Progress in long-pulse production of powerful negative ion beams for JT-60SA and ITER

Kojima, Atsushi; Umeda, Naotaka; Hanada, Masaya; Yoshida, Masafumi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Akino, Noboru; Komata, Masao; Mogaki, Kazuhiko; et al.

Nuclear Fusion, 55(6), p.063006_1 - 063006_9, 2015/06

https://doi.org/10.1088/0029-5515/55/6/063006

Significant progresses in the extension of pulse durations of powerful negative ion beams have been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long pulse production/acceleration of negative ion beams in JT-60SA and ITER, the new technologies have been developed in the JT-60SA ion source and the MeV accelerator in Japan Atomic Energy Agency. As for the long pulse production of high-current negative ions for JT-60SA ion source, the pulse durations have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA ion source, which satisfies the required pulse duration of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform negative ion productions with the modified tent-shaped filter field configuration. Moreover, the each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER ion source because the sustainment of the cesium coverage in large extraction area is one of the common issues between JT-60SA and ITER. As for the long pulse acceleration of high power density beams in the MeV accelerator for ITER, the pulse duration of MeV-class negative ion beams has been extended by more than 2 orders of magnitude by modifying the extraction grid with a high cooling capability and a high-transmission of negative ions. A long pulse acceleration of 60 s has been achieved at 70 MW/m (683 keV, 100 A/m) which has reached to the power density of JT-60SA level of 65 MW/m.

Measurement of pure water resistivity in a high temperature region

Yamanaka, Haruhiko; Maejima, Tetsuya; Terunuma, Yuto; Watanabe, Kazuhiro; Kashiwagi, Mieko; Hanada, Masaya

JAEA-Technology 2014-037, 12 Pages, 2014/12

JAEA-Technology-2014-037.pdf:4.27MB

Resistivity of a high temperature pure water has been measured up to 180C which is the maximum water temperature in the ITER Neutral Beam Injector. The resistivity of the pure water is decreased by increasing the water temperature. It was found that even different resistivity water of 9 Mcm and 5 Mcm showed almost the same resistivity at the higher temperature region of 100C. The resistivity of 0.36 Mcm was measured at the temperature of 180C. This resistivity agreed well to the calculated value for the theoretical pure water.

Development of negative ion extractor in the high-power and long-pulse negative ion source for fusion application

Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Kojima, Atsushi; Yoshida, Masafumi; Taniguchi, Masaki; Dairaku, Masayuki; Maejima, Tetsuya; Yamanaka, Haruhiko; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 85(2), p.02B320_1 - 02B320_3, 2014/02

https://doi.org/10.1063/1.4852297

The negative ion extractor for high power and long-pulse operations is newly developed toward the neutral beam injector (NBI) for heating & current drive of future fusion machines such as ITER, JT-60 Super Advanced (SA) and DEMO reactor. The satisfactory cooling capability is designed in the thermal analysis. A negative ion production and a suppression of electrons are experimentally validated for this new extractor. As the results, the negative ion current shows increases by a factor of 1.3 with suppressing the electron current. The beam divergence angle is also maintained small enough, 4 mrad.

Compensations of beamlet deflections for 1 MeV accelerator of ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; Dairaku, Masayuki; Tobari, Hiroyuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Inoue, Takashi; DeEsch, H. P. L.*; Grisham, L. R.*; et al.

AIP Conference Proceedings 1515, p.227 - 236, 2013/02

https://doi.org/10.1063/1.4792789

In a five stage multi-aperture multi-grid (MAMuG) accelerator for the ITER neutral beam injector (NBI), 1 MeV, 40 A D ion beam is required for 1 hour. However, beamlets are deflected due to (1) magnetic field for electron suppression and (2) space charge repulsion between beamlets, and consequently, cause excess grid heat load. A three dimensional beam analysis has been carried out to compensate the beamlet deflections. This paper shows that the beamlet deflections due to (1) and (2) are compensated by an aperture offset of only 0.6 mm applied to the aperture of 17 mm in diameter in the extractor and by a metal bar attached around aperture area beneath the extractor, respectively. When the metal bar is increased to 3 mm in thickness and installed 30 mm away from the aperture area, the beamlet is steered gently by the weaker electric field distortion. The beam optics was confirmed not deteriorated by those compensations. The presentation also discusses application of these compensation techniques to the ITER design.

Voltage holding study of 1 MeV accelerator for ITER neutral beam injector

Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Dairaku, Masayuki; Takemoto, Jumpei; Tobari, Hiroyuki; Tsuchida, Kazuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Kojima, Atsushi; et al.

Review of Scientific Instruments, 83(2), p.02B121_1 - 02B121_3, 2012/02

https://doi.org/10.1063/1.3675389

JAEA has developed the MeV accelerator to demonstrate 1 MeV, 200 A/m H ion beam acceleration required for ITER NBI. A key to realize such a high power accelerator is improvement of voltage holding capability. Based on detailed investigation of the voltage holding characteristics, MeV accelerator was modified to reduce electric field concentration by extending gaps between the grid supports and increasing curvature radiuses at the support corners. After the modifications, accelerator succeeded in sustaining -1 MV in vacuum without beam acceleration. Moreover, beam deflection due to the magnetic field for electron suppression and space charge repulsion was compensated by aperture displacement technique. As the result, beam deflection was compensated and voltage holding during the beam acceleration was improved. Beam parameter of the MeV accelerator was increased to 980 keV, 185 A/m, which is close to the requirement of ITER accelerator.

Study of beamlet deflection and its compensations in a MeV accelerator

Kashiwagi, Mieko; Inoue, Takashi; Taniguchi, Masaki; Umeda, Naotaka; Grisham, L. R.*; Dairaku, Masayuki; Takemoto, Jumpei; Tobari, Hiroyuki; Tsuchida, Kazuki; Watanabe, Kazuhiro; et al.

