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A 2.45 GHz ECR ION SOURCE FOR METALLIC IONS
M. Delaunay, R. Geller
To cite this version:
M. Delaunay, R. Geller. A 2.45 GHz ECR ION SOURCE FOR METALLIC IONS. Journal de Physique
Colloques, 1989, 50 (C1), pp.C1-773-C1-778. �10.1051/jphyscol:1989182�. �jpa-00229383�
JOURNAL DE PHYSIQUE
Colloque CI, supplement au n°l. Tome 50, Janvier 1989 Cl-773
A 2.45 GHz ECR ION SOURCE FOR METALLIC IONS
M. DELAUNAY and R. GELLER
CER - CENG - DRF/PADSI, 85 X, F-38041 Grenoble Cedex, France
Résumé - Une source d'ions métalliques E.C.R. de dimensions réduites et de faible consommation électrique a été développée. La structure magnétique, en forme de cuspe, est réalisée uniquement avec des aimants permanents en SmCo . Des plasmas d'yttrium et de titane ont été produits en utilisant l'argon ou le krypton comme gaz support. L'analyse spectroscopique des photons émis par le plasma a permis de détecter simultanément les atomes neutres et les ions pour augmenter les rendements d'ionisation.
Abstract - A compact ECR metal ion source has been developed with a very low power consumption. The magnetic structure (cusp geometry) is built exclusively with SmCo,_ permanent magnets. Plasmas of yttrium and titanium have been produced
b
with argon and krypton as support gas. Spectroscopic measurements of photons emitted by the plasma enable to detect both metallic ions and neutrals in order to increase ionization yield.
1 - INTRODUCTION
Electron cyclotron resonance (ECR) discharge configuration /l/ enable to construct robust ion sources without cathodes and with high plasma density. The majority of the experiments having a minimum B magnetic structure use mirror coils and a permanent magnet hexapole. Recently the study of a such magnetic geometry built exclusively with permanent magnets was performed /2/ but with the same general structure : an hexapole and two rings of magnets which create the axial magnetic field. On the other hand, magnetic bottles built with two coils fed by opposite currents (cusp geometry) were proposed /3/ / 4 / with the disavantages described in Ref. 5. In this work, we have developed a very simple ECR ion source with a magnetic bottle in a cusp geometry built exclusively with permanent magnets (a MARCE ion source is a "source d'ions Miniature a Aimant's a la R. C. E . " ) .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989182
C1-774
2
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APPARATUS-
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DE
PHYSIQUEThe magnetic s t r u c t u r e (cusp geometry) is b u i l t w i t h SmCo5 permanent magnets ( F i g . l a ) and t h e s i z e o f t h e plasma i s i n c r e a s e d with t h e number of o p p o s i t e magnets ( F i g . l b ) . Axial magnetic f i e l d p r o f i l e s were measured f o r magnets with 0.35 T on t h e p o l e s ( F i g . 2 ) and 0 . 4 5 T o n ' t h e p o l e s ( F i g . 3 ) . L is t h e d i s t a n c e between two p o l e s and Br is t h e ECR resonance f i e l d (0.0875 T f o r f = 2.45 GHz). C r o s s - s e c t i o n a l view of t h e MARCE s o u r c e i s shown i n f i g . 4 . Metal sample e x t r e m i t y is i n t r o d u c e d i n t h e plasma by a l i n e a r motion d r i v e (MV). The microwave d i s c h a r g e power i s 50-100 Watts a t a frequency of 2.45 GHz
.
T o t a l i o n beam c u r r e n t d e n s i t y ( ~ i + and ~ r + i o n s ) i s measured with an e x t r a c t i o n a p e r t u r e of 4 mm diameter a t an e x t r a c t i o n v o l t a g e 0 . 5 kV. Photon emission from t h e plasma i s analyzed by a monochromator i n t h e wavelength range 4000-5000 A w i t h a 1200 grooves p e r mm g r a t i n g / 6 / . .Background p r e s s u r e i sloT7
mbar.3
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MEASUREMENTS AND ANALYSIS-
a . T o t a l i o n beam c u r r e n t d e n s i t y : plasmas of y t t r i u m and t i t a n i u m have been produced with argon and krypton a s s u p p o r t g a s i n t h e p r e s s u r e range of 1 0 - ~ - 1 0 - ~ mbar and a i o n c u r r e n t d e n s i t y of 3-5 m~/cm' was measured ( F i g . 5 and 6 ) . Gas i n j e c t i o n was n o t optimized : t h e plasma i g n i t i o n p r e s s u r e h a s t o be high ( w i t h low R.F. power) and we have t o d e c r e a s e t h e p r e s s u r e ( F i g . 6.) i n o r d e r t o l i m i t i o n - n e u t r a l p a r t i c l e s c o l l i s i o n s .
