PROCESSES OF IMPULSE BREAKDOWN IN N2-O2 GAS MIXTURES AND IN AIR AT LOW PRESSURE

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PROCESSES OF IMPULSE BREAKDOWN IN N2-O2 GAS MIXTURES AND IN AIR AT LOW PRESSURE

M. Akazaki, K. Nishijima, M. Hara

To cite this version:

M. Akazaki, K. Nishijima, M. Hara. PROCESSES OF IMPULSE BREAKDOWN IN N2-O2 GAS

MIXTURES AND IN AIR AT LOW PRESSURE. Journal de Physique Colloques, 1979, 40 (C7),

pp.C7-145-C7-146. �10.1051/jphyscol:1979771�. �jpa-00219477�

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JOURNAL DE PHYSIQUE CoZZoque C?, suppZ6ment au n07, Tome 40, JuiZZet 1979, wgeC7-

145

PROCESSES OF IMPULSE BREAKDOWN IN N2-O2 GAS MIXTURES

AND

IN AIR AT LOW PRESSURE

M. Akazaki, K. Nishijima and

M.

Hara.

FacuZty of Engineering, Kyushu University, Fukuoka, Japan.

.INTRODUCTION: The impulse breakdown processes were observed f o r N2- O2 gas mixtures and f o r dry a i r a t low pressure by an image converter camera. The re- s u l t s of time-resolved photographs a r e presented and t h e influence of t h e electro-negative gas O2 on t h e breakdown process i s discussed.

EXPERIMENTAL COKDITIONS: The t e s t e d e l e c t r o d e ar- r a n g e n t was a needle point ( l m m

4

tungsten rod with he- mi-spherical cap) t o plane(l6cm b r a s s ) gap 8 cm 'long

+

and was i n s t a l l e d i n a Pyrex g l a s s c y l i n d e r of 18cm diameter and 45 cm i n l e n g t h . A p o s i t i v e impulse voltage, 1 . 6 ~ 1 5 0 ps, with breakdown p r o b a b i l i t y between 20% and 80% was applied t o t h e p o i n t . The gas p r e s s u r e reduced t o 20°C was kept a t 1 5 t o r r . The gases used i n t h e gas mixtures i n d i c a t e d by t h e o x y - gen content Po% were 99.995% pure f o r both N2and 0 _2' Dry a i r was a l s o used f o r comparing t h e r e s u l t s with t h o s e obtained i n t h e gas mixtures.

RESULTS AND DISCUSSION: A) Breakdown Process The breakdown process can be divided i n t o two t y p e s e a c h w i t h t h r e e phases ofdischarge. A s t h e i n i t i a l p h a s e of t h e process, t h e f i r s t corona s t r e a m e r ( ~ ~ ~ ) , t h e i o n - i z i n g wave( I W )

,

secondary mid-gap streamers (cathode d i r e c t e d streamer(CD~) and anode d i r e c t e d streamer (ADS)) and t h e d i f f u s e d luminous w a v e ( ~ ~ W ) occure i n a sequence and i s independent of t h e oxygen content.

After t h e DLW reaches t h e anode glow(AG) i n f r o n t of t h e anode, t h e intermediate phase of t h e process

s t a r t s . I n t h i s phase, a p o s i t i v e column forms and

filamentary p o s i t i v e column(FPC). However , t h i s phase of discharge can be divided i n t o two d i s t i n c t types of t h e t r a n s i e n t glow, a s shown i n F i g . l ( a ) . I n t h e

f i r s t type, f o r t h e range between Po= 0% and 91, no cathode streamers ( C S ) / l / appear. The second type

i s a s follows; f o r t h e range between Po= 10% and

loo%,

a s e r i e s of t h e CS advancing f r o m t h e negative g l ~ ~t o t h e DPC appear. Furthermore, t h e b r e a k - ( ~ ~ ) down process f o r P =21% shown i n F i g . l ( a ) becomes very s i m i l a r t o t h e one i n a i r a s shown i n F i g . l ( b ) , and t h e mean frequencg(fs ) of t h e CS i n c r e a s e s from about 20Mz t o 300kHz with t h e oxygen content i n t h e range 10-loo%, a s shown i n Fig.2, As t h e f i n a l phase of t h e process, t h e DPC reaches t h e NG , t h e discharge current increases r a p i d l y and t h e t r a n s i e n t glow changes i n t o t h e t r a n s i e n t a r c without a Faraday dark space (FDS). I n s h o r t , two types of t h e breakdown process i n t h e N 2

-

^O2 gas mixtures may be il- l u s t r a t e d schematically a s shown i n Fig.3.

