Introduction Magnetic reconnection is Very powerful energy - - PDF document

▶
introduction
SMART_READER_LITE
LIVE PREVIEW

Introduction Magnetic reconnection is Very powerful energy - - PDF document

Nov 15, 2023 22 likes •174 views

Self-similar evolution of fast magnetic reconnection in free-space: A new model for astrophysical reconnection Shin-ya Nitta The Graduate University for Advanced Studies, Hayama Center for Advanced Studies E-mail:

slide-1
SLIDE 1

Self-similar evolution of fast magnetic reconnection in free-space: A new model for astrophysical reconnection

Shin-ya Nitta 新田 伸也

The Graduate University for Advanced Studies, Hayama Center for Advanced Studies E-mail: snitta@koryuw02.soken.ac.jp

Magnetic reconnection is ・Very powerful energy converter ・Very common in the universe e.g., Solar Flares

§Introduction

slide-2
SLIDE 2

Astrophysical Reconnection is characterized by

huge dynamic range of expansion

e.g., Solar flares

Initial system scale

(Initial Current Sheet Thickness )

Final system scale

(Maximum scale of reconnection system )

⇩ intrinsically Time-Dependent

Should be treated as

Spontaneous Evolution in Free Space Cannot be described by previous models! §§Astrophysical Reconnection

Aim of this work

Suitable reconnection model for astrophysical application?

⇩

Self-Similar Evolution

slide-3
SLIDE 3

§Evolution Process

!"#$%& !"##$%&!'($$& )*+) ,- . ./00"1/2%!*$3/2%

1) Onset (Resistive Stage) 2) Induction of Inflow 3) Similarity Stage (Petschek-like at center) Sweet-Parker-like or tearing ⇩ Formation of Fast-mode Rarefaction Wave Propagation of FRWF ⇩ Induction of Inflow Formation of Slow-Shock ⇩ Fast-mode Rarefaction Dominated (Petschek-like) Fast Reconnection

slide-4
SLIDE 4

Parameters & Normalization

Parameters Normalization ⇨

§Numerical Approach

Initial Equilibrium （Harris solution） Code: 2-step Lax-Wendroff

CurrentSheet x y D:InitialCurrentSheetDepth 2D ResistiveRegion

slide-5
SLIDE 5

Self-Similarly Expanding！ with Fast-mode Rarefaction Wave Front

§§Simulation Result

slide-6
SLIDE 6

§Analytical Approach

§§Inflow Region Zoom-out coordinate

Linear perturbation method

Equilibrium (0th)+Deviation (1st) by reconnection Grad-Shafranov Eq.

slide-7
SLIDE 7

§ § Solution for Inflow Region

Fairly Consistent!

slide-8
SLIDE 8

§§Reconnection Outflow

Quasi-1D structure divided by several discontinuities

Reconnection jet collides with current sheet plasma

⇩ Shock tube approximation

22 eqs. (junction conditions) for 22 unknowns ⇩ Quantities in outflow spontaneously determined!!

! "

#$%&'(!%)'*+ ,'-(.-/!%&'(!%)'*+ 0'12.*2!345*'16 7898-58!,.52!%)'*+ 0:--812! %)882

  • 8;4'1!<
  • 8;4'1!=
  • 8;4'1!>
  • 8;4'1!?

!!!%2-:*2:-8!'@!-8*'118*24'1!':2@&'(

%&'(!%)'*+

!@ !* !5

slide-9
SLIDE 9

§§Reconnection Rate

  • Rec. rate R ~ 0.05 for low β

(almost const. indep. of β) ⇧ Spontaneous inhalation of inflow (induced by fast-mode rarefaction)

! !"!# !"!$ !"!% !"!& !"!' !"!( !"!!!# !"!!# !"!# !"# # #! #!! #!!!

Reconnection Rate vs. beta

  • Vyp*Bxp

Beta0

slide-10
SLIDE 10

(Rem*≡VA0/Vdif*) converging inflow: |Vxp|↑ as Rem*↑ ⇨Vp, Bp → parallel at inflow region R ≡Vp×Bp ∝Rem*^(-1)

!"!# !"# #! #!!

Reconnection Rate vs. Mag. Reynolds Num.

  • Vyp*Bxp+Vxp*Byp

Rem*

S S L S S D R ! "

slide-11
SLIDE 11

§Observational Inspection

“Dimming” around reconnection point ⇧ Rarefied region by FRW Existence of inflow~10[km/s] Expanding in VA0 ~1000[km/s] Duration ~100[s]

1.185 1.040 0.715 0.930 1.000

0.00 0.20 0.40 0.60 0.80 1.00 0.00 0.20 0.40 0.60 0.80 1.00 x y Emission Measure

We can inspect Self-Similar Model by Solar-B

slide-12
SLIDE 12

§Summary

Spontaneous Evolution of Fast Magnetic Reconnection in Free Space

⇩ Self-Similar Solution

（verified by numerical simulation/analytical study） A new model of Magnetic Reconnection

Self-Similar Evolution of Fast Reconnection

Properties ・Expanding with propagation of FRW ・Petschek-like structure in central region （Fast-mode rarefaction dominated） ・Reconnection rate R ~ 0.05 (for small Rem*<20, insensitive to β) ⇦ spontaneous inhalation of inflow ・ Reconnection rate R ∝Rem*^(-1) (for large Rem*≫20, insensitive to β)

References

Nitta, Tanuma, Shibata, Maezawa ApJ, 550, 1119 (2001) Nitta, Tanuma, Maezawa ApJ, 580, 538 (2002) Nitta ApJ, 610, 1117 (2004)

slide-13
SLIDE 13

§§Simulation Result Evolution in Zoom-Out Coordinate

Self-Similarly Expanding！ with propagation of Fast-mode Wave Front Features of reconnection system

slide-14
SLIDE 14

R ≡Vp×Bp ∝Rem*^(-1) (Rem*≡ VA0/Vdif*) ⇧ converging inflow: |Vxp|↑ as Rem*↑ ⇨Vp, Bp → parallel at inflow region ⇨ R≡Vp×Bp↓

!"!# !"# #! #!!

Reconnection Rate vs. Mag. Reynolds Num.

  • Vyp*Bxp+Vxp*Byp

Rem*

slide-15
SLIDE 15

A new model of magnetic reconnection: Self-similar evolving model

Shin-ya Nitta

新田 伸也

The Graduate University for Advanced Studies, Hayama Center for Advanced Studies E-mail: snitta@koryuw02.soken.ac.jp

Magnetic reconnection is ・Very powerful energy converter ・Very common in the universe e.g., Solar Flares

§Introduction