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TIARA electrostatic accelerators for multiple ion beam application
Nuclear Instruments and Methods in Physics Research B 89 (1994) 23-26 North-Holland
TIARA electrostatic
accelerators
k!lUNl B
barn Interactions with Materials A Atoms
for multiple ion beam application
Y. Saitoh a~*, S. Tajima a, I. Takada a, K. Mizuhashi a, S. Uno a, K. Ohkoshi a, Y. Ishii a, T. Kamiya a, K. Yotumoto a, R. Tanaka a, E. Iwamoto b aJapan Atomic Energy Research Institute, Takasaki, Gunma, 370-12, Japan b N&n-High Voltage Co., Maebashi, Gunma, 371, Japan
A unique electrostatic accelerators facility has been constructed mainly for application of multiple beam and microbeam to materials science research at JAERI Takasaki. The facility consists of a 3 MV single-ended accelerator with an extremely high voltage-stability of + 1 x lo-‘, a 3 MV tandem accelerator and a 0.4 MV ion implanter, which cover various ion particles in an energy range of 10 keV to 20 MeV. A voltage ripple of f 1 X lo-’ (60 V,,) at 3 MV has been achieved for the single-ended machine. The performance of accelerators, beam lines and their applications to various research activities are outlined.
1. Introduction The TIARA (Takasaki Ion accelerators for Advanced Radiation Application) facilities [l] have been constructed at the Takasaki Radiation Chemistry Establishment of Japan Atomic Energy Research Institute (JAERI) since 1987 for an R&D project using various ion beams in a wide range of acceleration energy. The facilities consist of an AVF cyclotron [2] and three different types of electrostatic accelerators (Fig. 1): a 3 MV tandem accelerator, a 3 MV singleended accelerator and 0.4 MV ion implanter. The AVF cyclotron and the 3 MV tandem accelerator were already completed in 1991 and have since then been operated for research experiments. Two other accelerators and multiple beam lines have just been completed in July 1993. The outstanding feature of the beam characteristics in the electrostatic accelerators facility is that the three machines are operating simultaneously in three different combinations of a triple beam and two dual beam modes. Both 3 MV accelerators provide light and heavy ion microbeams with the beam size of 1 pm or less. This report describes the outline of the accelerators, beam lines, and their applications to a wide variety of research fields.
2. The characteristics of accelerators 2.1. 3 MV single-ended electrostatic accelerator This machine (Fig. 2) manufactured by Nissin-High Voltage Co. was designed to require an extremely high
* Corresponding author.
voltage-stability of f 1 X lo-’ to provide a stable submicron microbeam. A balanced type Schenkel DC power supply (Fig. 3) was selected for the high voltage generator. The induction voltage at the geometric center axis of the DC power supply should be zero, because a couple of RF electrodes mounted at the top and bottom sides symmetrically along the inside wall of the pressure vessel have the same absolute alternating voltage with different polarity. However, geometric deviation from the complete symmetry results in an increase of the voltage ripple compared with the theoretical value. To minimize this influence, a ripple tuning coil was installed at the high-voltage side of the transformer connected with the RF electrodes. The ripple tuning coil tunes the inductance of a resonance circuit that consists of the coil inductance of the high-voltage side of the transformer and the conductance between all the constructions of the post transformer and the earth. The tuning coil balances the charging voltage to the RF electrodes. Fig. 4 shows an example of reduction of the voltage ripple with the ripple tuning coil measured by a high-voltage universal divider [3] shown in Fig. 5. The high-voltage control system of the accelerator is shown in Fig. 6. The terminal voltage is monitored by precision voltage measuring resistors. A feedback signal is produced by comparing the monitored signal and a setting signal. We are aiming at the voltage stability of + 1 x lo-’ including voltage ripple and drift. An accelerated beam is analyzed by a 90” analyzing magnet with a radius of 1.5 m and an energy resolution of f 1 X lo-‘. There are five beam lines; two beam lines are connected with the multiple beam target chamber, and others connected the submicron mi-
0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDZ 0168-583X(93)E0792-F
I. ION ACCELERATORS/SOURCES
Y. Saitoh et al. /Nucl.
24
Imtr. and Meth. in Phys. Res. B 89 (1994) 23-26
3 MV single-ended accelerator
Fig. 1. General
layout of the electrostatic
accelerators
facility.
