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Submitted on 1 Jan 1979
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EXPERIMENTAL STUDY OF FAST
RECONNECTION OF THE MAGNETIC FIELDS THROUGH PLANE PINCH CURRENT SHEET
S. Bogdanov, V. Markov, A. Franck, A. Khodzhaev
To cite this version:
S. Bogdanov, V. Markov, A. Franck, A. Khodzhaev. EXPERIMENTAL STUDY OF FAST RECON- NECTION OF THE MAGNETIC FIELDS THROUGH PLANE PINCH CURRENT SHEET. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-221-C7-222. �10.1051/jphyscol:19797109�. �jpa-00219079�
JOURNAL DE PHYSIQUE CoZZoque C7, supp2dment au n07, Tome 40, J u i Z Z e t 2979, v a g e C7- 221
EXPERIMENTAL STUDY OF FAST RECONNECTION OF THE MAGNETIC FIELDS THSIWGH PLANE PINCH CURRENT SHEET
S. Yu. Bogdanov, V.S. Markov, A.G. Franck and A.Z. Khodzhaev.
P.N. Lebedev P h y s i c s I n s t i t u t e , Academy of S e i e n e e s o f t h e U.S.S.R.
Pinch c u r r e n t s h e e t s a r e those d i e - tinguished regions i n t h e plasma where con- s i d e r a b l e cumulation of magnetic energy and f a s t energy r e l e a s e with conseqnent transformation i n plasma flows and high energy p a r t i c l e s beam i s possible. The atudg , of formation and s t a b i l i t y of t h e
exazrmt
s h e e t s is bighlg e s s e n t i a l f o r e l u c i d a t i o n t h e nature of such astrophy- s i c a l phenouena as s o l a r f l a r e s , magneto-Hx=3-6 kG, $he trancnverse component
was e e v e r a l times l e a s than
%
everywhere i n s i d e t h e sheet. During t h e c u r r e n t s h e e t formation plasma from t h e chamber volume was e f f e c t i v e l y swept i n t o t h e sheet re- gion, thus t h e r e s u l t i n g e l e c t r o n densityof t h e plasma eheet reaches ~ ~ e = 8 . 1 0 ~ ~ c m - ~ and maintains p r a c t i c a l l y uniform along
the eheet width. On t h e contrary t h e den- s i t y g r a d i e n t i n - t r a n s v e r s e d i r e c t i o n is s p h ~ r i c s u b s t o ~ m s and so on. The develop- q u i t e ahaap leaching
2%r
= 5.~016em-4.ment of d i s r u p t i v e i n s t a b i l i t i e s i n toko- Theory p r e d i c t s t p a t t h e current mak plasmas is apparent19 r e s u l t s from t h e
formation and the d e s t r u c t i o n of current sheets.
I n our experiment t h e c u r r e n t pinch eheet (plane 2-pinch) was produced i n t h e v i c i n i t y of eero ( n e u t ~ a l ) l i n e of two- dimentional quadrupol magnetic f i e l d i n argon plasma prepared by a u x i l i a r y d i s c h a r ge ,when t h e e l e c t r i Q f i e l d Ez=250-400 v/cm was .applied along t h e n e u t r a l l i n e . The g r a d i e n t of i n i t i a l magnetic f i e l d was h=2-3 kG/cm. The t y p i c a l parameters of t h e sheet e s t a b l i s h e d 1 p s e c a f t e r cur-
sheet'becomes unstable i n r e s p e c t t o Ohe tearing-mode i f i t s width t o thickness r a t i o exceeds A ~ A $ >2fl.~owever i n expe- riment we observed t h e s t a b l e behaviour of t h e sheet during 2.5peec a t t h e elon- g a t i o n r a t i o of order of 15. But i f - w e increarae t h e i n i t i a l magnetic f i e l d gra- d i e n t and decrease i n i t i a l gas pressure then a new phenomenon occurs
-
t h e rapid change i n magnetf c f i e l d conf 1gurat.ion of t h e c u r r e n t sheet. I n I-1.5paec a f t e r t h e c u r r e n t i g n i t i o n we obsertae f a s t de- crease of the l o n g i t u d i n a l component of r e n t i g n i t i o n were t h e fol10wing:thet h e sheet and t h e increaee of the, length determLned
&
t h e e l e c t r o d e sepa- t r a n s v e r s e componentj ,
f i g . 1. Thus??a-tion was &a40 c@, t h e wiath
-
2 A X a t h e f a s t d i s s i p a t i o n of ,magnetic energgs 6-7 om, t h e thickness 2 A j l = 0.7 cm,, aooumulated previouelg near t h e c u r r e n t the current I2 = 40g60 Lb* the tan- s h e e t o c c u r s t h r o u g h t h e reconnection of g e n t - i a l component of t h e magnetf c f i e l d t h e a n t i p a r a l l e l magnetic fluxes. The
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797109
change of t h e
7 -
l o n g i t u d i n a l com- 5 4 - 1
\
ponent i s L/-
6%=3 kG and t h e %.k6 y = o z < m I= U 4cm
time d e r i v a t i v e i s . - - - - - - - - G O
=
10 G/sec. 10- - - -
The c u r r e n t d e n s i t y 2.0 d e c r e a s e s s i g n i f i-
c a n t l g i n t h e mid- 0 3 4 6 r * c
d l e of t h e sheet.So
f a r a s t h e t o t a l c u r r e n t I, does n o t chan- g e s , r e d i s t r i b u t i o n of t h e c u r r e n t along t h e s h e e t width t a k e s place.
