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Submitted on 1 Jan 1979
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EXPERIMENTAL INVESTIGATION OF
TRANSPORT IN LASER-TARGET IRRADIATION EXPERIMENTS
François Amiranoff, R. Fabbro, E. Fabre, C. Garban, J. Virmont
To cite this version:
François Amiranoff, R. Fabbro, E. Fabre, C. Garban, J. Virmont. EXPERIMENTAL INVESTI-
GATION OF TRANSPORT IN LASER-TARGET IRRADIATION EXPERIMENTS. Journal de
Physique Colloques, 1979, 40 (C7), pp.C7-769-C7-770. �10.1051/jphyscol:19797372�. �jpa-00219369�
JOURNAL
D3PHYSIQUE CoZZoque C7, suppze'ment au n07,
Tome 40,JuiZZet 1979, page
C7- 769EXPERIMENTAL INVESTIGATION OF TRANSPORT IN LASER-TARGET IRRADIATION EXPERIMENTS
F. A m i r a n o f f , R. F a b b r o , E. F a b r e , C. G a r b a n a n d 3. Virmont.
Laboratoire de Physique des P4iZieu.x Ionise's, EcoZe PoZytechnique,
91128PaZaiseau Cedex, France.
The p u r p o s e o f t h i s w o r k i s t o s t u d y by e x p e - r i m e n t t h e p e n e t r a t i o n d e p t h o f t h e h e a t f r o n t i n a s o l i d s u b m i t t e d t o t h e s t r o n g i r r a d i a t i o n o f a l a - s e r , and a l s o t o a n a l y s e t h e e f f e c t o f t h e l a s e r w a v e l e n g t h on t h e t h e r m a l h e a t t r a n s p o r t .
The t a r g e t a r e i r r a d i a t e d by t h e o u t p u t beam o f a Neodymiun g l a s s l a s e r w h i c h d e l i v e r s 1 0 J i n 1 0 0 p s a t 1 , 0 6 p w a v e l e n g t h , a n d when f r e q u e n c y
d o u ~ i e d , 5 2 i n 6 0 p s a t G , 5 3 p. Tile i i g h t i ~ t i t ~ ~ s i t y o n t o t h e t a r g e t a r e t h e n 2.1 0'' w/cm2 a t 1 , 0 6 p a n d 1 0 1 5 W/cm 2 a t 0,513 p. T h e t a r g e t s e m p l o y e d a r e t h i n f i l m s o f p o i y s t e r e n e w h o s e t h i c k n e s s c a n r a n g e f r o m 3 0 0
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t o a f e w m i c r o n s . T h e d i a g n o s t i c s o f t h e r m a l t r a n s p o r t w e r e t h e f o l l o w i n g : t r a n s m i s s i o n o f r e - f l e c t i o n o f l a s e r l i g h t by t h e t a r g e t , X r a y e m i s - s i o n , t h e r m a l i o n v e l o c i t y i n t h e f r o n t a n d t h e r e a r o f t h e t a r g e t . A l l m e a s u r e m e n t s w e r e made a s a f u n c t i o n o f f o i l t h i c k n e s s . D e p e n d i n g u p o n t h e d i a - g n o s t i c s , c r i t e r i a w e r e c h o o s e n f o r p e n e t r a t i o n d e p t h s c h a r a c t e r i z a t i o n : 9 0 % f o i l a n d p l a s m a o p a - c i t y , s a t u r a t i o n i n p l a s m a r e f l e c t i v i t y o r i n X r a y e m i s s i o n , c h a n g e i n t h e i o n v e l o c i t y o f t h e t h e r m a l i o n s e m i t t e d o n t h e r e a r s i d e o f t h e f o i l . F i g . a g i v e s a n e x a m p l e o f f o i l t r a n s m i s s i o n a n d r e f l e c t i o n a t 2 . 1 0 ~ ~ W/cm 2.
