DYNAMICS OF PLASMA PHENOMENA IN "PLASMA FOCUS" UNDER THE ACTION OF POWERFUL LASER RADIATION

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DYNAMICS OF PLASMA PHENOMENA IN

”PLASMA FOCUS” UNDER THE ACTION OF POWERFUL LASER RADIATION

V. Gribkov, A. Dubrovsky, N. Kalachev, T. Kozlova, V. Nikulin

To cite this version:

V. Gribkov, A. Dubrovsky, N. Kalachev, T. Kozlova, V. Nikulin. DYNAMICS OF PLASMA PHE- NOMENA IN ”PLASMA FOCUS” UNDER THE ACTION OF POWERFUL LASER RADIATION.

Journal de Physique Colloques, 1979, 40 (C7), pp.C7-763-C7-764. �10.1051/jphyscol:19797369�. �jpa-

00219365�

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JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment a u n07, Tome 40, J u i Z Z e t 1979, page C7- 763

DYNAMICS OF PLASMA PHENOMENA.IN "PLASMA FOCUSn W E R THE ACTION OF POWERFUL LASER RADIATION

V.A. Gribkov, A.V. Dubrovsky, N.V. Kalachev, T.A. Kozlova and V.Ya. Nikulin.

P.'N. Lebedev PhysicaZ I n s t i t u t e , U.S.S.R. Academy o f S c i e n c e s , Leninsky p r o s p e c t 53, 117924 Moscow, U.S. S. R.

Afanasiev Yu.V.,Basov N.G. et.al.Trudy A combined beam-laser method (CBLNI)

FIAN (Proc.Lebedev I n s t i t u t e ) 1978, f o r plasma h e a t i n g up t o thermonuclear

t e m p e r a t u r e s h a s been proposed i n p a p e r s /I ,2/. An i n s t a l l a t i o n of "Plasma Focus1*

(DPF) t y p e h a s been used a s t h e r e l a t i - v i s t i c e l e c t r o n beam (REB) source / I / .

1.The i n f l u e n c e of a powerful l a s e r ra- d i a t i o n (PLR) on plasma phenomena i n t h e DPF a t t h e magnetohydrodynamic s t a g e i s d i s c u s s e d i n t h e p r e s e n t paper,Experiments have been c a r r i e d out on t h e i n s t a l l a t i o n wFLORAn s p e c i a l l y designed f o r CBLM i n v e e t i g a t i o n s /3/. The DPF parameters a r e t h e f o l l o w i n g : c a p a c i t o r bank energy, 50kJ;

n e u t r o n y i e l d , 5.10 9 n / p u l s e ; maximum c u r r e n t , 800 kA. The Hd-glass l a s e r h a s t h e f o l l o w i n g parameters: p u l s e d u r a t i o n , 2 n s e c ; energy, 500 J. We have used t h e f o l l o w i n g d i a g n o s t i c methods: s i m u l t a

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neous Ru-laser 5-frame i n t e r f e r o m e t r i c and shadow photography, s o f t X-ray pin- -hole camera, mica convex epectrograph, and t h e temporal e v o l u t i o n of h a r d X-ray r a d i a t i o n ( E > 8 0 keV).

2. The t y p i c a l 5-frame i n t e r f e r o g r a m s , pin-hole p i c t u r e and shadowgram o b t a i n e d d u r i n g one "shotn without PLR a r e shown i n Fig. 1.

Moscow, wBauka~~,~v.103,,202-230. _{- -}

~

5

Am

C---(

anode

Fig. 1,

The window diameter i s 4 e m .

2. Gribkov V.A. e t a l . JETP Lett., 1977, v.26, N 4, 209-214.

3. Veretennikov V.A., Gribkov V.A. e t a l . Proc. of t h e X I 1 1 Conf. on Phenom. i n I o n i z e d Gases, 1977, B e r l i n , 881 -882.

Fig. 2.

Pig. 2 p r e s e n t s R-t diagrams o f t h e pinch 1. Gribkov V.A., Krokhin 0.N. e t al.Pistma i n t h e DPF i n r e s p e c t t o hard X-ray p u l

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JETP 1973, v.18, B 9, 541, s e s . We have observed two c o a p r e s s i o n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797369

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p h a s e s of t h e DPF w i t h t h e time i n t e r v a l of 100 nsec.The minimum pinch r a d i u s a t t h e moment of t h e f i r s t compression i s about 5 mm, t h a t i s good agreement w i t h t h e b r i g h t image of plasma column g i v e n by t h e pin-hole p i c t u r e s . The e l e c t r o n

18 3

d e n s i t y a t t h i s moment i s 4x10 cm-

.

