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ON X-RAY SPECTRAL LINES OF HIGH n RYDBERG TRANSITIONS IN Ar16+ OBSERVED
FROM A TOKAMAK PLASMA
E. Källne, J. Källne, J. Dubau, E. Marmar, J. Rice
To cite this version:
E. Källne, J. Källne, J. Dubau, E. Marmar, J. Rice. ON X-RAY SPECTRAL LINES OF HIGH n
RYDBERG TRANSITIONS IN Ar16+ OBSERVED FROM A TOKAMAK PLASMA. Journal de
Physique Colloques, 1987, 48 (C9), pp.C9-379-C9-382. �10.1051/jphyscol:1987967�. �jpa-00227385�
JOURNAL DE PHYSIQUE
Colloque C9, supplbment au n 0 1 2 , Tome 48, dbcembre 1987
ON X-RAY SPECTRAL LINES OF HIGH n RYDBERG TRANSITIONS I N OBSERVED FROM A TOKAMAK PLASMA
E. KALLNE, J. KALLNE, J. DUBAU*, E.S. M A R M A R * * and J.E. R I C E * "
JET Joint Undertaking, GB-Abingdon OX14 3EA. Great-Britain
" ~ b s e r v a t o i r e de Paris, 5, Place Janssen, F-92195 Meudon Cedex, France
" " M I T Plasma Fusion Center, Cambridge, MA 02139, U.S.A.
Abstract
The He-like spectrum of l s 2
-
I s n p t r a n s i t i o n s and s a t e l l i t e s i n A r 1 6 + have been measured f r a n t h e plasma of t h e Alcator C tokamak. I n t h e wavelength r e g i o n of X = 3.0 t o 3.4 A, t h r e e groups of s a t e l l i t e l i n e s l s 2 2 0-
Is20 n l a r e observed which accompany each of t h e resonance l i n e s emanating frcm t h e upper o r b i t a l s f r a n n = 4 t o n = 10. R e s u l t s of new c a l c u l a t i o n s a r e presented and used f o r i d e n t i f i c a t i o n of t h e observed s p e c t r a and f o r d i s c u s s i o n of l i n e i n t e n s i t i e s and wavelengths. A l l s a t e l l i t e l i n e s belonging t o t h e h i g h n s t a t e s observed ( n = 4 t o n = 1 0 ) have been i d e n t i f i e d i n t h e c a l c u l a t i o n s .1
.
INTRODUCTIONI n high temperature plasmas t h e dominant e x c i t a t i o n mechanism is e l e c t r o n impact e x c i t a t i o n f rcm t h e ground s t a t e of t h e various i o n s p e c i e s . The r a d i a t i v e
t r a n s i t i o n s mostly observed i n t h e X-ray r e g i o n a r e t h e An = 1 (n = 2 t o n = 1 ) and i n t h e VW r e g i o n t h e An = 0 ( n = 3 t o n = 3 and n
-
2 t o n = 2) t r a n s i t i o n s . However, p r e s e n t day r e s e a r c h of h o t l a b o r a t o r y plasmas involve many o p e r a t i o n schemes which can enhance o t h e r population mechanisns. So, f o r example, w i t h n e u t r a l beam i n j e c t i o n t h e charge exchange process becomes important and o t h e r n s t a t e s a r e populated t h a n t h o s e populated by e l e c t r o n impact e x c i t a t i o n .Furthermore, t h e i o n s a r e moving i n t h e plasma, d i f f u s i n g t o h o t t e r o r c o l d e r regions t h a n where they were produced and f a s t i o n i z a t i o n , maybe double i o n i z a t i o n , a s well as r a d i a t i v e reccmbination processes must be t a k e n i n t o account. I n t h e p r e s e n t paper we d e s c r i b e r e s u l t s of a n experiment undertaken t o s t u d y h i g h n states of A r l 6 + , s t a t e s which normally a r e n o t s t u d i e d but which become important i n t h e cases when charge exchange recombination has t o be considered. I n o r d e r t o i d e n t i f y t h e s p e c t r a and t h e acccmpanying s a t e l l i t e l i n e s we have a l s o performed c a l c u l a t i o n s f o r t h e s a t e l l i t e l i n e s accompanying t h e n=4 and 5 s t a t e s . A d e t a i l e d d e s c r i p t i o
r .
of t h e c a l c u l a t i o n s and canparison w i t h experimental d a t a w i l l be given elsewhere
,
t h i s paper g i v e s t h e f i r s t i d e n t i f i c a t i o n of t h e s p e c t r a l f e a t u r e s .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987967
JOURNAL DE PHYSIQUE
2. THE PLASMA SOURCE
X-ray s p e c t r a were recorded by observing t h e X-ray emission from t h e plasma of t h e Alcator C tokamak. The c e n t r a l e l e c t r o n density and tenperature were 2.101' c K 3 and 1.4 keV a s measured with a f a r i n f r a r e d interferometer and with an X-ray pulse-height system, respectively. Argon was introduced i n t o t h e plasma by gas puffing, t h e amount of argon w a s adjusted t o allow observation of t h e weakest l i n e i n t h e X-ray s p e c t r a and s t i l l keeping t h e argon density low enough s o as not t o d i s r u p t t h e plasma. The X-ray spectrometer viewed t h e plasma along a c e n t r a l chord and a l l s p e c t r a were recorded during t h e quiescent phase of t h e plasma discharge
( s e e Fig.1).
