Шестая ежегодная конференция "Физика плазмы в солнечной системе"
Структура электродинамических сил, ускорение плазмы и...
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Структура электродинамических сил, ускорение плазмы и генерация
обратных токов в токовых слоях
А.Г. Франк, Н.П. Кирий, С.Н. Сатунин
Институт общей физики им. А.М. Прохорова РАН
VI Конференция «Физика плазмы в солнечной системе»
в рамках Программы ОФН-15 РАН «Плазменные процессы в солнечной системе»
18 февраля 2011 г.
Цели и задачи исследований
= Изучение динамики токовых слоев и процессов магнитного пересоединения на основе лабораторных экспериментов позволяют сопоставлять структуру магнитных полей, электрических токов и электродинамических сил, с одной стороны, с параметрами плазменных потоков, которые ускоряются в пределах слоя, с другой стороны.
= В лабораторных экспериментах были зарегистрированы направленные движения плазмы со сверхтепловыми скоростями, которые можно, по-видимому, интерпретировать как аналог корональных выбросов массы (CME). Эти исследования дают возможность приблизиться к пониманию физической природы динамических явлений в атмосфере Солнца.
Основные задачи данной работы:
= Определение пространственно-временных характеристик электрического тока и электродинамических сил на основе анализа магнитных полей токовых слоев, развивающихся в различных условиях;
= Регистрация направленных потоков плазмы, которые генерируются в токовых слоях;
= Сопоставление направленных скоростей и энергий плазменных потоков с работой сил Ампера; выявление характерных особенностей ускорения плазмы.
Schematic of the CS-3D device
= 2D magnetic field B = {-hy; -hx; 0} with the null-line at the z-axis, h 1 kG/cm;
= Guide field Bz aligned with the null line: Bz 8 kG;
= Superposition of B and Bz forms a 3D magnetic configuration with the X line;= Vacuum chamber: quartz, 18 cm, L = 100 cm, is filled with a gas: He, Ar, Kr or Xe; = The initial plasma, Ne
0 = 1014 1016 cm-3, is produced by -discharge;
= Both magnetic fields and the initial plasma are uniform in the z-direction: ∂/∂z = 0; = Current along the X line: Jz 100 kA, T / 2 = 6 s, results in current sheet formation;
= Diagnostics: magnetic probes, interference-holography; spectroscopy, X-ray detectors.
Cross-section Side view
Propagation of the magneto-acoustic wave and the in-plane plasma motions in the vicinity of the X line
Magnetic field with the X line:
B = {-hy; -hx; BZ}
Perturbations of the magnetic field propagate as a converging magneto-acoustic wave (MAW) toward the X line in the (x, y) plane.
A typical time interval for MAW propagation is defined by the local Alfven velocity:
tA = (4NiMi)1/2 / h.
Plasma current: j = c /(4 ) rot B.
Plasma dynamics is controlled by the Ampere forces: f = 1/c [jB].
Excitation of jZ currents behind the front of
MAW brings about plasma compression in the y – direction and the outward motion in the x – direction.