RF ion source RF electrode
Precision
Fig. 2. 3 MV single-ended
Fig. 3. The Schenkel
voltage
measuring
resistor
accelerator.
DC power supply.
Fig. 5. The high-voltage universal divider; Rl = 99 MR, R2 = 100 MR, R3 = 99 kR, Cl = 1700 pF.
25
Y. Saitoh et al./Nucl. Instr. and Meth. in Phys.Res. B 89 (1994) 23-26
+ DC
---2.
10 kV
-
P.S.
-
DClOV
Resonator -
schenke’ DC P.S.
I+
P.S.
A ~
/I O.P.
amp
-*
O.P. amp (fine)
Reference
Fig. 6. The block diagram of the voltage control system.
crobeam apparatus, a target chamber exclusively for electron beams, and a general purpose chamber. The polarity of the terminal voltage can be changed to negative by reversing the polarity of diodes. 2.2. Other accelerators A 3 MV tandem accelerator mainly accelerating heavy ions covering the middle energy range of 0.8 to 20 MeV is the model 9SDH-2 manufactured by National Electrostatics Corp. It has two negative ion sources; one is a charge exchanging RF ion source exclusively for generating negative helium ions, and the other a cesium sputter ion source producing a wide variety of high intensity negative ions. The injection beam with energies up to 80 keV is analyzed by a 90 bending magnet of which the mass resolution m/Am is 100. A voltage stability in the accelerator of 3 x 10m4 is controlled by a corona probe using both signals of a generating voltmeter and a capacitive pick off (CPO), or by means of slit currents and the CPO. Three accelerating beam lines are connected with experimental apparatus in the target room No. 1, and other two beam lines are transported to the target room No. 2 for multiple beam applications. A 0.4 MV ion implanter covering an energy range of 10 to 400 keV was manufactured by Nissin Electric
Corp. The ion source mounted at the high voltage terminal is of a Freeman type equipped with either an oven or a sputter electrode to generate a plasma of interest. Source materials with high melting points can be ionized by the sputter electrode. Beams extracted from the ion source with energies up to 30 keV are analyzed by a 90” bending magnet with the mass resolution (m/Am) of 100, mounted at the high-voltage terminal. Three beam lines are connected with different multiple beam experimental apparatus, and the fourth is connected with an integrated 400 kV analytical electron microscope in the target room No. 4, which is in the underground. The main parameters of the three accelerators are listed in Table 1.
3. Experimental
apparatus
and applications
Eleven experimental apparatus are to be connected with each beam line of three accelerators. Some of them are outlined below. A triple beam target chamber is installed for basic study of high-energy neutron induced damage of various materials of a nuclear fusion reactor in the target room No. 2. The high-energy neutrons give rise not only to atomic displacement damage by recoil atoms but also to the production of hydrogen and helium by transmutation reactions. Simultaneous irradiation with one heavy ion beam and two light ion beams from the three machines allows the simulation of the above irradiation environment. This chamber is equipped with a precision quadropole mass analyzer and a six-axes goniometer, and the sample temperature can be controlled in a range of 80 to 1000 K. Two dual-beam analysis systems designed for experiments of in-situ or successive analysis are installed in the target room No. 2. The one, connected with the tandem and implanter beam line, will be used mainly for nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA) using heavy ion probes from the tandem accelerator. The other, connected
Table 1 The parameter of three accelerators
Model Charging system Accelerating voltage Accelerated ion mass Beam intensity
Ion source
Tandem
Single-ended
Ion implanter
9SDH-2 (NEC) Pellet chain 0.4-3.0 MV l-200 amu C 3+ 12.0 MeV 10 JLA Ni 4+ 15.0 MeV 4 FA Au 3 + 12.0 MeV 15 FA Charge exchanging RF Cs sputter type
NC30OOB(NHV) Schenkel DC P.S. 0.4-3.0 MV H, d, He and e H 3.0 MeV 300 PA He 3.0 MeV 200 PA e 3.0 MeV 100 FA RF ion source
NH-40SR (NE) Cockcroft-Walton lo-400 kV l-200 amu P 400 keV 100 I.LA As 400 keV 100 p,A Ag 400 keV 20 PA Freeman type with sputter electrode
I. ION ACCELERATORS/SOURCES
26
Y. Saitoh et al. / Nucl. Instr. and Meth. in Phys. Res. B 89 (1994) 23-26
