NEGATIVE ION PRODUCTION IN SURFACE-PLASMA SOURCES WITH UNCLOSED ELECTRON DRIFT DISCHARGES

(1)

HAL Id: jpa-00219227

https://hal.archives-ouvertes.fr/jpa-00219227

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

NEGATIVE ION PRODUCTION IN

SURFACE-PLASMA SOURCES WITH UNCLOSED ELECTRON DRIFT DISCHARGES

Yu. Bel’Chenko, V. Dudnikov

To cite this version:

Yu. Bel’Chenko, V. Dudnikov. NEGATIVE ION PRODUCTION IN SURFACE-PLASMA SOURCES WITH UNCLOSED ELECTRON DRIFT DISCHARGES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-501-C7-502. �10.1051/jphyscol:19797243�. �jpa-00219227�

(2)

JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, page C7- 501

NEGATIVE ION PRM3W=TION IN SURFACE-PLASMA SOURCES WITH UNCLOSED ELECTRON DRIFT DISCHARGES

Yu. I. Bel'chenko, V.G. Dudnikov.

Institute o f NueZear P h y s i c s , Novosibirsk, U. S. S . R.

1. In developed v a r i a n t s of surface- plasma sources / 2 , 3 / the minimum energy necessary f o r H- generation ^, is about

704 eV/ion. The f u r t h e r i n c r e a s e i n e f f i - ciency of negative ion generation ia de- s i r a b l e f o r construction of long term ope- r a t i o n sources. The most evident way t o increase the energy e f f i c i e n c y i s the more complete u t i l i a a t i o n of negative ions em- i t t e d from e l e c t r o d e s /2/, In experiments presented here, more complete e x t r a c t i o n of generated negative ions was provided with l o c a l i z a t i o n of the discharge near the emission s l i t and with geometrical focusing o r negative ions emitted by a h a l f - c y l i n d r i c a l cathode s u r f a c e t o the

emission s l i t .

2. The diagram of the source with discharge l o c a t i o n n e a r t h e emission s l i t (so-called semiplanotron

-

^SP)^is

shown i n Pig. 1

.

a

Fig. 1 Semiplanotron diagram:

a

-

with one groove, b

-

with f i v e grooves; 1

-

cathode, 2

-

^anode,

3

-

magnetic i n s e r t s , 4

-

^{poles of}

magnet, 5

-

^emissions l i t , 6

-

^ex-

t r a c t o r , 7

-

cathode groove, 8

-

end cathode hollow.

Similar t o t h e planotron /2/, the discharge takes place i n a t h i n gap between t h e - l o n g cathode 1 and enode 2, which em- braces the cathode. For the e f f e c t i v e

plasma u t i l i z a t i o n , S P discharge i s main- tained only i n e region near the emission s l i t . I n t h i s place the magnetic f i e l d l i n e s a r e s p e c i a l l y bent with magnetic i n s e r t s 3. The magnetic f i e l d l i n e s two times cross the h a l f - c y l i n d r i c a l cathode s u r f a c e without crossing the anode, prov- i d i n g conditions f o r confinement of f a s t e l e c t r o n s emitted by cathode, These elec- t r o n s o s c i l l a t e i n the cathode groove and d r i f t along t h e emission s l i t sawed per- pendicular t o magnetic f i e l d l i n e s , The deeper hollow 8 is made a t one of t h e cathode end f o r b e t t e r discharge t r i g g e r - ing. Electromagnetic valve and heated container provide t h i s hollow with hydrogen p o r t i o n s and cesium vapour. For preventing discharge i n o t h e r p a r t s of the cathode-anode gap, SF e l e c t r o d e s have the s p e c i a l shape preventing e l e c t r o n os- c i l l a t i o n s i n these regions. Electrons i n the s i d e gaps f a l l quickly t o the anode along the magnetic f i e l d l i n e s . . A h a l f - c y l i n d r i c a l shape of t h e cathode operation s u r f a c e provides geometrical focusing of negative ions emitted by the surface t o emission s l i t . Extraction voltage of up t o 35 ^kVis a p p l i e d t o discharge chamber, e x t r a c t o r 6 i s under ground p o t e n t i a l , The pulse mode of such sources was under study. An amplitude of the discharge c u r r e n t pulse was up t o 0.2M1, d u r a t i o n 7mS, r e p e t i t l o n r a - t e up t o 10 Hz.

