PECULIARITIES OF PULSED NON-SELF-SUSTAINED DISCHARGES IN MIXTURES CONTAINING CO

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PECULIARITIES OF PULSED

NON-SELF-SUSTAINED DISCHARGES IN MIXTURES CONTAINING CO

K. Klopovsky, G.B. Lopantseva, A. Pal, I. Persiantsev, A. Starostin

To cite this version:

K. Klopovsky, G.B. Lopantseva, A. Pal, I. Persiantsev, A. Starostin. PECULIARITIES OF PULSED NON-SELF-SUSTAINED DISCHARGES IN MIXTURES CONTAINING CO. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-343-C7-344. �10.1051/jphyscol:19797169�. �jpa-00219145�

JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, ~ u i Z Z e t 1979, page C7-343

PECULIARITIES OF PULSED NON-SELF-SUSTAINED DISMARGES IN MIXTURES CONTAINING CO

K.S. Klopovsky, G.B. Lopantseva, A.F. Pal, I.G. Persiantsev and A.N. Starostin.

I n s t i t u t e o f NucZear P h y s i c s , Moscow S t a t e U n i v e r s i t y , 127234, Moscou U. S. S. R.

We have studied pulsed non-self-s&stai- ned discharges controlled by the electron be= with the energy ~ 1 0 0 keV and a curre- ntjb-300 mkA in gaseous mixtures contai- ning CO with N2,Ar and He.The gas was pum- ped through a quartz discharge chamber at a rate of 1 m/sec.The electrode area was 1x1 cm ,with distance 2 L=l cm.

It has been found that at small energy inputs the discharge current j in the mix- tures behaves similarly to the current in pure N2.As the energy input increased,the behaviour of j(t) altered and one could ob serve a fall-off of the curve,followed by instability (fig.l).As >;he jb wae further enhanced,the discharge turned into an arc without the stage of j fall-off.Such a de- pendence of j(t) was observed for all stu- died mixtures.Eio such behaviour was obser- ved in pure N2 and in N2

-

He mixtures.

0 _Csec

1

-

jb= 70 mcA 2

-

^{jb= 160 mcA}

3

-

^{jb= 250 mcA}

Mixture

600

^10%

co +

90% N2

big. I

L Fig. 2

4

gt,10-~sec

may be associated with a change in the ra tes of elementary processes during the discharge.It is well knoun that the disso ciative attachment (d.a.1 to gas molequ- lee and the dissociative recombination (d.r.) with molecular ions proceeding via the formation of an autoionizing state have a resonance character.The cross-sec- tion for the above processes are strongly dependent upon the vibrational number.

It may be shown that as the energy in- put increases, the d.a. coefficient also increases, both due to electron heating caused by impact of the second kind with vibrationally excited molecules and the increas in the d.a. cross sections with the increasing vibrational number h , 25.

However, because of the strong associativ detachment from +'O CO--CO

+

e (kaad

2 4.1 0-I Ocm3/sec) 1 the discharge current nonmonotonousness can not be associated Fig.2 shows the dependence of W=jmaxE/NCO

with the dependence of the kdea.upon Tv on the time of reaching Dhe maximum

.

whose value does not exceed 0'13cm3,ec-1 The nonmonotonic behaviour of the j(t)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797169

[3] In our experimental conditions,at su- fficiently high euergy inputs the main por tion of energy is transferred to the vib- rational degrees of freedom of the molecul (the translational temperature of plasma particles is an order of magnitude lower than the vibrational one Tv) .The main cha- nnels of formation of CO+ ions on the buf- fer-gas particles are as follows:

~0 + eb-c

co + ₊

2s 9

co +

^{M+ 4} CO*~.

I

The location of the adiabatic terms CO (XI=+) and CO+(X~~+) are such [4] that the transitions from the upper vibrational le- vels of CO to the upper one of CO+ occur in the region allowed by the Frank-Condone principle. Theref ore, CO+ ions are formed in vibrationally excited states and their Tv may be high.Estimates show that during the recombination time .r10-~sec Tv of CO' ions do not relax to the gas temperature.In the se conditions the form of the distribution function for vibrational states of ions and the magnitude of Tv are found to be es sential for the d.r.process

[q

.Assuming that the CO+ is formed in a vibrational stated due to the ionization of CO by the electrons of the beam (with the density n 2 and-that the loss-channel is associated with the d.r.,we find that the population of the state of CO' ion is given by

ff!%d+=~oh?fn/?I)<6&

VISJ(TV)$(~$,I)(~)

N+= f

= n e

Here

6 : g n

the cross section for the ioni- zation of CO,

V

the relative collieion ve- locity,

Sv

(

'E,)

the Frank-Condone factor averaged over the vibrational distribution of CO,ne the electron density in the disc- harge.The equation for the electron balan- ce in the discharge has the form:

cient of d.r. of the ion in the state

.

The t ~ t a l $ ~ . ~ . = ~ ~ ~ ~ . ~ ~ obtain a qu- alitative dependence o on the deg- ree of vibrational excitation of ',OC we use a known cross section for d.r. and as- sume that the distributdon of ions over ^-).

vibrational levels is the Bo1tl;man distri- bution with the temperature '?*.If i the cap- ture of an electron by an ion results in the formation of only one repulsive auto- ionizing etate

- .

^{e - r L 1}

antum of the ion,Te is the electron tempe- rature,A is coefficient associated with the repulsive term parameters.The quasi-

B &

steady

~ n . =L<GL~ .""& p m Yh

⁽⁴⁾

From (3) an ( 4 ) it fol on(6 that as :T in- creases the ne decreases.lhus,the typical behaviour j shown in fig.1 may be qualita- tively explained by the dependence of on the energy input to the discharge.

The above considerations have a model character,because we considered only CO+.

At p 1 atm it is necessary to take into account the conversion of simple ions by

triple collisions, e

.

^g.

^,

C O + + ~ C O - ~ ~ O ~ C O . Yet,a dependence

pd.t

on energy input will be observed in this case as well.

References

[l]~.~.~mirnov "Ions and excited atoms in a plasman ,Noscow, Atomizdat

,

( 1974). [2] 0.?&l ly 'P.F. Phys.Rev.,~,14,(1966).

[q

Yu.B.

Konev et al.,Preprint IAE lVo.2821,Moscow,

(1977).

[a]~.A.~adte in Plasma Chemist-,

~,p.3,Moscow,Atomi5dat, (1975). [S] A.V.

Eletsky. Thesea,W0~c0~,BIPTI (1 970).