EFFECT OF GAS PURITY ON THE CURRENT OF A NON-SELF SUSTAINED DISCHARGE IN NITROGEN

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EFFECT OF GAS PURITY ON THE CURRENT OF A NON-SELF SUSTAINED DISCHARGE IN

NITROGEN

G. Lopantseva, A. Pal, A. Perevoznov, I. Persiantsev, A. Starostin

To cite this version:

G. Lopantseva, A. Pal, A. Perevoznov, I. Persiantsev, A. Starostin. EFFECT OF GAS PURITY

ON THE CURRENT OF A NON-SELF SUSTAINED DISCHARGE IN NITROGEN. Journal de

Physique Colloques, 1979, 40 (C7), pp.C7-499-C7-500. �10.1051/jphyscol:19797242�. �jpa-00219226�

JOURNAL DE PHYSIQUE ColZoque C7, supptdment au n07, Tome 40, J u i l l e t 1979, page C7- 499

EFFECT OF GAS PURITY ON THE CURRENT

A NON-SELF SUSTAINED DISCHARGE D l NITROGEN

G.B. Lopantseva, A.F. pal: A.F. Perevoznov, I.G. Persiantsev and A.N. Starostin.

I n s t i t u t e of Nuclear Physics, Moscow State UniversiQ, ¹¹ 7234, Moscow, U . S. S. R.

Commercial nitrogen contafns about 0,01 the concentrations of all positive ions

$ of oxygen, whereas nitrogen of special in the discharge, B i are the corresponding purity (s.p.), only 0.001 %. ~t turns out coefficients of recombination of the i-th that even so small admixtures may essenti- ion with electrons of the discharge ZPd= ^L

ally alter the energy characteristics of ⁼ pel _,[?el is the discharge-electron den- the discharge. This effect is considered sity. In our case

for a non-self -sustained discharge indu- / P ' = by ^{t [ U Z ]} fi/[ffP]),(h - - [

^{02 -} ]&/~PI&)

ced by an electron beam. At gas pressures 1% is seen that, if 0 K % n K ~ . J ~ ~ ~ ~ ~

1 2 1 5 [el of 1 atm,positively charged nitrogen ions

i?;, N+( 1,2) are effectively converted in

triple collisions[l] to ione H+ 4' I+, 3 reapec- tively (3). Here and in follows,the number in par&heses indicates a re~ction corres- ponding to that number in the table. The density of N; and ' N in a discharge is 10 6 cm-3 and the N; ion, which recombines with the electrons produced in the disc- harge ( 4 ) , is the principal ion.

On the other hand, when the above 8mo- unt of oxygen is present, the 8; ions may

is determined by the dissociative recom- bination of $:ions with the electrons.At

N ^{'5'bJ ' 6} +efim&(l+[&] K~/[Q] K ~ )

i .e . ^, thehigher the oxygen content in the gas employed, the closer the recombination coefficient to that on the O2 molecule.

However, as the concentration of O2 exce- eds 0,1%, the conversion (8) of : 0 to the more complex ions [ I ] as well as electron attachment in the presence of a third par- ticle (9), becomes of greater importance.

The effect just mentioned have been obser- disappear due to charge-exchsnge ( 5) [121, ved( en an installation described in [3].

Estimates show that at density _[02] * 2 , 4p , 608 , ffcspe o ^{I C ,} tne O; Ion oecomes

at a ¹ - ^{N2 S.P.}

rate of electron production in the disch- 3 - ^{N2 + 0,5% O2}

arge 10' 7cm-3sec-' tne principal positxve

ion and the electron balance In the disc- fw-

Pig.?

barge rill be determined by dissociative I

racombinatlon on the ions of Q2 (6) [l]ra- pig01 shows the oscillograms of the disc- ther than M2. The effective electron-reco h a w e current in nitrogen of various puri- mbin t on coefficient is given b y a effz tY at a be- current of 250 mcll/cm2 and

s-&/n>~/'l'il,where 7 ^is the sum of ^a p ~ p i n g rate 100 m/sec. The higheat

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797242

C7- 500

discharge current is observed in commerci- al nitrogen, the lowest in nitrogen of spe cia1 purity to which 0,5% of oxygen was added.

It should be noted that, if before the field is applied the gas is subject to electron-beam radiolysis, then in the dis- charge gap there will accumulate atomic nitrogen whose amount is proportional to the time of electron beam operation, When the field is applied, the 0 ; ions that ap- pear in the discharge will partly exchange ch'arges with nitrogen atoms, thus leading to the formation of the positive ion NO+

(7) [ 4 ] . Since the constant for the recom-

bination rate for the NO+ ion (10) is abo- ut an order of magnitude lower than that of oxygen, the N O ' ion may affect the elec tron balance, thereby increasing!

Similarly, the gas is subject to the e- beam radiolysis when the voltage is swit- ched on at instances close to those at which the beam current is maximum'Tf the e-beam operation time'&yV (L/v being cha racteristic time of passage of the gas th- rough the discharge gap of length L).In commercial N2 the current will be lower than in 8.p. nitrogen, because the relati- ve number of NO+ ions in the former will

be higher. This is confirmed by the expe- rimental results presented in fig.2.Here the rate of gas flow through the discharge gap is 1-2 m/sec, L=l cm, G & 6.10'~sec.

En - ^{1 0-16v cm2 ,jje} 250 rnc~/cm~.one should mention that at low flow rates there occu- rs an effective occupation of the vibrati- onal levels of the N2 molecule. In this case, the NO+ ions may form also in the

reaction (1 1) 141 .

D , 200 , 497 , ^nrsPr

1 - ^{N2 S.P.}

2 - ^{It2 c.p.}

3 - ^{N2 + 0,5%02}

MA ^{Fig. 2}

NO Reaction Rate constant

@ +

1 N2--R2 + ^{e 1} ~ ~ ~ c m ~ s e c - ~ 2 B2-N es + ^{N 10 -8 cm 3 sec"}

-8 3 2a + H % { N + N + e 10 cm sec- 1 3 ^a2+ ZX~+M; + a2 8.10-~9cm~sec-~

4 N4+e-2N2 + 8 . 1 ~ ' ~ c m ~ s e c - ~ 5 a; + o,--0; +2% 4 . 1 0 - ~ ~ c m ~ s e c - ~ 6 02+ +e--20 2.10 -8 cm 3 sec-I

? P+O:--NO'+ 0 1,8.10-'0cm3sec-'

-7 3

10 NO'+^-N+O 1,5.10 cmsec"

11 % ^{+ 0;--NO++} NO 5.10-'~ t g 9 ) ( J

X3 is the relative population of the vib-

rationallevels of the molecule 5 , jv -

the ratio of the rate constant for the level 3 to that for the Level 3 = 0.

References [

I ] B.1.Smirnov "Ions and excited atoms in plasman Atomizdat, Moscow (1974)

[2] T.L.McCrumb, P.Warneck. J. Chem, Phys.,

"A theoretical investigation of infrared

radiation in the upper atmosphere,aerono- mica1 processes and radiatdon mechanisms"

Preprint PIAN 140.84, Moscow (1976).