EFFECT OF THE ION MOTION AT LOW ELECTRON DENSITIES ON THE PROFILES OF THE LINES 4471 Å AND 4922 Å OF HeI

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EFFECT OF THE ION MOTION AT LOW ELECTRON DENSITIES ON THE PROFILES OF

THE LINES 4471 Å AND 4922 Å OF HeI

C. Fleurier, G. Coulaud, J. Chapelle

To cite this version:

C. Fleurier, G. Coulaud, J. Chapelle. EFFECT OF THE ION MOTION AT LOW ELECTRON

DENSITIES ON THE PROFILES OF THE LINES 4471 Å AND 4922 Å OF HeI. Journal de Physique

Colloques, 1979, 40 (C7), pp.C7-81-C7-82. �10.1051/jphyscol:1979740�. �jpa-00219399�

JOURNAL

DE PHYSIQUE

CoZZoque C7, suppZSment au n07, Tome 40, ~ u i l Z e t

1979,

vageC7- 81

EFFECT OF THE ION MOTION

AT LOW ELECTRON D E N S m E S

ON THE PROFILES OF THE LINES

4471

i ^AND

⁴⁹²²

i ^OF

^He1

C. Fleurier, G. Coulaud and J. chapelleZ.

Centre de Recherches sur Za Physique des Hautes Temp6ratures

C.N.R.S.

45045 OrZdans C6dex.

'u.

E. R.

Sciences FondarnentaZes, UniversitS dr0r16ans, 45045 OrZbans Cddex.

Introduction

: We have shown r e c e n t l y /1/ /2/ /3/

an i o n mass e f g e c t on t h e S t a r k p r o f i l e of t h e l i n e He1 4471 A. These r e s u l t s show, f o r e l e c t r o n d e n s i t i e s , ne

3

3 x 1 0 1 ~ cm-3, a smearing o f t h e c e n t r a l s t r u c t u r e of t h e l i n e between t h e allowed and t h e f o r b i d d e n components, when t h e reduced mass

( r )

of t h e couple helium atom-perturbing i o n d e c r e a s e s . The c o n c l u s i o n was t h a t t h i s e f - f e c t could be imputed, r e a s o n a b l y , t o t h e i o n mo- t i o n , because t h e e x t r a p o l a t i o n of our r e s u l t s a t

~ 4 0 0(Vionh. 0 ) showed an e x c e l l e n t agreement f o r t h e v a l u e s C/P ( s e e below, f i g . 1 ) w i t h t h e t h e o r e t i c a l ( s t a t i c ) p r e d i c t e d ones /4/ / 5 / . However, although t h i s e f f e c t was c l e a r l y demons- t r a t e d , it i s i n c o n t r a d i c t i o n with t h e t h e o r e t i - c a l p r e d i c t i o n s /6/ and some o t h e r t h e o r e t i c a l e s t i m a t e s f o r which t h e i o n motion e f f e c t i s o n l y a p p r e c i a b l e a t low e l e c t r o n d e n s i t i e s (ne& 1015 cm-3 )

.

!leverthe1 e c s

,

t h e r e e x i s t s no c1 e a ~ ex?erimental evidence o f a n ior, e f f e c t a t 1051 d e n s i t i e s . We can only n o t e some t h e o r e t i c a l a t t e m p t s /7/ t o o b t a i n a b e t t e r f i t w i t h experiment t h a n t h e s t a - t i c c a l c u l a t i o n s .

So, t h e aim o f t h i s work, i s t o p u t f o r t h expe- r i m e n t a l evidence of an i o n mass e f f e c t a t low e l e c t g o n d e n s i t i e s i n t h e p r o f i l e s of t h e l i n g s 4471 A of HeI, and, f o r f u r t h e r p r o o f s , 4921 A of HeI, f o r which t h e same e f f e c t is expected.

Yethods

: The l i n e s were emltted i n a conventional plasma j e t with a d d i t i o n of a t r a n s f e r anode /2/ / 3 / . Three d i f f e r e n t plasmas were used, each one c h a r a c t e r i z e d by a d i f f e r e n t reduced mass o f t h e r a d i a t o r - p e r t u r b i n g ion c o u p l e , s p e c r f i c a l l y :

r ⁼

0.8 f o r t h e He-H plasma,

r =

² f o r t h e He-He plasma and

P =

3.34 f o r t h e He-Ne plasma.

The plasma composition was choosen such a s more than 99 % of t h e i'ons t n t h e plasma came from t h e second g a s (H o r ^Np).

