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Operation of the negative-ion based NBI for JT-60U
Fusion Engineering and Design 39 – 40 (1998) 115 – 121
Operation of the negative-ion based NBI for JT-60U M. Kuriyama *, N. Akino, T. Aoyagi, N. Ebisawa, N. Isozaki, A. Honda, T. Inoue, T. Itoh, M. Kawai, M. Kazawa, J. Koizumi, K. Mogaki, Y. Ohara, T. Ohga, Y. Okumura, H. Oohara, K. Ohshima, F. Satoh, T. Takenouchi, Y. Toyokawa, K. Usui, K. Watanabe, M. Yamamoto, T. Yamazaki, C. Zhou 1 Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Mukouyama, Naka-machi, Naka-gun, Ibaraki-ken 311 -01, Japan
Abstract A beam injection experiment with the negative-ion based NBI system (N-NBI) started in March 1996 on JT-60U. After achieving the first neutral beam injection of 180 keV, 0.1 MW for 0.4 s into the JT-60U plasmas, the operation parameters of the ion source and power supply had been optimized for increasing the beam energy and beam current. In September 1996, a deuterium neutral beam of 2.5 MW at 350 keV was injected into JT-60U using two ion sources. In the operation with hydrogen at the beginning of 1997, a negative ion beam current of 18.4 A at 350 keV has been obtained, and a neutral beam of 3.2 MW at 350 keV for 1 s has been injected into the plasma with one ion source. A neutralization efficiency of negative ion beam has been confirmed to be about 60% at the beam energies of 250–385 keV as predicted theoretically. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction In JT-60U, a high energy neutral beam injection program with the negative-ion based NBI (N-NBI) system [1] has been progressed for a demonstration of non-inductive NBI current drive and plasma core heating in a high density plasma. The beam injection into JT-60U plasmas with the N-NBI started in March 1996 just after the completion of the system. A key issue of the N-NBI is to confirm the feasibility in both physical and technical aspects for the application of the high * Corresponding author. 1 Present address: Southwestern Institute of Physics, Beijing, China.
beam energy N-NBI to next generation tokamaks such as ITER [2]. The JT-60U N-NBI aims at delivering a deuterium/hydrogen neutral beam injection power of 10 MW at 500 keV for 10 s with one beamline. As shown in Fig. 1, the N-NBI is composed of a 24-m long beamline with two negative-ion sources, a 500 kV/64 A acceleration power supply, negative ion generation and extraction power supplies which are installed in the high voltage table floated on 500 kV in maximum and subsystems such as a cooling water system, a refrigeration system for cryopumps, a control system and an auxiliary vacuum pumping system. The ion source composed of a negative-ion generator and a three-stage electrostatic accelerator has a capability of producing 500 keV/22 A D −
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00183-5
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M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 1. Negative-ion based neutral beam injection system (N-NBI) for JT-60U.
beams with a low beam divergence angle of 5 mrad [3–5]. To verify the performance of a full scale ion source and 500 kV power supply before the beam injection into JT-60U, a part of the system including one ion source and power supplies for one ion source was manufactured in 1995. In a preliminary test of the negative-ion generation and acceleration test with one ion source executed in 1995, a negative-ion beam power of 5.4 MW (400 keV× 13.5 A/D − ) was obtained [6], which was the highest negative ion beam power in the world. After having completed the whole system in the beginning of 1996, the beam injection test with two ion sources started. The first neutral beam of 180 keV, 0.1 MW for about 0.4 s with deuterium was injected successfully into JT-60U in March 1996. The beam energy and beam power,
subsequently, have been increased through optimizing the operation parameters of the ion source, beamline and power supply. In this report, we describe the characteristics of the negative ion generation and acceleration with both deuterium and hydrogen, the neutralization efficiency and the neutral beam injection into JT-60U.
