Magnetic reconnection and current sheets in 2D and 3D magnetic configurations
Experimental results are presented on the study magnetic reconnection phenomena and current sheet formation and evolution in 2D and 3D magnetic configurations with some topological singularities: null-lines, null points, singular lines. Current sheet evolution in 2D fields with null-lines manifests...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
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| Цитувати: | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations / A.G. Frank, S.Yu. Bogdanov, N.P. Kyrie, V.S. Markov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 94-96. — Бібліогр.: 20 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859643958684024832 |
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| author | Frank, A.G. Bogdanov, S.Yu. Kyrie, N.P. Markov, V.S. |
| author_facet | Frank, A.G. Bogdanov, S.Yu. Kyrie, N.P. Markov, V.S. |
| citation_txt | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations / A.G. Frank, S.Yu. Bogdanov, N.P. Kyrie, V.S. Markov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 94-96. — Бібліогр.: 20 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Experimental results are presented on the study magnetic reconnection phenomena and current sheet formation and evolution in 2D and 3D magnetic configurations with some topological singularities: null-lines, null points, singular lines. Current sheet evolution in 2D fields with null-lines manifests qualitative agreement with principal features of flare-type phenomena. Current sheet formation was revealed to occur in various 3D magnetic
configurations, both with and without isolated magnetic null-points, specifically in agnetic configurations with Xlines. Results demonstrate self-organization of current sheets to be a general process for plasma dynamics in nonuniform magnetic fields.
|
| first_indexed | 2025-12-07T13:25:02Z |
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UDC 533.9
94 Problems of Atomic Science and Technology. 2000. № 6. Series: Plasma Physics (6). p. 94-96
MAGNETIC RECONNECTION AND CURRENT SHEETS IN 2D AND 3D
MAGNETIC CONFIGURATIONS
A.G. Frank, S.Yu. Bogdanov, N.P. Kyrie, V.S. Markov
General Physics Institute Russian Academy of Sciences, Moscow, Russia
Annfrank@fpl.gpi.ru; FAX: +7(095) 135-8011; Tel.: +7(095) 132-8240
Experimental results are presented on the study magnetic reconnection phenomena and current sheet formation
and evolution in 2D and 3D magnetic configurations with some topological singularities: null-lines, null points,
singular lines. Current sheet evolution in 2D fields with null-lines manifests qualitative agreement with principal
features of flare-type phenomena. Current sheet formation was revealed to occur in various 3D magnetic
configurations, both with and without isolated magnetic null-points, specifically in magnetic configurations with X-
lines. Results demonstrate self-organization of current sheets to be a general process for plasma dynamics in non-
uniform magnetic fields.
Introduction
Magnetic reconnection in high-conductivity
magnetized plasma pertains to the most important
fundamental problems of modern plasma physics. At the
same time reconnection is a basis for a variety of flare-
type phenomena, such as solar and stellar flares,
substormes in magnetospheres of the Earth and planets,
sawtooth instabilities in tokamaks, rapid changes of the
magnetic field structure in reversed field pinches, Z-
pinches, theta-pinches, etc. Magnetic reconnection
phenomena occur at some discrete regions that separate
magnetic fields of different, or opposite directions and
where electric currents of high density are concentrated.
These regions take ordinarily the form of quasi-one-
dimensional sheets, so possibilities and conditions for
current sheet (CS) formation are of a crucial importance
[1]. We have studied experimentally CS formation and
evolution in a variety of 2D and 3D magnetic
configurations with some topological singularities: null
points, singular lines [2,3]. A basic principle for
formation a configuration was a combination of two
fields with different symmetry properties. One was 2D
magnetic field of translational symmetry with a null-line
at the z-axis:
Bq = {Bx; By; Bz} = {h⋅x; -h⋅y; 0} (1)
h is the field gradient in (x,y) plane, h≅ const. The
second was an axial symmetric magnetic field with an
axis along the null-line; the field could be presented
near any point (0,0,Z) at z-axis in a form:
Bas={Bx; By; Bz } = Bz (Z) + hr(Z)⋅{x;⋅y; -2(z–Z)} (2)
hr(Z) is the radial field gradient. We have used
several types of axisymmetric fields: the uniform Bz-
field with hr(Z)=0, the cusp-field with a null-point,
where Bz(Z)=0, the non-uniform Bz-field without null-
points. A combination of (1) and (2) produced a novel
3D magnetic configuration:
BΣΣΣΣ = Bq + Bas =
Bz(Z) + h {[1+γ(Z)]⋅x; -[1-γ(Z)]⋅y; -γ(Z)⋅(z-Z)} (3)
γ(Z) = hr(Z) / h is the ratio of two gradients. Both (1)
and (2) fields could be varied independently, providing
formation diversified 3D configurations (3) with gradual
transitions between them.
