ON THE GENERATION OF FAST ELECTRONS DURING INTERACTION OF MICROWAVE FIELDS WITH COLLISIONLESS PLASMA OF SUBCRITICAL DENSITY

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ON THE GENERATION OF FAST ELECTRONS DURING INTERACTION OF MICROWAVE FIELDS WITH COLLISIONLESS PLASMA OF SUBCRITICAL

DENSITY

I. Gekker

To cite this version:

I. Gekker. ON THE GENERATION OF FAST ELECTRONS DURING INTERACTION OF MI- CROWAVE FIELDS WITH COLLISIONLESS PLASMA OF SUBCRITICAL DENSITY. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-217-C7-218. �10.1051/jphyscol:19797107�. �jpa-00219077�

JOURNAL DE PHYSIQUE CoZZoque C7, supptdment au n07, Tome 90, JuiZZet 1979, page C7- 217

ON M E GENERATION OF FAST ELECTRONS WRING INTERACTION OF MICROWAVE FIELDS W I T H COLLISIONLESS PLASMA OF SUBCRITICAL DENSITY

I.R. Gekker.

Lebedev Physical I n s t i t u t e o f t h e U.S.S.R. Academy o f Sciences, Plasma Physics kzboratory, Moscow, U. S. S. R.

Abstzwtr'Pheoretioalic a d . ~ e r i m e n t a l work$

on the acceleration of electrons wha mic- rowme f i e l d s act on a collisionless (W

m ~8

%&) i s o s o p i c plasma ( n ~ n , = = ) h a ~ e been eolalped,In the region of r a e f i e d plas- ma (&Q) in t h e absence of a c r i t i c a l point

(H=@ t h e energy of suprathamoal. electrons decreases abruptly ^epd, as a rule,does not

exceed the mdprirawP value of *thpe osaillato- r y e n e r g of elwtrons & g p e e ~ e r e a0 +s the a p U t u d e ^{o f} n~Lcrowame field.8 control

axparimat on the intaraceion of a abcro- ware ^{w i t h} plasma ( 6(0:$~~3 s a ~ p&ormed ia a wmeguide izr w h i c h acaelerated e l e c t Eons had been registered (see /+/).

1ntroduil;ik:~ectron acr&el&atdm was ob- s h e d during the Werrrctioar of a 14cmwe

ye w i t h a inhomo~traeoas isotropii /4-41 and magaetoaotiie 15/ N m m d B e aocelera- tian o f electrons _in dense plasma ( m i % usually i s aonne&ted wZ%h processes ^:in tihe region ^of. the c r i t i c a l point ( ~ = h ~ ) /2,6/,

and h a ; x a ~ e & ,@lama (v\6hC) w i f h the d+

v+Lopntmt of paraneteic instabilitw /4,5,-76 and acperimental. dep&

-kEo pres-ta 4 - ^o,,

oscillatory thermal

tron v e ~ i t i e s ~ ~ / ~ , ~ n o ~ e d density of.

p e a r w e (regis%aaticar) of actelarated el*

btE048 (see /4,5/)r~alcttlat~d depgldeuees vaiarxs values of 'P,Ft teken from /7/ ad

Prom /5/ me also Presented*A sifpificaPle decrsase ^ia t;hreshold values, as the, derasi- ty agprodes ^y\, can be seen.% 2ig.2, a p e rirneerfadl dependences of the r a t i o of ^magi- mum asaillatory energy of eleciams .in mi-

QPOWLIP~ ^pi* Eew5 ^{90 m- merw}

of acaelerated elas- on p l a s m dmsity b/ul, a r e -;It c a ~ l be seen that

~sl &st of the erxperimats t ~r a t i s s

cremes shmly aD ~ ~ 1 . 0 a l c u l a t e d values

ede,in ^PI,, CY,~<I)

not exceed I in the trm- wme r e 9 when aud 4 in the st- ware re&-

me when & 2 ~ , (all this. f o r fi/rn,el ).For in- creasing p3-a density,thare mw take place an -ease in. ffelQ (for a f l a t layer DELE whare &~~-~/w,);~alculatedcat de- pdaL&esr a e W c a t e d by curoea 1 and 2 respeetivdy, t&ing in account t h e fieild

-=ease in plasma a t WO ~UCI &23e, (Pig, 2).'It C a be s e m t h a t ~ o c p 8 ~ i m ~ ~ ~ t a l curves, except f o r those emuse& by a dotted line /4,8/,a~e near We oaUulated.JPhfs requi- res e a r p l ~ a t l o s ~ ~ o m / 6 / ,

where t;he coefficient A may assume values t o 2 n .Jehen,near yr =M, ,we hewe the calcu- lated value

L u 4 Lw

~ e W r k , ~ * = ZA*

-

*

P P O ~ o a ~ p l & i o s , f o r L 2 w , ^{X+3k~/em, OQ-=}

nl~-'os4 #d &loqwe 0bta2nC%.,~2.56

m2 (decreasing So to 3OOV/rn gives 2.5' . q d ) , v x ~ c h i s not so f e r from.tbe axper%- mental vd.ues presented in Big020

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797107

~xperirnattUnder the conditions of /4/, the generation of acoeleratdl electrons w a s slxdied i n d e t a i l &,in particular,the re-

giton of t h e i r birt;b was fozmd /8/.Plasma flow w i t h ~ ~ c 5 . 1 0 ~ o 9 1 s tPd kTee5eV, created by a mica spark injecrtior, &tar 65cm int&

sect'ad a recltaugu3.a wavegnide (12X6cm) normally t o L t s broad w a l l whai w a s cove- red by a metalYc grid ( c e l l 0,5)t0.Wm, trasparency.c0.5) over a l a g t h of Ificm.

