NON IDEALITY EFFECTS IN A HIGH PRESSURE ARGON ARC MEASURED BY INFRARED CONTINUUM ABSORPTION

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NON IDEALITY EFFECTS IN A HIGH PRESSURE ARGON ARC MEASURED BY INFRARED

CONTINUUM ABSORPTION

J. Glasser, R. Viladrosa, J. Chapelle

To cite this version:

J. Glasser, R. Viladrosa, J. Chapelle. NON IDEALITY EFFECTS IN A HIGH PRESSURE ARGON

ARC MEASURED BY INFRARED CONTINUUM ABSORPTION. Journal de Physique Colloques,

1979, 40 (C7), pp.C7-687-C7-688. �10.1051/jphyscol:19797333�. �jpa-00219326�

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J0URiVA.Z DE PHYSIQUE

NON

IDEALITY

EFFECTS

IN

A HIGH

PRESSURE

ARGCJN ARC MEASURED BY WRARED CONTINUUM ABSORPTION

J. Glasser, R. Viladrosa and J. Chapelle.

CRPHT

(CAWS)

and

GREM

(Universitd drOrZdans), 45045 OrZdans Cddex, France.

Introduction

: A t t h e p r e s e n t t i m e , non i d e a l i t y e f f e c t s have been measured e s s e n t i a l l y on t h e d . c . c o n d u c t i v i t y o f plasmas produced by v a r i o u s t y p e s o f d v i c e s For moderately non i d e a l plasma ( i . e . ND=

#T

n e h o 3

<

1, ne e l e c t r o n d e n s i t y ,

A

D Debye l e n g h ) , t h e k i n e t i c t r a n s p o r t t h e o r y , o n l y a p p l i - c a b l e i n p r i n c i p l e f o r N D ) > l , h a s been prolonga- t e d down t o N D < 0 . 5 , p r e d i c t i n g an i n c r e a s e o f t h e d . c . c o n d u c t i v i t y with d e c r e a s i n g ND. S u r p r i - s i n g l y t h i s was not t h e r e s u l t o b t a i n e d by some a u t h o r s ( / 1 / , / 2 / ) s i n c e t h e i r measured c o n d u c t i v i - t y was s m a l l e r t h a n t h e S p i t z e r one (ND>>

l).

T h e i r r e s u l t i s supported by o t h e r theoretical e s - t i m a t i o n s / 3 / . However o t h e r e x p e r i m e f i t a l i s t s /4/

d i d f i n d c o n d u c t i v i t i e s i n accordance w i t h t h e u s u a l k i n e t i c t h e o r y . It was t h u s i n t e r e s t i n g t o t r y t o c l a r i f y t h i s p u z z l i n g problem u s i n g ano- t h e r approach.

Here we have used i n p l a c e o f t h e d.c. conducti- v i t y t h e ^Z.C. c o n d u c t i v i t y measurement c f t h e i n f r a r e d continuum a b s o r p t i o n of a n high p r e s s u r e argon plasma. T h i s method should be a b l e t o g i v e a t l e a s t t h e s e n s e o f t h e non i d e a l i t y e f f e c t , i . e . whether it must I n c r e a s e o r d e c r e a s e t h e c o n d u c t i v i t y of a moderately non i d e a l plasma.

Estimation of the now ideatz'ty effect on the infrared continuwn a6sorpCion

; The i n f r a r e d continuum a b s o r p t i o n o f an h i z h p r e s s u r e areon

- .

a r c plasma ( 1 bar,( p

6

30 b a r s ) Is e s s e n t i a l l y due t o i n v e r s e Bremsstrahlung. The a b s o r p t i o n c o e f f i c i e n t i n c l u d i n g induced emission can be r e - l a t e d t o t h e a . c . c o n d u c t i v i t y of t h e plasma /5/

where %(W)=Q~+ is tlie a . c . complex con-

d u c t i v i t y a t a n g u l a r f r e q u e n c y & .