2. System performance obtained with the N-NBI
2.1. Negati6e ion generation The cesium effect of the negative ion generation is shown in Fig. 2 with deuterium. The acceleration current (Iacc) increases with time for cesium seeding, and an extraction current (Iext), which
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 2. Cesium effect of negative deuterium ion production in the ion source. (Cs injection started at t = 0. Iext: extraction current including both negative ions and electrons, Iacc: acceleration drain current).
contains both negative ions and electrons, decreases rapidly. The enhancement factor of the Iacc is about 4 compared with no cesium injection. An arc efficiency (Iacc/Parc), which means efficiency of negative ion generation, also increases up to 0.075 – 0.08 after the cesium seeding of 6 h as against 0.015 – 0.02 before seeding. The ion source should be operated at a pressure as low as possible to decrease the stripping loss of negative ions in the accelerator. Fig. 3 shows the pressure dependence of the acceleration current and the extraction current at an arc power of 110 kW with hydrogen. Both the acceleration and extraction current decrease with the filling pres-
Fig. 3. Pressure dependence of the acceleration current and the extraction current.
117
Fig. 4. Arc power dependence of the acceleration current, the extraction current and the negative ion beam on the calorimeter. (Iext: extraction current including both negative ions and electrons, Iacc: acceleration drain current, IH − : negative ion current).
sure above a pressure of 0.2 Pa. The optimum operating pressure is less than 0.2 Pa which is lower than the design value of 0.3 Pa.
2.2. Negati6e ion acceleration The Iacc, Iext and H − current (IH − ) with hydrogen beam at 300 keV are shown in Fig. 4, as a function of the arc power. The IH − was measured with a water calorimeter. The ratio of Iacc to Iext is 80–90%, which means that much of the current extracted from the negative ion generator are negative ions, and the rate of electron component is lower than that of the negative ions. The IH − is too low in comparison to the Iacc in this experiment. The reason of the lower IH − is that the accelerating negative ions are lost largely in the accelerator through a direct impingement onto the acceleration grids and a neutralization loss. The loss through the direct impingement could be decreased by optimizing the operation limit of the ion source. The ratios of heat load to the acceleration power, P/(Vacc Iacc), in the beamline are shown in Fig. 5. A calorimeter power, that is the neutral beam power, reaches roughly 35% of the beam power at an optimum Iacc of 24 A. Each negative and positive ion dump receives about 12% of the beam power and does not change
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M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 5. Fractional heat loads on the beamline components.
greatly in a Iacc range of 21 – 31 A. The heat load of the beam limiter positioned at the ion source tank and neutralizer cell are about 5%, respectively. Fig. 6 shows a power flow diagram in the beamline measured at an acceleration power of 350 kV 30 A. The negative-ion beam power of the ion source is 6.4 MW (18.4 A/H − ) which corresponds to 62% of the acceleration drain power (Vacc Iacc). The beam powers of 0.5 MW (5%) are lost for a geometrical loss on the beam limiter and the neutralizer, respectively. The neutral beam power of 3.4 MW (32%) injects on the calorimeter and the residual ion beam powers of 1.1 MW (11%) are deposited on each of the ion dumps (for H − and H + ). In the beam injection
into JT-60U after retracting the calorimeter, we have injected a neutral beam power of 3.2 MW taking into account a loss in the drift duct of 0.2 MW which corresponds to a geometrical loss caused by beam divergence and a reionization loss in the duct. The reionization loss in the hydrogen beam injection has been measured to be the order of 1.5–2% of neutral beam power. Fig. 7 shows the negative ion current and power as a function of the beam energy obtained in the N-NBI using one ion source. The negative ion currents of 18.4 A/H − at 350 keV and 13.5 A/D − at 400 keV have been obtained, which are close to the target value of 22 A in both D − and H − . In a higher beam energy operation over 400 keV, we have operated 2.4 A/D − at 460 keV. The negative ion beam power achieved per source is 6.4 MW at 350 keV with hydrogen, and 5.4 MW at 400 keV with deuterium.
2.3. Neutralization efficiency The neutralization efficiency has been measured in a beam energy range of 250–385 keV with both deuterium and hydrogen. Fig. 8(a) shows power fraction of neutral beam and residual ion beams of D − and D + at 375 keV as a function of the neutral gas line density for neutralization. The maximum neutralization efficiency was confirmed to be about 60% at a line density of 8.5×1015 molecules cm2. At around
Fig. 6. Typical power flow diagram measured in the beamline.
