003edissipation region (EDR) where electron frozen-in condition is broken due to micro-\u003cbr /\u003escopic electron kinetic effect, and how energy conversion process takes place there, \u003cbr /\u003eespecially from magnetic energy to that of electrons, in steady collisionless driven\u003cbr /\u003ereconnection. \u003cbr /\u003e The simulation domain is implemented on 2D and 3D rectangular open systems, \u003cbr /\u003eand a one-dimensional Harris equilibrium is employed as an initial condition. Plasma\u003cbr /\u003einflow enters the simulation domain in y direction and the outflow leaves it in x\u003cbr /\u003edirection in our coordinate system. In order to supply plasma inflow into the system\u003cbr /\u003eand initiate reconnection, a driving electric field, which is stronger within the input\u003cbr /\u003ewindow around x = 0 at initial stage, is imposed in z direction at the upstream\u003cbr /\u003eboundary. Plasma outflow goes through the downstream boundary at x = \u0026plusmn;x\u003csmall\u003eb\u003c/small\u003e , \u003cbr /\u003ewhich is open for plasma particles and electromagnetic fields. In the 3D simulation\u003cbr /\u003ecase, the boundary conditions at z= \u0026plusmn; z\u003csmall\u003eb\u003c/small\u003e along the z axis are periodic. The following\u003cbr /\u003esummary focuses mainly on the physical processes of steady reconnection based on\u003cbr /\u003ethe 3D simulation results. \u003cbr /\u003e It is found that a dissipation region with an enhanced electron current density\u003cbr /\u003eextends from the reconnection point toward the downstream region, and a long thin\u003cbr /\u003eEDR with dual structure is formed in a steady state. We show that the force balance\u003cbr /\u003ein the direction of the reconnection electric field (the z direction) is quite different\u003cbr /\u003efrom that in the upstream direction (the y direction) in the EDR\u003cbr /\u003e In the z direction, the Lorentz force balances the electric force just outside the\u003cbr /\u003eEDR, and then decreases rapidly inside the EDR and vanishes at the reconnection\u003cbr /\u003epoint. The electron inertia term has a local peak around the electron skin depth, but\u003cbr /\u003eit is canceled out by the electron pressure tensor term. Only pressure tensor term\u003cbr /\u003esustains the electric field at the reconnection point, i.e., reconnection electric field.\u003cbr /\u003e Because the driving electric field works mainly on magnetized electrons inside\u003cbr /\u003eion dissipation region and pushes them into the EDR, strong electrostatic field is\u003cbr /\u003egenerated through the charge separation. Thus, a new force balance state is realized\u003cbr /\u003ein the upstream direction in the steady state. Although the pressure gradient force\u003cbr /\u003ebalances the Lorentz force in the Harris equilibrium, the electrostatic force balances\u003cbr /\u003ethe Lorentz force in the y direction in the new equilibrium state. \u003cbr /\u003e The energy conversion process inside the EDR is also studied intensively. Ac-\u003cbr /\u003ecording to the force balance in the upstream direction it is expected that magnetic\u003cbr /\u003eenergy is effectively converted to electron kinetic or thermal energy in a short time\u003cbr /\u003escale since only electron dynamics is dominant there. \u003cbr /\u003e We show that spatial variation of electron kinetic energies in the downstream\u003cbr /\u003edirection is quite different from that in the upstream direction, which is deeply related\u003cbr /\u003eto the dual structure of the EDR along the downstream direction. Electron inflow\u003cbr /\u003ekinetic energy drops quickly as electrons come into the EDR in the upstream direction, \u003cbr /\u003ewhile only z component of electron kinetic energy increases there through the electron\u003cbr /\u003eacceleration by strong reconnection electric field in the EDR. \u003cbr /\u003e In the downstream direction, z component of electron kinetic energy decreases as\u003cbr /\u003ethey move away from the reconnection point, and it finally drops to a constant at\u003cbr /\u003ethe edge of the inner structure of the EDR. On the other hand, outflow component\u003cbr /\u003eof electron kinetic energy increases and reaches its maximum around the edge of\u003cbr /\u003ethe inner structure of the EDR. It is also found that total electron kinetic energy\u003cbr /\u003eis almost conserved in the inner structure region of the EDR, and thus the electron\u003cbr /\u003ekinetic enerry is converted from the z component to its outflow component by the\u003cbr /\u003eLorentz force. \u003cbr /\u003e We have clarified two important physical processes controlled by electron dynamics\u003cbr /\u003ein steady collisionless driven reconnection, i.e., the relaxation into a new equilibrium\u003cbr /\u003estate in upstream direction and effective conversion from magnetic energy to electron\u003cbr /\u003eone in the EDR. Electron