with the single-ended and implanter beam lines, will be used mainly for Rutherford back scattering (RBS) and high-resolution nuclear resonance reaction analysis using light ions from the single-ended accelerator. Both apparatus are equipped with a three-axis goniometer, a YAG laser for annealing samples and a vacuum deposition system. The sample temperature can be controlled in a range from 15 to 320 K. The 400 kV analytical electron microscope connected with the beam line in the No. 4 target room at an angle of 50” with the horizontal line from the implanter is designed to permit in-situ observation of the dynamic process of structural change of materials under simultaneous irradiation with beams from the implanter and a 40 kV inner ion source. A light ion microbeam apparatus connected with the single-ended accelerator is now under construction. To easily achieve a submicron beam spot size within 0.5 pm, we have to minimize the energy spread of the accelerated beam. For this reason, we selected the accelerator design described above within a voltage stability of k 1 x 10m5. This system will be applied for microbeam analysis, high resolution single event upset analysis, etc. R&D of cell surgery technique aiming to establish a new technology for cell treatment has also been started by using an apparatus for heavy ion irradiation to cells
with penetration depth control, connected with tandem accelerator. The beam penetration into the membrane is precisely controlled by changing the celeration energy. The beam is taken out in the through a thin organic film to irradiate the cell.
the cell acair
4. Conclusion Three electrostatic accelerators covering an energy of 10 keV to 20 MeV were completed mainly for materials science research in the TIARA. In the 3 MV single-ended accelerator, we obtained an extremely high voltage-stability of 6OV,, ripple at 3 MV. This result gives a good reason to be optimistic about providing a submicron microbeam. To operate these accelerators independently or simultaneously, various combinations of ion beams can be supplied to research experiments.
Reference [l] S. Sato, Proc. Int. Conf. on Evolution in Beam Applications (1991) p. 239. [2] K. Arakawa et al., Proc. Int. Conf. on Evaluation in Beam Applications (1991) p. 264. [3] Harada et al., the IEEE Annals, No. F75560-3, 1975.
TIARA electrostatic
accelerators
k!lUNl B
barn Interactions with Materials A Atoms
for multiple ion beam application
Y. Saitoh a~*, S. Tajima a, I. Takada a, K. Mizuhashi a, S. Uno a, K. Ohkoshi a, Y. Ishii a, T. Kamiya a, K. Yotumoto a, R. Tanaka a, E. Iwamoto b aJapan Atomic Energy Research Institute, Takasaki, Gunma, 370-12, Japan b N&n-High Voltage Co., Maebashi, Gunma, 371, Japan
A unique electrostatic accelerators facility has been constructed mainly for application of multiple beam and microbeam to materials science research at JAERI Takasaki. The facility consists of a 3 MV single-ended accelerator with an extremely high voltage-stability of + 1 x lo-‘, a 3 MV tandem accelerator and a 0.4 MV ion implanter, which cover various ion particles in an energy range of 10 keV to 20 MeV. A voltage ripple of f 1 X lo-’ (60 V,,) at 3 MV has been achieved for the single-ended machine. The performance of accelerators, beam lines and their applications to various research activities are outlined.
1. Introduction The TIARA (Takasaki Ion accelerators for Advanced Radiation Application) facilities [l] have been constructed at the Takasaki Radiation Chemistry Establishment of Japan Atomic Energy Research Institute (JAERI) since 1987 for an R&D project using various ion beams in a wide range of acceleration energy. The facilities consist of an AVF cyclotron [2] and three different types of electrostatic accelerators (Fig. 1): a 3 MV tandem accelerator, a 3 MV singleended accelerator and 0.4 MV ion implanter. The AVF cyclotron and the 3 MV tandem accelerator were already completed in 1991 and have since then been operated for research experiments. Two other accelerators and multiple beam lines have just been completed in July 1993. The outstanding feature of the beam characteristics in the electrostatic accelerators facility is that the three machines are operating simultaneously in three different combinations of a triple beam and two dual beam modes. Both 3 MV accelerators provide light and heavy ion microbeams with the beam size of 1 pm or less. This report describes the outline of the accelerators, beam lines, and their applications to a wide variety of research fields.
