ON EXPANSION OF THE COLLISIONLESS PLASMA INTO VACUUM

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ON EXPANSION OF THE COLLISIONLESS PLASMA INTO VACUUM

V. Yeselevich, V. Fainstein

To cite this version:

V. Yeselevich, V. Fainstein. ON EXPANSION OF THE COLLISIONLESS PLASMA INTO VAC- UUM. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-359-C7-360. �10.1051/jphyscol:19797177�.

�jpa-00219154�

JOURiVAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JxiZZet 1979, page C7- 359

ON EXPANSION OF THE COLLJSIOM-ESS PLASMA INTO VACUUM

V.G. Yeselevich, V.G. Fainstein.

Sibizmir, Ireutsk 33, P.O. Box 4, U.S.S.R.

I n l a b o r a t o r y experiments on plasma ex- pansion i n t o vacuum c a r r i e d o u t t i l l t h e p r e s e n t , t h e maximum r e c o r d e d speeds of i o n sound were s e v e r a l times l e s s t h a n t h e recorded v e l o c i t i e s of a c c e l e r a t e d i o n s (cS9 = ( ~../ht; : U (2+3 )C!,

- ^mi lax

max

*,ax 2

(2f 4 p 5 ) ro /f-9/

I n t h i s paper, i t i s e x p e r i m e n t a l l y shown t h a t a t plasma expansion i n t o vacu- um, t h e i o n s may be a c c e l e r a t e d up t o ve- l o c i t i e s U 7 7 C S ,

.

And due t o i n s t a b i l i - t y development, t h e flow of e l e c t r o n h e a t from s o u r c e t o f r o n t p r o v i d i n g energy s u p p l y t o e l e c t r o n s which a c c e l e r a t e i o n s

5 6

t u r n s o u t t o be about 1 0

+

1 0 t i m e s i e s s 3han i t follows from t h e t h e o r y of p a i r c o l l i s i o n s

/5/.

The experiments were performed i n a cy- l i n d r i c a l va

b"

uum volume w i t h a 200 cm l e n g t h , 60 cm diameter. The r e s i d u a l gas p r e s s u r e P--, 5 x 1 0 - ~ mm Hg. On one end o f t h e chamber, a p u l s e s o u r c e is a r r a n g e d / 6 / , whose plasma having i n s p a c e a s t e e p

f r o n t w i t h a w i d t h ~ = ( l + 5 ) c m , was expan- d i n g i n t o t h e chamber. The parameters of argon plasma a t t h e o u t l e t of t h e s o u r c e on f r o n t t o p :

XO%

(14- 5 ) e v ; G <

xa

⁹

a,=

(1 O ~ + I ~ ' ) c m - ~ . The d u r a t i o n of sou-

r c e o p e r a t i o n was s i g n i f i c a n t l y g r e a t e r t h a n t h e time of passage of t h e plasma of t h e chamber l e n g t h . Measurements of

e l e c t r o n and i o n d e n s i t i e s , e l e c t r o n tem- p e r a t u r e a s w e l l a s of plasma f r o n t moti- on v e l o c i t y were made w i t h a c y l i n d r i c Langmuir probe ( 1 = 15cm,

jd

⁼ 0.05 cm) d i s p l a c i n g a l o n g t h e chamber a x i s .

The experiments ahowed t h a t a s plasma i s moving from t h e s o u r c e , t h e plasma d e n s i t y n i n f r o n t t o p drops a p p a r e n t l y ( ~ i g . 1 ) (and Te changes comparatively l i t t l e ) . T h e r e f o r e , t h e v a l u e of t h e l o - c a l Debye r a d i u s r D s ( % / 4 r n e 2 ) i n c r e a - s e s . The f r o n t w i d t h s e p a r a t e d f r o m t h e s o u r c e b y x s 7 0 c m , becomes of t h e o r d e r of/f 2 g r D and a phenomenon l i k e d i s p e r - s i o n i s observed: d e n s i t y v a r i a t i o n s with a t y p i c a l length-AD l a g g i n g behind t h e f r o n t . A t f u r t h e r movement, t h e v a l u e

A

from

x

changes approximately a s I/&&.

A s i o n s a r e moving, t h e i r v e l o c i t y i n - c r e a s e s c o n t i n u o u s l y w i t h i n c r e a s i n g

x

t o

%a,=150cm i n c l u s i v e l y (Pig.2). T h i s me- a n s t h a t X r l 5 0 c m i m p l i e s f u r t h e r i n c r e o s e of t h e v e l o c i t y U. The v a l u e o f i o n acce- l e r a t i o n i s determined by t h e g r a d i e n t of e l e c t r o n p r e s s u r e i n t h e f r o n t and i n o r - d e r of magnitude a g r e e s w i t h t h e v a l u e

a - ^{m; a L fi 3}

^m,

^{A&) L}

^{( Z = 1}

^-

^{i o n cha-}

r g e

.

The a c c e l e r a t i o n d e c r e a s e w i t h i n c r e a s - i n g x (curve i n c l i n a t i o n i n Pig.2) i s l a r g e l y due tos i n c r e a s i n g

h

( x ) . Under

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797177

conditions of the experkment the maximum velocity of accelerated ions at a distan- ce of 150cm was e (1 5+20) Cso, which corresponds to the energy E

=

=

(100+200) T , ,

The electron temperature gradient along the oxaxis measured on a 20cm portion L O X

L

40cm is about (0.OZt0.03) ez

The electron heat flow connected withh/

dr assuring electron energy restoring, eaergy being given to ions, is in order of magnitudepnulE (here

4

EB& is the in- crement of front kinetic energy on 20i40 cm portion). Por this case (Figs. 1 and 2

T e e

2eV) this value is approx. 5

+ 6

ord- ers less than the heat flow obtained from the theory of pair collisions /5/.

As one is moving away from the source,

h

an increase in level (up to410.2 on OX

h

L?:

40cm) of electrostatic density oscil- lations with a typical wavelengthur,, and frequency in the frame of reference con-

2 1/2 rrected with the front-uOf (4f;ne /mi) ,

is observed in the front region and be- hind.

According to /7/, excitation of such a type is due to instabilities of the non- isothermic plasma with inhomogeneous tem- perature.

Electron scattering on oscillations le- ads up to a decrease in electron thermal conductivity whose calculated value /8/in order of magnitude agrees with the expe- rimental one.

R E F E R E N C E S

1. P.F.Little, Journal of Nuclear Energy Part C, v.4, 15-22 (1962).

2. H.W.Hende1, T.T.Rebou1, Phys.Fluids,

5 ,

360 (79629.

3. A.A.Plutto, N.N.Ryzhkov, A.T,Kapin, JETPy 42, 494 (1964).

4. N.A.Tyulina, mTP, 35, 511 (1965).

5.

L.

Jr .Spit zer, R.H%~, Phys .Rev. 89, 977 (1953).

6. V.G.Eselevich, Yu.S.Karavaev, V.I.Ko- roteev, V.G.Fainshtein. Preprint Sib- IZMIR, 18-77 (1977).

7. D.V.Porslund, J.Geophys.Res., Space Physics, v.75, No.1, 17-27 (1970).

8.

E.V.Miahin, DAI?, 215, 565 (1974).

Fig.1. Spatial distribution of ion den- sity in the front of plasma expanding in- to vacuum at different

t i m e

moments:

a 1- t ,

=

20-c , - ^{t 2 = 26nw:}

c>- t 3

⁼

31.57hc&xz

Fig.2. Change of velocity of the front

of plasma expanding into vacuum, with

the distance from the source'.