A principle scheme of CS-3D device (Three-
Dimensional Current Sheet) is shown in the Fig.1. 2D
magnetic field with a null-line at the axis of vacuum
chamber was formed by a system of straight external
conductors. Four coils with various directions and
magnitudes of electric currents produced axial
symmetric magnetic fields. Both fields were quasi-
steady. Vacuum chamber was filled with He or Ar gas,
and initial plasma was produced by pre-ionization. Then
perturbations were excited by applying a pulsed voltage
between two electrodes, giving rise to plasma flows and
electric currents, which might result in appearance of
CS. Maximum plasma current Iz≅ 100 kA, its half-period
T/2=5 µs.
Fig.1. Experimental device CS-3D: 1-straight
conductors to produce 2D field (1); 2-four coils to
produce axial-symmetrical magnetic fields; 3-vacuum
chamber ∅ =18 cm, l=100 cm. 4-grid electrodes; 5-CS;
6-Rogowskii coil. 7-quartz windows; 8-50% mirror; 9-
lenses; 10-interference filter; 11-frame-camera; 12-
quartz optical fiber; 13-monochromator; 14- multi-
channel optical registration system MORS-3; 15-PC
Current sheets in 2D magnetic fields with
null-lines
The best-known example of a singular line is the
null-line of 2D magnetic field. Plasma dynamics in
magnetic fields with null-lines has been actively
investigated for many years, both theoretically and
experimentally [1,2]. It has been established that a
planar CS, which accumulates an excess magnetic
energy, can be formed in a vicinity of the null-line. The
tangential magnetic field component increased in ≅ 10
mailto:Annfrank@fpl.gpi.ru;
95
times near the sheet surface, the electric current density
≅ 10 kA/cm2 peaked at the CS middle plane, the CS
thickness ≅ 0.8 cm was about 10 times smaller than its
width [4]. Plasma was rapidly compressed into the
planar sheet: the electron density Ne
sh = (1÷2)⋅1016 cm-3
exceeded both the initial and surrounding plasma
densities in 10-15 times [5]. It was revealed [4-5] that
CS was rather stable relatively the tearing-mode
instability [6]. Internal magnetic structure of CS was
dictated by initial conditions of its formation allowing
produce CS either as an open magnetic configuration
with the X-type null-line, or as a closed configuration
containing null-lines of both O- and X-types, or as a
neutral CS [7]. Plasma was accelerated in open
configurations along CS surface, from the middle to the
edges, so that super-thermal plasma flows appeared near
CS edges. An increase in thermal plasma energy
dominated in CS with closed magnetic field lines [8].
Comparing with solar flares, one should treat the
metastable CS as pre-flare situation [1].
The flare itself appeared as fast impulsive phase of
magnetic reconnection terminating long-lived
metastable stage and resulting in CS disruption [2,4,7].
We observed the change in the magnetic field topology,
electric current density redistribution, excitation of a
nonlinear wave, propagating along the CS surface with
a super-Alfvenian velocity vx≅ 107cm/s, while
va≅ 1.5⋅106 cm/s. The planar plasma sheet was also
destroyed rapidly [5]. Generation inductive electric
fields resulted in bursts of accelerated electrons
(Ee ≥ 10 keV) [9]. Thus, impulsive phase of magnetic
reconnection displayed obviously the qualitative
agreement with principal features of solar flares [1,2].
An analysis of experimental data made us conclude
that an interruption the metastable stage and the start of
flare-type events were triggered by magnetic island
formation inside CS followed by super-fast increase in
the thermal plasma energy. As a result the balance of
CS transverse equilibrium was disturbed [7,8]. Plasma
turbulence registered by spectroscopic methods was
seemingly of a secondary nature [8,10].
Current sheet formation in 3D magnetic
configurations
Considerable recent attention has been focussed on
3D magnetic configurations, which are more general
and much more typical for both astrophysical objects
and laboratory plasma confinement devices.
Theoretically CS formation has been predominantly
associated with the presence of isolated magnetic null-
points, and these configurations have been examined
analytically and by computer simulation [11-13].
Experimentally 3D configurations containing null points
were produced by a combination of 2D-field (1) and a
cusp field, so that a new configuration was built up [14]:
BΣΣΣΣ = h {(1+γ)⋅x; -(1- γ)⋅y; -2γ⋅z} (3′)
Characteristics of the configurations (3′), namely
magnetic field derivatives in different directions,
separatrix plane position depend essentially on γ
parameter [3, 15].
Magnetic measurements [16], and registration of
plasma images in HeII spectral line [17] were employed
as well as spectroscopic techniques [18], Fig.1.
It has been established experimentally for the first
time [15] that generation plasma electric current
resulted in CS formation near the null-point, with
plasma compressed into the sheet. CS assumed an
intermediate angular position in a cross-section
perpendicular to plasma electric current, between 2D
case (α=0) and a separatrix plane of initial 3D magnetic
configuration with the null-point (α=45°). CS formation
was revealed over wide range of configurations with
null-points, while CS angular orientation was
determined by the parameter γ, Fig.2 (points 1,2) [3,15].