The a.c. c o n d u c t i v i t y can b e c a l c u l a t e d u s i n g Chapman Enskog k i n e t l c t h e o r y c o r r e c t e d f o r s m a l l

&,A

( A = 9 m N D ) . However, a s we have shown i n /5/, t h e f i n a l formalism t u r n s o u t t o be much s i m p l e r t h a n f o r t h e d.c. c o n d u c t i v i t y . Sin- c e t h e zeroth_ o r d e r o f expansion i s s u f f i c i e n t f o r a c c u r a t e d e t e r m i n a t i o n o f t h e a b s o r p t i o n coef- f i c i e n t , a l l o w i n g a l s o a decoupling o f t h e e l e c - tron-ion and e l e c t r o n n e u t r a l c o n t r i b u t i o n , T h i s 1\6 an advantage of t h i s method s i n c e f o r t h e d . c . c o n d u c t i v i t y 3gd o r d e r i s a t l e a s t n e c e s s a r y , i n - t r o d u c i n g perhaps a n o t h e r cause o f u n c e r t a i n t y .

' The i n v e r s e e l e c t r o n i o n bremsstrahlung a b s o r p t i o n coefficient can t h e n b e w r i t t e n a s

The non i d e a l behaviour o f t h e plasma o n l y i n f l u - ences t h e Gaunt f a c t o r G

The c o e f f i c i e n t C e x p r e s s e s t h e sign and magnitude of t h e non I d e a l i t y e f f e c t . The u s u a l k i n e t i c t h e o r y p r e d i c t s a n e g a t i v e C ; t h i s means t h a t

t h e Gaunt f a c t o r o f a non i d e a l plasma must be s m a l l e r t h a t t h e same q u a n t i t y f o r an i d e a l p l a s - ma. The c o r r e c t i o n t u r n s o u t t o be o f o p p o s i t e d i r e c t i o n compared t o t h e d . c . c o n d u c t i v i t y , and a l s o is g r e a t e r , which can f a c i l i t a t e i n p r i n c i - p l e i t s measurement. C can be e s t i m a t e d u s i n g d i f f e r e n t methods / 5 / . Here f o r comparison we have chosen t h e u n i f i e d t h e o r y which g i v e s C

=

1.56 and ~ a & y u ~ i n and Norman formula which g i - ves an o p p o s i t e c o r r e c t i o n ( C > 0 ) i n accordance with t h e r e s u l t s of /1/ and /2/.

Experimental set up and diagnostics

: We use t h e same experimental s e t up f o r plasma p r o d u c t i o n a s i n /6/. I t i s an h i g h p r e s s u r e t r a n s f e r r e d d . c . a r c plasma j e t . T h i s g i v e s a s t a b l e C.W. s o u r c e w i t h t e m p e r a t u r e o f 12500 K and e l e c t r o n d e n s i - t y between 1x1017 cm-3 and 5x1017 cm-3 ( 2 6

~~6

^{4 ) .}

S p e c t r o s c o p i c o b s e r v a t i o n and a b s o r p t i o n measurements a r e made through X'aC1 windows. The absorp- t i o n s o u r c e i s a low power ( N 5 W ) home made c.w.

C02 l a s e r . Conventional i n f r a r e d s o u r c e s would be very d i f f i c u l t t o u s e due t o t h e i n t e n s e emission of t h e plasma i t s e l f . The l a s e r i s a l s o used f o r t h e S c h l i e r e n method which i s exposed f u r t h e r . The l i n e broadening measuremenbin t h e v i s i b l e range a r e made w i t h a c o n v e n t i o n a l g r a t i n g spec- t r o m e t e r . Fig. 1 shows t h e experimental a r r a n g e -

1 iment

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797333

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The i n f r a r e d d e t e c t o r i s a c a l o r i m e t e r t y p e one, used only f o r r e l a t i v e measurements, s i n c e absorp- t i o n does not i n v o l v e c a l i b r a t i o n which i s an advantage i n comparison with s i m i l a r emission expe- r i m e n t s /6/.

We have shown /5/ t h a t t h e r e a l p a r t of t h e r e f r a c - t i v e index of a dense plasma was not i n f l u e n c e d by non i d e a l i t y e f f e c t s down t o ND 0.5. T h i s pro- v i d e s a r e f e r e n c e d i a g n o s t i c method t o e n s u r e t h e v a l c d i t y o f a n o t h e r method, l i k e l i n e broadening f o r example, which could i n p r i n c i p l e b e s e n s i t i v e t o non i d e a l i t y e f f e c t s . Thus we have used an i n - f r a r e d S c h l i e r e n method / 7 / . The beam of t h e C02 l a s e r i s f o c a l i s e d i n t h e plasma and i t s d e v i a t i o n a s a f u n c t i o n of t h e l a t e r a l plasma c o o r d i n a t e i s measured v i a t h e p o s i t i o n o f t h e c a l o r i m e t e r ( F i g . 1 ) . I n o u r c o n d i t i o n s of measurement a simple r e - l a t i o n e x i s t s between t h e a x i s e l e c t r o n d e n s i t y and t h e d e v i a t i o n :

A

: probe wavelength.

