"MASS-DIFFUSION" MECHANISM OF ISOTOPE SEPARATION IN GASEOUS DISCHARGE SYSTEM WITH TRAVELLING MAGNETIC FIELD

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Submitted on 1 Jan 1979

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”MASS-DIFFUSION” MECHANISM OF ISOTOPE SEPARATION IN GASEOUS DISCHARGE SYSTEM

WITH TRAVELLING MAGNETIC FIELD

A. Karchevsky, E. Potanin

To cite this version:

A. Karchevsky, E. Potanin. ”MASS-DIFFUSION” MECHANISM OF ISOTOPE SEPARATION IN

GASEOUS DISCHARGE SYSTEM WITH TRAVELLING MAGNETIC FIELD. Journal de Physique

Colloques, 1979, 40 (C7), pp.C7-213-C7-214. �10.1051/jphyscol:19797105�. �jpa-00219075�

JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, page C7- 213

"MASSDIFFUSION" MECHAMSM

lSOTOPE SEPARATION IN GASEOUS DISCHARGE SYSTEM W I T H TRAVELLING MAGNETIC FIELD

A.I. Karchevsky, E.P. Potanin.

I . V. Kurchatov I n s t i t u t e o f Atomic Energy, Moscow, U.S.S. R.

The p o s s i b i l i t y of isotope enrich- ment in discharge, system with t r a v e l l i n g magnetic f i e l d was researched in diffe-

$ant papers /I-3/. !Che separation appara- t u s i s a long closed-ended cglinder,along t h e a x i s of which t h e t r a v e l l i n g magnetic wave propagates. H. F .-electromagnetic f i e l d of t h e wave makes t h e ionization of t h e mixbure and i t s acceleration i n t h e d i r e c t i o n of t h e axis. A s a r e s u l t a lon- g i t u d i n a l gradient of pressure g & aPPe- a r e s and t h e separation e f f e c t t es pla- ce, which c o n s i s t s in weightLng of t h e mixture in t h e area of higher pressure and i t s lightening in t h e zone of l o w e r pressure. The value of t h e experimentally measured e f f e c t in a complicated way de- pends on t h e parameters of t h e discharge and s o r t of gas. For e x y l e ) 3,ind~ase of

isotope mixture ependen-

ce of t h e enrichment coefficient of mass difference per u n i t within t h e range hi- t i a l pressures 4 = loe2- /0-'tozz is i n a good agreement with t h e known barodiffusi- on c o r r e l a t i o n / 4/

where 8 and 4 - pressures o f t h e

mixt;ure in t h e areas of high and low pre- ssure, LQ - averaged molecular wei$ht.At t h e same f o r t h e Kc isotope mixture t h e

ewerimental & values cannot be descri- bed by ^(I), though t h e i r proportion t o

th$

value & 2 is preserved:

plasma f l o w s . It was shown-that termodi- ffusion should play t h e most important r o l e f o r r e l a t i v e l y high pressures ( P > q to-) , when t h e value of circula-

t i o n due t o r a d i a l inhomogenity of -

electromagnetic volume force 5 =

2.4 i s enough f o r e f f e c t i v e

transportation of components in t h e direc- t i o n of t h e axis. For t h e low i n i t i a l d e n s i t i e s (6 = /o-a i /o-'

and remarkable electromagnetic influence on t h e plasma which causes t h e appearance in t h e discharge t h e zones of high and low pressures with d i f f e r e n t c h a a c t e r i s - t i c s of ionization and recombinat ion processes, t h e r e should be discharge with intensive longitudinal flow of chm- ge p a r t i c l e s similar t o r a d i a l ambipolar diffusion one in dc-discharge. The diffe- rence in t h e value of f r i c t i o n forces which a c t on t h e n e u t r a l components of isotope mixt;ure from t h e s i d e of iones s h a l l bring t h e separation process, which is i n its character s i m i l a r t o mass-diffusion e f f e c t / 5,6/ '.

