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Submitted on 1 Jan 1979
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TEMPORAL INCREASE OF IONIZATION CURRENT IN N2 GAS
Haruo Itoh, Nobuaki Ikuta
To cite this version:
Haruo Itoh, Nobuaki Ikuta. TEMPORAL INCREASE OF IONIZATION CURRENT IN N2 GAS.
Journal de Physique Colloques, 1979, 40 (C7), pp.C7-445-C7-446. �10.1051/jphyscol:19797216�. �jpa-
00219197�
JOURNAL DE PHYSIQUE Colloque C7, s u p p l h e n t au n07, Tome 40, J u i l l e t 1979, page C7- 445
TEMPORAL INCREASE OF IONIZATION CURRENT IN Np GAS
Haruo Itoh and Nobuaki Ikuta.
Chiba I n s t i t u t e o f Technology, Tokushim University.
I n t r o d u c t i o n
A c o n s i s t e n t i n c r e a s e of rm component of i o n i z a t i o n s t a b l e molecules!)2) The wave shapes of c u r r e n t a t c u r r e n t i n N2 f o r s e v e r a l t e n minuteswasobserved. UV o f f a r e a s Fig.1. I n s t a n t a n i o u s decrease Ip i s The a f t e r e f f e c t of i o n i z a t i o n c u r r e n t flow i n t h e M u l t i p l i e d c u r r e n t o f Photo-emitted e l e c t r o n s by UV.
gas doesn't disappear f o r a long time more than Almost exponential p a r t shows t h e Im component by s e v e r a l hours. The c u r r e n t i n c r e a s i n g r a t e depends metastable molecules. The time constant o f which on t h e e l e c t r i c f i e l d i n t e n s i t y , i n j e c t i n g e l e c t r i c doesn't t a k e a f i x e d v a l u e corresponding t o gas pre- power i n t o t h e gap space, t h e product of p r e s s u r e s s u r e and e l e c t r o d e s e p a r a t i o n but v a r i e s depending and gap length pod and t h e wall-gas temperatures. on t h e degree of e l e c t r o n m u l t i p l i c a t , i o n and i t ' s
In our measurement, N p gas i s q u i t e v i v i d and has c a r e e r i n t h e gas. The amount of rm component Im is a long l i f e of a c t i v i t y . The phenomena o f c u r r e n t a good measure of r e g e n e r a t i o n c h a r a ~ t e r i s ~ i c s . The i n c r e a s e a r e considered t o be caused by t h e long i n c r e a s e o f c u r r e n t i s almost due t o t h e i n c r e a s e o f l i v e d e x c i t e d molecules t h a t a c t s d i r e c t l y and i n d i - 1, component.
r e c t l y f o r t h e secondary e l e c t r o n emission from t h e S e l f - s u s t a i n i n g o f c u r r e n t : When t h e i n c r e a s i n g cathode. Current i n c r e a s e was a l s o o b s e r v e d i n o t h e r c u r r e n t comes near s e l f - s u s t a i n i n g condition, ano- gases such a s Hz and A r . t h e r r e s i d u a l component of very long decay time ap-
Experimentals p e a r s a f t e r im fades o u t . The decay is r a t h e r l i n e a r
For t h e measurement of c u r r e n t , a couple of gold and t h e r a t e is dependent on t h e i o n i z a t i o n , a c t i - p l a t e d e l e c t r o d e s of 10 cm i n diameter, an a r t i f i - v a t i o n and t h e i r c a r e e r i n t h e gas. S e l f - s u s t a i n i n g c i a 1 wall o f 16 cm i n diameter and 12 cm i n h i g h t o f i o n i z a t i o n c u r r e n t can occur only by t h i s long were s e t i n a s t a i n l e s s s t e e l tank o f 30 cm i n d i a - decay component I s t h a t grows following t h e b u i l d up meter and 50 cm i n length. For t h e i n i t i a l e l e c t r o n of I,. The decay time T s gradually becomes longer,
emission, a hydrogen discharge lamp was used with and f i n a l l y , s e l f - s u s t a i n i n g s t a t e i s achieved with a q u a l t z window. A high vacuum system and h i g h g r a d e i n f i n i t e 7s. A f t e r reaching t o s e l f - s u s t a i n i n g s t a t e , N p gas o f f i v e n i n e were used t o prevent erronious t h e c u r r e n t i n c r e a s e s f u r t h e r and tends t o s a t u r a t e
r e s u l t s . above ~ x ~ o - ~ A a s Fig.2.