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
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Fig. 7. Negative ion current and the power per one ion source as a function of the beam energy.
the optimum line density, the fractions of D − and D + are roughly 20% each. The optimum line density does not agree with the theoretically calculated value of 5.5×1015 molecules cm2. The reason of the disagreement is being investigation. Fig. 8(b) shows the neutralization efficiency for hydrogen beam at 385 keV. The neutralization efficiency has been obtained to be 60% same as deuterium. The optimum line density is 9.5× 1015 molecules cm2, which is consistent perfectly with theoretically predicted density. Fig. 9 shows the neutralization efficiency as a function of beam energy. We have confirmed in the beam energy range of 250 – 385 keV that the optimum neutralization efficiency of negative ion beam for both deuterium and hydrogen is almost constant at 60%.
Fig. 8. Neutralization efficiency of (a) deuterium beam at 375 keV and (b) hydrogen beam at 385 keV.
beam injection power. After the first neutral beam was injected into JT-60U successfully in March 1996, the neutral beam power has been increased steadily. A deuterium neutral beam
3. Neutral beam injection into JT-60U Fig. 10 shows the progress of the neutral
Fig. 9. Measured neutralization efficiency as a function of the beam energy.
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Fig. 11. Typical result of high energy neutral beam injection into the JT-60U plasma.
ment with the results of a theoretical simulation [7].
4. Summary Fig. 10. Progress of the neutral beam power delivered to the JT-60U plasmas.
power of 2.5 MW at 350 keV was injected for 0.9 s using two ion sources in September 1996, and 1.2 MW at 400 keV was also injected with one ion source. After some modification of the ion source and acceleration power supply, we have operated for 4 weeks from the middle of January 1997. A hydrogen neutral beam power of 3.2 MW as mentioned in Section 2 has been injected for 1 s at 350 keV with one ion source. It could be said that we are convinced of the neutral beam injection of over 8 MW at around 400 keV using two ion sources. Fig. 11 shows a typical result of the N-NBI beam injection into JT-60U plasma. In a beam injection of 350 keV/2 MW into a high bp plasma under an injection power of 8 MW at 90 keV with the positive ion based NBI, the plasma stored energy and neutron yield through D–D reaction increased sharply. The results obtained so far in the high energy beam injection with the N-NBI are very much in agree-
The N-NBI for JT-60U has been operated successfully since March 1996. In the operation, the following results have been obtained. (1) The highest negative ion beam currents obtained so far, are 18.4 A/H − (6.4 MW) at 350 keV with hydrogen, 13.5 A/D − (5.4 MW) at 400 keV for deuterium. (2) A neutral beam injection power of 3.2 MW at 350 keV has been attained using one ion source with hydrogen in February 1997. (3) The neutralization efficiency of negative ion beams has been confirmed to be 60% as theoretically predicted for both deuterium and hydrogen in a beam energy range of 250–385 keV. (4) The whole NBI system has been operated under tokamak plasma environment without any problems.
Acknowledgements The authors would like to thank the members of JT-60 group. They are also grateful to Drs A. Funahashi, H. Kishimoto, M. Shimizu, M. Azumi for their continuous encouragement.
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
References [1] M. Kuriyama, et al., High energy negative-ion based neutral beam injector for JT-60U, Fusion Eng. Des. 26 (1995) 445. [2] R.S. Hemsworth, et al., Neutral beams for ITER (invited), Rev. Sci. Instrum. 67 (3) (1996) 1120. [3] K. Watanabe, et al., Beam acceleration test in negative-ion based NBI system for JT-60U, Proc. 6th Symp. on Production and Neutralization of Negative Ions and Beams, BNL, 1992, p. 326. [4] Y. Okumura, et al., Development of a large D − ion source for the JT-60U negative ion-based neutral beam injector,
.
121
Proc. IEEE 14th Symp. Fusion Eng., Hyannis, MA, 1993, pp. 466 – 469. [5] Y. Okumura, et al., Development of a 500-keV, 22A D − ion source for the neutral beam injector for JT-60U, Rev. Sci. Instrum. 67 (1996) 1018. [6] K. Watanabe, et al., Recent progress of high-power negative ion beam development for fusion plasma heating, Proc. 7th Int. Symp. Advanced Nuclear Energy Research, Takasaki, Japan, 18 – 20 March, 1996. [7] K. Ushigusa and the JT-60 Team, Steady-state operation research in JT-60U, 16th IAEA Fusion Energy Conf., Montreal, Canada, 7 – 11 October 1996, F1-CN-64/01-3.
