HAL Id: jpa-00219171
https://hal.archives-ouvertes.fr/jpa-00219171
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.
COLLISIONAL PROCESSES IN THE HE’-CO22 ATOMIC CARBON NUCLEAR PUMPED LASER
1,454µ
A. Mark Preslas, G. Miley
To cite this version:
A. Mark Preslas, G. Miley. COLLISIONAL PROCESSES IN THE HE’-CO22 ATOMIC CARBON NUCLEAR PUMPED LASER 1,454µ. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-391-C7- 392. �10.1051/jphyscol:19797192�. �jpa-00219171�
JOURNAL DE PHYSIQUE CoZZoque C7, suppl6ment a u n07, Tome 40, J u i Z l e t 1979, page C7- 391
A. Mark Prelas and G.H. Miley.
f l u e l e a r ~ n ~ i n e e r i n ~ Progrm, 214, NueZear-Engineering Laboratory, Urbana, Illinois 61801.
An i n t e n s i v e study o f t h e k i n e t i c s o f the mixtures, no metastable species i s s u f f i c i e n t l y atomic carbon ~ u c l e a r pumped l a s e r (NPL) has been e n e r g e t i c t o populate t h e upper l a s e r l e v e l w i t h a undertaken because of t h e observation o f m i l l i - s i n g l e c o l l i s i o n , thereby making m u l t i p l e c o l - second time delays between t h e l a s e r o u t p u t and l i s i o n s necessary.
t h e neutron ( i . e . , e x c i t a t i o n ) i n p u t . This NPL Another important f a c t i s t h a t o n l y us delays represents t h e best candidate f o r an energy have been observed i n an g l e c t r i c a l pumped l a s e r storage NPL a t near atmospheric pressures d i s - (EPL) using t h e same mixtures b u t pulsed e l e c t r i - covered t o date. The atomic carbon NPL on t h e c a l discharge techniques. I n EPL's, t h e h i g h 3 1 PI) -C(3S 'P:) t r a n s i t i o n B 1 . 4 5 4 ~ operates e l e c t r o n temperature d u r i n g t h e e l e c t r i c a l d i s - v i a t h e d i s s o c i a t i o n o f C02 i n He-C02 m i x t u r e s (50 charge destroys t h e ULL p o p u l a t i o n i n t h e atomic T 5 P H e 1 4 0 0 T + .25 r n T ~ P C O 2 ~ 2 5 mT). Exci- carbon, r e s t r i c t i n g l a s i n g t o t h e a f t e r g l o w . ( 4 ) t a t i o n of t h e l a s e r gas i s achieved by MeV alnha I n c o n t r a s t , i n a nuclear pumped plasma, ~qhere th e p a r t i c l e s from t h e 1 ° ~ ( n , a ) L i r e a c t i o n i n a t h i n 7 average e l e c t r o n temperature i s - 0.04 eV, energy boron c o a t i n g on the i n n e r w a l l o f t h e l a s e r i s t r a n s f e r r e d through the metastable o r o t h e r tube." ) This n u c l e a r r e a c t i o n i s d r i v e n by a 12- l o n g l i v e d s t a t e s o f t h e b u f f e r gas. ) ~ o n s e - ms (FIJHI1) p u l s e o f thermal neutrons obtained from quently, nuclear pumped plasmas simulate an t h e Univ. o f I l l i n o i s TRIGA r e a c t o r . Delays o f up a f t e r g l o w throughout t h e e x c i t a t i o n pulse, so t o 5 ms between t h e peak o f t h e 1.454 p l a s e r t h a t t h e atomic carbon NPL i s a b l e t o operate s i g n a l and t h e thermal neutron p u l s e have been throughout t h e neutron, i.e., e x c i t a t i o n p u l s e
observed. (2) time.
The k i n e t i c modeling has been d e r i v e d from A computer study demonstrates t h a t t h e delays experimental observations i n v o l v i n g d i f f e r e n c e s i n observed i n t h e NPL experiments can be a t t r i b u t e d o p e r a t i o n o f t h e l a s e r f o r v a r i o u s gas m i x t u r e s t o a s e r i e s o f slow r e a c t i o n s i n v o l v i n g t h e and f o r e l e c t r i c a l e x c i t a t i o n . A s i m i l a r time 1 i e ( 2 ~ ~ ) metastable species. B a s i c a l l y , t h e t h r e e delay has a l s o been observed f o r t h e same carbon step model used f o r t h e He-C02 NPL i n v o l v e s t h e t r a n s i t i o n i n Ne-CO and Ne-C02 gas f o l l o w i n g r e a c t i o n s :
k
I n c o n t r a s t , i n m i x t u r e s o f He-CO, no s i g n i f i c a n t 1 ) H ~ ( z ~ s ) + Cop 2 CO(X'I,V .. - > 10) + 0 + He
delay i s observed. I n t h e l a t t e r case, as shown I 0 cmj
klmax = 5.75xi0- (Ref. 5 )
by Atkinson and Sanders,(4) a s i n g l e c o l l i s i o n
1
3 2) c0(x1C,V, 10) 5 cO(X C, v = 0)
between t h e He(2 S) metastable species and the CO
-rmin = 208 f 3 0 ~ s - Torr(C0) (Ref. 6 )
rnol ecul e d i r e c t l y populates t h e g p e r l a s e r l e v e l (ULL) . However i n He-C02, Ne-CO rmd Ne-C02
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797192
11 cm3
k = 9.85~10- (Ref. 5 ) .