The e l e c t r o n denszty was e s t i m a t e d from t h e l i n e width of

Hp

(plasma He-H) o r by means of t h e S t a r k width of some i s o l a t e d l i n e s a r i s i n g from l e v e l s n

=

5 o r 6 which s u f f e r an important S t a r k broadening. The e l e c t r o n temperature was determi- ned by means of t h e Saha law r e l a t i v e t o high e x c i t e d l e v e l s and by use of t h e c o l l i s i o n a l - r a d i a t l v e model.

The i o n temperature was o b t a i n e d from t h e Doppler width of t h e i s o l a t e d l i n e s o f He1 a r i s i n g from low energy l e v e l s .

S p e c t r o s c o p i c measurements were achieved on a s p e c t r o m e t e r having a r e c i p r o c a l dispersTon of 4.4 a / m m i n t h e f i r s t o r d e r (1200 l / m m g r a t i n g 1.7.m f o c a l l e n g t h ) . The l i n e p r o f i l e s were o b t a i - ned by u s i n g an o p t i c a l multichannel a n a l y s e r (OMA) p r o v i d i n g an e x c e l l e n t s r g n a l over n o i s e r a t i o . Moreover, t h e l i g h t i n t e n s i t y , w a s v e r y s t a b l e

( 2

1 % ) and t h e j e t had an e x c e l l e n t cy- l i n d r i c a l symmetry, t h u s , even t h e Abel i n v e r s r o n

y i e l d e d v e r y a c c u r a t e l i n e p r o f i l e s . The e r r o r was e s t i m a t e d t o be lower t h a n 5 % f o r t h e i n - i t e n s i t y o f t h e l i n e .

Results

: Four parameters c h a r a c t e r i z i n g t h e l i n e p r o f i l e s were measured : t h e peak s e p a r a - t i o n S ( i n

I ) ,

t h e r a t i o s I / P and C/P and t h e h a l f w i d t h of t h e allowed component Ah ( i n

2).

( F i g . 1 ) . Our p r e v i o u s s t u d i e s /3/ have shown t h a t

A X

and S v a r y only s l i g h t l y

with^,

w i - t h i n t h e experimental e r r o r s . I n t h e p r e s e n t work, we have used A h a s a common r e f e r e n c e parameter f o r comparison of t h e d i f f e r e n t pro- f i l e s i n p l a c e of ne f o r which t h e u n c e r t a i n t y i s about

+

15 % w h i l e f o r A X t h i s u n c e r t a i n t y i s lower Than 5 %. The peak s e p a r a t i o n S was not used a s i n /1/ /2/ /3/ because it v a r i e s t o o slowly i n t h i s r a n g e of e l e c t r o n d e n s i t y while Ah v a r i e s approximately l i n e a r l y with ne.

n

The r e s u l t s f o r t h e l i n e 4471

A

a r e , p a r t i a l l y , summsd up i n g i g s . 2 and 3 f o r t h e AX r a n e : 0.5 A

-+

2 A (ne 5 x 1 0 ~ ~ ~ m t o 4 ~ 1 0 ~ ~ - ~ ~ m - ~ ) . The f i g . 2 shows c l e a r l y t h e e f f e c t of t h e v a r i a - t i o n o f p on t h e r a t i o s I / P and C/P : t h e d i p i n t e n s i t y i n c r e a s e s while t h e peak i n t e n s i t y d e c r e a s e s . AQ example i s given i n Fig. 1, f o r

A X r 0.80 A , where t h e two p r o f i l e s a r e norma- l i z e d i n amplitude. Good agreement i s observed between t h e two p r o f i l e s , mainly i n t h e allowed peak and i n t h e wings b u t t h e c e n t r a l s t r u c t u r e is smoothed i n t h e He-H p r o f i l e i n comparison of t h e He-He p r o f i l e . The observed d i f f e r e n c e s between t h e t h r e e c a s e s ( f i g . 2 ) f o r 1/P, C/p ( o r I/P-C/P) a r e g r e a t e r t h a n t h e experimental u n c e r t a i n t i e s , s o we can f i r m l y e n s u r e t h a t an i o n mass e f f e c t e x J s t s a t low e l e c t r o n d e n s i t i e s f o r t h e l i n e 4271 A of HeI, and a l s o ( f i g . 4 ) f o r t h e l i n e 4922 A .

F i n a l l y , we have p l o t t e d ( f i g . e r a t i o s I / P and C/P a s func+ions of

' ' ' Y

^{which i s}

p r o p o r t i o n a l t o t h e i o n v e l o c i t y .

