A CO2 LASER -PLASMA INTERACTION EXPERIMENT- THE SCATTERED SPECTRUM OF LANGMUIR WAVES DRIVEN VIA THE ELECTRON-ION DECAY INSTABILITY

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Submitted on 1 Jan 1979

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A CO2 LASER -PLASMA INTERACTION

EXPERIMENT- THE SCATTERED SPECTRUM OF LANGMUIR WAVES DRIVEN VIA THE

ELECTRON-ION DECAY INSTABILITY

M. Forrest, R. Kirk, N. Peacock

To cite this version:

M. Forrest, R. Kirk, N. Peacock. A CO2 LASER -PLASMA INTERACTION EXPERIMENT- THE SCATTERED SPECTRUM OF LANGMUIR WAVES DRIVEN VIA THE ELECTRON- ION DECAY INSTABILITY. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-745-C7-746.

�10.1051/jphyscol:19797360�. �jpa-00219356�

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JOURNAL DE PHYSIQUE CoZZoque C7, suppZdment au n07, Tome 40, JuiZilet 1979, page C7-

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A C02 LASER -PLASMA INTERACTI(UU EXPERIMENT- THE SCATTERED SPECTRUM OF LANGMUIR WAVES DRIVEN VIA THE ELECTRON-ION DECAY INSTABIUW

M.J. Forrest, R.E.

irk'

and N.J. peacock.

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m o r a t o r y , Abingdon, Oxon, OX14 3DB, UK fEuratom/UKAEA Fusion AssoOiation)

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- 3 t h e h i g h k i n e t i c e n e r g y o f t h e p l a s m a ( 5 k j cm I c o m p a r e d t o t h e l a s e r pump e n e r g y ( 1 5 j o u l e s l , n o n - l i n e a r p l a s m a p r o c e s s e s c a n b e e x c i t e d w i t h o u t a l t e r i n g t h e b a s i c p l a s m a p a r a m e t e r s .

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P b e i n g t h e r a t i o o f t h e pump i n t e n s i t y t o t h e t h r e s h o l d i n t e n s i t y o f t h e i n s t a b i l i t y , a n d v e i s t h e e l e c t r o n t h e r m a l y e l o c i t y . U s i n g t h e a n a l y s i s o f P e r k i n s a n d F l i c k ( 1 9 7 1 1 ( 3 1 f o r a n i n h o m o g e n e o u s p l a s m a w h e r e Te >> T . , t h e t h r e s h o l d pump i n t e n s i t y , when t h e s w e l l i n g o f t h e pump w a v e i s t a k e n i n t o

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i t i s p o s s i b l e f o r L a n g m u i r w a v e s t o b e d r i v e n w e l l a b o v e t h e i r t h e r m a l l e v e l , w h i l e t h e i o n a c o u s t i c w a v e s a r e h e a v i l y L a n d a u d a m ~ e d .

P O - s w i t c h e d r u b y p r o b e l a s e r ( 5 0 0 NWI h a s b e e n u s e d t o p r o d u c e a c o - o p e r a t i v e l y s c a t t e r e d s p e c t r u m . T h e p r o b e beam i s c o - a x i a l t o t h e CO 'pump beam a n d

2

b o t h h a v e h o r i z o n t a l l y p o l a r i s e d o u t p u t s . T h e s c a t t e r i n g c o l l e c t i o n o p t i c s a r e a r r a n g e d t o g i v e a f o r w a r d sc:ttering a n g l e o f 8 f 2.4', F i g . 1. T h i s r e s u l t s i n t h e s c a t t e r i n g p a r a m e t e r

a = k ( D e b y e l . / k ( L a n g m u i r 1 > 6

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Fig.1 Schematic showing coaxiai! C02 pump beam and ruby probe beam and coZZection optics. The perspect- 2vs veetdr diagram-iSLiustrates in00 t h e scattering vectoiq k i s arranged t o be paraZZe2 t o the excited k Langmuir ' s

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T h e s c a t t e r i n g o f t h e s e e n h a n c e d L a n g m u i r w a v e s r e s u l t s i n d i s c r e t e s h i f t e d e l e c t r o n f e a t u r e s , e a c h s i d e o f t h e r u b y l a s e r w a v e l e n g t h 6 9 4 3

8.

T h i s s c a t - t e r e d s p e c t r u m i s g i v e n by

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wruby, w i t h a w i d t h o f 2 6w. T h e r e i s , i n cO?

addition, a s p r e a d i n f r e q u e n c y d u e t o t h e f i n i t e r a n g e o f w a v e v e c t o r s a c c e p t e d by t h e s c a t t e r i n g o p t i c s .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797360

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A g a t e d i n t e n s i f i e d o p t i c a l m u l t i c h a n n e l a n a l y s e r REFERENCES

( O N A ) , i n c o n j u n c t i o n w i t h a o n e m e t r e f o c a l l e n g t h 1. FORREST M J e t a l , P h y s . R e v . L e t t s . 3 7 ( 1 9 7 9 ) 1681-1684

g r a t i n g s p e c t r o m e t e r , h a s been used t o r e s o l v e t h e

2. PEACOCK N J e t a l , J o u r n a l d e P h y s i q u e (19771 d o w n - s h i f t e d w a v e l e n g t h e l e c t r o n f e a t u r e . The e x - Tome 38 C6 43-54

p e r i m e n t a l l y d e r i v e d p r o f i l e was compared w i t h t h e o - _{3 m} a n d FLICK J , Phys. of Fluids, r e t i c a l p r e d i c t i o n s o f a m p l i t u d e and s h a p e . 14(1971 I 2012-2018

* A t t a c h e d from Royal Holloway C o l l e g e , U n i v e r s i t y o f London, E n g l e f i e l d Green, S u r r e y , U K .