RADIATION TEMPERATURE MEASUREMENT OF ARGON ARC PLASMA BY SUBMILLIMETER DIAGNOSTIC TECHNIQUES

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RADIATION TEMPERATURE MEASUREMENT OF ARGON ARC PLASMA BY SUBMILLIMETER

DIAGNOSTIC TECHNIQUES

E. Tishchenko, A. Golubev, V. Lazarev

To cite this version:

E. Tishchenko, A. Golubev, V. Lazarev. RADIATION TEMPERATURE MEASUREMENT OF ARGON ARC PLASMA BY SUBMILLIMETER DIAGNOSTIC TECHNIQUES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-859-C7-860. �10.1051/jphyscol:19797415�. �jpa-00219416�

JOURNAL DE PHYSIQUE CoZZoque C7, supple'rnent a u n07, Tome 40, J u i Z Z e t 1979, page C7- 859

RADIATION TEMPERATURE MEASUREMENT OF ARGON ARC PLASMA BY SUBMILLIMETER DIAGNOSTIC TElJiNIQUES

E.A. Tishchenko, A.V. Golubev and V.B. Lazarev.

I n s t i t u t e f o r PhysicaZ ProbZems, Moscow U.S.S.R.

Abstract : Methods of radiation temperatu- re measurement of the plasma filament by active and passive submillimeter diagnostic are described-The profiles of the side-on brightness of plasma thermal emission are measured at two wavelengths, one of them be-

ing selfabsorbed. These data are used to determine the radiation temperature and op- tical depth of plasma

El 3 .

Simultaneous probing of the plasma filament by submilli- meter radiation at two wavelengths allows

to check this method and find out the degree of plasma equilibrium as well as the nature of electron collisions.

Emerfment : Diagnostic installation con- sists of D.C. arc, heterodyne H20-laser ( 2 -1 1 y p m ) l2] interferometer, homodyne backwave tube (BWT, ;\ =350pm) interfero- meter, high sensitive two-channel radio- meter and measuring apparatus.

Fig.1 Arc configuration Pig.1 shows the cross-section of D.C. arc chamber (1 ) (1 0x1 0x1 0 cm3). Its diagnostio windows (2) were made of crystalline quartz.

The a m electrodes.(50 mm apart) were cooled by water and have molibden tips (4). To fa- cilitate the local side-on diagnostic of plasma by narrow submillimeter beams formed by the lenaes

(7)

3 the plasma filament is moved with a frequency aboui; several Hz by

oscillating magnetic field H of the coils ( 6 ) .

Fig.2 Diagnostic set-up : P,-P6

-

^one-di-

mentional grids (period 20pm), I -M

-

1 4 metal mirrbrs, L2-L4

-

polyethylenelenses

(diameter-54 mm, focal length-140 mm).

Optical system of the experimental in- stallation (Fig.2) is a twin-wave Each- Zehnder interferometer. H20-laser radiation consists of two ortogonally polarized wa- ves with a frequency shift 18 kHz, orien-

tated at the angles of -45O and +45O to the vertical. It is directed into the in- terferometer by means of mirror I,. BWT- radiation is formed in the quasioptical beam by the lens L1. Horizontal polariza- tion-, provided by polarizer P5, is di- rected into the interferometer by the mir- rors M1 and M2 and grid GI. The frequency of BWT radiation is modulated by saw-tooth law w&th a ffequenoy of 27 kHz;. At the output of the interferometer there are vertically orientated polarizer ' P3 and two-channel detector Dl with photocon- ductors n-GaAa and Ge:B at 4.2 K. The transmittivity signal-$(P) (

2

~ 3 5 0 p m ) is detected by n-GaAs at 27-kHz. Laser signal (

3

=119pm) is detected by Ge:B at 18 kHe and emplsyed to measure phase

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797415

shift

y(9)

by fast "phase-voltageq1 conver- ter 131

.

D3 signal is used as the refe- rence one. 'Phe distribution of plasma emis- sion is measured by two-channel radiometer D2 at tO8pm (GerB) and 285pm (n-Galls).

Functions

Y

( )

,

^{( )} and spectral brigh- tneases

IZgC P ^~j

anc?lOB(P)are registered by the two-beam oscilloscopes OSC, and OSC2.

The impact parameter

9

is measured by the scanner system [ 4 )

.

Results : Typical experimental curves are shown in Fig.3aYb. Data processing is per- formed under assumption that plasma tempe- rritnre gradients are negligible, In this case one obtains from radiation transfere equation the expression for J ( ~ , O ) :

r

⁽

^%

⁰⁾

^{= B ( 4 x2j[+} -

M ; ~ ~ - T ( U , O ) ~ ~ (I]

where

B (g%%s

blackbody spec tnun,T(J, 5 )

is plasma optical depth at

9

=O, %'is the mean radiation electron temperature and 3 is wave number. .If

Id

^and

r2

^{are the}

surface brightnesses at two frequencies and

Q2 ,

then using eqn.fl) one can calculate the plasma optical depth at the frequency

'%

^{from eqn. :}

where

# =($p

⁽

8

-0.144 for n-GaAs and Ge:B detectors). Radiation temperature a.

(in K) is given by the formula :

(3) where

4

is brightness inpwt/cm?cm-l.

steradn,

2

is the root of eqn. (2). Plasma optical depth 'T is measured independen- tly using modulus of the complex transmit- tivity

9

( 0 ) at the frequency $ r28.6 em-'

(

2

=350pm) x 9 ( o ) = v [ - ~ ( ~ 0 ) / 2 ] Fig.3~ shows the optical depth of the AT arc dis~hargta~. for regimes of constant current 1%. 2 A.

In the pressure range of 1-2.25 atm the mean radiation temperature %'within experimental errors is independent on the gas pressure P and is equal to (7.8%.5)*

to3

K. On the other hand, phase -measure- ments show that electron density is p m - portional to p1l2

,

as it must be at the equilibrium. In this ~ a a e linearity of the functionT(P) gives an evidence that

electron-ion collisions dominate other collision processes. The equilibrium tem- perature

%?

at 2 =O calculated by Saha equation, is equal to 9.2-10 3 K, i.e.

it is 10-2C% higher than

z2 .

Fig.3 Characteristics of Ar arc (dis- charge current equaled to 18.2 A) Phase

Y('j(2

=119pm) and modulusg(P)

' ( 2 =350pm) of the transmittivity.

b) Plasma spectral surface brightness

-

(top curve :

2

-285 my Y-scale

-

^0,54

pt/cm2* st eradn-cm-i(k div* loner curve :

2

-1 08pm, Y-scale

-

¹ jnwt/cm2. st eradn*

cm". div)

c ) Optical depth 7 at L) =35 cmel

( 2

-

285pm1, clear ciroles

-

selfabsorption measurements, dark circles

-

^active

diagnostic at 2 = 3 5 0 ~ u m (data conver- ted to

2

~285pm).

References :

[I E,A.Tishchenko, L.A.Vainstein, Fie.

Plaamg, N1, 124 (1977)

[2] V.V.Zavl yalov, G.D.Bogomolov, Pist ma v ZETF,.B, 6, 393 (1974)

[3 V.B.Laaarev, Prib.Tech.Exper, 2, 85, (1976)

143 -

K.A.Zdanov et al., Prib.Tech.Exper, (1 9791, to be published