Soft X-R
.,,'bf
D 100 im x ~ 1 rm soo
FIG.l Time evolution of plasma c u r r e n t FIG.2 Layout of t h e spectrometer i n t h e ( I ) , e l e c t r o n density (Eel, van Hamos geometry; t h e r a d i u s of c e g t r a l s o f t X-ray emission and curvature w a s 50 cm.
t h e A r 1 6 + resonance l i n e i n t e n s i t y during t h e plasma discharge
3. THE X-RAY SPECTROMETER SYSTEM
Fig.2 shows a schematic of t h e X-ray spectrometer set-up with a c e n t r a l line-of- s i g h t through t h e plasma. The X-ray s p e c t r a t o be recorded, t h e f u l l Rydberg s e r i e s from He-like argon, has a r e l a t i v e amplitude range of t h r e e orders of magnitude.
Thus, t h e s p e c t r a n e t e r system must have a l a r g e dynamic range i n order t o be a b l e t o record t h e high i n t e n s i t y p a r t of t h e spectrum together with t h e weak l i n e s
accompanying t h e high n s t a t e s . A small instrument b u i l t i n van Hamos geanetry was used together with a s p e c i a l l y designed high count r a t e , hi'gh r e s o l u t i o n multiwire proportional counter. The c r y s t a l (quartz 10i1, 25x25 an) was curved i n t h e van Hamos g e m e t r y t o a radius of 50 c by glueing t h e t h i n c r y s t a l (-0.2 mn) t o a
"T 9
machine polished c ved c r y s t a l holder
.
The d e t a i l s of t h e X-ray d e t e c t o r has been described elsewhere ; the s p a t i a l r e s o l u t i o n i s 80 pm and it has a count r a t e c a p a b i l i t y of 1 MHz l i m i t e d by t h e e l e c t r o n i c read-out modules.4. EXPERIMENTAL RESULTS
Fig.3 shows the complete X-ray s p e c t r a of t h e n =I0 t o n = 3 t o ground s t a t e n = 1 t r a n s i t i o n s both on a l i n e a r and on a logarithmic i n t e n s i t y s c a l e ( t h e l a t t e r i n order t o more c l e a r l y show t h e s a t e l l i t e s t r u c t u r e i n t h e s p e c t r a ) . The s p e c t r a were recorded with two d i f f e r e n t s e t t i n g s of t h e s p e c t r a n e t e r ; t h e two p a r t s a r e separated i n t h e f i g u r e with a s o l i d v e r t i c a l l i n e . I d e n t i f i c a t i o n of t h e t h r e e groups of s a t e l l i t e l i n e s belonging t o each diagram t r a n s i t i o n np
-
I s (n = 4 t o 10) a r e marked with v e r t i c a l l i n e s i n t h e f i g u r e .FIG.3 The measured He-like spectrum of A r . The lsnp ' P I
-
I s 2 IS1 resonance l i n e s (Wn) and acccmpanying s a t e l l i t e s (SI,, S2, and S3 ) a r e indicated as well a s t h e ls3p 'Pz-
I s 2 intercanbination l i n e ( ~ 3 7 , and t h e 1 s-
3p resonance l i n e of H-like A r ( W a ) .5. IDENTIFICATION OF SATELLITE STRUCTURE
The d i e l e c t r o n i c s a t e l l i t e spectrum of t r a n s i t i o n s from n = 4 and n = 5 i n A r 1 6 + were c a l c a t e d using t h e numerical methods previously applied t o n
"4
= 3 s a t e l l i t e s t r u c t u r e s.