The shadowgrams show a s t r o n g anode (Cu) e r o s i o n d u r i n g t h e first compression.

The second compression i n t h e DPF be- g i n s w i t h t h e p i n c h c a t c h i n g by t h e mag- n e t i c f i e l d n e a r t h e anode

,

r e s u l t i n g i n c o n s i d e r a b l e p a r t i c l e s f e j e c t i o n t o t h e v e r t i c a l d i r e c t i o n . I n t h i s c a s e t h e l i n e a r plasma d e n s i t y d e c r e a s e s by one o r d e r of magnitude up t o 3.10 17 cm", t h e s h a r p p i n c h compression t o t h e r a d i u s 1 mm t a k e s p l a c e , and Te a p p e a r s t o be i n keV r e g i o n , t h a t i s confirmed by t h e c h a r a c t e r i s t i c s of t h e l i n e i m p u r i t i e s t s p e c t r a , A t t h i s s t a g e t h e pinch l i f e - t i m e i s about 20-30 nsec.Then, t h e pinch i s r a p i d l y d i s r u p t e d , and t h e hard X-ray b u r s t i s observed.

4. Veretennikov V.A., Gribkov V.A. e t a l . Proc.of IV S.U.Confer. on Plasma Acce- l e r a t o r s and I o n I n j e c t o r s , 1978 Moscow, VNTIC, 84-85.

5. Vikhrev V.V. e t a l . "Plasma P h y s i c s

Fig. 3 shows. t h e DPF i n t e r f e r o g r a m a f t e r t h e a c t i o n of PLR focused on t h e anode w i t h f l u x of 1012 w/cm2. Due t o t h e a c t i o n of PLR 30-50 nsec b e f o r e t h e f i r s t compression s t a g e t h e r e t a k e s p l a c e t h e f o r m a t i o n of t h e evaporated copper f l a r e t h a t moves v e r t i c a l l y w i t h t h e speed of 3.10 cm/sec.In 7 t h i s c a s e pin-hole p i c t u r e shows t h e luminous "plumew 3mm i n diameter, which c o i n c i d e s w i t h t h e one on i n t e r f e - rograms.The second compression, i s n o t observed due t o PLR i n t e r a c t i o n w i t h DPF.One may observe t h e r a p i d pinch d i s r u p t u r e ac- companing h a r d X-ray and n e u t r o n b u r s t s /4/.

3.0bserved pinch c a t c h i n g . n e a r t h e anode may be e x p l a i n e d by s t r o n g anode e r o

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s i o n , r e s u l t i n g i n plasma c o n d u c t i v i t y decrease. C o n d u c t i v i t y d e c r e a s e may be caused by e x i t a t i o n of plasma i n s t a b i l i t i e s . These p r o c e s s e s r e s u l t i n c u r r e n t s h e a t h p e r t u r b a t i o n s /5/, and a r e r e s p o n s i b l e f o r sharp pinch c a t c h i n g n e a r t h e anode zone a f t e r PLR action.The energy of t h e observed Cu s t r e a m s c o n s i s t i n g of 30keV i o n s does n o t exceed 30J.Existance of such t h i n Cu- i o n s t r e a m seems t o i n d i c a t e t h e presence of magnetic f i e l d i n s i d e t h e pinch of t h e o r d e r of 10 5 G.

I n t h i s way t h e performed experiments r e v e a l e d PLR i n t e r a c t i o n w i t h DPF t o have

e s s e n t i a l i n f l u e n c e on t h e dynamics of plasma phenomena i n DPI?, and may l e a d t o new p o s s i b i l i t i e s i n CLBU experiments.

Authors would l i k e t o e x p r e s s deep g r a t i - t u d e t o I s a k o v A.I.,Krokhin O.M.,Filippova T.I. f o r u s e f u l d i c c u s s i o n s , and Semenov 0. G. ,Veretennikov V. A. ,Korzhavin V.M. , S i l i n

P.V.

f o r a s s i s t a n c e i n t h e experiments.