Operation of the negative-ion based NBI for JT-60U M. Kuriyama *, N. Akino, T. Aoyagi, N. Ebisawa, N. Isozaki, A. Honda, T. Inoue, T. Itoh, M. Kawai, M. Kazawa, J. Koizumi, K. Mogaki, Y. Ohara, T. Ohga, Y. Okumura, H. Oohara, K. Ohshima, F. Satoh, T. Takenouchi, Y. Toyokawa, K. Usui, K. Watanabe, M. Yamamoto, T. Yamazaki, C. Zhou 1 Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Mukouyama, Naka-machi, Naka-gun, Ibaraki-ken 311 -01, Japan
Abstract A beam injection experiment with the negative-ion based NBI system (N-NBI) started in March 1996 on JT-60U. After achieving the first neutral beam injection of 180 keV, 0.1 MW for 0.4 s into the JT-60U plasmas, the operation parameters of the ion source and power supply had been optimized for increasing the beam energy and beam current. In September 1996, a deuterium neutral beam of 2.5 MW at 350 keV was injected into JT-60U using two ion sources. In the operation with hydrogen at the beginning of 1997, a negative ion beam current of 18.4 A at 350 keV has been obtained, and a neutral beam of 3.2 MW at 350 keV for 1 s has been injected into the plasma with one ion source. A neutralization efficiency of negative ion beam has been confirmed to be about 60% at the beam energies of 250–385 keV as predicted theoretically. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction In JT-60U, a high energy neutral beam injection program with the negative-ion based NBI (N-NBI) system [1] has been progressed for a demonstration of non-inductive NBI current drive and plasma core heating in a high density plasma. The beam injection into JT-60U plasmas with the N-NBI started in March 1996 just after the completion of the system. A key issue of the N-NBI is to confirm the feasibility in both physical and technical aspects for the application of the high * Corresponding author. 1 Present address: Southwestern Institute of Physics, Beijing, China.
beam energy N-NBI to next generation tokamaks such as ITER [2]. The JT-60U N-NBI aims at delivering a deuterium/hydrogen neutral beam injection power of 10 MW at 500 keV for 10 s with one beamline. As shown in Fig. 1, the N-NBI is composed of a 24-m long beamline with two negative-ion sources, a 500 kV/64 A acceleration power supply, negative ion generation and extraction power supplies which are installed in the high voltage table floated on 500 kV in maximum and subsystems such as a cooling water system, a refrigeration system for cryopumps, a control system and an auxiliary vacuum pumping system. The ion source composed of a negative-ion generator and a three-stage electrostatic accelerator has a capability of producing 500 keV/22 A D −
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00183-5
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M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 1. Negative-ion based neutral beam injection system (N-NBI) for JT-60U.
beams with a low beam divergence angle of 5 mrad [3–5]. To verify the performance of a full scale ion source and 500 kV power supply before the beam injection into JT-60U, a part of the system including one ion source and power supplies for one ion source was manufactured in 1995. In a preliminary test of the negative-ion generation and acceleration test with one ion source executed in 1995, a negative-ion beam power of 5.4 MW (400 keV× 13.5 A/D − ) was obtained [6], which was the highest negative ion beam power in the world. After having completed the whole system in the beginning of 1996, the beam injection test with two ion sources started. The first neutral beam of 180 keV, 0.1 MW for about 0.4 s with deuterium was injected successfully into JT-60U in March 1996. The beam energy and beam power,
subsequently, have been increased through optimizing the operation parameters of the ion source, beamline and power supply. In this report, we describe the characteristics of the negative ion generation and acceleration with both deuterium and hydrogen, the neutralization efficiency and the neutral beam injection into JT-60U.
2. System performance obtained with the N-NBI
2.1. Negati6e ion generation The cesium effect of the negative ion generation is shown in Fig. 2 with deuterium. The acceleration current (Iacc) increases with time for cesium seeding, and an extraction current (Iext), which
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 2. Cesium effect of negative deuterium ion production in the ion source. (Cs injection started at t = 0. Iext: extraction current including both negative ions and electrons, Iacc: acceleration drain current).
contains both negative ions and electrons, decreases rapidly. The enhancement factor of the Iacc is about 4 compared with no cesium injection. An arc efficiency (Iacc/Parc), which means efficiency of negative ion generation, also increases up to 0.075 – 0.08 after the cesium seeding of 6 h as against 0.015 – 0.02 before seeding. The ion source should be operated at a pressure as low as possible to decrease the stripping loss of negative ions in the accelerator. Fig. 3 shows the pressure dependence of the acceleration current and the extraction current at an arc power of 110 kW with hydrogen. Both the acceleration and extraction current decrease with the filling pres-
Fig. 3. Pressure dependence of the acceleration current and the extraction current.