'max
Then, f o r example, f o r 100 T He + 2 mT COZY a d e l a y o f - 1 ms i s p r e d i c t e d which compares favorably t o t h e experimental observations.
Other mechanisms f o r p o p u l a t i n g t h e ULL have been considered; however, t h e two most l i k e l y , i o n i z a t i o n - r e c o m b i n a t i o n and cascading t o t h e ULL, have been e l i m i n a t e d based on experimental obser- v a t i o n o f s e l e c t l i n e s . ( 7 )
The assumption t h a t t h e d i s s o c i a t e d C02 i s formed i n a h i g h e r v i b r a t i o n a l s t a t e o f CO ( r e - a c t i o n 2) i s e s s e n t i a l t o t h e above model. Thus if r e a c t i o n 1 produced CO(X 1 C,v = 0) such t h a t r e a c t i o n 3 c o u l d f o l l o w immediately, t h e p r e d i c t e d d e l a y would be reduced t o - 300 vs, we1 1 below e x p e r i m e n t a l l y observed values.
I n an EPL e x c i t e d w i t h a p o s i t i v e column d i s - charge, Sn m i x t u r e s o f He-C02 ( 5 T 2 PHe 5 40 T
< 10 mT), a t an average power
+ .25 P ~ 0 2 - 3 3
d e p o s i t i o n r a n g i n g from 250 W/cm t o 1500 W/cm ,
and a t r e p e t i t i o n r a t e s from 10 Hz t o 100 Hz, l a s i n g , - 23 us i n t o t h e a f t e r g l o w was observed o n l y a f t e r t h e f i r s t pulse. This behavior i s a t t r i b u t e d t o t h e f o r m a t i o n and accumulation o f CO which i n l a t e r pulses undergoes l a s i n g v i a r e - a c t i o n 3 once t h e e l e c t r o n temperature f a l l s t o a s u f f i c i e n t l y low v a l u e i n t h e a f t e r g l o w regime.
For a p p l i c a t i o n s where l a s e r o u t p u t delays on t h e o r d e r o f 1 ms a r e required, such as l a s e r feedback fusion,(' ) such a mu1 t i p l e step process may prove valuable. R e l a t i v e l y 1 ow pressures and l a r g e volumes (possible due t o t h e l a r g e t r a n s p o r t d i s t a n c e o f neutrons) o f t h e b u f f e r species c o u l d be used t o maximize t h e energy storage and t h e d e l a y times.
I n conclusion, t h e l o n g delays (5 5 ms), ob-
served between t h e peak o f t h e He-C02 atomic carbon NPL s i g n a l and t h e thermal neutron pulse, a r e a t t r i b u t e d t o a twostep d i s s o c i a t i o n o f C02 w i t h an i n t e r m e d i a t e step i n v o l v i n g v i b r a t i o n a l r e l a x - a t i o n o f e x c i t e d CO. Computer modeling o f t h i s process g i v e s r e s u l t s i n agreement w i t h experiment and w i t h o t h e r observations i n c l u d i n g t h e disap- pearance o f t h e delay i n He-CO m i x t u r e s and EPLs.
References
(1 ) t l i l e y , G. H., " D i r e c t Nuclear Pumped Lasers- Status and P o t e n t i a l A p p l i c a t i o n s , " Laser I n t e r a c t i o n s and Related Plasma Phenomena, H.
Schwarz and H. Hora, eds., Plenum Press, N.
Y., Vol . 4A, 1977, pp. 181-229.
(2) Prelas, M. A., Akerman, E l . A., Boody, F. P., and M i l e y , G. H., Appl. Phys. L e t t . , Vol. 31, Oct. 1977, p. 428.
(3) Prelas, tl. A., Anderson, J. H., Boociy, F. P., Nagal ingam, S. J . S., and bliley, G. H.,
"Nuclear Pumping o f a Neutral Carbon Laser,"
R a d i a t i o n Energy Conversion i n Space, K. W. Billman, ed., Vol. 61 o f Prog. i n Astro. and Aero., AIAA, NY pp. 411-417
(1 978).
(4) Atkinson, J. B., Sanders, J. H., J. Phys. B (Proc. Phys. Soc.) Ser. 2, Vol. 1, p. 1171 (1968). ( 5 ) Schmeltekopf, A.
(5) Schmeltekopf, A. L., Fehsenfeld, F., The
Jour. o f Chem. Phys., Vol. 53, No. 8, pp.
3173-3177, October 1970.
(6) W i l l e t t , C. A., I n t r o d u c t i o n t o Gas Lasers:
P o p u l a t i o n I n v e r s i o n Elechanisms, Pergamon Press, Maxwell House, F a i r v i e w Park, Elmsford, N.Y., p . 317, (1974).
( 7 ) Prelas, M. A., Boody, F. P., and Miley, G.
H., "Recent Results w i t h t h e Atomic Carbon Laser B 1 .4539pYN 3 1 s t Annual Gaseous Elec- t r o n i c s Conference, Oct. 1978.