2. The characteristics of accelerators 2.1. 3 MV single-ended electrostatic accelerator This machine (Fig. 2) manufactured by Nissin-High Voltage Co. was designed to require an extremely high
* Corresponding author.
voltage-stability of f 1 X lo-’ to provide a stable submicron microbeam. A balanced type Schenkel DC power supply (Fig. 3) was selected for the high voltage generator. The induction voltage at the geometric center axis of the DC power supply should be zero, because a couple of RF electrodes mounted at the top and bottom sides symmetrically along the inside wall of the pressure vessel have the same absolute alternating voltage with different polarity. However, geometric deviation from the complete symmetry results in an increase of the voltage ripple compared with the theoretical value. To minimize this influence, a ripple tuning coil was installed at the high-voltage side of the transformer connected with the RF electrodes. The ripple tuning coil tunes the inductance of a resonance circuit that consists of the coil inductance of the high-voltage side of the transformer and the conductance between all the constructions of the post transformer and the earth. The tuning coil balances the charging voltage to the RF electrodes. Fig. 4 shows an example of reduction of the voltage ripple with the ripple tuning coil measured by a high-voltage universal divider [3] shown in Fig. 5. The high-voltage control system of the accelerator is shown in Fig. 6. The terminal voltage is monitored by precision voltage measuring resistors. A feedback signal is produced by comparing the monitored signal and a setting signal. We are aiming at the voltage stability of + 1 x lo-’ including voltage ripple and drift. An accelerated beam is analyzed by a 90” analyzing magnet with a radius of 1.5 m and an energy resolution of f 1 X lo-‘. There are five beam lines; two beam lines are connected with the multiple beam target chamber, and others connected the submicron mi-
0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDZ 0168-583X(93)E0792-F
I. ION ACCELERATORS/SOURCES
Y. Saitoh et al. /Nucl.
24
Imtr. and Meth. in Phys. Res. B 89 (1994) 23-26
3 MV single-ended accelerator
Fig. 1. General
layout of the electrostatic
accelerators
facility.
RF ion source RF electrode
Precision
Fig. 2. 3 MV single-ended
Fig. 3. The Schenkel
voltage
measuring
resistor
accelerator.
DC power supply.
Fig. 5. The high-voltage universal divider; Rl = 99 MR, R2 = 100 MR, R3 = 99 kR, Cl = 1700 pF.
25
Y. Saitoh et al./Nucl. Instr. and Meth. in Phys.Res. B 89 (1994) 23-26
+ DC
---2.
10 kV
-
P.S.
-
DClOV
Resonator -
schenke’ DC P.S.
I+
P.S.
A ~
/I O.P.
amp
-*
O.P. amp (fine)
Reference
Fig. 6. The block diagram of the voltage control system.
crobeam apparatus, a target chamber exclusively for electron beams, and a general purpose chamber. The polarity of the terminal voltage can be changed to negative by reversing the polarity of diodes. 2.2. Other accelerators A 3 MV tandem accelerator mainly accelerating heavy ions covering the middle energy range of 0.8 to 20 MeV is the model 9SDH-2 manufactured by National Electrostatics Corp. It has two negative ion sources; one is a charge exchanging RF ion source exclusively for generating negative helium ions, and the other a cesium sputter ion source producing a wide variety of high intensity negative ions. The injection beam with energies up to 80 keV is analyzed by a 90 bending magnet of which the mass resolution m/Am is 100. A voltage stability in the accelerator of 3 x 10m4 is controlled by a corona probe using both signals of a generating voltmeter and a capacitive pick off (CPO), or by means of slit currents and the CPO. Three accelerating beam lines are connected with experimental apparatus in the target room No. 1, and other two beam lines are transported to the target room No. 2 for multiple beam applications. A 0.4 MV ion implanter covering an energy range of 10 to 400 keV was manufactured by Nissin Electric
Corp. The ion source mounted at the high voltage terminal is of a Freeman type equipped with either an oven or a sputter electrode to generate a plasma of interest. Source materials with high melting points can be ionized by the sputter electrode. Beams extracted from the ion source with energies up to 30 keV are analyzed by a 90” bending magnet with the mass resolution (m/Am) of 100, mounted at the high-voltage terminal. Three beam lines are connected with different multiple beam experimental apparatus, and the fourth is connected with an integrated 400 kV analytical electron microscope in the target room No. 4, which is in the underground. The main parameters of the three accelerators are listed in Table 1.
