{"created":"2023-06-20T13:21:16.853760+00:00","id":1418,"links":{},"metadata":{"_buckets":{"deposit":"8186b4e2-0936-4535-a9a0-5bcebecbffc0"},"_deposit":{"created_by":21,"id":"1418","owners":[21],"pid":{"revision_id":0,"type":"depid","value":"1418"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00001418","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":"李, 斌"}],"nameIdentifiers":[{"nameIdentifier":"0","nameIdentifierScheme":"WEKO"}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"リ, ビン"}],"nameIdentifiers":[{"nameIdentifier":"0","nameIdentifierScheme":"WEKO"}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2009-03-24"}]},"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":" Magnetic reconnection process has been investigated over half a century. Still, some
problems remain unsolved. The typical one is the onset problem, namely, how fast
reconnection is initiated. Another important issue is how huge magnetic energy is
converted to plasma energies in a short time scale.
Collisionless reconnection sets in when the current sheet is compressed as thin as
ion kinetic scale by the external driving sources. After experiencing some transient
phase the system can relax to a steady state in which reconnection rate balances the
inflow rate of magnetic flux from the external region, and then a new equilibrium
state is realized there through kinetic processes. Accordingly, driven reconnection
model is applied to study physical processes of collisionless reconnection in a steady
state in this thesis.
The research focus of this thesis is on the electron force balance in the electron
dissipation region (EDR) where electron frozen-in condition is broken due to micro-
scopic electron kinetic effect, and how energy conversion process takes place there,
especially from magnetic energy to that of electrons, in steady collisionless driven
reconnection.
The simulation domain is implemented on 2D and 3D rectangular open systems,
and a one-dimensional Harris equilibrium is employed as an initial condition. Plasma
inflow enters the simulation domain in y direction and the outflow leaves it in x
direction in our coordinate system. In order to supply plasma inflow into the system
and initiate reconnection, a driving electric field, which is stronger within the input
window around x = 0 at initial stage, is imposed in z direction at the upstream
boundary. Plasma outflow goes through the downstream boundary at x = ±xb ,
which is open for plasma particles and electromagnetic fields. In the 3D simulation
case, the boundary conditions at z= ± zb along the z axis are periodic. The following
summary focuses mainly on the physical processes of steady reconnection based on
the 3D simulation results.
It is found that a dissipation region with an enhanced electron current density
extends from the reconnection point toward the downstream region, and a long thin
EDR with dual structure is formed in a steady state. We show that the force balance
in the direction of the reconnection electric field (the z direction) is quite different
from that in the upstream direction (the y direction) in the EDR
In the z direction, the Lorentz force balances the electric force just outside the
EDR, and then decreases rapidly inside the EDR and vanishes at the reconnection
point. The electron inertia term has a local peak around the electron skin depth, but
it is canceled out by the electron pressure tensor term. Only pressure tensor term
sustains the electric field at the reconnection point, i.e., reconnection electric field.
Because the driving electric field works mainly on magnetized electrons inside
ion dissipation region and pushes them into the EDR, strong electrostatic field is
generated through the charge separation. Thus, a new force balance state is realized
in the upstream direction in the steady state. Although the pressure gradient force
balances the Lorentz force in the Harris equilibrium, the electrostatic force balances
the Lorentz force in the y direction in the new equilibrium state.
The energy conversion process inside the EDR is also studied intensively. Ac-
cording to the force balance in the upstream direction it is expected that magnetic
energy is effectively converted to electron kinetic or thermal energy in a short time
scale since only electron dynamics is dominant there.
We show that spatial variation of electron kinetic energies in the downstream
direction is quite different from that in the upstream direction, which is deeply related
to the dual structure of the EDR along the downstream direction. Electron inflow
kinetic energy drops quickly as electrons come into the EDR in the upstream direction,
while only z component of electron kinetic energy increases there through the electron
acceleration by strong reconnection electric field in the EDR.
In the downstream direction, z component of electron kinetic energy decreases as
they move away from the reconnection point, and it finally drops to a constant at
the edge of the inner structure of the EDR. On the other hand, outflow component
of electron kinetic energy increases and reaches its maximum around the edge of
the inner structure of the EDR. It is also found that total electron kinetic energy
is almost conserved in the inner structure region of the EDR, and thus the electron
kinetic enerry is converted from the z component to its outflow component by the
Lorentz force.
We have clarified two important physical processes controlled by electron dynamics
in steady collisionless driven reconnection, i.e., the relaxation into a new equilibrium
state in upstream direction and effective conversion from magnetic energy to electron
one in the EDR. Electron dynamics manifests itself in two aspects; the first is that
continuous in-place electron inflow enhances strong electrostatic field, and the second
is that current density is mainly sustained by z directed electron motion accelerated by
reconnection electric field. Thus, the new force balance between electrostatic force and
Lorentz force associated with enhanced current density is realized in the steady state.
Furthermore, strong electron current density provides a path to convert magnetic
energy to electron energy in the EDR through the interaction between particles and
electric field.
","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_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","filename":"甲1226_要旨.pdf","filesize":[{"value":"315.2 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/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"],"pubdate":{"attribute_name":"公開日","attribute_value":"2010-03-24"},"publish_date":"2010-03-24","publish_status":"0","recid":"1418","relation_version_is_last":true,"title":["Electron Dynamics in Steady Collisionless Driven Reconnection"],"weko_creator_id":"21","weko_shared_id":-1},"updated":"2023-06-20T16:05:18.949321+00:00"}