The dynamics of t h e magnetic f i e l d reconnection i n t h e s h e e t w e observed w i t h t h r e e magnetic probes arranged on a l i n e (yi0.7 cm,e=IS cm) p a r a l l e l t h e s h e e t eurface.The s h e e t formation corresponds t o d e c r e a s e of t h e t r a n s v e r s e component By comparing t o i t s v a l u e a t t h e i n i t i a l f i e l d (dashed l i n e s , fig.2) i n t h e time
t h e l e v e l , corresponding t o t h e v a l u e of t h e i n i t i a l quadrupole f i e l d , and t h e n exceeds its essentiallg.The magnetic f i e l d v a r i a t i o n reaches
(guy=
850 G.The r i s e of t h e s i g n a l on t h e eecond pro- be i s delayed i n r e s p e c t t o t h e f i r s t pro- be signal_ on 0.3 ,q e e c , t h e time d e r i v a t i - ve is
a$zt
= 8.10 9 G/sec and t h e t o t a l v a r i a t i o n of magnetic f i e l d r e a c h e s@
fff = l l O O G. Thus t h e f e a t reeonnect- i o n of t h e magnetic f l u x e s a r i s i n g i n t h e middle of t h e s h e e t propagates alongs h e e t width ( i n x d i r e c t i o n ) . I f t h e s t a r t of t h e process i n two a p a t i c a l l g s e p a r a t - ed p o i n t s had t h e time s h i f t about 0.2- 0.3 p s e c , t h e maximal reconnection l e v e l of order of 10 3 G can be a t t a i n e d with
s i g n i f i c a n t l y reduced time s h i f t o f ' or- d e r 0.1 p s e c . T h i s corresponds t o t h e n o n l i n e a r p e r t u r b a t i o n wave propagating w i t h t h e mean v e l o c i t y = 7,3x10 7 i n t e r v a l 0-1.4 flsec. Then t h e f i r s t probe cm/sec which approximately one order of - .
(x1=0.3 cm) s h d s t h e magnitude exceeds c h a r a c t e r i e t i c Alfven increaalftig of t h e
u%L-,-
o v e l o c i t y f o r given s h e e t = 1 . 5 ~ 1 0 6L kA
t r a n s v e r s e component. cm/sec. Then t h e p e r t u r b a t i o n of t r a n s - I n i t i a l l y t h e change 0
v d
v e r s e component i a thrown t o t h e edge of i s r a t h e r smooth,"%kt
I ~ 6 . 1 0 8 ~ / s e c . A ti t
t h i s time t h e second
@
- - - - - - and t h e t h i r d probes 0s i t u a t e d a t Y if t1.8 cm
-
and ~ ' = 3 . 3 cm do not
,,
0 L ; - t --
d e t e c t any change of r J ~ ~ C P C t h e s i g n a l e . With t h e growth of magnetic f i e l d p e r t u r b a t i o n its time d e r i v a t i v e i n c r e a s e s approximatelg six f o l e a , t h u s -#/at
=
4 . 1 0 ~ O/aec. During t h i st h e s h e e t , where t h e magnetic f i e l d va- r i a t i o n reaches (AH)' = ,800 G. The- r e f o r e we can conclude t h a t t h e observed phenomenon r e p r e s e n t s i t s e l f t h e process of f a s t magnetic f l u x e s reconnection through t h e c u r r e n t s l i e e t , i n i t i a l l y .ae- p a r a t e d t h e s e f l u e s . By a n o t h e r words, t h e f a s t breaking of t h e c u r r e n t s h e e t , having t h e e x p l o s i v e behaviour,has been produced experimentally,
process t h e t r a n s v e r s e component reaches