Kr, p=36 mTorr; h=0.57 kG/cm; BZ0 = - 2.9 kG; JZ=70 kA
Formation of a current sheet in magnetic field with an X line
(in-plane component BX )
-8 -6 -4 -2 0 2 4 6 8-3
-2
-1
0
1
2
3
0.5 μs 1.0 μs
1.5 μs
2.0 μs 3.0 μs
δB
kGx
,
y , cm
B = -h yx0
·
-8 -6 -4 -2 0 2 4 6 8-1,0
-0,8
-0,6
-0,4
-0,2
0,0
0,2
0,4
1.0 μs
1.5 μs2.0 μs
3.0 μs
y , cmδB
k G
z,
B = -2.9 kGz0
Amplification of the excess guide field BZ
A.G. Frank, S.G. Bugrov, V.S. Markov // Phys. Lett. A 373, 1460 (2009)
Structure of the magnetic force lines in the (x, y) plane:AZ = const; AZ = 103 Gcm
2D vacuum magnetic field
Ar 20 mTorr; h = 0.64 kG/cm; JZ = 65 kA; t = 1.9 s
In-plane magnetic field of the current sheet
-2 0 2 4 6
-4 -2 0 2 4 6
-4 -2 0 2 4 6
-2
-1
0
1
2
-2
-1
0
1
2
3
-1
0
1
2
Y, cm
X, cm
a
b
c
1 2 3 4 5 6 70
Ne, 10 cm15
2D distributions of plasma density at successive time moments
t = 2.95 μs
t = 3.95 μs
t = 4.35 μs
h = 0.43 kG/cm; BZ0= 2.9 kG; Ar filling, 28 mTorr; JZ
max = 50 kA
= Formation of a current sheet is accompanied by effective plasma compression into the sheet, with the maximum density 10 times higher than the initial density:
Nemax 1016 cm-3
= Plasma sheet can evolve in the 3D magnetic configuration, in the presence of the strong guide field BZ
0 along the X line.
Frank A G et al. Phys. Plasmas 12 052316 (2005)
0 2 4 6
0,0
0,1
0,2
0,3
Ne
Zef
fZeff
ArVI
ArV
ArIV
ArIIIArII
Ne,
1016
cm-3
;
t, s
Ni,
1016
cm-3
0
2
4
6
0 2 4 64
6
8
10
12
14
t, s
Te,
eV
As the temperature increases, Ar+1 and Ar+2 ions become depleted successively turning to higher ionization states.
As a result, the spectral lines Ar IV, Ar V, with Ar VI in some cases, should appear in the plasma emission spectrum. These lines, however, fall within a shorter-wavelength UV range (λ < 300 nm).
Time evolution of plasma parameters in the sheet midplane: Effective ion charge Zeff
Densities of argon ions Ni (Ar+1 ÷ Ar+5)
Electron density Ne
Electron temperature Te
Voronov G.S. et al. Plasma Phys. Rep. 34, 999 (2008)
h = 430 G/cm; Ar, 28 mTorr; Jz
max= 70 kA
Current distribution in the (x,y) plane is characterized by 2 different sizes: x /y 6 15
Ar, 20 mTorr; h = 0.64 kG /cm; JZmax = 65 kA; t = 1.9 s
In-plane magnetic field components BX, BY and current density jZ in the current sheet
Distributions along the sheet width (x-axis), y = 0.8 cm
Distributions along the sheet thickness (y-axis), x = 0.8 cm and x =-5 cm
Evolution of the current density jz0 in the CS midplane and
the y-dimensions of CS at the levels 0.5jz0 and 0.1jz
0
Ar, x = 0.8 cm
He, x = 0.8 cm He, x = -5 cm
Ar, x = -5 cm
Scheme of two-channel spectral measurements with the use of a Nanogate 1-UF fast programmable CCD camera
Øz 1.5 cm
Øx 2.5 cm
Time behavior of the ion temperature Ti and
averaged energy of plasma flows Wx
Ar, 28 mTorr, h = 0.5 kG/cm, Jz 75 kA
Kyrie N.P. et al. Plasma Phys. Rep.36, 357 (2010)
= Ti, Te, Zi,av are maximum in
the sheet midplane and increase with time;
= Ti > Te
= The plasma is in transverse equilibrium (along the y-axis) with the magnetic field:
Ne (Te+Ti /Zi) + (BZ)2 /8
BX2 /8; 1
The Ampere force Fx acting along the current sheet surface
= 1.2 cm
Iz (x) = – c /2 {BxJ (x) – [By
J (x)/ x] }; jz (x) = Iz (x) / 2
Fx (x) = fx (x) 2 = -1/c Iz (x) ByT (x); By
T = hx + ByJ
h = 0.57 kG/cm BZ
0= 0 (2D)
Ar, 28 mTorr JZ 100 kA;
t 1.9 s
Fxmax 6105 dynescm-2
Plasma acceleration along the current sheet surface
MiNidv/dt = -p + 1/c[jB]
= p is negligible along the current sheet surface (x-direction).
