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  = {-h  y; -h  x; 0} with the null-line at the z-axis, h  1 kG/cm; = Guide field B z aligned with the null line: B z  8 kG; = Superposition of B  and B z 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, N e 0 =  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: J z  100 kA, T / 2 = 6  s, results in current sheet formation; = Diagnostics: magnetic probes, interference-holography; spectroscopy, X-ray detectors. Cross-sectionSide 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 = {-h  y; -h  x; B Z } 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: t A = (4  N i M i ) 1/2 / h. Plasma current: j = c /(4  ) rot B. Plasma dynamics is controlled by the Ampere forces: f = 1/c [j  B]. Excitation of j Z 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; B Z 0 = kG; J Z =70 kA Formation of a current sheet in magnetic field with an X line ( in- plane component  B X ) Amplification of the excess guide field  B Z 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: A Z = const;  A Z = 10 3 G  cm 2D vacuum magnetic field Ar 20 mTorr; h = 0.64 kG/cm; J Z = 65 kA; t = 1.9  s In-plane magnetic field of the current sheet

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; B Z 0 = 2.9 kG; Ar filling, 28 mTorr; J Z 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: N e max  cm -3 = Plasma sheet can evolve in the 3D magnetic configuration, in the presence of the strong guide field B Z 0 along the X line. Frank A G et al. Phys. Plasmas (2005)

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 Z eff  Densities of argon ions N i (Ar +1 ÷ Ar +5 )  Electron density N e  Electron temperature T e Voronov G.S. et al. Plasma Phys. Rep. 34, 999 (2008) h = 430 G/cm; Ar, 28 mTorr; J z 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; J Z max = 65 kA; t = 1.9  s In-plane magnetic field components B X, B Y and current density j Z 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 j z 0 in the CS midplane and the y-dimensions of CS at the levels 0.5  j z 0 and 0.1  j z 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 Ø z  1.5 cm Ø x  2.5 cm

Time behavior of the ion temperature T i and averaged energy of plasma flows W x Ar, 28 mTorr, h = 0.5 kG/cm, J z  75 kA Kyrie N.P. et al. Plasma Phys. Rep.36, 357 (2010) = T i, T e, Z i,av are maximum in the sheet midplane and increase with time; = T i > T e = The plasma is in transverse equilibrium (along the y-axis) with the magnetic field: N e (T e +T i /Z i ) + (  B Z ) 2 /8    B X 2 /8  ;   1

The Ampere force F x acting along the current sheet surface  = 1.2 cm I z (x) = – c /2   {B x J (x) – [  B y J (x)/  x]   };  j z (x) = I z (x) / 2  F x (x) = f x (x)  2  = -1/c  I z (x)  B y T (x); B y T = h  x + B y J   h = 0.57 kG/cm B Z 0 = 0 (2D) Ar, 28 mTorr J Z  100 kA; t  1.9  s F x max  6  10 5 dynes  cm -2

Plasma acceleration along the current sheet surface M i  N i  dv/dt = -  p + 1/c  [j  B] =  p is negligible along the current sheet surface (x-direction). = In the 2D magnetic configurations (B z = 0) the Ampere forces f x сome to play only in the presence of the normal magnetic field component B y T : f x = 1/c  [j  B] x ≡ -1/c  (j z  B y T ) = The average density of the Ampere force f X (x) was calculated on the basis of magnetic measurements:  f x (x)  -1/c  I z (x)  B y T (x) / 2   f X (x)  dx  N i  W X  3.5  eV  cm -3 At N i  3  cm -3  W X max  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-directionz-direction  z = 2.4 Å  x = 6.0 Å  z = 1.6 Å  x = 4.6 Å He, 320 mTorr; h = 500 G/cm; B z =0; J z max = 70 kA; t  3  s

Тепловые и направленные скорости ионов HeII в токовых слоях, He, 320 mTorr; h = 0.5 kG/cm; B z =0; B z = 2.9 kG J z max = 70 kA N e 0  (0.9  1.3)  cm -3 N e x  3.4  cm -3 T i  50 eV W x  400 eV (B z = 0) развивающихся в 2D магнитном поле (B z = 0) или в 3D магнитной конфигурации (B z = 2.9 kG) Н.П. Кирий и др. Труды ФАС-XIX, С (2009) SLs: HeII nm; HeII nm

The Ampere force F x acting along the surface of a current sheet formed in the He plasma  = 1.2 cm I z (x) = – c /2   {B x J (x) – [  B y J (x)/  x]   };  j z (x) = I z (x) / 2  F x (x) = f x (x)  2  = -1/c  I z (x)  B y T (x); B y T = h  x + B y J   h = 0.5 kG/cm B Z 0 = 0 (2D) He, 320 mTorr J Z  70 kA; t  2.1  s F x max  3.5  10 5 dyn  cm -2 x  cm  

The y-dependence of the Ampere force f x (y) at x = -5 cm At the CS midplane (y = 0) there is a maximum in the current density j z (y), and a minimum in the value of the normal component  B y T (y) . The force f x (y) = -1/c  j z (x)  B y T (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; J Z  70 kA; B Z 0 = 0

Ampere force f x (y) and plasma density N e (y) at x = -5 cm He, 320 mTorr h = 0.5 kG/ cm J z max = 70 kA The N e (y) distribution is very narrow as compared with the f x (y) distribution, so that the low-density plasma at wings of the N e (y) distribution can be effectively accelerated

Distributions of the current I z (x) at successive times. Development of reverse currents E z i  1/c  (v x  B y T ) h = 0.63 kG/cm Ar, 28 mTorr J Z  70 kA t = 2.3  s t = 3.5  s t = 4.5  s t = 5.0  s

Evolution of the currents I z (x) integrated over one-half the sheet (- R  x  0) J z (+) =  I z (+) (x)  dx - direct currents in the region (x R  x  0); J z (-) =  I z (-) (x)  dx - reverse currents in the region (-R  x  x R ); J z (S) =  I z (x)  dx - the total current in the whole region (-R  x  0). x R (t) – the x-coordinate where the current I z (x) reverses its direction: I z (x R ) = 0. t,  s The current I z (x) is concentrated in the region  y    = 0.8 cm h = 0.63 kG/cm Ar, 28 mTorr J Z  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 [j  B] 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 B X (y), current density j Z (у) and excess guide field  B Z (у) Ar, 28 mTorr; h = 0.57 kG/cm; B Z 0 = 4.3 kG; J Z  70 kA = The excess guide field  B Z (у) is localized only in the regions where the basic current j Z flows. = The excess guide field  B Z is supported by additional plasma currents in the (x, y) plane. = The total current on one side of the current sheet, J X  57 kA, is of the same order as the total basic current along the X line, which gives rise to the current sheet formation, J Z  70 kA.

Plasma dynamics in 3D magnetic field with the X-line and the guide field B z 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 B z into the sheet

h = 430 G/cm; Ar, 28 mTorr; J z max = 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 T e and N e T e 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 nm (Ar +1 ions)  Intensity of spectral line Ar III nm (Ar +2 ions)  Electron density N e and electron temperature T e