• Aucun résultat trouvé

EXPERIMENTAL DETERMINATION OF THE SPATIO-TEMPORAL DISTRIBUTION OF THE SPACE CHARGE FIELD IN A BREAKDOWN

N/A
N/A
Protected

Academic year: 2021

Partager "EXPERIMENTAL DETERMINATION OF THE SPATIO-TEMPORAL DISTRIBUTION OF THE SPACE CHARGE FIELD IN A BREAKDOWN"

Copied!
3
0
0

Texte intégral

(1)

HAL Id: jpa-00219094

https://hal.archives-ouvertes.fr/jpa-00219094

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.

EXPERIMENTAL DETERMINATION OF THE SPATIO-TEMPORAL DISTRIBUTION OF THE

SPACE CHARGE FIELD IN A BREAKDOWN

P. Bayle, Maxime Bayle, E. Morales

To cite this version:

P. Bayle, Maxime Bayle, E. Morales. EXPERIMENTAL DETERMINATION OF THE SPATIO-

TEMPORAL DISTRIBUTION OF THE SPACE CHARGE FIELD IN A BREAKDOWN. Journal

de Physique Colloques, 1979, 40 (C7), pp.C7-249-C7-250. �10.1051/jphyscol:19797122�. �jpa-00219094�

(2)

JOURNAL DE PHYSIQUE CoZZoque C7, suppldment au n07, Tome 40, JuiZZet 1979, page C7- 249

EXPERIMENTAL DETERMINATION

W

THE SPATIO-TEMPORAL DISTRIBUTION OF

THE

SPACE CHARGE FIELD IN A BREAKDOWN

P. Bayle, M. Bayle, E. Morales.

Centre de Physique Atomique, Laboratoire associd au C.N.R.S. n o 277, Universitd Paul Sabatier, TouZouse.

Ionizing processes occuring during a breakdown c i s the mean decay time constant of excited s t a t e s a r e generally analysed through optical devices,

e F q [ - m,]

G P

photomultipliers o r image converters. Though l e s s i s the light excitation coefficient by electrons (4) sensitive than photomultipliers, the s t r e a k image

the drift velocity converters have the advantage of giving a conti-

P

ne(%,t)

i s the electron density distribution nuous spatio temporal representation of the dis-

charge ; this i s particularly interesting in the case n a ~ t ~ r n e e r r [ ~ ~ ( ~ . ~ ) ~ e ~ ~ . ~ ) ~ ~ l ( 1 1

cw(*,t) I p = A ecp I- a P / E 1%.

t )

I

of non r e c u r r e n t discharges. We have thus deve- As the macroscopic coefficients a r e functions of lopped a technique to interpret streak c a m e r a r e - the e l e c t r i c field, we obtain from relations (1) and cords that give us the parameters governing the (2), the electric field. 1f E

(*.&I[$*

we obtain.

$D z

3%

b, + 3 b

discharge, and in particular the space charge field.

39- - b ) zI~S(+?

f - +

It i s known that a breakdown i s essentially gover

- a t - P & t qg,+

f

(BPI * a t

ned by the field resulting from the superposition of Equation (3) shows the dependency of the electric the applied field and the space-charge field (1)(2). field on the f i r s t derivatives of the optical density

of the s t r e a k c a m e r a record. This dependency indi- It i s possible to s o r t out two kinds of informations

cates important perturbations of the field that will from the streak camera records :

appear a t the bounderies of the light and d a r k a- a ) information of geometric order that gives the di-

r e a s . mension, the position of the discharge and i t s pro-

pagation speed (3). These a r e essentially qualitati- A diagram of the s t r e a k c a m e r a r e c o r d i s given in

ve informations. fig. 1 ;analysis of the record was c a r r i e d out by

b) information about the energies related to the means of scanning microdensitometer that gives blackening density of the film. F o r a film emulsion, the m a t r i x D(x, t). The isodensity curve a r e shown the characteristic curve links the image density in fig. 1. One can s e e the propagation of a cloud of D(x, t ) to the luminous energy received. The blac- electrons between the cathode and the anode. The kening density D ( x , t) i s related to the number+ of cloud widens out and i s then followed by a second photons present at the corresponding point (x, t ) in discharge canal of lower speed. The impact of the the discharge. As a f i r s t approximation this r e l a - electrons cloud on the anode gives r i s e to a r e t u r n tion can be expressed by D(x, ~ ) = V L ~ { T + (x, tj) front in the direction of the cathode, where i t pro- where

r

i s the film contrast ratio and T i s the duces a second luminous front that goes back to- transmission function of the experimental s e t up. wards the anode.

