PHYSICAL PROCESSES IN ARC HOLLOW CATHODE

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Submitted on 1 Jan 1979

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PHYSICAL PROCESSES IN ARC HOLLOW CATHODE

G. Dyuzhev, E. Startsev, V. Yur’Ev

To cite this version:

G. Dyuzhev, E. Startsev, V. Yur’Ev. PHYSICAL PROCESSES IN ARC HOLLOW CATHODE.

Journal de Physique Colloques, 1979, 40 (C7), pp.C7-199-C7-200. �10.1051/jphyscol:1979798�. �jpa- 00219504�

JOURNAL DE PHYSIQUE ~ o l t o q u e ~ 7 , suppl6ment au n07, TOM 40, JuiZzet 1979, page ~ 7 - 199

PHYSICAL PROCESSES lk4 ARC HOLLOW CATHODE

G.A. Dyuzhev, E.A. Startsev and V.G. Yur'ev.

A. F. I o f f e Physical Technical I n s t i t u t e , Academy of Sciences o f t h e U . S. S . R., Leningrad, K-21, U. S. S . R.

Hollow cathodes, either single or multichannel, are considered now as high-

current extensive lifetime electron emit- ters in different discharge devices. De- spite the amount of works some physical processes inside hollow cathodes are

still poorly understood /I/. It is caused by difficulties of detailed diagnostics

of the cavity plasma in the conventional high-temperature hollow cathodes /2/.

In this communication on the grounds of detailed diagnostics of the plasma in the "active zone" is carried out the in- vestigation of ionization, current con- duction, energy balance of the cavity plasma i n dependence of external condi-

tions. The experimental studies described in present paper involve highly ionized cavity plasma HC operated at arc currents from I0 to I00 A and cesium or argon pres- sures from I to I0 Torr.

The assembly used is presented in Fig.1. To maintain constant cathode tem- perature which is determined by auxiliary heater, the discharge is supplied by sta- bilized rectangular pulse of I msec dura-

tion and 12.5 Hz repetition rate. The measurements are performed on the end of

supply pulse, when relaxation processes are terminated ,by systems of gating inte- gration (strob duration -1 usec).

Adsorbtion of cesium on the cathode /

surface dimhishes its work function to as low values as j,- 1.3

-

1.4 eV and allows to obtain high thermoionic current dehsities

& -

^{'-10 1o2~/cn2 at low}

emitter temperatures (

Ltk -

10'~6)/3/.

The diagnostics of the cavity plasma is made by the probe moving axially in the KC. The evaluation of the probe data

'is carried out by diffusion theory assum- ing charge-particle generation in the probe sheath /4/. Outside the HC the probe data are compared with optical ones.

Fig.1 shows plasma potential distri- bution V, (in respect to the cathode), 'electron temperature (probe charac-

teristics point that Maxwellian distribu- tion function exist) and plasma density profiles at different points of current- voltage characteristics.

Analysis of obtained distributions show that the current conduction is de- termined mainly by field component of electron current

js - ^{~ ( q )}

^{f (where}

G ( % )

- ^-

is fully ionized plasma conductivity and is field strength).

In Fig.2 the values of total current

I .

~ & ( Z ) J R ~ passed though z-cross-sec- tion of HC and ionic current

h f

-

I ~ =

( j i . = a 4 3 g n G

R

ionic c&r"ent density) are presented. The good agreement of I ~ ( @ ) with the dis- charge current

I

indicates the radial uniformity of the cavity plasma.

The linear dependence of

1,

(2) and

I;(!&)

upon z is explained by the emission current constancy in the "active zone" of HC.

Some parameters that characterize the HC operation at different values of the

current

1

are given in the Table.

Plasma penetration depth

L ,

^ionic

current portion = Ii(o)/I emission current density

&

are presented.

The ratio of power, carried out by elec- tron current from .the cavity plasma, to total power and the rabio. of ,power, car- ried out by ionic current, to total po- wer are presented also.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979798

The evolutions show that radiation losses are the most significant ones bet- ween the other losses.

Physical processes which occur in the HC with highly ionized plasma are well described by the equations presented in /51. Received results show that the HC operated at constant current without auxi- liary heating is hzated mainly by ionic current

%* =

2rR/[Ei, ^{-Jc +} 9 Y,(w] jir(a)ds

-a and cooled by electron emission _MU,,

= 2 r R ~ & ,

( 2 x 5 + J c )

and by the heat conduction to the cathode holder. At low current values, when

w;-YI,,

the ionic current heating is ba- lanced by the electron emission cooling.

At higher currents Wia > WU, that can create the important temperature gradi- ents on the HC. The current limitation occurred at lower cesium pressures 161 is caused by the achievement of the current density which is comparable with random electron current density ₌

tpn

at exit of the HC.

/I/.

J.L.Delcroix, A.R.Trindade. Adv. in Electr. and Electr. Phys.

3,

^88,

1974. ^2,cm

/2/. A.Brunet. Proc. XI1 Int. Conf. on Fip.

2

Phen. in Ion. Gases, p.231, Eindho- Ten, Holland, 1975.

/3/. G.A.Dyuzhev, E.A.Startsev, S.M.Shko1- nik, V.G.Yuraev. J. fechn. Phys. 48, 21x3, 1978.

/4/. F

.

^G.Bakst

^,

^G. A.Dyuzhev, N .K .iviitrof a- nov, S.M.Slik;olnik, V.G.Yur8ev.

.J. 'Pechn. Phys.

&

2574,

1973.

/5/. F.G.Bakst, A.B.Rybakov. Proc. XI11

In%. Conf. on Phen. in Ion. Gases.

p.527, Berlin, G.D.B. 1977.

/ 6 / . G.A.Dyuzhev, E.A.Startsev, S.M.Shko1- nik. J. Techn. Phys. 48,

2495,

1978.