Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets J. Büchner+collaborators, at different times, were: J.
Download ReportTranscript Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets J. Büchner+collaborators, at different times, were: J.
Consequences of LHDI for three-dimensional collisionless reconnection through thin current sheets J. Büchner+collaborators, at different times, were: J. Kuska, B. Nikutowski, I.Silin, Th.Wiegelmann all at: Max-Planck Institut für Sonnensystemforschung in Katlenburg-Lindau, Germany (for „Solar System Research“ starting 1.7.2004 after being „for Aeronomy“ the last 40 years) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Topics • • • • Gradient and current-driven plasma instabilities in current sheets Initiation of 3D collisionless reconnection (PIC->Vlasovsimulation approach) in / through – anti-parallel magnetic fields – creation / annihilation of helicity density – non-anti-parallel, finite guide magnetic field case – asymmetric (magnetopause) current sheet case „Anomalous resistivity“ approach to introduce kinetic results into large scale MHD EUV Bright Points (BP): MHD modeling of the dynamic evolution (photospheric flows) + anomalous transport => Null point <or> finite B <or> QSL reconnection ??? Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 3D current sheet instabilities • • • • 1970th: quasi/linear theory: LHD-instability at the edges (Drake, Huba, Davidson, Winske, Tanaka & Sato ... ) 1996: 3D PIC simulations showed: global (kink/sausage) mode current sheet instabilities can initiate reconnection (Pritchett et al.; Zhu & Winglee; Büchner & Kuska 1996) 1998...now: New theory - and simulation results about current-driven and drift instabilities at sheet center (Horiuchi & Sato; Büchner, Kuska & Silin; Daughton et al.) Our latest move: From PIC to Vlasov-codes to test wave-particle interactions, resonances etc. which can initiate current sheet instabilities and reconnection Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Kinetic stability investigation Vlasov equation: Linear perturbation of distribution functions f j f j e j 1 f j v E (v B) 0 t r m j c v f 0 j cE1 v B1 dt f1 j (t ) m j c v ej Resulting perturbation of density and current Maxwell equations for the fields or wave equation for the potentials Magnetic Reconnection Theory, Newton Institute t 1 j e j f1 j dv j1 j e j v f1 j dv 1 21 1 2 2 41 c t 2 1 A1 4 A1 2 2 j1 c t c Cambridge, August 20, 2004 Linear stability of oblique eigenmodes at current sheet center -> > 20o: Eigenmodes are linearily stable (k=k0 cos ex +k0 sin ey) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Vlasov simulation code f i ,e f i ,e ei ,e 1 f i ,e v E (v B ) 0 t r mi ,e c v j e f j i ,e i ,e i ,e d 3v V e v i ,e f i ,e d 3v j i ,e V 1 21 1 2 2 41 c t 1 2 A1 4 A1 2 2 j1 c t c Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Nonlinear LHDI (anti-parallel fields: Vlasov kinetic simulation) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Non-local penetration of unstable waves Magnetic Reconnection Theory, Newton Institute LHD Cambridge, August 20, 2004 Simulation shows: the Ey fluctuations grow also at the center Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Drift-resonance instability (DRI) 1D ion distribution in the current direction 1D electron distribution in the current direction Ions drive waves → plateau-formation → electron-heating Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 DRI: 3D distribution function 3D Ion distribution function Magnetic Reconnection Theory, Newton Institute 3D electron distribution Cambridge, August 20, 2004 3D current sheet instability (Plasma density perturbation; case of antiparallel fields) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Current sheet thickness C1<->C4 (7.9.01, 19:00>23:00) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Current sheet waves ~21:00 UT Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Current sheet waves – observed by Cluster as predicted Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Waves initiate 3D reconnection Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Mechanism: Wave- reconnection coupling: Dashed: LHDI (edge) ; Solid: LHDI at the center; Dashed-dotted: reconnecting mode Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 3D reconnection island: Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 2.) Helicity density evolution: a.) 3D antiparallel reconnection Spheres: quadrants 1 and 4 Solid line - total helicity: Squares: quadrants 2 and 3 HM (A B)d 3 x const. 