The number of photons emitted between time t and Equation (3) i s solved with respect to time for each t

+

dt at a distance x from the cathode i s given by value of x. This give us the continuous evolution

t

of the electric field with position and time. In fig.

d#,k)i$

$ ~ , & ) & X , P ) ~

( ~ , ~ ) e ~ ~ ~ $ ! ' ] d t ]

2 we show the analysis corresponding to the line in-

o

'

dicated by a r r o w s on fig. 1. The field i s derived,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797122

(3)

which amounts to heglecting m e m o r y effects on the

CATHODE recorded picture due to the lifetime of the excited

s t a t e s . We have for example in fig. 2 the evolution E ( x ~ , t ) of the field i n time a t a given point in the gap. The optical density i n c r e a s e s in a n almost monotonous manner. The f i r s t luminous front c o r - responds to a maximum in optical density, while the two other fronts, the anode and cathode r e t u r n waves give a modification of the gradient of the op-

Fig. 1 . Microdensitogram of s t r e a k photograph tical density a s a function of time (5). of discharge in N2+CH4(2. 5 %), Each luminous front can be associated to the pro- P = 130 t o r r , E ~ / P = 118 ~ / c m . t o r r . pagation of a strong perturbation of the e l e c t r i c

fields a s one can s e e on fig. 2. T h e propagation of

I

D ( x , t ) a luminous' front indicates the propagation of an io-

nizing wave. The perturbation of the field happens in the following way : in front of the wave t h e r e

exists a strong field that corresponds to a zone of 50

high optical density gradient, this wave leaves a 0

zone of almost neutral plasma characterized by a 40

50 weak e l e c t r i c field behind. The wave after reflec-

tion on the anode reinforces the e l e c t r i c field. The 20.

a r r i v a l of the ionizing wave a t anode gives r i s e to

r y strong space charge field due to the electron

2 , , J r

an intense anodic spot. The spot i s related to a ve- 0 --.-

10 15 20 t

Ins 1

.

,

cloud just in front of the anode. The gradual absorp-

Fig. 2. E l e c t r i c field (1) and optical density (2) tion of the electrons by the anode modifies the net a t x = 33. 5 m m f r o m the cathode.

charge n e a r the electrode. Once the electrons a r e absorbed, the cloud of remaning positive ions lo- w e r s the field a t the anode, while the field towards the cathode ,become m o r e strong fig. 3. T h i s p e r t u r - bation goes towards the cathode. T h e propagation speed of the luminous front and that of the ionizing wave a r e little different, because the propagation i s , in fact governed by the ionizing wave. The stron- ger the ionization of the gas the f a s t e r i s the propa- gation. The l a s t wave can c r o s s the gap (5 c m ) in one nanosecond.

(1) Yoshida (K. ), Tagashira (H.) : J. Phys. D.

Appl. Phys. 9, 485-490 (1976).

(2) Davies (A. J. ), Evans

(c.

J.), Townsend (P. ), Wbodison (P.M. ) : P r o c . IEE, Vo1.124, n o 2.

179-182 (1977). Fig. 3. Perturbation of e l e c t r i c field a t the anode.

(3) Bayle (P. ), Bayle (M. ), Crokaert (M. ) : J. (x = distance f r o m the cathode).

Phys. D. Appl. Phys. 8,2181-2189, (1975).

(4) L e g l e r (W. ) : Zeit. Phys. 143, 173-190, (1955).

(5) Bayle (P. ), Bayle (M. ), Morales (E. ) : J.

Phys. D. Appl. Phys. T o be published.

Références

Documents relatifs

To test whether the vesicular pool of Atat1 promotes the acetyl- ation of -tubulin in MTs, we isolated subcellular fractions from newborn mouse cortices and then assessed

Néanmoins, la dualité des acides (Lewis et Bronsted) est un système dispendieux, dont le recyclage est une opération complexe et par conséquent difficilement applicable à

Cette mutation familiale du gène MME est une substitution d’une base guanine par une base adenine sur le chromosome 3q25.2, ce qui induit un remplacement d’un acide aminé cystéine

En ouvrant cette page avec Netscape composer, vous verrez que le cadre prévu pour accueillir le panoramique a une taille déterminée, choisie par les concepteurs des hyperpaysages

Chaque séance durera deux heures, mais dans la seconde, seule la première heure sera consacrée à l'expérimentation décrite ici ; durant la seconde, les élèves travailleront sur

A time-varying respiratory elastance model is developed with a negative elastic component (E demand ), to describe the driving pressure generated during a patient initiated

The aim of this study was to assess, in three experimental fields representative of the various topoclimatological zones of Luxembourg, the impact of timing of fungicide

Attention to a relation ontology [...] refocuses security discourses to better reflect and appreciate three forms of interconnection that are not sufficiently attended to