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Submitted on 1 Jan 1979
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DETERMINATION OF QUENCHING CROSS SECTION OF RESONANT Cs(6P) STATE BY CO2
MOLECULES IN DISCHARGE IN He - CO2 - Cs.
G. Naidis, V. Sinelshikov
To cite this version:
G. Naidis, V. Sinelshikov. DETERMINATION OF QUENCHING CROSS SECTION OF RESO- NANT Cs(6P) STATE BY CO2 MOLECULES IN DISCHARGE IN He - CO2 - Cs.. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-107-C7-108. �10.1051/jphyscol:1979753�. �jpa-00219459�
JOURNAL DE PHYSIQUE CoZZoque C7, suppzdment au n07, Tome 40, JuiZZet 1979, page C7-107
DETERMINATION OF QUENCHING CROSS SECTION OF RESONANT Cs(6P) STATE BY Cop MOLECULES I N DISCHARGE IN He
-
C02-
Cs.G.V. Naidis, V.A. Sinelshikov.
I n s t i t u t e of High Temperatures, U.R. S.S. Academy o f sciences, Moscow, U.S. S. R.
A s molecular plasmas w i t h a l k a l i see- dings a r e widely used in d i f f e r e n t de-
v i c e s t h e d a t a on elementary processes in such plasmas a r e o f g r e a t i n t e r e s t . One of t h e main processes ;Ln t h i s type of plasmas which influences b o t h energy ba-
lance and i o n i z a t i o n balance of plasma i s t h e c o l l i s i o n a l d e a c t i v a t i o n of resonant s t a t e of alkali atoms by molecules. 1n[I]
a d e t a i l e d review is given of experimen- t a l and t h e o r e t i c a l d a t a on quenching c r o s s s e c t i o n s f o r d i f f e r e n t p a i r s : a l k a l i atom
+
molecule. However t h e r e i s no in- formation in l i t e r a t u r e about such pro- c e s s f o r pairtcesium+
carbon dioxide.I n t h i s work t h e c o l l i s i o n a l deactiva- t i o n c r o s s s e c t i o n of resonant C s s t a t e by C02 is obtained. He
-
C02-
C s mixturew a s pumped w i t h veloci* 6.10~ em/sec tMo$h g l a s s discharge tube (glow dis- charge c u r r e n t
I =
50-
200mB, tube ra- d i u s R = 1.15cm). P a r t i a l p r e s s u r e s of components were PHe = 20 t o r r , PCO = 0.2-
2 t o r r . Cesium concentration NCs 2 w a s changed from 10" t o 10'~ cmw3. Because of chemical r e a c t i o n between C s and C02 t h e v a l u e of NCs is d r a s t i c a l l y changing along t h e discharge and so a r e plasma c h a r a c t e r i s t i c s . Therefore s p e c t r a l measurements were made a c r o s s t h e dis- charge.
Cesium concentration i n ground s t a t e was determined by t o t a l absorption of resonant cesium l i n e >= 8521
81
( 62~3/2--6 2 SII2 t r a n s i t i o n ) , hyperf i n e s t r u c t u r e w a s taken i n t o account in accordance w i t h [2]
.
An a b s o l u t e i n t e n c i t y measure- ments of t h e same l i n e were used (with account of reabsorption) f o r determina- t i o n of t h e first resonant Cs(6PZ s t a t e density. Simultaneously with o p t i c a l measurements in t h e same discharge tubec r o s s s e c t i o n t h e l o n g i t u d i n a l e l e c t r i c f i e l d w a s measured with double electro- s t a t i c probe.
The quenching constant K was obtained from balance equation f o r resonant s t a t e d e n s i t y NC$
.
