AXIAL SEGREGATiON IN Hg-T1-I DISCHARGES OPERATED AT 50 Hz

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AXIAL SEGREGATiON IN Hg-T1-I DISCHARGES OPERATED AT 50 Hz

J. Damelincourt, M. Sevigne, M. Aubes, L. Scoarnec

To cite this version:

J. Damelincourt, M. Sevigne, M. Aubes, L. Scoarnec. AXIAL SEGREGATiON IN Hg-T1-I DIS- CHARGES OPERATED AT 50 Hz. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-273-C7-274.

�10.1051/jphyscol:19797134�. �jpa-00219107�

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JOURiVAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, Page C7- 273

AXIAL SEGREGATION IN Hg-T1-I DISCHARGES OPERATED AT 50 Hz

J.J. Damelincourt, M. Sevigne, M-Aubes and L. scoafnecX

.

Csntre de Physique Atomique, Laboratoire associe' au C.N.R.S. n0277, Universite' PauZ Sabatier, gTouZouse, France.

Centre Technique de Za Compagnie des Zampes, Puteaux France.

Both axial and r a d i a l segregation generally o c c u r s in a r c s containing m i x t u r e s of g a s e s . In m e t a l h a - lides a r c s used a s s o u r c e s of light, this phenome- non i s v e r y indesirable because the light emitted f r o m the a r c i s highly non uniform.

-Physical m e c h a n i s m s responsible f o r additive s e - gregation have been particularly studed by F i s c h e r (1) who explains the segregation by the combined action of r a d i a l diffusion and a x i a l convection.

In the work presented h e r e , the experimental r e - s u l t s f o r axial segregation of thallium atoms i n Hg- T1-I d i s c h a r g e s operated a t 50 Hz a r e compared to those calculated f r o m a simplified model proposed by F i s c h e r (1).

EXPERIMENTAL. A r c s a r e operated vertically on a 50 Hz supply with an inductance in s e r i e s . T h e supply voltage i s 300 V and d i s c h a r g e s a r e 1000 w loaded. T h e a r c tube i s a q u a r t z tube with an inner d i a m e t e r of 2 c m . T h e distance between electrodes is 1 0 cm. T h e tube contains 50 m g of m e r c u r y and 3. 3 m g ( l . 6 o r 0. 8 m g ) of thallium iodide and 20 t o r r of a r g o n (at room t e m p e r a t u r e ) a s an ingnition gaz.

Corrections f o r absorption of s p e c t r a l lines and absorption in s i l i c e tubes a r e obtained f r o m r e l a - tive absorption m e a s u r e m e n t a s s u m i n g a unity value of plasma t r a n s p a r e n c y f o r the 491.6 n m m e r c u r y line. Wall t e m p e r a t u r e a r e determined with a "710 C Ircon" p y r o m e t e r .

TEMPERATURE AND THALLIUM ATOMS DENSI- TIES. An i t e r a t i v e p r o c e s s allows u s t o obtain values of t e m p e r a t u r e s , m e r c u r y neutral a t o m s densities and p r e s s u r e s a s a function of time and position.

Reference (2) gives a detailed study of the e x p e r i - mental apparatus and m e a s u r i n g method(*). Den- s i t i e s of neutral thallium a t o m s a r e determined f r o m m e a s u r e m e n t s of 655 n m thallium line inten- s i t i e s . We used the A.. value of reference.43) :

6 -1 ^1J

A. .=4. 25 10 s

.

Whith experimental values of l o -

1J

c a l instantaneous t e m p e r a t u r e s and n e u t r a l thallium a t o m s densities the thermodynamic analysis of the s y s t e m Hg-T1-I gives atomic r a t i o s H ~ / T ~ . In o r d e r to simplify the theoretical analysis we shall only consider i n the following t'ime averaged values of atomic r a t i o s .

The instantaneous and spatialy resolved a r c tempe- T h e s e r e s u l t s a r e given i n fig. 1. Assuming a pos- r a t u r e s and densities of neutral thallium a t o m s a r e sible experimental e r r o r of 2

%

i n t e m p e r a t u r e s , obtained f r o m s i d e on m e a s u r e m e n t s of absolute the corresponding e r r o r for atomic r a t i o i s 25

%.

s p e c t r a l radiancesof 588 n m m e r c u r y line and 655 As i t c a n be s e e n i n fig. 1 , the atomic r a t i o (Hg/

nm thallium line. T1) v a r i e s a s

- A z R e

Following approximationsare made : o

-

T h e m e r c u r y plus a r g o n p r e s s u r e i s constant with 0. 18(

A

^{(0. 25}

along the axis of the discharge, and close to the total p r e s s u r e .

-

Atomic r a t i o s a r e radialy constant and local t h e r -

($) It i s to be noticed that value

C

p. 1033 i n r e f e - modynamical equilibrium i s assumed.

r e n c e (2) i s 1.256 and not 1.276

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797134

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T a b l e 1 shows a reasonably good a c c o r d a n c e between theoretical and e x p e r i m e n t a l r e s u l t s for l a m p s 1 and 2 where the modulation of atomic r a - tio is negligible ; for l a m p 3 d i s a g r e e m e n t occur whis r e s u l t s obtained f r o m the steady s t a t e model.

REFERENCES.

(1) F i s c h e r ( E . ) : J. Appl. P h y s . , 1976, 47,2954.

(2) Damelincourt (J. J. ), Karabourniotis (D. ), Scoarnec (L. ) and H e r b e t (P. ) : J. Phys. D . , App;. P h y s . , 1978,

11,

1029.

(3) P r e u s s (E. ) : 2 . Physik, 1970, 2 3 9 , 133.

F i g . 1. atomic r a t i o H ~ / T ~ v e r s u s distance f r o m lower electrode. T o t a l p r e s s u r e :

1 . 6 Atm.

COMPUTATION O F

A.

T h e n u m e r i c a l procedure flollows the simplified one proprosed i n r e f e r e n c e (1 ). We shall c o n s i d e r only the diatomic molecule T1 I and neglect a l l o t h e r m o l e c u l a r s p e c i e s . With this hypothesis the s y s t e m to be solved w r i - t e s a s follow.

The notations a r e those of r e f e r e n c e (1) and G(h) i s a c o r r e c t i n g factor

1

<

^G(&)^{g 2}

TABLE I

-

T h e o r e t i c a l and e x p e r i m e n t a l values of

X

The theoretical and e x p e r i m e n t a l values obtained f o r the t h r e e d i s c h a r g w a r e given i n table I.

l a m p

1 2 3

H g 5 0 50 50

X.h 0.22 0 . 2 0: 11 T 1 1

3 . 3 1 . 6 0. 8

L

X e x p 0.24 0.22 0 . 1 8

L