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THE RF-ION SOURCE RIG 10 FOR INTENSE HYDROGEN ION BEAMS
J. Freisinger, S. Reineck, H. Loeb
To cite this version:
J. Freisinger, S. Reineck, H. Loeb. THE RF-ION SOURCE RIG 10 FOR INTENSE HY- DROGEN ION BEAMS. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-477-C7-478.
�10.1051/jphyscol:19797231�. �jpa-00219214�
JOURNAL DE PHYSIQUE CoZZoque C7, suppte'ment au n07, Tome 40, J u i Z Z e t 1979, page C7- 477
THE RF-ION SOURCE RIG 10 FOR INTENSE HYDROGEN ION BEAMS
J. Freisinger, S. Reineck and H.W. Loeb.
I s t I n s t i t u t e o f P h y s i c s , Heinrich-Buff-Ring 16, D-6300 G i e s s e n , F. R. G.
1. I ~ R O W C M O N : Neutral injection is a new field of application of rf-ion sources (1). In catparison with arc discharge sources there are s- advantages of our rf-plasma source called RIG 1 0 (-Radio-Frequency- Ion-erator of
10
an in diameter): This type of ion-
source has no discharge electrodes immersed in the discharge plasma. As there are no filamnts in con- tact with the plasm, there are no lifetime (and im- purity) problem by filament detoriation. The re- canbination rate of atcanic hydrogen (2 H-+
H2) atz wal s of the discharge vessel is much less
.
1 0-3
) than on metallic ones (2).
This results in a high proton fraction of about 90% (1,3). Basic investigations shmed that it 3s possible to gain current densities of 55 ma/an at an rf-power of1 kw. In the running experiments the discharge power is increased up to 20 kw. The profile of the plasma density and the radial distribution of the plasma temperature are measured by floating double probes in dependency of the discharge pressure, the rf- frequency, and the rf-power.
2.1 Definition of the Compnents: Concerning the me- chanical set-up, the rf-plasma source R I G 10 is very shple. As shown in the half-schematical Fig. 1, it consists of the following mmpments:
1. H2-inlet and regulator valve
2. Discharge vessel made of quartz (inner diam.:lO an) 3. Distributor: The hydrogen gas enters the discharge
chamber radially. Therefore, the stay of the atoms inside the discharge region is enlarged and the probability to be ionized will be increased.
4. R£-induction coil (air cooled)
5. Extraction system w i t h subc-ents (extraction anode, extraction cathode, decel electrode).
2.2 W eof Working:- In radial direction the hydro- gen gas enters the discharge chamber, which is sur- rounded by the induction coil of an rf-generator. Due to the Maxellian laws, a high frequency magnetic field BRF and in consequence an electrical rf-field ERF (Fig. 2) is induced. Free electrons inside the hscharge region are accelerated by the rf-field.
When they gave gained sufficient energy, they are able to ionize neutral atcans by inelastic collisions.
Thereafter, the secondary electrons- created in this ionization process
-
are accelerated, too, by the s wmechanism. We obtain an intense electrodeless, non-them1 rf-plasma. The ham extraction is ac- q l i s h e d by'the conventional accel-decel-technique.The maximum rf-per is 1.2 kw. The currents to the extraction electrodes and the return current are registered.
-
Double probes are introduced from the downstream side of the beam into the plasm in the level of the first extraction grid for measuring the plasm parameters in dependance of the radial po- sition. The discharge pressure, the r f - p e r , and the rf-frequency are varied.3. ION CURRFhJT DENSITY PFOFIIXS (Experimental Results) 3.1 Pressure Depdancy: In Fig. 4 you see typical ion beam density profiles. The profiles are rotation- ary w t r i c a l to the axis of the plasma source.
The ion beam density increases with increasing dis- charge pressure2(broken curves). It reaches a maxi- mum of 55 m/an at a discharge pressure of 13 bbar;
then the curves for the current densities (solid lines) decrease. In the shape the radial profiles are very similar. Tfiey s h w a plateau, and shift only in the intensity (Fig. 4)
.