The experimental v a l u e s l i e approximately on a s t r a i g h t l i n e s and t h e e x t r a p o l a t i o n (dashed l r n e s ) a t an i n f i n i t e reduced mass shows an e x c e l - l e n t agreement with t h e t h e o r e t i c a l s t a t i c v a l u e s of t h e r a t i o s I / P and C/P by /4/ / 5 / . T h i s f e a - t u r e m a k e s u s t o t h i n k t h a t t h e observed e f f e c t , p r o p o r t i o n a l t o t h e i o n v e l o c i t y , is an i o n mo- t i o n e f f e c t .

Discussion

: These r e s u l t s confirm our p r e v i o u s measurements a t h i g h e r e l e c t r o n d e n s i t i e s . Howe- v e r we n o t e i n t h i s experiment a v a r i a t i o n i n t h e r a t i o I / P which had no be d e t e c t e d ( o r which was w i t h i n t h e experimental e r r o r s ) a t h i g h e r d e n s i t y . That g i v e s an i n d i c a t i o n t h a t t h e i o n motion e f f e c t i s more marked a t low e l e c t r o n d e n s i t y , i n agreement with t h e t h e o r e t i c a l assump- t i o n s . Then it seems t o d e c r e a s e t o z e r o u e l e c t r o n d e n s i t y of about 6 t o 1 0 x 1 0 ~ ~ an-8

;;/an

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979740

I n a n o t h e r c o n n e c t i o n , t h e comparison w i t h t h e t h e o r y / 7 / i n c l u d i n g a t r e a t m e n t o f t h e i o n dyna- m i c s , would show a b e s t f i t w i t h o u r p r o f i l e s t h a n t h e s t a t i c t h e o r i e s , b u t t h e c o r r e c t i o n s t o t h e p r o f i l e s g i v e n by t h i s c a l c u l a t i o n a r e s t i l l tooweak t o p e r f e c t l y f i t t h e o b s e r v e d e f - f e c t

.

F i n a l l y , a n o t h e r c a l c u l a t i o n , u s i n g t h e model m i c r o - f i e l d method /8/ seems t o g i v e a n e x c e l l e n t a g r e e m e n t , f o r ne & 3 . 1015 ~ m - ~ , w i t h o u r p r o f i - l e s . (The r e s u l t s w i l l b e p r e s e n t e d a t t h e c o n f e - r e n c e ) . I n t h i s model, t h e i o n dynamic i s t a k e n i n t o a c c o u n t i n t h e same way a s t h e e l e c t r o n dy- namic.

References :

/1/ C. F l e u r i e r and J . C h a p e l l e , ~ 1 1 1 ~ ~ ICPIG B e r l i n ( 1 9 7 7 ) .

/2/ C . F l e u r i e r , G . Coulaud and J . C h a p e l l e , Phys. Rev. A

2,

575 ( 1 9 7 8 ) .

/3/ C. F l e u r i e r , T h s s e , U n i v e r s i t y o f ~ r l k a n s ( 1 9 7 8 ) .

/ 4 / H.R. Griem, A s t r o p h y s . J

154,

1111 ( 1 9 6 8 ) . / 5 / A . J . B a r n a r d , J . Cooper and L.J. Shamey,

Astron-Astrophys. 1, 28, ( 1 9 6 9 ) .

/ 6 / D . D . B u r g e s s , J. Phys. B 3 , L 67 ( 1 9 7 0 ) .

/ 7 / A . J . Barnard, J . Cooper axd E.W. S m i t h ,

J.Q.S.R.T. 1 4 , 1025 ( 1 9 7 4 ) .

/ 8 / A . ~ r i s s a u d ; ~ . Goldbach, J . L k o r a t , A. Mazure and G. N o l l e z , J . Phys. B

9,

1129 ( 1 9 7 6 ) .

I a ,

A

X=1 -I

A

^{k0.7 3}

He-Ne He-He He-H

-

--

0 0.3 0.6 0.9 l/dp

Fig.3: V a r i a t i o n o f I / P and C/P vs

(p)

J2 .The

-

dashed l i n e s represent t h e e x t r a p o l a t i o n of o u r r e s u l t s a t p = * o .

-6 -4 - 2 0

A X (A)

⁶

Fig.1: P r o f i l e s of the l i n e He1 4471 from

-

He-He plasma ( f u l l 1 in e ) and He-H plasma ( 0 ) .

01

^{I I I I} b

0 0 A 0.8 12 A A ( &

F i g . E : V ? r i a t i o n o f t h e r a t i o s I / P and C/P as func- - t i o n s of t h e h a l f w i d t h A A ( p r o p o r t i o n n a 1 t o n,).

03.

0.2.

0.1

Fig : 4

A i'P,CJP He

I 4471

He-H + He-He A He-Ne

Fig: 2

.

01

0.5 1.0 2.5

AA&

Fig.4: V a r i a t i o n o f I / P and C/P v s A A f o r

0

t h e l i n e He1 4922 A.