= In the 2D magnetic configurations (Bz = 0) the Ampere forces fx сome to
play only in the presence of the normal magnetic field component ByT :
fx = 1/c[jB]x ≡ -1/c(jz ByT)
= The average density of the Ampere force fX (x) was calculated on the basis of
magnetic measurements:
fx(x) -1/cIz (x)ByT(x) / 2
fX(x)dx NiWX 3.51017 eVcm-3
At Ni 31015 cm-3 WXmax 115 eV.
= The time interval for accelerating the Ar(+1) ions is 3-5 s.
= These estimations correlate with the measured energy of the Ar ions and the typical acceleration time.
Comparison between HeII 4686 Å and HeII 3203 Å line profiles observed in the x- and z-direction
HeII 4686 Å
HeII 3203 Å
x-direction z-direction
z = 2.4 Åx = 6.0 Å
z = 1.6 Åx = 4.6 Å
He, 320 mTorr; h = 500 G/cm; Bz=0;
Jzmax = 70 kA;
t 3 s
Тепловые и направленные скорости ионов HeII в токовых слоях,
He, 320 mTorr; h = 0.5 kG/cm; Bz=0; Bz = 2.9 kG
Jzmax = 70 kA
Ne0 (0.91.3)1016 cm
-3 Ne
x 3.41016 cm-3
Ti 50 eV
Wx 400 eV (Bz= 0)
развивающихся в 2D магнитном поле (Bz = 0)
или в 3D магнитной конфигурации (Bz = 2.9 kG)
Н.П. Кирий и др. Труды ФАС-XIX, С.59-67 (2009)
SLs: HeII 468.6 nm; HeII 320.3 nm
The Ampere force Fx acting along the surface of a
current sheet formed in the He plasma
= 1.2 cm
Iz (x) = – c /2 {BxJ (x) – [By
J (x)/ x] }; jz (x) = Iz (x) / 2
Fx (x) = fx (x) 2 = -1/c Iz (x) ByT (x); By
T = hx + ByJ
h = 0.5 kG/cm BZ
0= 0 (2D)
He, 320 mTorr JZ 70 kA;
t 2.1 s
Fxmax 3.5105 dyncm-2
x - 4.4 cm
The y-dependence of the Ampere force fx (y) at x = -5 cm
At the CS midplane (y = 0) there is a maximum in the current density jz (y), and a
minimum in the value of the normal component ByT (y).
The force fx (y) = -1/c jz (x) ByT (x) can have a local minimum near the
midplane.
We might expect effective plasma acceleration where plasma density is lower than at the CS midplane, i.e. at some distance along the y – axis. h = 0.63 kG/cm; Ar, 28 mTorr; JZ 70 kA; BZ
0= 0
Ampere force fx (y) and plasma density Ne (y) at x = -5 cm
He, 320 mTorr h = 0.5 kG/ cm Jz
max = 70 kA
The Ne (y) distribution is very narrow as compared with the fx (y) distribution, so that the
low-density plasma at wings of the Ne (y) distribution can be effectively accelerated
Distributions of the current Iz (x) at successive times.
Development of reverse currents
Ezi 1/c(vx By
T)
h = 0.63 kG/cm Ar, 28 mTorr JZ 70 kA
t = 2.3 s
t = 3.5 s
t = 4.5 s
t = 5.0 s
Evolution of the currents Iz (x) integrated over
one-half the sheet (- R x 0)
Jz(+) = Iz
(+)(x)dx - direct currents
in the region (xR x 0);
Jz(-) = Iz
(-)(x)dx - reverse currents
in the region (-R x xR);
Jz(S) = Iz(x)dx - the total current
in the whole region (-R x 0).