3. Experimental
apparatus
and applications
Eleven experimental apparatus are to be connected with each beam line of three accelerators. Some of them are outlined below. A triple beam target chamber is installed for basic study of high-energy neutron induced damage of various materials of a nuclear fusion reactor in the target room No. 2. The high-energy neutrons give rise not only to atomic displacement damage by recoil atoms but also to the production of hydrogen and helium by transmutation reactions. Simultaneous irradiation with one heavy ion beam and two light ion beams from the three machines allows the simulation of the above irradiation environment. This chamber is equipped with a precision quadropole mass analyzer and a six-axes goniometer, and the sample temperature can be controlled in a range of 80 to 1000 K. Two dual-beam analysis systems designed for experiments of in-situ or successive analysis are installed in the target room No. 2. The one, connected with the tandem and implanter beam line, will be used mainly for nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA) using heavy ion probes from the tandem accelerator. The other, connected
Table 1 The parameter of three accelerators
Model Charging system Accelerating voltage Accelerated ion mass Beam intensity
Ion source
Tandem
Single-ended
Ion implanter
9SDH-2 (NEC) Pellet chain 0.4-3.0 MV l-200 amu C 3+ 12.0 MeV 10 JLA Ni 4+ 15.0 MeV 4 FA Au 3 + 12.0 MeV 15 FA Charge exchanging RF Cs sputter type
NC30OOB(NHV) Schenkel DC P.S. 0.4-3.0 MV H, d, He and e H 3.0 MeV 300 PA He 3.0 MeV 200 PA e 3.0 MeV 100 FA RF ion source
NH-40SR (NE) Cockcroft-Walton lo-400 kV l-200 amu P 400 keV 100 I.LA As 400 keV 100 p,A Ag 400 keV 20 PA Freeman type with sputter electrode
I. ION ACCELERATORS/SOURCES
26
Y. Saitoh et al. / Nucl. Instr. and Meth. in Phys. Res. B 89 (1994) 23-26
with the single-ended and implanter beam lines, will be used mainly for Rutherford back scattering (RBS) and high-resolution nuclear resonance reaction analysis using light ions from the single-ended accelerator. Both apparatus are equipped with a three-axis goniometer, a YAG laser for annealing samples and a vacuum deposition system. The sample temperature can be controlled in a range from 15 to 320 K. The 400 kV analytical electron microscope connected with the beam line in the No. 4 target room at an angle of 50” with the horizontal line from the implanter is designed to permit in-situ observation of the dynamic process of structural change of materials under simultaneous irradiation with beams from the implanter and a 40 kV inner ion source. A light ion microbeam apparatus connected with the single-ended accelerator is now under construction. To easily achieve a submicron beam spot size within 0.5 pm, we have to minimize the energy spread of the accelerated beam. For this reason, we selected the accelerator design described above within a voltage stability of k 1 x 10m5. This system will be applied for microbeam analysis, high resolution single event upset analysis, etc. R&D of cell surgery technique aiming to establish a new technology for cell treatment has also been started by using an apparatus for heavy ion irradiation to cells
with penetration depth control, connected with tandem accelerator. The beam penetration into the membrane is precisely controlled by changing the celeration energy. The beam is taken out in the through a thin organic film to irradiate the cell.
the cell acair
4. Conclusion Three electrostatic accelerators covering an energy of 10 keV to 20 MeV were completed mainly for materials science research in the TIARA. In the 3 MV single-ended accelerator, we obtained an extremely high voltage-stability of 6OV,, ripple at 3 MV. This result gives a good reason to be optimistic about providing a submicron microbeam. To operate these accelerators independently or simultaneously, various combinations of ion beams can be supplied to research experiments.
Reference [l] S. Sato, Proc. Int. Conf. on Evolution in Beam Applications (1991) p. 239. [2] K. Arakawa et al., Proc. Int. Conf. on Evaluation in Beam Applications (1991) p. 264. [3] Harada et al., the IEEE Annals, No. F75560-3, 1975.