dynamics manifests itself in two aspects; the first is that\u003cbr /\u003econtinuous in-place electron inflow enhances strong electrostatic field, and the second\u003cbr /\u003eis that current density is mainly sustained by z directed electron motion accelerated by\u003cbr /\u003ereconnection electric field. Thus, the new force balance between electrostatic force and\u003cbr /\u003eLorentz force associated with enhanced current density is realized in the steady state. \u003cbr /\u003eFurthermore, strong electron current density provides a path to convert magnetic\u003cbr /\u003eenergy to electron energy in the EDR through the interaction between particles and\u003cbr /\u003eelectric field. \u003cbr /\u003e", "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1226号", "subitem_description_type": "Other"}]}, "item_1_select_14": {"attribute_name": "所蔵", "attribute_value_mlt": [{"subitem_select_item": "有"}]}, "item_1_select_16": {"attribute_name": "複写", "attribute_value_mlt": [{"subitem_select_item": "複写不可"}]}, "item_1_select_17": {"attribute_name": "公開状況", "attribute_value_mlt": [{"subitem_select_item": "要旨のみ公開"}]}, "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": "2008"}]}, "item_creator": {"attribute_name": "著者", "attribute_type": "creator", "attribute_value_mlt": [{"creatorNames": [{"creatorName": "LI, Bin", "creatorNameLang": "en"}], "nameIdentifiers": [{"nameIdentifier": "0", "nameIdentifierScheme": "WEKO"}]}]}, "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", "download_preview_message": "", "file_order": 0, "filename": "甲1226_要旨.pdf", "filesize": [{"value": "315.2 kB"}], "format": "application/pdf", "future_date_message": "", "is_thumbnail": false, "licensetype": "license_11", "mimetype": "application/pdf", "size": 315200.0, "url": {"label": "要旨・審査要旨", "url": "https://ir.soken.ac.jp/record/1418/files/甲1226_要旨.pdf"}, "version_id": "63391d79-be09-48d5-af41-1ef954bba68f"}]}, "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": "Electron Dynamics in Steady Collisionless Driven Reconnection", "item_titles": {"attribute_name": "タイトル", "attribute_value_mlt": [{"subitem_title": "Electron Dynamics in Steady Collisionless Driven Reconnection"}, {"subitem_title": "Electron Dynamics in Steady Collisionless Driven Reconnection", "subitem_title_language": "en"}]}, "item_type_id": "1", "owner": "21", "path": ["12"], "permalink_uri": "https://ir.soken.ac.jp/records/1418", "pubdate": {"attribute_name": "公開日", "attribute_value": "2010-03-24"}, "publish_date": "2010-03-24", "publish_status": "0", "recid": "1418", "relation": {}, "relation_version_is_last": true, "title": ["Electron Dynamics in Steady Collisionless Driven Reconnection"], "weko_shared_id": -1}
Electron Dynamics in Steady Collisionless Driven Reconnection
https://ir.soken.ac.jp/records/1418
https://ir.soken.ac.jp/records/14188094e58c-1fb5-4716-975a-60fd73f56e27
名前 / ファイル | ライセンス | アクション |
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Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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公開日 | 2010-03-24 | |||||
タイトル | ||||||
タイトル | Electron Dynamics in Steady Collisionless Driven Reconnection | |||||
タイトル | ||||||
言語 | en | |||||
タイトル | Electron Dynamics in Steady Collisionless Driven Reconnection | |||||
言語 | ||||||
言語 | eng | |||||
資源タイプ | ||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
資源タイプ | thesis | |||||
著者名 |
李, 斌
× 李, 斌 |
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フリガナ |
リ, ビン
× リ, ビン |
|||||
著者 |
LI, Bin
× LI, Bin |
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学位授与機関 | ||||||
学位授与機関名 | 総合研究大学院大学 | |||||
学位名 | ||||||
学位名 | 博士(理学) | |||||
学位記番号 | ||||||
内容記述タイプ | Other | |||||
内容記述 | 総研大甲第1226号 | |||||
研究科 | ||||||
値 | 物理科学研究科 | |||||
専攻 | ||||||
値 | 10 核融合科学専攻 | |||||
学位授与年月日 | ||||||
学位授与年月日 | 2009-03-24 | |||||
学位授与年度 | ||||||
2008 | ||||||
要旨 | ||||||
内容記述タイプ | Other | |||||
内容記述 | Magnetic reconnection process has been investigated over half a century. Still, some<br />problems remain unsolved. The typical one is the onset problem, namely, how fast<br />reconnection is initiated. Another important issue is how huge magnetic energy is<br />converted to plasma energies in a short time scale. <br /> Collisionless reconnection sets in when the current sheet is compressed as thin as<br />ion kinetic scale by the external driving sources. After experiencing some transient<br />phase the system can relax to a steady state in which reconnection rate balances the<br />inflow rate of magnetic flux from the external region, and then a new equilibrium<br />state is realized there through kinetic processes. Accordingly, driven reconnection<br />model is applied to study physical processes of collisionless reconnection in a steady<br />state in this thesis. <br /> The research focus of this thesis is on the electron force balance in the electron<br />dissipation region (EDR) where electron frozen-in condition is broken due to