xR(t) – the x-coordinate where the current Iz (x) reverses its direction:
Iz (xR ) = 0.
t, s
The current Iz (x) is concentrated
in the region y = 0.8 cm h = 0.63 kG/cm Ar, 28 mTorr JZ 70 kA
Magnetic structure of current sheets, by S.I. Syrovatskii, JETP 1971
A current sheet with the reverse currents at the edges
A current sheet without the reverse currents
Заключение = В экспериментах по изучению динамики токовых слоев и процессов магнитного пересоединения была исследована эволюция магнитных полей, что позволило определить основные особенности структуры электрических токов и электродинамических сил.
= Измерены температуры ионов, электронов и энергии направленных движений плазмы. Обнаружены потоки плазмы, которые движутся вдоль поверхности токового слоя с энергиями, значительно превышающими тепловую энергию ионов.
= Проведен анализ пространственной структуры сил [jB] и показано, что под действием этих сил должно происходить постепенное увеличение кинетической энергии направленного движения ионов вдоль поверхности токового слоя.
= В результате энергия ионов у боковых концов слоя может достигать 100 эВ, что согласуется с непосредственно измеренными энергиями потоков плазмы при формировании слоя в Ar.
= Обнаружено, что у боковых краев слоя возникают токи обратного направления по отношению к основному току, протекающему в центральной области слоя.
= = Генерация обратных токов и их усиление со временем свидетельствуют о новых динамических эффектах в токовых слоях, возникающих при движении потоков плазмы в сильном поперечном магнитном поле, что, в свою очередь, приводит к изменению магнитной структуры слоя.
Спасибо за внимание!
Coronal Mass Ejections (CME) X-ray images of the Sun recorded with
the SPIRIT device mounted on the Coronas-F satellite.
Experimental device CS-3D Institute of General Physics, Moscow, Russia
100 cm
Distributions over the current sheet thickness of the tangential magnetic field component BX(y), current
density jZ(у) and excess guide field BZ (у)
Ar, 28 mTorr; h = 0.57 kG/cm; BZ
0 = 4.3 kG; JZ 70 kA
= The excess guide field BZ (у)
is localized only in the regions where the basic current jZ flows.
= The excess guide field BZ is
supported by additional plasma currents in the (x, y) plane.
= The total current on one side of the current sheet, JX 57 kA,
is of the same order as the total basic current along the X line, which gives rise to the current sheet formation, JZ 70 kA.
-3 -2 -1 0 1 2 3-3
-2
-1
0
1
2
3
-6
-4
-2
0
2
4
6
Bx , kGBz jz kA/cm2
2.6 μs
0 1 2-1-2
0
-1
-2 -4
-2
0
2
42
1
y
xfy
fy
fxfx
Iz
fy(2 )
fy(2 )
fx(2 )fx
(2 )I
IB//
Plasma dynamics in 3D magnetic field with the X-line and the guide field Bz
Deterioration of the current and plasma compression due to amplification of the guide field in the sheet
Compression of the current, plasma and
the guide field Bz
into the sheet
0,0
1,0
2,0
3,0
0,40,8
1,2 02
40
4
8
12
0,40,8
1,21,6 0
24
0,00,4
0,8 0
24 0,0
0,4
0,8 02
4
Ne T
e
Ar II Ar III
h = 430 G/cm; Ar, 28 mTorr; Jzmax = 70 kA
Voronov G.S. et al. Plasma Phys. Rep. 34, 999 (2008)
Ar+1 and Ar+2 ions are depleted in the sheet midplane with increasing Te and Ne
Te was determined from
time behaviour of various spectral lines by using the SIMPTOS code including the processes of ionization, excitation and plasma flows.
Spatiotemporal evolution of plasma parameters under study: Intensity of spectral line Ar II 480.6 nm (Ar+1 ions)
Intensity of spectral line Ar III 379.5 nm (Ar+2 ions)
Electron density Ne and electron temperature Te