b E-oduction of m e t a l l i c i o n s : metal sample e x t r e m i t y i s heated i n t h e plasma ECR zone by e l e c t r o n impacts. Vapor p r e s s u r e of t i t a n i u m a t t h e m e l t i n g p o i n t ( F = 1668OC) is 5 X mbar. For y t t r i u m , t h e p r e s s u r e a t t h e m e l t i n g p o i n t (F = 1509OC) is 5.3 x 10- 2 mbar. Extremity o f t h e s e two m e t a l l i c samples have been melted and d i a m e t e r of metal r o d i s decreased i f melting p o i n t s a r e n o t reached.
c . Photon spectrums : s p e c t r o s c o p i c measurements of photons e m i t t e d by t h e plasma ( F i g . 7 ) e n a b l e t o d e t e c t both m e t a l l i c i o n s and n e u t r a l s i n o r d e r t o i n c r e a s e i o n i z a t i o n yie1.d. A s shown i n f i g . 8 , i n c r e a s e of t i t a n i u m i o n s ( b and c ) i n t h e plasma i s d e t e c t e d f o r d i f f e r e n t p o s i t i o n s of t h e m e t a l l i c T i sample w i t h krypton a s s u p p o r t g a s ( a ) .
4 - CONCLUSION
We have developed a compact ECR metal ion source with titanium and yttrium samples. The plasma confinement is provided by a cusp magnetic geometry built exclusively with permanent magnets. A total ion beam current density of 5 m ~ / c m ~ has been produced with.a microwave power of 85 Watts at a frequency of 2.45 G H z .
magnet
Y l ~ r n
Fig. 1 Structure of the magnetic trap (cusp geometry) created exclusively with permanent magnets (a). The size of the plasma is increased with the number of opposite magnets (b).
Fig. 2 Axial magnetic field profile created with two SmCo5 magnets with 0.35 T on the poles (see fig. la). L is the distance between two poles and Br is the ECR resonance field.
JOURNAL DE PHYSIQUE
,1Bz1 ( T ) L =2.Gcm 0.45T magnet
Fig. 3 Axial magnetic field profile created with two SmCo5 magnets with 0.45 T on the poles.
Fig. 4 Cross-sectional view of the MARCE source : (M) Metal, (G) gas injection, (W1, W2) windows, (El) extraction electrode, (P) pump, (T) Target, ( M V ) linear motion drive, (C) air cooling, (GR) grid, (L) lens, (S) monochromator, (N) SmCo5 magnets.
ARGON +Ti
Vex = SOOV
i?UHF=85W&
Vex
=
5 0 0 V3
4 5 G 7 8 xld3rnbar
GAS PRESSURE Fig. 6
F i g . 5 T a r g e t c u r r e n t d e n s i t y v e r s u s microwave i n p u t power.
F i g . 6 T a r g e t c u r r e n t d e n s i t y v e r s u s a r g o n g a s p r e s s u r e .
be b bs.b P. .f‘ fibs. .p\ s. or- s.0
$% 5 gsz g g 2% 2 2 3 NU q.2 a,
x (A)
F i g . 7 Spectrum o f photon e m i s s i o n of Y t t r i u m plasma w i t h argon a s s u p p o r t g a s .
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Fig. 8 Increase of titanium ions and neutrals ( b and c) for different positions of the metallic Ti sample with krypton as support gas (a).
References
/1/ R. Geller, B. Jacquot and M. Pontonnier
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Rev. Sci. Instr. 56(8) 1985/2/ P. Sortais, J. Debernardi, R. Geller, P. Ludwig and R. Pauthenet. Int. Conf. on ECR ion sources - Nov. 1987. East Lansing Michigan
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USA./3/ B. Jacquot - Patent n08510066
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July, 10, 1986. B-8941-
3LC./4/ K. Sudlitz
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Int. Conf. on ECR ion sources - Nov. 1987. East Lansing Michigan-
USA.
/5/ M. G. Haines - review paper
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Nuclear Fusion 17-4 (1977)./6/ M. Delaunay - Thesis