γ
Fig.2. CS angular positions in 3D magnetic
configurations vs local γ -value, curve I: points
1,2,3–configurations with null-points; points 4,5
configurations without null-points. Data obtained from
plasma images (1,5) and from magnetic measurements
(2,3,4): (2) - section z1=0 (Fig.13); (3; 4) - section (z1 =
– 1). Curve II – angular position of the normal to the
field lines of the vacuum magnetic field with a null-point
at the section z1=0
A vicinity of an isolated null-point forms only a
small part of 3D magnetic configuration, so there was a
question how far from a null-point CS formation could
take place? It was shown on the base of magnetic
measurements that electric current acquired a sheet
shape in every cross-section, while CS angular
orientations differed from one cross-section to another
both in direction and in magnitude following the local
value of the parameter γ(Z), Fig.2 (points 3) [19]. So CS
formation occurred also far away from a null-point, and
constituted a twisted surface throughout the whole 3D
configuration. Moreover, we registered CS in non-
uniform magnetic fields containing no null-points, Fig.2
(points 4,5) [19]. Thus CS formation was observed in a
presence of relatively strong longitudinal magnetic field
component Bz.
The effect of Bz-field was studied in 3D
configurations containing singular X-lines with a
uniform longitudinal Bz-component [20]. 2D images,
Fig.3, demonstrated peculiarities of plasma structures
arising after plasma electric current generation along the
X-line. Various combinations of transverse gradient h
and Bz-component were used. Images 1,2 correspond to
formation planar CS, which were practically similar to
96
2D case (1), though Bz exceeded the transverse field
B⊥ = h×|r| in the most part of plasma volume. Plasma
density inside CS decreased with enhancement of Bz,
displaying a transition to a behavior of uncompressible
plasma. Images 3,4 correspond to sheet-like double-
piece structures separated by a slopping split. These
structures appeared under condition Bz /h>15 cm that
was presumably related to geometrical factors. It is
apparent now that CS formation, magnetic reconnection
and related processes can take place within rather wide
but limited range of initial conditions, while the gradient
of transverse magnetic field is the most important
among other parameters.
Fig.3. Plasma images in HeII 468.6 nm spectral line
under different gradients h of 2D field (1): h = (1) 570,
(2) 420, (3) 280 and (4) 200 G/cm. Bz = 4.3 kG,
Iz
max ≅ 100 kA, t ≅ 2.5 µs
Acknowledgements
Supported by the Russian Foundation for Basic
Research, project 99-02-18351.
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MAGNETIC RECONNECTION AND CURRENT SHEETS IN 2D AND 3D MAGNETIC CONFIGURATIONS
A.G. Frank, S.Yu. Bogdanov, N.P. Kyrie, V.S. Markov
General Physics Institute Russian Academy of Sciences, Moscow, Russia
Introduction
Current sheet formation in 3D magnetic configurations
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| id | nasplib_isofts_kiev_ua-123456789-78557 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T13:25:02Z |
| publishDate | 2000 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Frank, A.G. Bogdanov, S.Yu. Kyrie, N.P. Markov, V.S. 2015-03-18T19:18:35Z 2015-03-18T19:18:35Z 2000 Magnetic reconnection and current sheets in 2D and 3D magnetic configurations / A.G. Frank, S.Yu. Bogdanov, N.P. Kyrie, V.S. Markov // Вопросы атомной науки и техники. — 2000. — № 6. — С. 94-96. — Бібліогр.: 20 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/78557 533.9 Experimental results are presented on the study magnetic reconnection phenomena and current sheet formation and evolution in 2D and 3D magnetic configurations with some topological singularities: null-lines, null points, singular lines. Current sheet evolution in 2D fields with null-lines manifests qualitative agreement with principal features of flare-type phenomena. Current sheet formation was revealed to occur in various 3D magnetic configurations, both with and without isolated magnetic null-points, specifically in agnetic configurations with Xlines. Results demonstrate self-organization of current sheets to be a general process for plasma dynamics in nonuniform magnetic fields. Supported by the Russian Foundation for Basic Research, project 99-02-18351. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma dynamics and plasma-wall interaction Magnetic reconnection and current sheets in 2D and 3D magnetic configurations Article published earlier |
| spellingShingle | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations Frank, A.G. Bogdanov, S.Yu. Kyrie, N.P. Markov, V.S. Plasma dynamics and plasma-wall interaction |
| title | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations |
| title_full | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations |
| title_fullStr | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations |
| title_full_unstemmed | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations |
| title_short | Magnetic reconnection and current sheets in 2D and 3D magnetic configurations |
| title_sort | magnetic reconnection and current sheets in 2d and 3d magnetic configurations |
| topic | Plasma dynamics and plasma-wall interaction |
| topic_facet | Plasma dynamics and plasma-wall interaction |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78557 |
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