117
Fig. 4. Arc power dependence of the acceleration current, the extraction current and the negative ion beam on the calorimeter. (Iext: extraction current including both negative ions and electrons, Iacc: acceleration drain current, IH − : negative ion current).
sure above a pressure of 0.2 Pa. The optimum operating pressure is less than 0.2 Pa which is lower than the design value of 0.3 Pa.
2.2. Negati6e ion acceleration The Iacc, Iext and H − current (IH − ) with hydrogen beam at 300 keV are shown in Fig. 4, as a function of the arc power. The IH − was measured with a water calorimeter. The ratio of Iacc to Iext is 80–90%, which means that much of the current extracted from the negative ion generator are negative ions, and the rate of electron component is lower than that of the negative ions. The IH − is too low in comparison to the Iacc in this experiment. The reason of the lower IH − is that the accelerating negative ions are lost largely in the accelerator through a direct impingement onto the acceleration grids and a neutralization loss. The loss through the direct impingement could be decreased by optimizing the operation limit of the ion source. The ratios of heat load to the acceleration power, P/(Vacc Iacc), in the beamline are shown in Fig. 5. A calorimeter power, that is the neutral beam power, reaches roughly 35% of the beam power at an optimum Iacc of 24 A. Each negative and positive ion dump receives about 12% of the beam power and does not change
118
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 5. Fractional heat loads on the beamline components.
greatly in a Iacc range of 21 – 31 A. The heat load of the beam limiter positioned at the ion source tank and neutralizer cell are about 5%, respectively. Fig. 6 shows a power flow diagram in the beamline measured at an acceleration power of 350 kV 30 A. The negative-ion beam power of the ion source is 6.4 MW (18.4 A/H − ) which corresponds to 62% of the acceleration drain power (Vacc Iacc). The beam powers of 0.5 MW (5%) are lost for a geometrical loss on the beam limiter and the neutralizer, respectively. The neutral beam power of 3.4 MW (32%) injects on the calorimeter and the residual ion beam powers of 1.1 MW (11%) are deposited on each of the ion dumps (for H − and H + ). In the beam injection
into JT-60U after retracting the calorimeter, we have injected a neutral beam power of 3.2 MW taking into account a loss in the drift duct of 0.2 MW which corresponds to a geometrical loss caused by beam divergence and a reionization loss in the duct. The reionization loss in the hydrogen beam injection has been measured to be the order of 1.5–2% of neutral beam power. Fig. 7 shows the negative ion current and power as a function of the beam energy obtained in the N-NBI using one ion source. The negative ion currents of 18.4 A/H − at 350 keV and 13.5 A/D − at 400 keV have been obtained, which are close to the target value of 22 A in both D − and H − . In a higher beam energy operation over 400 keV, we have operated 2.4 A/D − at 460 keV. The negative ion beam power achieved per source is 6.4 MW at 350 keV with hydrogen, and 5.4 MW at 400 keV with deuterium.
2.3. Neutralization efficiency The neutralization efficiency has been measured in a beam energy range of 250–385 keV with both deuterium and hydrogen. Fig. 8(a) shows power fraction of neutral beam and residual ion beams of D − and D + at 375 keV as a function of the neutral gas line density for neutralization. The maximum neutralization efficiency was confirmed to be about 60% at a line density of 8.5×1015 molecules cm2. At around
Fig. 6. Typical power flow diagram measured in the beamline.