E ) Negative Glow and Transient P o s i t i v e Column Fig.

4 ( a ) and ( b ) show t h e current d e n s i t y ,JN, i n t h e NG and ,Jp, i n t h e p o s i t i v e column obtained a s a r a t i o of t h e discharge c u r r e n t , I , t o t h e luminous c r o s s s e c t i o n which was measuredin t h e framing photograph.

I-J c h a r a c t e r i s t i c s a n d t h e v a l u e s o f J a r e approxi-

N N

mately t h e same a s t h o s e of dc glow discharge. On t h e o t h e r hand, t h e current d e n s i t y of t h e DPC i n

t h e range 0.05-2 A/cm2 and t h e FPC i n t h e range 2-30

~ / c m 2 i s t h e same a s t h a t of t h e p o s i t i v e column i n develops from anode t o cathode with t h e growth of dc glow discharge and t h e a r c column i n dc a r c , r e - discharge c u r r e n t . The t r a n s i e n t p o s i t i v e column s p e c t i v e l y / 2 / . According t o a spectroscopic study, c o n s i s t s of a d i f f i s e d p o s i t i v e cblumn(DPC) and a 1 s t and 2nd p o s i t i v e bandsystemsof N a r e s t r o n g i n

2

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979771

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0

**1 * 2 0**

( a ) The breakdown p r o c e s s f o r Po= 0-9

%

( T Y P ~ 1 )

FCS:

CDsJ ( b ) The break-

'

I

--

t i m e ( p s )

40 60

I 1

down process f o r Po= 10-100 % ,

( c ) Framing pic- t u r e of t h e f i g -

u r e ( b )

v

-&-w

& @

F i g . 3 Conceptual f i g u r e s o f t h e breakdown p r o c e s s e s i n N2- O2 g a s m i x t u r e s

!a I-

band of N

+

becomes recognizable only i n t h e s p e c t r a 2

of t h e FPC and t h e Arc, i n Fig.5. These r e s u l t s a r e ( a ) N2

-

02 g a s m i x t u r e s

10

-

( b ) A i r 0.15

4

F i g . 1 S t r e a k photo-

- '

0 . 1 ~

graphs of t h e break- N "'O

,-

down process i n N2

3 -

^O2 gas mixtures

;;;

and dry a i r . w 3.0

-

H : 20 PS V] d.2 d.4 d E d.8

20

U

I

⁽ ^A ⁾

I

⁽ ^A ⁾

'+I o ( a ) Negative glow ( b ) P o s i t f e column a t t h e di-

& 2.0

-

s t a n c e 1 cm from anode

2'

F i g . 4 Discharge c u r r e n t v e r s u s c u r r e n t d e n s i t y i n t h e n e g a t i v e glow and t h e p o s i t i v e column

C

Fig. 2 Mean frequen- '+I

( a ) N 2 1st p o s . band

-

⁰

cy f s of cathode

( 9-6 ) streamer versus ox-

ygen content

oxygen c o n t e n t P, ( $ 1

+

( c ) N2 1 s t neg. band $0 t h e s p e c t r a of t h e DPC and t h e CS and 1st negative ( 0-0 )

s i m i l a r t o t h o s e i n glow and a r c discharge131 re-

d

^:O ⁴⁰

80 do 100

time

(PSI

s p e c t i v e l y .

+

F i g . 5 R e l a t i v e i n t e n s i t y o f N2 and N2 band s p e c t r a CONCLUSION: ( 1 ) Discharge process i n t h e N 2 -0 2 gas f o r v a r i o u s d i s c h a r g e p h a s e s a t Po=21 %

mixtures a t low p r e s s u r e changes s i g n i f i c a n t l y with /1/ T. Oshige: J. Appl. Phys.,

38,

2528 (1967) /2/ A. von Engel: "Ionized Gases", (2nd ~ d i t i o n ) t h e oxygen content. ( 2 ) The s t a t e s i n t h e DPC and

Clarendon P r e s s (1965)

FPC a r e t h e same a s t h o s e i n glow and a r c discharge, / 3 / K.R. Allen and K. P h i l l i p s : Proc. Phys. Soc.,

r e s p e c t i v e l y . London,

my

168 (1964)