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Journal Articles

Progress of the ITER NBI acceleration grid power supply reference design

Toigo, V.*; Zanotto, L.*; Bigi, M.*; Decamps, H.*; Ferro, A.*; Gaio, E.*; Guti$'e$rrez, D.*; Tsuchida, Kazuki; Watanabe, Kazuhiro

Fusion Engineering and Design, 88(6-8), p.956 - 959, 2013/10

 Times Cited Count:17 Percentile:78.88(Nuclear Science & Technology)

This paper reports the progress in the reference design of the Acceleration Grid Power Supply (AGPS) of the ITER Neutral Beam Injector (NBI). The design of the AGPS is very challenging, as it shall be rated to provide about 55 MW at 1 MV dc in quasi steady-state conditions; moreover, the procurement of the system is shared between the European Domestic Agency (F4E) and the Japanese Domestic Agency (JADA), resulting in additional design complication due to the need of a common definition of the interface parameters. A critical revision of the main design choices is presented also in light of the definition of some key interface parameters between the two AGPS subsystems. Moreover, the verification of the fulfillment of the requirements in any operational conditions taking into account the tolerance of the different parameters is also reported and discussed.

Journal Articles

Vacuum insulation and achievement of 980 keV, 185 A/m$$^{2}$$ H$$^{-}$$ ion beam acceleration at JAEA for the ITER neutral beam injector

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

Plasma Science and Technology, 15(2), p.179 - 183, 2013/02

 Times Cited Count:1 Percentile:4.48(Physics, Fluids & Plasmas)

Vacuum insulation is a common issue for the accelerator and the HV bushing for the ITER NBI. The HV bushing has five-stage structure and each stage consists of double-layered insulators. Hence, several triple points exist around the insulators. To reduce electric field at those points simultaneously, three types of stress ring were developed. In voltage holding test of a full-scale mockup equipped with those stress rings, 120% of rated voltage was sustained and the voltage holding capability required in ITER was verified. In the MeV accelerator, voltage holding capability was not sufficient due to breakdown triggered by electric field concentration at edge and corner on grid components. By extending gap length, 1 MV was sustained in vacuum. Furthermore, with new accelerator grids which compensates beam deflection due to magnetic field and space charge repulsion between beamlets, 980 keV, 185 A/m$$^{2}$$ H$$^{-}$$ ion beam acceleration was demonstrated, which was close to ITER requirement.

Journal Articles

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

 Times Cited Count:11 Percentile:47.6(Instruments & Instrumentation)

JAEA has developed the MeV accelerator to demonstrate 1 MeV, 200 A/m$$^{2}$$ 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$$^{2}$$, which is close to the requirement of ITER accelerator.

Journal Articles

Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion source

Shibata, Takanori; Koga, Shojiro*; Terasaki, Ryo*; Inoue, Takashi; Dairaku, Masayuki; Kashiwagi, Mieko; Taniguchi, Masaki; Tobari, Hiroyuki; Tsuchida, Kazuki; Umeda, Naotaka; et al.

Review of Scientific Instruments, 83(2), p.02A719_1 - 02A719_3, 2012/02

 Times Cited Count:2 Percentile:12.56(Instruments & Instrumentation)

In the NBI for large fusion devices, production of uniform negative ion beam is one of important issues. A physical model is proposed to understand the non-uniformity. It has been qualitatively shown that the non-uniform beam intensity is due to the following process; (1) formation of non-uniform EEDF, (2) localized production of hydrogen atoms/ions (H$$^0$$/H$$^+$$) due to (1), (3) non-uniform flux of H$$^0$$/H$$^+$$ to the PG and (4) localized surface production of negative ions. However, in the past studies, the EEDF was assumed as two temperature Maxwellian distribution from measurements. Thus effects of high energy electrons are not taken into account precisely. In the present research, local EEDF is calculated by the 3D Monte-Carlo kinetic model which takes into account the spatial and magnetic configurations of the real negative ion source. The numerical result show that high energy component of the EEDF enhances the spatial non-uniformity in the production rate of H$$^0$$/H$$^+$$.

Journal Articles

Improvement of voltage holding and high current beam acceleration by MeV accelerator for ITER NB

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

AIP Conference Proceedings 1390, p.449 - 456, 2011/09

 Times Cited Count:2 Percentile:53.6

At JAEA, MeV accelerator has been developed as a proof-of-principle accelerator for ITER NBI. To achieve the acceleration of 1 MeV, 200 A/m$$^{2}$$ beam required for ITER, improvement of the voltage holding capability is essential. Review of voltage holding results ever obtained with various geometries of the accelerators showed that voltage holding capability was about a half of that for ideal small electrode. This is due to local electric field concentration in the accelerators, such as edge and corner between grids and its support structures. Based on these results, accelerator was modified to reduce the electric field concentration by reshaping the support structures and expanding the gap length. After the modifications, voltage holding capability in vacuum was increased from 835 kV to 1 MV. Voltage holding progressed the energy and current to 879 keV, 0.36 A (157 A/m$$^{2}$$).