R e s u l t s E f f e c t o f wall and gas temperature: When an a r t i -
Measurement of t r a n s i e n t c u r r e n t : Transient c u r r e n t ficial is Put surrounding the elctrOdes, cur- a t t h e "on" o r "pff" of W i r r a d i a t i o n c l a r i f i e s t h e r e n t i n c r e a s e s i n suppressed mode a s shown i n Fig.3, behavior o f secondary e l e c t r o n emission by meta-
J U V o f f
im (time c o n s t a n t : 7, )
time t (ms)
time t ( s )
Fig.1 Trangent wave forms of c u r r e n t a f t e r W o f f .
0 10 20 30
time (min)
F i g . 2 Wall temperature dependence of
i o n i z a t i o n c u r r e n t i n c r e a s e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797216
and reaches to the self-sustaining state only at as calculated by ~olnart) Many researchers has given higher level of current. This may be caused by the the lifetimes and collisional deactivation rate con- efficient deactivation of metastable molecules at stant for this state of ~ ~ 3 ) ~ ) ~ s i n ~ these data and wall surface. Depending on the wall temperature, supposing proper deactivation rate at the electrode current increasing behavior varies as Fig.2, which surface, reasonable analysis can be obtained for the shows that the deactivation of metastable molecules trangent characteristics having various time constants.
is strongly suffered from wall temperature, though The long after-effectofactivatedN2gasis considered convection flow of gas also aid the loss of meta- to be based on the vibrationally excited molecules, stables from discharge region. If wall temperature the radiative lifetime of which is almost infinite.
is changed periodically, increasing current also That is, the collisional deactivation rate depends varies in the same phase of wall temperature as on the population of vibrationally excitedmolecules shown in Fig.4. Even in the case that wall and gas through mutual energy transfer5)J.n low gas density temperatures are the same, current increases faster as this case, diffusion may be dominant lossprocess, in higher temperature condition. where the deactivation at wall surface can give a
Difference of voltage-current characteristics: considerable influence on the population. Consequ- As the results of ionizing current flow in N2 gas ently, temporal increase of current depends on the for long hours, voltage-current characteristics population distribution of excited species within changes seriously as Fig.5. The change in characte- the tank, and is suffered from circumstances. Is ristics appears consistently with a long lifetime component can be understood as the regeneration depending on the surrounding conditions. behavior of metastable species based on the vibra-
Discussion tionally excited population in N2, but it is imposi-
The most importantevidence in these experimentsis ble for Ar. Further experimental research is needed that the career of ionization and activation of the to confirm these mechanisms with refering the colli- gas can't be extinguished for several or several ten sion data.
hours. Once ionizing current increases for a long References
time in N2 gas, even after a pause of voltage appli- 1) J.P.Molnar: Phy~.Rev.,E,933,('51),ibid,940,('51):
cation for some duration, almost instant recoveryof 2) S.C.Haydon and 0.M.Williams: J.Phys.D,?,523,('76) ionization current to the same level as before is 3) N.P.Carletonand O.Oldenberg:J.Chem.Phys.,~,3460 achieved. Contrary to it, if the gas is exchanged, 4) E.C.Zipf: Can.J.Chem.,z,1863,('69) ('62) the current starts from the initial low level. This 5) G.N.Hays and H.J.Oskam: J.Chem.Phys.,E,1507,('73) fact shows that the activated gas has somedifferent J.F. Noxon: J.Chem. Phys. ,=, 926, ('62)
internal conditions from virgin gas. P.H.Vidaud and A.von Engel: Proc. Roy.Soc.Lond., The dominant metastable species that give 1 , Compo- lo5 - A.313,531, ('69)
N 2 -
nent of time constant within several ten [ms] are
p o = 0 . 5 Torr considered to be ,431; state of N2
Np, 0.5 Torr d = 1.1 cm
1c6 - E/po = 600 V/cmTorr
h V
4
1,j7 - without wall
C,