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
119
Fig. 7. Negative ion current and the power per one ion source as a function of the beam energy.
the optimum line density, the fractions of D − and D + are roughly 20% each. The optimum line density does not agree with the theoretically calculated value of 5.5×1015 molecules cm2. The reason of the disagreement is being investigation. Fig. 8(b) shows the neutralization efficiency for hydrogen beam at 385 keV. The neutralization efficiency has been obtained to be 60% same as deuterium. The optimum line density is 9.5× 1015 molecules cm2, which is consistent perfectly with theoretically predicted density. Fig. 9 shows the neutralization efficiency as a function of beam energy. We have confirmed in the beam energy range of 250 – 385 keV that the optimum neutralization efficiency of negative ion beam for both deuterium and hydrogen is almost constant at 60%.
Fig. 8. Neutralization efficiency of (a) deuterium beam at 375 keV and (b) hydrogen beam at 385 keV.
beam injection power. After the first neutral beam was injected into JT-60U successfully in March 1996, the neutral beam power has been increased steadily. A deuterium neutral beam
3. Neutral beam injection into JT-60U Fig. 10 shows the progress of the neutral
Fig. 9. Measured neutralization efficiency as a function of the beam energy.
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M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
Fig. 11. Typical result of high energy neutral beam injection into the JT-60U plasma.
ment with the results of a theoretical simulation [7].
4. Summary Fig. 10. Progress of the neutral beam power delivered to the JT-60U plasmas.
power of 2.5 MW at 350 keV was injected for 0.9 s using two ion sources in September 1996, and 1.2 MW at 400 keV was also injected with one ion source. After some modification of the ion source and acceleration power supply, we have operated for 4 weeks from the middle of January 1997. A hydrogen neutral beam power of 3.2 MW as mentioned in Section 2 has been injected for 1 s at 350 keV with one ion source. It could be said that we are convinced of the neutral beam injection of over 8 MW at around 400 keV using two ion sources. Fig. 11 shows a typical result of the N-NBI beam injection into JT-60U plasma. In a beam injection of 350 keV/2 MW into a high bp plasma under an injection power of 8 MW at 90 keV with the positive ion based NBI, the plasma stored energy and neutron yield through D–D reaction increased sharply. The results obtained so far in the high energy beam injection with the N-NBI are very much in agree-
The N-NBI for JT-60U has been operated successfully since March 1996. In the operation, the following results have been obtained. (1) The highest negative ion beam currents obtained so far, are 18.4 A/H − (6.4 MW) at 350 keV with hydrogen, 13.5 A/D − (5.4 MW) at 400 keV for deuterium. (2) A neutral beam injection power of 3.2 MW at 350 keV has been attained using one ion source with hydrogen in February 1997. (3) The neutralization efficiency of negative ion beams has been confirmed to be 60% as theoretically predicted for both deuterium and hydrogen in a beam energy range of 250–385 keV. (4) The whole NBI system has been operated under tokamak plasma environment without any problems.
Acknowledgements The authors would like to thank the members of JT-60 group. They are also grateful to Drs A. Funahashi, H. Kishimoto, M. Shimizu, M. Azumi for their continuous encouragement.
M. Kuriyama et al. / Fusion Engineering and Design 39–40 (1998) 115–121
References [1] M. Kuriyama, et al., High energy negative-ion based neutral beam injector for JT-60U, Fusion Eng. Des. 26 (1995) 445. [2] R.S. Hemsworth, et al., Neutral beams for ITER (invited), Rev. Sci. Instrum. 67 (3) (1996) 1120. [3] K. Watanabe, et al., Beam acceleration test in negative-ion based NBI system for JT-60U, Proc. 6th Symp. on Production and Neutralization of Negative Ions and Beams, BNL, 1992, p. 326. [4] Y. Okumura, et al., Development of a large D − ion source for the JT-60U negative ion-based neutral beam injector,
.
121
Proc. IEEE 14th Symp. Fusion Eng., Hyannis, MA, 1993, pp. 466 – 469. [5] Y. Okumura, et al., Development of a 500-keV, 22A D − ion source for the neutral beam injector for JT-60U, Rev. Sci. Instrum. 67 (1996) 1018. [6] K. Watanabe, et al., Recent progress of high-power negative ion beam development for fusion plasma heating, Proc. 7th Int. Symp. Advanced Nuclear Energy Research, Takasaki, Japan, 18 – 20 March, 1996. [7] K. Ushigusa and the JT-60 Team, Steady-state operation research in JT-60U, 16th IAEA Fusion Energy Conf., Montreal, Canada, 7 – 11 October 1996, F1-CN-64/01-3.