T h i s simple method h a s an accuracy comparable with t h e one o f l i n e broadening method. It t u r n s o u t t h a t t h e S c h l i e r e n r e s u l t s a g r e e w e l l with t h e ones o b t a i n e d u s i n g t h e AT 4159

8

l i n e broadening parameters c a l c u l a t e d by Griem / 8 / , f o r e l e c t r o n d e n s i t y . This i s a l s o shows t h a t i n t h i s ND r a n g e t h e l i n e broadening seems t o be i n s e n s i t i v e t o non i d e a l i t y e f f e c t s .

The r e l a t i v e r a d i a l e l e c t r o n d e n s i t y p r o f i l e i s de- termined from t h e r e l a t i v e r a d i a l continuum emis- s i o n p r o f i l e i n t h e v i s i b l e . Applying Abel i n v e r - sins aad knnr.rtcg t h e axis c l e e t r c n d z - c i t y we can o b t a i n t h e e l e c t r o n d e n s i t y p r o f i l e . Temperature p r o f i l e i s o b t a i n e d by a p p l i c a t i o n of Saha.equation.

~esuZi5.s and concZusion : The a b s o r p t i o n experiment g i v e s us t h e r a t i o Im/Io, I m and 10 being t h e i n - t e n s i t y o f t h e beam a f t e r and b e f o r e i t s c r o s s i n g through t h e plasma. Those q u a n t i t i e s a r e measured a s a f u n c t i o n o f t h e l a t e r a l c o o r d i n a t e x. Then t h e

local

a b s o r p t i o n c o e f f i c i e n t i s o b t a i n e d by an Abel t y p e e q u a t i o n ~- - : a

d x

T h i s a b s o r ~ t i o n c o e f f i c i e n t i n c l u d e s t h r e e terms.

t h e first being preponderant :

/ XI=

X / ~ L

/

)Cei

i s t h e i n v e r s e e l e c t r o n Ion bremsstrahlung a b s o r p t i o n c o e f f i c i e n t , %)en t h e same f o r e l e c t r o n n e u t r a l i n t e r a c t i o n .

X'

corresponds t o photoio- n i z a t i o n . This l a s t t e r g comes p r i n c i p a l l y from t h e s h i f t of t h e s e r i e s l i m i t of t h e n e a r i n f r a r e d . F i g . 2 g i v e s t h e r e s u l t s o b t a i n e d f o r t h e Gaunt f a c t o r a t v a r i o u s p r e s s u r e s corresponding t o tem- p e r a t u r e s between 11000 K and 13000 K and e l e c t r o n d e n s i t y between 1 and 4 x 1017 ~ m - ~ .

The r e s u l t s i n d i c a t e t h a t t h e Gaunt f a c t o r i s

a-

l e r t h a n i n t h e i d e a l p l a s m a c a s e , confirming t h a t

-

f o r t h e d . c . c o n d u c t i v i t y t h e non i d e a l i t y e f f e c t should i n c r e a s e t h e c o n d u c t i v i t y a s p r e d i c t e d by t h e u s u a l k i n e t i c t h e o r y . Experiments a r e underway t o e x t e n d ' t h o s e r e s u l t s i n a wider range of e l e c - t r o n d e n s i t y . T h i s approach h a s t h u s proved t o be a b l e - t o g i v e a t l e a s t t h e s i g n and a l s o a r e a s o - n a b l e e s t i m a t e of t h e magnitude o f t h e e f f e c t o f non i d e a l i t y on t h e t r a n s p o r t p r o p e r t i e s of p l a s - mas w i t h a s m a l l number of charged p a r t i c l e s i n t h e Debye sphere.

References

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K.,

Lang S . , Radtke R . , Popovic M.

and Popovic S . , Proc. of t h e ~ 1 1 1 ~ ~ ICPIG VEB Buch, L e i p z i g , p 577 (1977).

/2/ Goldbach C . , Nollez G . , Popovic S. and Popovic M . , Z . Natiirforsch =a, 11 (1978).

/ 3 / Kaklyugin A.S. and Norman G.E., High Tempera- t u r e

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238 (1973).

/4/ Bauder O.H., Appl. Phys.

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( i n p r e s s ) (1979).

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