3. The c h a r a c t e r i s t i c s of high cur- r e n t glow discharge i n SP, t h e i r dependencies on magnetic f i e l d , hydrogen and cesium d e n s i t y , discharge c u r r e n t were s i m i l a r t o those of planotron discharge /2/. The dependencies of e x t r a c t e d H- and 'D c u r r e n t on discharge current a r e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797243

(3)

g i v e n i n Pig.2.

Fig.2 Current of H- and D- ( c r o s s e d ) beams a s a f u n c t i o n of d i s c h a r g e c u r r e n t . F i g u r e s n e a r t h e c u r v e s

-

^{width of}

t h e emission s l i t . The emission s l i t l e n g t h i s 40 ma.

Taxinurn H- emission d e n s i t y up t o 3-4A/cm 2 was achieved w i t h d i s c h a r g e c u r r e n t d e n s i - t y a t cathode 50 ~ / c m ~ . A t l i n e a r p l o t of dependence e m i s s i o n H- c u r r e n t d e n s i t y mounts t o 17$ of , t h e cathode d i s c h a r g e cur-

r e n t d e n s i t y and energy e x p e n d i t u r e on H- g e n e r a t i o n was 5 keV/ion. It i s explain- ed by more e f f e c t i v e plasma u t i l i z a t i o n i n SP and by g e o m e t r i c a l f o c u s i n g of n e g a t i v e i o n s t o emission s l i t . Negative i o n s focus- i n g a l s o i s confirmed by i n t e n s e s p u t t e r i n g of anode p a r t s l o c a t e d o p p o s i t e t o t h e h a l f - c y l i n d r i c a l cathode s u r f a c e of t h e groove, S p u t t e r i n g t r a c e l o o k s l i k e a ca- nel of 0;8 mm width.

Under t h e same c o n d i t i o n s H- c u r r e n t was two times l e s s t h a n D- c u r r e n t . Becau- se of t h e l a r g e r deuterium mass t h e l e a v i n g times a r e i n c r e a s e d b o t h f o r d i s c h a r g e po- s i t ive i o n s and n e g a t i v e i o n s moving from cathode t o emiasion s l i t . These e f f e c t s can v i s i b l y i n t e n s i f y t h e D- d e s t r u c t i o n i n plasma /2/. Also, due t o lower energy

0." bombarding deuterium p a r t i c l e s /4/ t h e

r e d u c t i o n of secondary D- emission c o e f f i - c i e n t may play a c e r t a i n r o l e .

The f i v e - g r o o v e s SP w i t h m u l t i p l e - a p e r t u r e e x t r a c t i o n system was t e s t e d ( ~ i g . ? b ) . Quite a uniform g l o w , d i s c h a r g e ' w a s achiev- cd a t a l l t h e c a t h o d e s grooves & i t h cathode c u r r e n t d e n s i t y up t o 30 ~/cm'. With l a r g e s i z e e of emission s l i t some d i f f i - c u l t i e s a r i s e f o r p r o v i d i n g n e c e s s a r y den-

s i t y of hydrogen i n d i s c h a r g e grooves.

The hydrogen d e n s i t y g r a d i e n t a l o n g t h e groove r e s u l t e d i n non-uniform d i s c h a r g e and brought t o v i s i b l e r e d u c t i o n of nega- t i v e i o n s a l o n g t h e emission s l i t .

I n t h e d e s c r i b e d v e r s i o n s of SP t h e problem of e l e c t r o d e c o o l i n g i s q u i t e sim- p l y aolved. To t h i s end, t h e c h a n n e l s f o r c o o l i n g l i q u i d a r e d r i l l e d c l o s e t o work- i n g p a r t s o f t h e c a t h o d e , anode and ex- t r a c t o r . Note, that SP w i t h one groove of + 3 x 15 nun2 is' e f f e c t i v e as compact dc s o u r c e o f n e g a t i v e i o n s . 7 i t h d i s c h a r - ge c u r r e n t ^.v5 A and average power a t cathode d l k!V/crn2 i t i s r e a l l y t o ob- t a i n dc H- c u r r e n t of 0.1 A.

References:

/ I / "Proc. Symp. on Production and Neut- r a l i z a t i o n o f Negative Hydrogen I o n s and Beams, 1977", BNL, 50 727, N.Y.

/2/ Yu.I.Belchenko, G.I.Dimov, V,G.Dud- nikov, i n / I / , p.79.

/3/ K.?relec, i n / I / , p.111.

/4/ P.J.Schneider, K.H.Berkner, W.G.Gra- ham e t a l . , i n / I / , p.63.