In experimental conditions convective and d i f f u s i o n t r a n s f e r of Cs*
and quenching of C: by helium and elec- t r o n s a r e n e g l i g i b l e , so t h e balance equation is:
where n, and NCO
-
d e n s i t i e s of e l e c t r o n s and C02 m o l e c u l e s , < ~ ~ ~ ~ ~ ) 2-
r a t e cons- t a n t of C s e x i t a t i o n by e l e c t r o n s . TermC
contains cascades from higher C s s t a t e s and r a d i a t i v e deactivation" of C s Yt o p o u n d s t a t e . For determination of K t h e regimes were chosen where t h e value of w a s l e s s than 10% of
npNC5(~Diae>.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979753
Radiative l i f e t i m e of C; was evaluated w i t h account of reabsorption.
The e x c i t a t i o n r a t e constant < G ~ ~ % ~ )
is s e n s i t i v e t o t h e form of e l e c t r o n energy d i s t r i b u t i o n function. The use of maawellian d i s t r i b u t i o n f u n c t i o n s f o r de- termination of
<~i,~3~,
may l e a d t o s e r i o u s e r r o r s . qherefore in t h i s work by neehod described in [3] electcon energy d i s t r i b u - t i o n f u n c t i o n s were c a l c u l a t e d f o r experi-mental conditions. The value of
(cUi%)
were obtained w i t h use of e x c i t a t i o n c r o s s s e c t i o n [4]
.
It i s worth noting t h a t00
t*electron temperaturen
T, ='$ S
e3I2f
(€)el€f o r c a l c u l a t e d d i s t r i b u t i o n f & c t i o n s
f (€1
p r a c t i c a l l y coincides with Te determined from e l e c t r o n e n e r w balance equation where d i s t r i b u t i o n function is assumed t o be maxwellian.
This coincidence w a s used f o r calcula- t i o n of e l e c t r o n d e n s i t y ne from measure- ments of discharge c u r r e n t
I
and e l e c t r i c f i e l d E. Radial d i s t r i b u t i o n n e b ) was assumed t o b e parabolic, radial d i s t r i b u - t i o n s NHe(r) and N (r) were taken inCo2
a c c o r b n c e w i t h p r o f i l e of gas temperature T(r). Taking i n t o account tha* t h e main r a d i a l dependence of d r i f t v e l o c i t y Vd, corresponds t o r a d i a l p r o f i l e of gas den- s i t y , f o r ne(0) we obtain
T
where GO Q
corresponding t o gas d e n s i t y a t T(R).
Radial p r o f i l e of T(r) w a s c a l c u l a t e d w i t h t h e help of thermal conduction
equation.
From equation- ( I) t h e quenching cons- t a n t K was determined, and corresponding v a l u e of quenching c r o s s s e c t i o n S =
1.4*10-'~ cm2. Square mean e r r o r of mean
O: value i s 7%. The measurements were made in gae temperature range 500
-
800'~.However because of t h e experimental e r r o r it was not p o s s i b l e t o f i n d temperature dependence of G
.
Radial p m f i l e of r a t i o NC,+ /NCS which is present i n equation (I) was not measured and was assumed t o be uniform.
T h i s asswaption l e d t o systematic e r r o r in S values. EstFmations show t h a t
obtained value of m a y exceed t r u e value UP t o 40%.
The authors a r e g r a t e f u l t o D r . I.A.
V a s i l i e v a f o r h e l p f u l discussions and t o V.F.Kosov f o r t h e h e l p during t h e experi- ment.
RE-CES
I. E.A.Andreev, E.E.Nikitin. In "imiya plasmyn, No.3, M., Atomizdat, 1976, p.28.
2. V.A.Sinelehikov. X I 1 1 I C P I G , B e r l i n , 1977, ~ 0 1 4 1 .
3. A.Kh.Mnatsakanyan, G.V.Naidis. Pis.
Plasmy,
2,
(19761, 152.4. S.IP.Chen, A.C.Gallagher. Phys.Rev., (19781, 551.
e , I
-
charge and mass of e l e ~ t r o n . ~ ~ & € )-
t r a n s p o r t e l e c t r o n