AIP Conference Proceedings 1390, p.457 - 465, 2011/09

https://doi.org/10.1063/1.3637417

In a five stage multi-aperture and multi-grid (MAMuG) accelerator in JAEA, beam acceleration tests are in progress toward 1 MeV, 200 A/m H ion beams for ITER. The 1 MV voltage holding has been successfully demonstrated for 4000 s with the accelerator of expanded gap length that lowered local electric field concentrations. The led to increase of the beam energy up to 900 keV-level. However, it was found that beamlets were deflected more in long gaps and direct interceptions of the deflected beamlet caused breakdowns. The beamlet deflection and its compensation methods were studied utilizing a three-dimensional multi beamlet analysis. The analysis showed that the 1 MeV beam can be compensated by a combination of the aperture offset of 0.8 mm applied in the electron suppression (ESG) and the metal bar called a field shaping plate with a thickness of 1 mm attached beneath the ESG. The paper reports analytical predictions and experimental results of the MAMuG accelerator.

Development of full-size mockup bushing for 1 MeV ITER NB system

Tobari, Hiroyuki; Inoue, Takashi; Hanada, Masaya; Dairaku, Masayuki; Watanabe, Kazuhiro; Umeda, Naotaka; Taniguchi, Masaki; Kashiwagi, Mieko; Yamanaka, Haruhiko; Takemoto, Jumpei; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

http://www-naweb.iaea.org/napc/physics/FEC/FEC2010/html/node58.htm#14974

High voltage (HV) bushing in the ITER NBI is one of critical components, which acts as a feedthrough for electric power and cooling water from the -1 MV power supply in SF gas to beam source inside vacuum. JAEA has overcome a longstanding issue on manufacturing of a large bore ceramic ring with 1.56 m in diameter as the insulator of the five-stage HV bushing. Joining method of the ceramic and metal flange with thick Kovar plate to form vacuum boundary was also developed. By assembling components, a full-size mockup bushing simulating one stage of the HV bushing was successfully manufactured. In the voltage holding test, the high voltage of 240 kV including the margin of 20 % of a rated voltage was sustained for 3600 s without breakdown, and the voltage holding capability required in ITER was successfully verified.

Transient phenomena analysis of a DC -1MV power supply for the ITER NBI

Yamamoto, Masanori; Watanabe, Kazuhiro; Yamanaka, Haruhiko; Takemoto, Jumpei; Yamashita, Yasuo*; Inoue, Takashi

JAEA-Technology 2010-029, 60 Pages, 2010/08

JAEA-Technology-2010-029.pdf:10.49MB

A power supply for the ITER Neutral Beam Injector (NBI) is a DC ultra-high voltage (UHV) power supply to accelerate negative ion beams of 40 A up to an energy of 1 MeV. Japan Atomic Energy Agency as the Japan Domestic Agency for ITER contributes procurement of dc -1 MV main components such as step-up -1 MV transformers rectifiers, a high voltage deck 2, a -1 MV insulating transformer, a transmission line, a surge reduction system and equipments for site test. Design of the surge suppression in the NBI power supply is one of the key issues to obtain the stable injector performance. This report describes the design study using EMTDC code on the surge suppression by optimizing the core snubber and additional elements in the -1 MV power supply. The results show that the input energy from the stray capacitance to the accelerator at the breakdown can be reduced to about 25 J that is smaller than the design criteria of 50 J for the ITER NBI.

Voltage holding test of full-size mockup bushing for ITER NBI

Tobari, Hiroyuki; Inoue, Takashi; Dairaku, Masayuki; Yamanaka, Haruhiko; Umeda, Naotaka; Taniguchi, Masaki; Kashiwagi, Mieko; Takemoto, Jumpei; Watanabe, Kazuhiro; Sakamoto, Keishi

no journal, , 

The high voltage bushing in the ITER NBI has a five-stage structure composed of large bore ceramic rings. The ceramic ring must be 1.56 m in diameter because many conductors are located keeping insulation inside the ceramic ring. However, in conventional technique, the diameter has been limited less than 1 m. The joining technique of the brazing between the large ceramic ring with metal has not been established. Then, new forming method of the large ceramic ring and the brazing technique were developed. As a result, the large ceramic of 1.56 m in diameter was successfully manufactured and the ceramic ring was brazed to Kovar rings with vacuum tightness. To enhance voltage holding capability of the manufactured insulator, stress ring to suppress the breakdown staring from the joining point of the ceramic and metal was also developed. In the high voltage test of the insulator, 240 kV was sustained stably over 1 hour, and the voltage holding capability required in ITER was verified.

Voltage holding test of a full-size mockup bushing for ITER NBI

Tobari, Hiroyuki; Inoue, Takashi; Dairaku, Masayuki; Watanabe, Kazuhiro; Yamanaka, Haruhiko; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Takemoto, Jumpei; Sakamoto, Keishi

no journal, , 

The HV bushing in the ITER NBI is a feedthrough for electric power and cooling water located between gas-insulated transmission line and a beam source in vacuum. The bushing has five-stage structure composed of large ceramic rings of which diameter must be 1.56 m to sustain electric insulation between conductors inside the ceramic. However, in conventional technique, the diameter has been limited less than 1 m. The brazing to form vacuum boundary for such a large ceramic ring with metal has not been established. Then, new forming method of the large ceramic ring and the brazing technique were developed. As a result, manufacturing of the ceramic ring and the brazing with to Kovar rings were accomplished. To enhance voltage holding capability of the insulator, stress ring to suppress the breakdown staring from the triple point was also developed. In the high voltage test of the insulator, 240 kV was sustained over 1 hour, and the voltage holding capability required in ITER was verified.