0 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Antiparallel -> finite guide field By Quadrupolar By field guide field By -> flux ropes -> Bending of B-fields Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Finite guide field case -> non 180o magnetic shear Guide fields change the shear angle between the ambient Bfields Positive Co-helicity 180o Negative CoHMo > 0 HMo (A B)d 3 x 0 helicity HMo < 0 J MSP MSP MSH J MSH J 180 ° MSP MSH 210 ° 125 ° (J = direction of sheet current and of reconnection E- field) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 3D guide field reconnection: initially positive co-helicity case oi t = 1 Magnetic Reconnection Theory, Newton Institute oi t = 25 Cambridge, August 20, 2004 2D / 3D positive co-helicity reconnection („pull reconnection“) Dotted: quadrants 1 and 4 Solid line - total helicity: dHM - 2 (E B) d 3 x 0 Dashed: quadrants 2 and 3 dt Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 3D guide field reconnection: initially negative co-helicity case oi t = oi t = 23 1 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 2D / 3D negative co-helicity reconnection („push reconnection“) Dotted: quadrants 1 and 4 Solid line - total helicity: dHM - 2 (E B) d 3 x 0 Dashed: quadrants 2 and 3 dt Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 3.) Resonant DRI in the guide field case: For stronger guide fields the cross-field propagation direction turns further away from the current direction. The growth rate of the instability decreases proportionally to the number of resonant ions. Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Reconnection wave in a nonanti-parallel (guide field) current sheet Bz in log presentation turbulence -> structure Magnetic Reconnection Theory, Newton Institute Bz in linear presentation for the polarity of magnetic bubbles Cambridge, August 20, 2004 Result: patchy reconnection in the non-anti-parallel, guide field case: The B field opens the boundary throug local patches (blue: below, red: above) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 4: Non-symmetric case (MP) Simulation model The pressure being locally balanced; drift Maxwellians, drifts ui / ue Ti / Te currents c j B 4 -> fields rotate through a tangential magnetic boundary Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Instability of a non-symmetric magnetic boundary current sheet Magnetic field Bz: LHD instability first on magnetospheric side (z<0) -> penetrates to the magnetosheath side (z>0) and triggers reconnection - island formation Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Magnetopause observation (Cluster) A. Vaivads et al., 2004 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 5.) Quasilinear estimate of the WP momentum exchange (-> “anomalous collision frequency;-> “... resistivity”) (Davidson and Gladd, Phys. Fluids, 1975) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Anomalous momentum exchange due to nonlinear DRI in a current sheet: Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 6.) X-ray & EUV Bright Points (BPs): quiet-sun reconnection - XBP are formed inside diffuse clouds, which grow at 1 km/s up to 20 Mm and then form a bright core 3 Mm wide, they last, typically, 8 h Vaiana, 1970: rockets; Golub et al. 1974-77: Skylab More recently: SOHO and TRACE observations -Later (Soho...) : also many EUV BP investigated -> BP are assumed to be prime candidates for reconnection: they well correlate with separated photospheric dipolar (opposite polarity) photospheric magnetic fluxes Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Soho-MDI and EIT: EUV BP 17-18.10.1996 (M. Madjarska et al., 2003) MDI line-of sight magnetic field ( 40” x 40”) EIT (195 A) same field of view Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Reconnection models for BP - Due to the B separation in the photosphere -> Reconnection between bipoles assumed to take place in the corona, -> magnetohydrostatic models, e.g. - Newly Emerging Flux Model (EMF) Heyvaerts, Priest & Rust 1977 - Converging flux model Priest, Parnell, Martin & Gollup, 1994 - Separator Reconnection in MCC Longcope, 1998 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 But: dynamical footpoint motion: -> currents are driven into the chromosphere/corona Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Model, starting with extrapolated B-fields ... Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 ... and footpoint motion (here after 1:39 UT 18.10.96): Magnetic Reconnection Theory, Newton Institute ...and density-height profile (VAL): Cambridge, August 20, 2004 Density Evolution -> t=128 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Parallel electric fields and parallel currents at t=128 Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Transition region parallel electric fields Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Transition region reconnection Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Reconnection due to resistivity switched on enhanced current (velocity) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Not at a null, but between two nulls (separator through 35,20,5 ?) <- Isosurfaces of a small total magnetic field, hence embedding the nulls Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004 Further work planned on: • Current sheet instabilities for more realistic current and field models and their consequences for reconnection • resulting anomalous transport as an approach toward quantifying the coupling between MHD and kinetic scales for solar and magnetospheric applications • Reconnection at neutral points vs. separator reconnection vs. quasiseparatrix layer - reconnection in the course of the dynamically evolving „magnetic carpet“ („tectonics“) Magnetic Reconnection Theory, Newton Institute Cambridge, August 20, 2004