Journal Articles

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

 Times Cited Count:9 Percentile:89.39

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$$^{2}$$ 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.

Journal Articles

Development of high voltage power supply system for ITER neutral beam injector

Tsuchida, Kazuki; Watanabe, Kazuhiro; Tobari, Hiroyuki; Takemoto, Jumpei; Yamanaka, Haruhiko; Inoue, Takashi

Denki Gakkai Kenkyukai Shiryo, Genshiryoku Kenkyukai (NE-11-001$$sim$$004 $$cdot$$ 006$$sim$$010), p.17 - 22, 2011/09

A 1 MeV high-energy neutral beam injector is under developing for heating and current drive of ITER plasma in collaboration with EUDA. JADA will provide ultra-high voltage DC power supply components. Design of the 1 MV power supply, R&Ds on a HV bushing and a water choke will be presented. These results satisfy the requirements for the NBI system.

Journal Articles

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

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$$_{6}$$ 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.

Oral presentation

Development and procurement of the ITER NB power supplies

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

no journal, , 

no abstracts in English

Oral presentation

Development of water choke model for high-voltage deck of ITER neutral beam

Tsuchida, Kazuki; Watanabe, Kazuhiro; Yamanaka, Haruhiko; Takemoto, Jumpei; Inoue, Takashi; Tanaka, Shigeru*; Yamashita, Yasuo*

no journal, , 

In ITER Neutral Beam (NB) injection system, the negative ion source and the accelerator should be cooled to generate high energy and high power beam for the prolonged operation. Those devices will be settled at high electric potential of -1 MV and an water choke is needed in the cooling water line to insulate the high voltage. The water choke for ITER should meet the following specifications; high water pressure (2 MPa) and high leak current (several ten mA) due to the reduction of resistivity in hot water (65 $$^{circ}$$C), etc. So, we developed a ceramic insulation tube for the water choke of ITER NB system and it's performance was confirmed by mechanical and withstand voltage tests. From the test results, it was confirmed the developed ceramic tube has sufficient performance ($$>$$110 kV/tube) as a part of ITER water choke. The anti-corrosion and anti-dissolution of the sealing materials in the ceramic tube was also confirmed under the high leak current condition.

Oral presentation

Development of negative ion based neutral beam injector for ITER

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

no journal, , 

In the ITER project, negative-ion-based neutral beam injectors (NBI) which can inject deuterium neutral beams of 1 MeV, 16.5 MW per one injector are planned. The authors will report the subjects of the system and present status of the development for the major components of Japanese procurements for the ITER NBI and the ITER NBI test facility.

Oral presentation

Progress of procurement on the ITER NB ultra-high voltage power supplies

Yamanaka, Haruhiko; Watanabe, Kazuhiro; Tsuchida, Kazuki; Tobari, Hiroyuki; Takemoto, Jumpei; Inoue, Takashi

no journal, , 

JAEA, as a domestic agency of Japan (JADA) for ITER, is carrying out a research and development of a high-energy neutral beam injector for heating and current drive of ITER plasma in collaboration with European Domestic Agency. JADA will provide ultra-high voltage DC power supplies which can generate -1 MV DC power for the negative ion beam source. Present status of the design and manufacturing technology R&D on the power supply is reported as a part of contribution by JADA for the ITER Neutral Beam Injector. In particular, the current presentation highlights R&D status regarding the ceramic insulation tubes for water choke and the DC -1 MV insulating transformer.

Oral presentation

Development of 1 MeV accelerator for ITER; Achievement of 0.98 MeV, 185 A/m$$^2$$ negative ion beam acceleration

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

no journal, , 

In a MeV accelerator test for the ITER neutral beam injector (NBI), beam acceleration tests are progressed toward 1 MeV, 200 A/m$$^2$$ H$$^-$$ ion beams. As results of suppression of breakdowns due to local electric field concentrations and suppression of direct interception of deflected beamlets due to magnetic field and space charge repulsion, the beam parameters increased from 0.8 MeV to 0.98 MeV, 185 A/m$$^2$$. This is achieving the target value. After this achievement, the results of the MeV accelerator are applied to the ITER accelerator design.

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