For t h e estimation of coefficient of binar isotope mixture enrichment which i s caused by t h e proposed mecha- nism we'll use multicomponent hyhrody- namic approximation. lthe momentum balance f o r each components of weakly ionized plasma ( t h e charge of iones i s one) through averaged f o r period values i s given by / 6 / :

where C 5 i s constant ^(C 43). \

-

In / 2 / , t h e explanation of t h e measured e f f e c t s of enrichment on t h e b a s i s of t h e mechanism was proposed. The mechanism i s connected with t h e trans-

f

o r m t i o n of r a a i a l termodif

usion effect &

g - 4 ( 4 t ~ ~ + n , @ n , ~ Y 0 i n t o longitudinal one due t o c i r c u l a t i n g dif

It should be noted t h a t only i n case of i n e r t i a l f i e l d of forces t h e treatment -$+

of equilibrium separation e f f e c t gives t h e correlation ( I ) . A s in t h e above men- tioned H.F.-system t h e separation process

i s not caused by t h e i n e r t i a l forces and dP

t h e researched diffusion phenomenon can- - ^A +a, e ( ~ ~ ⁺ Z*y=.3 ~ / . j ~ % a ~ $ f & & I % ~ t

diz

not be described by t h e c o r r e l a t i o n (1) /1.4/ .

w)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797105

where Ez - longitudinal e l e c t r i c f i e l d in plasma; - longitudinal pro jecti- on of macroscopic velocity of i-compo- nent, Grn - amplitude value of macro-

scopic velocity ?f charged i-sort partic- l e in t h e direction of external e l e c t r i c f i e l d ; -density of i-sort p a r t i c l e s ;

fi - p a r t i a l i-component pressure ; dq and

dl, -coefficients charact erizing momentum e x w e due t o p a r t i c l e c o l l i s i - on. Index e r e f e r e s t o electrons, f and 2 - ^{t o ions, 3 and 9} - ^{t o}

neutrals of both s o r t s relatively. %us, t h e e l a s t i c scattering ion on atoms as well a s the process of charge - ^exchange

is taken i n t o account f o r description of f r i c t i o n force of ions with neutrals of t h e same gas. Using t h e condition of absence o f heavy p a r t i c l e flow of each s o r t i n 2 direction in t h e steady s t a t e as well a s taking i n t o account t h e f a c t t h a t i n usual h.f, dischages elect- ron temperature

i s considerably higher the ion temperature (7;:) , we get t h e correlation f o r enrichment coef f i c i - ent (Q~+~Q~(Q.-@~)A

& =

- L P ~ + ~ Q ? ~ ⁽⁴⁾

where %I and . ^{e o} - pressures of neutral gas i n hi@ and low pressure areas,

and 9, - diffusion e l a s t i c cross section ion and neutral atoms scattering, Q* - charge-exchange cross section; If 9 ^{<< in t h e}

range o f moderate values of

out o f (4) we s h a l l get 7

where - 4 , F - ^average

pressure in discharge. It should be noted t h a t equation ( 5 ) coinsides with t h e experimentally measured dependence (2) in the range of moderate pressure difference A p .

But, f o r estimating of quantitative agreement of t h e experiments and theory, data about t h e sections QL , ^Q* and

ljSr and plasma parameters i n each conc- r e t e case are necessary. Considering,

f o r example, t h e average p a r t i c l e density in t h e chamber n = 3./oZ'&. *

t h e electron density 4 = 3 . / 0

,

Refer enc es

I. R.A.Demirkhanov, e.a. XI11 ICPIG, P* 699, 1977.

2. A.M.Kapse~c~nB, B.JI.h?ztpqb~~Itb~~, X.A.IIOIIOB E . ~ . ~ o T ~ H E H , ~ I S H K ~ lVIa3NIbI, 2, 409, 1677.

3. E.Q.I'opBy~osa, A . H . E ~ ~ ~ Y B H K o , A.Yi.Kap

WBCKHM

@.A.M

A.lT.B6a¶e~, h c b ~ a kP3, 3,5!4 , 1979; 3,598,1977.

4. JI.A.JIaHzay, E.IVl.Jh m4 Wexa~m~a cnnommx cpez IIITfJI, 578, 1953.

5. B.M. K ~ ~ H o B , A.q.Kapse~c~n3, E.n.IIo- TaHmH,

3.m

4, 508, 1978.

6. A.M.Ka s e s c ~ ~ W , E . ~ . Z O T ~ H X H , XTQ,

48,

2097, 1978.