MEASUREMENT OF ELECTRON DENSITY BY ELECTROMAGNETIC WAVES WHICH PROPAGATE ON A MAGNETIZED PLASMA COLUMN

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MEASUREMENT OF ELECTRON DENSITY BY ELECTROMAGNETIC WAVES WHICH

PROPAGATE ON A MAGNETIZED PLASMA COLUMN

D. Šulik

To cite this version:

D. Šulik. MEASUREMENT OF ELECTRON DENSITY BY ELECTROMAGNETIC WAVES

WHICH PROPAGATE ON A MAGNETIZED PLASMA COLUMN. Journal de Physique Colloques,

1979, 40 (C7), pp.C7-823-C7-824. �10.1051/jphyscol:19797397�. �jpa-00219396�

JOURNAL DE PHYSIQUE Colloque C7, supplement au n°7 , Tome 40, Juillet 1979, page C7- 823

MEASUREMENT OF ELECTRON DENSITY BY ELECTROMAGNETIC WAVES WHICH PROPAGATE ON A MAGNETIZED PLASMA COLUMN

D.M. Sulic.

Geomagnetic Institute - Grooka, Yugoslavia.

INTRODUCTION THEORY AND INTERPRETATION

The determination o f e l e c t r o n d e n s i t i e s i n . . The d i s p e r s i o n r e l a t i o n o f a x i a l l y symmetric

plasmas from surface wave propagation data has . . .

K electromagnetic waves on an a x i a l l y magnetized

been performed by H i d / 1 / . I n t h i s paper we de- .

r J plasma column o f radins a enclosed i n a glass tube s c r i b e an extension o f t h i s technique t o a x i a l l y * * j - k , j - » » « j - j k *

o f outer radius b and surrounded by f r e e space i s magnetized plasma columns. d e H v e d f r o m a p p" ;o x i m a t i o n a n d b o u n d a r y c o n d i t i o n s

EXPERIMENTS a n d r e a d s

A x i a l l y symmetric waves have been launched .—

and propagated on the long p o s i t i v e column o f a i - ^ - j ^ a k W - g ) M a i Q - g f f i l j ^ S *Sr f e ( b k i s e a l e d - o f f mercury vapour diode. The tube i s cen- - ^ " f l . " W ^ r ^ ^ K o l a k ) J o t b k ,E rt v O t e r e d i n a magnetic bench producing a n e a r l y ho- " M ^ y S l ) S r - 1 [Ko(bk) Kt(bk) mogeneous a x i a l magnetic f i e l d ( F i g . 1 ) .

, I The plasma i s assumed t o be c o l d , l o s s l e s s and

I

1—I homogeneous. The n o t a t i o n i s as follows:iOn=c--iJr

I ?B °

1 and o = -jfn are e l e c t r o n plasma and c y c l o t r o n 1 jfj* = " " l f r e q u e n c i e s , £ x = 1 - J £ ^ j £» = 1 - ^ | - a r e r e s p e c t i -

— " ) " • ) v e 1 y t n e n o r m a l a n c l p a r a l l e l components o f the

* - ^ T j V j n f ' 1 i d i e l e k t r i c t'ensar, a n d £ r = 4 , 8 i s the d i e l e k t r i c 1/NI 1/x) p e r m i t t i v i t y o f the tube g l a s s . The n o t a t i o n f o r

I the various Bessel f u n c t i o n s i s standard. The r a t i o o f outer and inner glass r a d i i b/a i s 1,28.

. ! x 1 p i _ —1 —

g 1 1 l • T h e dispersion relation w a s solved by running , \ 1 an appropriate computer program 111. Depending on t-il T * T — 3 the radial structure of the plasma, an infinite

number of axially symmetric modes exist. Of these Fig. 1. Discharge tube (1), Thermostatic bath (2), only the lowest mode is acctually excised with Power supply for magnetic bench (3), Coaxial laun- launchers located outside the plasma. The excita- cher (4), Receiver (5), Signal Generator (6), tion of higher axially symmetric modes would Balance mixer (7), Selective amplifier (8), X-Y necessitate launchers within the plasma to appro- recorder (9). ximate the radial variatiouns of these modes,

which involves severel half wave variations along Measurements were made at constant mercury va- ^

J.

pour pressure of 1.2xl<f

torr and at various values

s i o n relation o f the lowest mode of magnetic induction which was veried from 0 to

46,1 m T . T h e oscillator frequency was changed in -*k«-./.i *

u

^ uj/uj =f(ak) w i t h n / u 3

a s a parameter. T h e m a m

steps o f 10MHz from 461 Gauss. The discharge ;. . .

y

difficulty o f the method is that a change in the current was either 50mA ar 100mA. .. .. .. . ... , , .

magnetic field causes both a change in electron The wavenumber k was determined from chart density and in the parametern/uJp . This was recorder plots of wave patterns obtained with the circumvented by running an iteration process aid o f an interferometer involving a balanced which departs from assumed values of electron

mixer. density.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797397

The consistency of the method was t e s t e d by p l o t t i n g electron plasma density vs. a r c current

(Fig 2). W i t h a fixed magnetic f i e l d , the electron temperature i s constant and electron density should consenquently be a l i n e a r function of a r c current.

50 100

Fig 2.

Figure

i s a p l o t of electron density vs.

magnetic induction. This provided another check of consistency, a s i t was possible t o prove t h a t plasma luminosity varies with magnetic f i e l d i n very much the same vay.

Fig 3.

CONCLUSION

In although many refinemants of the i n t e r p r e t a t i o n of wave data could be suggested, eg . t o include plasma i nhomogenei t y , warm and hot plasma e f f e c t s it appears t h a t the simple

ACKNOWLEDGMENTS

The author i s h d e b t e d t o Prof. B.AniEin of Faculty of Mechanical Engineering Belgrade f o r guidance i n t h e course of t h e above work.

REFERENCES

1 .

D.Ili6, Bulletin of the Boris KidriE I n s t i t u t e

of Nuclear Sciences 18 Physics, ~ ' 4 (1967).

2. D.Suli6, Master Thesis, Univ. of Belgrade (1978).

3. D.SuliC, Proc. of IXth SPIG p321 (1978).

4. A.W.Trive1 piece, Slow-Wave Propagation i n Plasma Waveguides, San Francisco Press, San Francisco (1967).

magneto-ionic theory i n the q u a s i s t a t i c version

r e f l e c t s most of the s a l i e n t features of the

experiment.