micro-<br />scopic electron kinetic effect, and how energy conversion process takes place there, <br />especially from magnetic energy to that of electrons, in steady collisionless driven<br />reconnection. <br /> The simulation domain is implemented on 2D and 3D rectangular open systems, <br />and a one-dimensional Harris equilibrium is employed as an initial condition. Plasma<br />inflow enters the simulation domain in y direction and the outflow leaves it in x<br />direction in our coordinate system. In order to supply plasma inflow into the system<br />and initiate reconnection, a driving electric field, which is stronger within the input<br />window around x = 0 at initial stage, is imposed in z direction at the upstream<br />boundary. Plasma outflow goes through the downstream boundary at x = ±x<small>b</small> , <br />which is open for plasma particles and electromagnetic fields. In the 3D simulation<br />case, the boundary conditions at z= ± z<small>b</small> along the z axis are periodic. The following<br />summary focuses mainly on the physical processes of steady reconnection based on<br />the 3D simulation results. <br /> It is found that a dissipation region with an enhanced electron current density<br />extends from the reconnection point toward the downstream region, and a long thin<br />EDR with dual structure is formed in a steady state. We show that the force balance<br />in the direction of the reconnection electric field (the z direction) is quite different<br />from that in the upstream direction (the y direction) in the EDR<br /> In the z direction, the Lorentz force balances the electric force just outside the<br />EDR, and then decreases rapidly inside the EDR and vanishes at the reconnection<br />point. The electron inertia term has a local peak around the electron skin depth, but<br />it is canceled out by the electron pressure tensor term. Only pressure tensor term<br />sustains the electric field at the reconnection point, i.e., reconnection electric field.<br /> Because the driving electric field works mainly on magnetized electrons inside<br />ion dissipation region and pushes them into the EDR, strong electrostatic field is<br />generated through the charge separation. Thus, a new force balance state is realized<br />in the upstream direction in the steady state. Although the pressure gradient force<br />balances the Lorentz force in the Harris equilibrium, the electrostatic force balances<br />the Lorentz force in the y direction in the new equilibrium state. <br /> The energy conversion process inside the EDR is also studied intensively. Ac-<br />cording to the force balance in the upstream direction it is expected that magnetic<br />energy is effectively converted to electron kinetic or thermal energy in a short time<br />scale since only electron dynamics is dominant there. <br /> We show that spatial variation of electron kinetic energies in the downstream<br />direction is quite different from that in the upstream direction, which is deeply related<br />to the dual structure of the EDR along the downstream direction. Electron inflow<br />kinetic energy drops quickly as electrons come into the EDR in the upstream direction, <br />while only z component of electron kinetic energy increases there through the electron<br />acceleration by strong reconnection electric field in the EDR. <br /> In the downstream direction, z component of electron kinetic energy decreases as<br />they move away from the reconnection point, and it finally drops to a constant at<br />the edge of the inner structure of the EDR. On the other hand, outflow component<br />of electron kinetic energy increases and reaches its maximum around the edge of<br />the inner structure of the EDR. It is also found that total electron kinetic energy<br />is almost conserved in the inner structure region of the EDR, and thus the electron<br />kinetic enerry is converted from the z component to its outflow component by the<br />Lorentz force. <br /> We have clarified two important physical processes controlled by electron dynamics<br />in steady collisionless driven reconnection, i.e., the relaxation into a new equilibrium<br />state in upstream direction and effective conversion from magnetic energy to electron<br />one in the EDR. Electron dynamics manifests itself in two aspects; the first is that<br />continuous in-place electron inflow enhances strong electrostatic field, and the second<br />is that current density is mainly sustained by z directed electron motion accelerated by<br />reconnection electric field. Thus, the new force balance between electrostatic force and<br />Lorentz force associated with enhanced current density is realized in the steady state. <br />Furthermore, strong electron current density provides a path to convert magnetic<br />energy to electron energy in the EDR through the interaction between particles and<br />electric field. <br /> | |||||
所蔵 | ||||||
値 | 有 |