A HIO-type wme was =cited i n the wwe-

&de (P&Kw, E~ZLO .~~v/c%%E & C ~ ~ , fo=2 I o9

Hz, F .2p, stauding, a w e regime* nc=5 .loq0

~ ~ - ~ , ~ A s . I o ~ ~ ~ o E E ) . T ~ the opposite w ~ I . , t h e r e was, a. lP;ulti&-d m b e (MGP).

741. Fig& curves of delay of c m r a t o f accelerated electrons on the MGP, obtaiaed f o r variow velues of E, a% %nC=O.rC,are

p r e s a t e d . ~ ~ y tplargies .reach &&00- -200ev &ks+63)(see pig. 2) .me. energy distzibution of ,el&txons f o r ~~&.b35kv/

om i s i d e n t i c a l t o h h ~ ~ c u r o e f o r E&O c2OeV)..!Phe field s t r q t ; h Eo ae which ac-

oeleratsd elec.&rons appear increases wi%h dewem* n/n, (see ~ i g . 1 , / 8 / f ~epmdeln- ces@bJbCI;5/ me in egreranent w i t h t a e oalculaiied /7/.0w? data /8/ give low= va- lues of(ahTe) ( a t EBEo ) b h ~ c h i s ai argu- ment fox the @para- origlp o f measured H-Ehreslaol&l ^in, %e appearance of acaele- rated slect;pons.

Ia order t o detemine the region of ac- celera.i;ed electron formation i n t h e wave- guide p s ~ c d l e l t o its bmaa wd.l,a

-

pZsodglaas framre wtth f h e uapron grid (trausparacg

-

aswemat accuracy) th& noticeable el*

troa a c & e l a r a t ; i ~ from ii&e k l ~ p ~ o f r e retEied plasma (%hc 5 0.5) inside .&he w e veguide i s absent. as was noted 51 /r(/,Ob-

s 4 a d e l e o ~ o n mcel~l?atios fm?oratQ ahotlld be & ~ i b u t & . t o . ~ o a e s s w occur-

r i n g ^{f p} i b regifan o f intt%r?m.tiim .of &-

crowave f i e l d w i t h plasma n e e the metal- l i c wid ia;put,i. e,, adopted t o the me%hod of introducing plasma in60 ^the waveguide.

We s h a l l try t o eluc2dat;e the possible meohEollsm of electron acceleration.At ^{t h e} EJnCS0,5 in the waveguide and approlclma-

tely ImofoM plasma d a s i * dewease by the metallic grid, i t s density dLrect1.y be- yond the g r i Q (on the injector side) can reach n/nc31 *Miwormre radia%ion can leak into this region..BIIoreover, .&he passage through the =id of narrow "tonguest* of dmse plasma can nttLntain their original density (n/b$l) t o distances at l e a s t of the ordar of the grid cell;~$,owing exparf- mental ~values€~,a, md Eo from (I ),we ^shall determine Lsc I-, 2 , e.cOqat?eble with the diaiension o f . the grid cell.

~ e s u l t s : ~ h u s ; i t i s shown that i n restric- ted volunes (a,*&) of rarefied plasma

(n/ns ¹ maximum e n e ~ g i e s of acceleated electrons (f ar f r o a the region P/PO=I ^{) do.}

not a c e e d cOway ⁱ . ^{e. , the enegg o f} o s p i l l a tions of electrons in microwwe fie&.

E. ~.Khathatury#,~hort connnmications on

~ h y s ~ c s , ~ ~ , 41 ?,,! '1 971

/2/ v . I . B ~ ~ v , I . . ~ . Q ~ ~ ~ w , v . A . I v ~ o v , D . M . K ~ ~ ~ ~ ~ O V , P P O C . E I B B T , s, ^35, 'WaukaW, 1 4 7

/3/ s.a.aelrlr~n~ht=a~tiop 02 strong el-- tromegneti ^G f i e l d s with pla~mat', fcAtomiz- datcc, 1 978

/4/ IC.8.s e r g ~ c h e v , 8 . E . T r o f i m o v , ~ Lettas,~,236,IT5,1971

/W ~ ; ? ~ e i c e r ert. aU+,P$L,31,427,W,1973

/6/ L ; I Y I . X O ~ ~ ~ z h n i k h , ~ .S .S a&arov,preprint;

FULE11,$118,148

/7/ v . ~ . ~ i l i n " ~ a r a n e t r i c action o f . ^high- power radiation on, plasma*', eWaukamy 1 973

/8/ 1.8.~ekke,!P. ~ . ~ u l a e r n ~ ~ l a s n t a physics (in piat)