EXPERIMENTAL INVESTIGATION OF THE BALMER SPECTRUM FROM A DENSE HYDROGEN PLASMA NEAR THE PHOTORECOMBINATION THRESHOLD

HAL Id: jpa-00219321

https://hal.archives-ouvertes.fr/jpa-00219321

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

EXPERIMENTAL INVESTIGATION OF THE BALMER SPECTRUM FROM A DENSE

HYDROGEN PLASMA NEAR THE PHOTORECOMBINATION THRESHOLD

K. Günther, S. Lang, R. Radtke, R. Ulbricht

To cite this version:

K. Günther, S. Lang, R. Radtke, R. Ulbricht. EXPERIMENTAL INVESTIGATION OF THE BALMER SPECTRUM FROM A DENSE HYDROGEN PLASMA NEAR THE PHOTORECOM- BINATION THRESHOLD. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-679-C7-680.

�10.1051/jphyscol:19797329�. �jpa-00219321�

JOURflAL DE PHYSIQUE CoZZoque C I , Y ~ p p Z 6 m e n t a u n07, Tome 40, JuiZZet 1979, page C7- 679

EXPERIMENTAL INVESTIGATION OF THE BALMER SPECTRUM FROM A DENSE HYDROGEN PLASMA NEAR THE PHOTORECOMBINATION THRESHOLD

K. Giinther, S. Lang, R. Radtke and R. Ulbricht.

Akadenrie d e r Wissenschaften der DDR, ZentraZinsti-but fiir Bzektronenphysik, B e r l i n , D.D.R.

Tn n e a r l y i d e a l p l a s k a s , i . e . i n plasmas where t h e s o - c a l l e d n o n - i d e a l i t y parameter y=e2(2ne,)1/3/k~ i s s m a l l compared t o u n i - t y , t h e spectrum i n t h e t r a n s i t i o n r e g i o n from l i n e t o continuum r a d i a t i o n may be d e s c r i b e d by l i n e d i s s o l u t i o n and t h e s t a - t i s t i c a l l y extended recornbination continu- um [I], Ii1;h i n c r e a s i n g degree of plasma n o n - i d e a l i t y , however, t h e model of t h e Debye s h i e l d e d Coulomb p o t e n t i a l breaks dovm-.

I n C2,31 a t h e o r y f o r o p t i c a l p r o p e r t i e s

d i s t r i b u t i o n under n o n i d e a l circumstances f o r a n element w i t h a more simple atomic s t r u c t u r e . For t h i s purpose we i n v e s t i - g a t e d a p u l s e d hydrogen a r c a t e l e v a t e d p r e s s u r e s ,

The e x p e r i m e n t a l arrangement f o r produc- i n g t h e hydrogen a r c and t h e d i a g n o s t i c methods used f o r i t s i n v e s t i g a t i o n have been d e s c r i b e d i n d e t a i l i n [61,* The spec-

t r a l d i s t r i b u t i o n of t h e hydrogen a r c was o b t a i n e d u s i n g a n o p t i c s 1 m u l t i c h a n n e l an- a l y z e r , ~ ~ l e a s u r e m e n t s were performed f o r of n o n i d e a l plasmas w i t h Y S 1 was devel- two d i f f e r e n t p u l s e d a r c s whose d a t a a r e oped whose main s t a t e m e n t s c o n s i s t i n t h e p r e s e n t e d i n t h e f o l l o w i n g t a b l e :

f o l l o w i n g : Due t o t h e s t r o n g e l e c t r i c m i - _{Arc no. l 2}

- -

c r o - f i e l d s , t h e s p e c t r a l l i n e s n e a r t h e

Arc temperature

CK]

photorecombination threshold d i s a p p e a r 1 5300

i k c p r e s s u r e Catml 2 7.5

l o n g b e f o r e t h e y merge i n each o t h e r a,s

E l e c t r o n d e n s i t y [ ~ m - ~ ] 2.7.1 017 6 -2- 10'7 p r e d i c t e d by I n g l i s and T e l l e r , The

Non-ideality 0.081 0,117

t h r e s h o l d i t s e l f p r a c t i c a l l y remains un- s h i f t e d s o t h a t t h e disappearance of Sped- t r a Z L i n e s consequently s h o u l d l e a d t o a n i n t e n s i t y gap i n t h e p r e t h r e s h o l d r e g i o n whose w i d t h i s g i v e n approximately by AB=3rkT a c c o r d i n g t o t31.

I n a' r e c e n t , paper C 4 1 some r e s u l t s were n o t i c e d f o ~ t h e mercury spectrum i n c a s e of y = 0.056 and 0.185 g i v i n g r i s e t o con- f i r m t h e proposed model [2,31. From t h e t h e o r e t i c p o i n t o f vie-;:, however, i t i s o f p a r t i c u l a r i n t e r e s t t o know t h e s p e c i a l

The s p e c t r a l d i s t r i b u t i o n s corresponding t o t h e a r c s l i s t e d above a r e shown in f i g , l f o r t h e p r e t h r e s h o l d r e g i o n , Begin- n i n g a t s h o r t wavelengths, i t c o n t a i n s t h e u n p e r t u r b e d recombination continuum, pos- s i b l y f o l l o x ~ ~ e d by a r e g i o n of merged l i n e s and, f o r a r c no. 1 , t h e l a s t v i s i b l e hy- drogen l i n e I+. Some comparatively narrow contamination l i n e s which were n o t iden- t i f i e d unambiguously cannot i n f l u e n c e t h e confidency of o u r f o l l o w i n g c o n c l u s i o ~ .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797329

! b e intensity distribution in fig.1 sug- gests that the charge-carrier interactiolz

only becomes apparent by a disappearance of spectral lines, Thus, in case of the low-pressure arc the last visible hydrogen line was Hy, whereas in case of higher pressure we only could observe HPyet. At the series limit an intensity gap could not be found (according to 133, for arc 2 its width should be AE 0.45 eV or a h

ss 48 nm). To confirm that the absence of this gap is not due to the high opacity of the observed plasma layer we proved in case of arc 2 that the intensity in the prethreshold region is proportional to the

optical path length lop% as shown in fig.

2. Shock tube experiments for a similar y range ( y = 0.102) [5'J lead to different conclusions concerning the influence of non-ideality on the radiation properties.

However, we should not overestimate this discrepancy since the structure of the spectral distribution in the prethreshold region observed in [ 5 ] was within the lim- its of experimental error yet,

[I] Ruedjak, V., V. Vujnovic, Astron.

Astrophys.

2,

[2] Kobzev, G.A. et al,, TVT

2,

131 Kobzev, G.A,

,

16;

[4] Kurilepkov, Ju.K., P.V. Ninaev, ZETP

2,

.[5] ITonkov, A.A. !et al., High Temp.- IIigh Press.

3,

[ 6 ] Radtke, R., K. Giinther, J. Phys.

2,

1131 (19761..

Fig.?. Spectral distribution of the arcs listed above in the prethreshold region,

WAroL€)(6t~

mf

Pig,2, Radiation intensity for arc no. 2 at the threshold for different

observation lengths.