For application (1 )w= allow a decrease in the beam plateau of 5%.
ear
the walls, hvc?r intensities must be cut-off. For the highest, the 13 bar-curve of Fig. 4 the area usable for extraction extends out to a distance of 1.5 an to the wall. This is a very good result
-
also ampared with other scnrces. The ion beam of R I G 10has, therefore, a usable diameter of 7 cm.
3.2 Plasma Density and Electron Taprature: The ra- dial distribution of the ~lasma densitv IFiu. 5:
broken curve) shaws a s-lar shape
&the
ion cur- rent d it~~profile. The plateau-value m u n t s to 2.
1Ovm. -
The ele-n tenprature (Fig. 5:solid curve) is highest near the chamber walls, about 80,000 K. It drops to 60,000 K at the axis.
This can be easily interpreted by fhe m eo£ wrk- ing of the rf-plasma source (skin-effect)
.
3.3 Pawer D e p d a n c y : At a fixed discharge pressure of 13 pbar the ion cut-rent profiles for different rf-generator pawer values are plotted in Fig. 6. The current intensity increases a h s t linear with the rf-pmer2and reaches an ion current density of 55 ma/m at 1 0 0 W.
3.4 Generator Frequency: The influence of the rf- generator frequency on the beam profile is relative- ly small. If we increase the rf-frequency from 1 to 7 MHz, q e beam current density changes only abut 2 m/an
.
Hmever, the operation was restrict- ed to this mall range of variation, because of ignition problems at higher and lower frequencies.2.3 Block Diagram: Fig. 3 shms the block diagram of the --supply of RIG 10. The rf-generator con- sists of an rf-driver stage and an air cooled rf- .amplifier. It can k tuned from 1 MHz to 30 MHz.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797231
Fig. 1 : Definition of the C o p -
nents of RIG 10
O 0 1 2 3 4 5
R A D I A L POSITION [ cm 1
Fig. 4: Ion beam density profile as function of the radid position in the ion source Discharge p e r : 1 0 0 0 w
EXTR.CATHODE
VOLTAGE VOLTAGE
RETURN CURRENT
EXTR. ANODE f l CURRENT
F ?
1
INDUCTION ?EkATOR7
Fig. 2: Principle Of rf-discharge
(8 electron, 0 neutral atom) f t t *
AIR -COOLING
Fig. 3: Blockdiagram of the pawer supply of RIG 10
RADIAL POSITION Fm]
Fig. 5: Radial profile of the electron temperature and the ion density
4. CONCLUSION: In conclusion we will sunmnarize the main results:
1. The plasna purity can be improved, because the rf-plasma source uses no filaments.
2. The proton fraction in the ham is high as the discharge chamber is made of quartz.
3. The ion density plateau extends out to a distance of 1.5 m to the plasma chamber walls.
4. The rf-plasma source delivers a total ion beam current of 1 amp at an rf-discharge
pwy
of 1 kw.The current density m u n t s to 55 ma/m
.
Investigations at higher discharge (20 kw) y e run- ning, current densities of 203 to 250 ma/m will be realized in near future.
5. ACKNOWLEDGFMENT: This paper is based on the Doctorate Theis of the second author. The w r k is supported by the Deutsche Forschungsgemeinschaft
(German Research Agency)
.
60[ PARAMETER: R F - P O W E R
5
~ s c l . n ~ ~ PRESSURE' ,\13 p bar
O 0 1 2 3 L
R A D I A L POSITION [cm]
Fig. 6: Ion beam density profile indepdance on the rf- discharge p e r
6. -CES
(1 ) J. Freisinger, S. Reineck, H.W. Loeb, "An Rf- Ion Source for Neutral Injection", Proc. of the.
10th Symposium on Fusion Technology, Padova, Italy, 4.-9. Sept. 1978
(2) L. Valyi, "Atom and Ion Sources", John Wiley John Wiley & Son, Iondon 1977
(3) S. Fliigge, "Handbuch der Physik"
,
Bd. -11,"Korpuskularoptik", Springer-Verlag, Berlin- Gattingen-Heidelberg 1956, p. 80/81