F i g . b g i v e s X r a y e m i s s i o n a s a f u n c t i o n o f f o i l t h i c k n e s s . F i g . c s h o w s t h e e f f e c t o f l a s e r w a v e l e n g t h o n f o i l t r a n s m i s s i o n . I n o r d e r t o a n a l y s e e x p e r i m e n t a l r e s u l t s , a n u m e r i c a l s i m u -l a t i o n o f t h e e x p e r i m e n t was made w i t h a ID L a g r a n - g i a n c o d e , i n p l a n a r g e o m e t r y , a n d n u m e r i c a l d e t e r - m i n a t i o n o f h e a t p e n e t r a t i o n was made. T h e t a b l e I s u m m a r i z e % t h e s e r e s u l t s a n d t h e i r c o m p a r i s o n t o t h e 1
e x p e r i m e n t s . The c o l u m n c o r r e s p o n d s t o t h e t y p e o f d i a g n o s t i c a n d t h e row t o d i f f e r e n t e x p e r i m e n t a l c o n d i t i o n s .
A s a r e s u l t i t a p p e a r s t h a t t h e e x p e r i m e n t a l v a l u e f o r h e a t p e n e t r a t i o n a r e s m a i l e r z h a n g i v e n by t h e n u m e r i c a l s i m u l a t i o n . T h i s i n v o l v e s s t r o n g f l u x l i m i t a t i o n and e v e n w i t h a f l u x l i m i t f a c t o r o f f = 0 . 0 5 t h e c o m p u t e d v a l u e ( r o w
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i n t a b l e I ) a r e s t i l l l a r g e r t h a n e x p e r i m e n t a l d e t e r m i n a t i o n . I t d o e s n o t s e e n r e a s o n a b l e a t t h a t t i m e t o a s s u m e t h a t t h e f l u x l i m i t i s e v e n m o r e s m a l l e r . One h a v e t o t h i n k o f t h e l i m i t o f t h e v a l i d i t y o f t h e compa- r i s o n b e t w e e n a o n e I D p l a n a r s i m u l a t i o n w i t h t h e e x p e r i m e n t w h i c h i n c l u d e some 2D a s p e c t on t r a n s - p o r t . A n o t h e r p o s s i b i l i t y t o o b t a i n a g r e e m e n t b e t - ween e x p e r i m e n t a n d s i m u l a t i o n w i l l b e t o r e d u c e a l s o t h e f l u x . However t h i s a r g u m e n t m u s t b e h a n d - l e d w i t h c a r e . I t i s n o t t h e l a s e r f l u x w h i c h s b u l d by r e d u c e d b u t t h e h e a t t h e r m a l f l u x f r o m c r i t i c a l ' r e g i o n t o w a r d t h e t a r g e t i n t e r i o r . E x p e r i m e n t a l r e - s u l t s c o u l d b e i n t e r p r e t e d by i n t r o d u c i n g some a n i - s o t r o p y i n h e a t t r a n s p o r t . A s s u m i n g f o r e x a m p l e a s t r o n g l a t e r a l c o n d u c t i o n . T h e s e c o n d r e s u l t o f t b e x p e r i m e n t i s t o s h o w t h e m o r e e f f i c i e n t t r a n s p o r tArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797372
when p l a s m a h e a t i n g i s made w i t h a s h o r t w a v e l e n g t h : t h e r m a l f r o n t p e n e t r a t e s d i p p e r i n t h e t a r g e t , howe- v e r t h e i n t e r p r e t a t i o n o f t h i s e f f e c t d o e s i m p l i e s o n l y t h a t t h e a b l a t i o n v e l o c i t y i s l a r g e r i n t h e c a s e o f t h e s h o r t w a v e l e n g t h s . I t a p p e a r s t h a t when c o m p a r i n g e x p e r i m e n t s a n d n u m e r i c a l s i m u l a t i o n , e v e n f o r t h e s h o r t w a v e l e n g t h , we m u s t i n c l u d e a f l u x l i m i t a t i o n w h i c h i s o f t h e s a m e o r d e r a t 0 , 5 3 p a n d 1 , 0 6 p.
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