A s e t of t h r e e groups c o n s i s t i n g of a l t o g e t h e r twelve l i n e s (SI, S2 and S3) a r e i d e n t i f i e d a s s a t e l l i t e s t o t h e main diagram l i n e f o r n = 4 (with s e p a r a t i o n of 44, &-and 72 mil; respectively). The same general s a t e l l i t e s t r u c t u r e of r e l a t i v e wavelengths and i n t e n s i t i e s is produced f o r t h e n=5 o r b i t a l which i s a l s o i n agreement with t h e measurement. For i n t e r p r e t i n g t h e n>5 t r a n s i t i o n spectrum, we r e l i e d on s m a l l systematic changes i n r e l a t i v e s a t e l l i t e i n t e n s i t i e s and wavelength separations a s a function of n.6. DISCUSSION
The i n t e n s i t y of t h e diagram l i n e s falls off as l / n 3 as shown i n Fig.4a i n f e r r i n g t h a t t h e l i n e s a r e a l l produced by e l e c t r o n impact e x c i t a t i o n f r a n t h e ground s t a t e of A r 1 6 + . I t m u s t be emphasized, however, t h a t all observations described i n t h i s paper a r e through a c e n t r a l line-of-sight, i e . , observing emission f r a n t h e c e n t r a l p a r t of t h e plasma. I n cases of observations off t h e c e n t r a l l i n e t h e high n s t a t e s have been b erved' populated t o a much l a r g e r degree than predicted by t h e 1 /n3
dependence5*'. h ( m i )
d -
6,
3
go'-
whl M l r n k n
FIG.4 The measured r e l a t i v e i n t e n s i t y v a r i a t i o n ( a ) of t h e lsnp
-
l s 2 resonance l i n e s Wnand ( b ) of t h e i n t e n s i t y r a t i o s 1(S3,)/I(Wn) of s a t e l l i t e t o resonance l i n e as a function of o r b i t a l number n.3950 4CQO
A ( m i )
d
'j--
e m - b I o , ,
O O o 0
I 0
FIG.5 Canparison of n = 4 3200 3250
t o n = 1 with n = 2 t o
of n t h e = He-like 1 t r a n s i t i o n s A r spectrum.
\
C9-382 JOURNAL DE PHYSIQUE
Three groups of s a t e l l i t e l i n e s have been i d e n t i f i e d and can f u l l y e x p l a i n t h e s a t e l l i t e spectrum belonging t o t h e s e high n s t a t e s . The t h r e e groups o r i g i n a t e f r a n t h e t r a n s i t i o n s l s 2 s ( ' S o ) n p
-
l s 2 2 s 2S1/2(S1 ) , 1 ~ 2 s ( ~ S l ) n p-
l s 2 2 s 2 S l / ~ ( S 2 ~ ) and Is2p('P)np-
l s 2 2 p 2P1/2 3/2(S3 1, r e s p e c t i v e r y . Thus, S1 and S2 a r e ground s t a t e t r a n s i t i o n s while S3, 6elong €0 t h e 2p e x c i t e d s t a t e .I?
i s i n s T r u c t i v e t o compare t h e s p e c t r a f r a n n = 2 t o n = 1 w i t h one f r a n n = 4 t o n = 1 (Fig.5) t o i d e n t i f y t h e t h r e e groups of s a t e l l i t e l i n e s belonging t o a diagram l i n e . The l i n e s a r e c l e a r l y s e p a r a t e d f ran t h e main diagram l i n e i n t h e h i g h e r n spectrum and ambiguity can o n l y a r i s e when s a t e l l i t e l i n e s frcm a higher n o r b i t a l o v e r l a p with a lower n diagram l i n e . The s a t e l l i t e i n t e n s i t y r e l a t i v e t o t h e diagram l i n e as a f u n c t i o n of n s t a y s constant as shown by Fig.4b implying t h a t t h e production mechanism of t h e s a t e l l i t e l i n e s a r e d i e l e c t r o l z i c recombination and i n n e r - s h e l l e x c i t a t i o n and not e l e c t r o n impact e x c i t a t i o n a s f o r t h e diagram l i n e s . This n dependence a l s o a i d i n t h e i d e n t i f i c a t i o n of t h e s a t e l l i t e l i n e s .The wavelength s e p a r a t i o n s of t h e s a t e l l i t e l i n e s t o t h e diagram l i n e a r e p r e d i c t e d frcm t h e t h e o r e t i c a l c a l c u l a t i o n s and a formula has been a p p l i e d t o p r e d i c t t h e wavelength s e p a r a t i o n s f o r S3,. S i m i l a r dependencies can a l s o be derived f o r t h e S2, and
Sin
s a t e l l i t e l i n e s .FIG.6 The measured s e p a r a t i o n i n wavelength A(S3n)-A(Wn) between t h e s a t e l l i t e groups S3, and t h e resonance l i n e s Wn a s f u n c t i o n of n.
7. CONCLUSIONS.
We have presented new measurements of n>2 s a t e l l i t e s f o r A r 1 6 + l s n p
-
I s z n24 frcm a tokamak plasma w i t h c e n t r a l e l e c t r o n t e n p e r a t u r e of about 1.5 keV. We found t h r e e d i s t i n c t i v e groups of s a t e l l i t e l i n e s (Sl,, S2, and S3,) of each resonance l i n e l s n p -1s' f o r n between 4 and 10. These were i d e n t i f i e d with t h e h e l p of atomic c a l c u l a t i o n s a s belonging t o t r a n s i t i o n s of t h e type l s 2 s ( l S o ) n p-
1 s Z 2 s and 1 ~ 2 s ( ~ S l ) n p-
l s 2 2 s and 1 ~ 2 p ( ~ P l ) n p-
l s 2 2 p , r e s p e c t i v e l y . The n dependences of i n t e n s i t i e s and wavelengths a r e d i s c u s s e d and compari sons were made w i t h t h e ccmmonly s t u d i e d He-like s p e c t r a of 1.329,-
l s 2 t r a n s i t i o n .REFERENCES
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6. J E
