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Journal Articles

Progress report of Japanese simulation research projects using the high-performance computer system Helios in the International Fusion Energy Research Centre

Ishizawa, Akihiro*; Idomura, Yasuhiro; Imadera, Kenji*; Kasuya, Naohiro*; Kanno, Ryutaro*; Satake, Shinsuke*; Tatsuno, Tomoya*; Nakata, Motoki*; Nunami, Masanori*; Maeyama, Shinya*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 92(3), p.157 - 210, 2016/03

The high-performance computer system Helios which is located at The Computational Simulation Centre (CSC) in The International Fusion Energy Research Centre (IFERC) started its operation in January 2012 under the Broader Approach (BA) agreement between Japan and the EU. The Helios system has been used for magnetised fusion related simulation studies in the EU and Japan and has kept high average usage rate. As a result, the Helios system has contributed to many research products in a wide range of research areas from core plasma physics to reactor material and reactor engineering. This project review gives a short catalogue of domestic simulation research projects. First, we outline the IFERC-CSC project. After that, shown are objectives of the research projects, numerical schemes used in simulation codes, obtained results and necessary computations in future.

Journal Articles

Numerical study of plasma generation process and internal antenna heat loadings in J-PARC RF negative ion source

Shibata, Takanori*; Nishida, Kenjiro*; Mochizuki, Shintaro*; Mattei, S.*; Lettry, J.*; Hatayama, Akiyoshi*; Ueno, Akira; Oguri, Hidetomo; Okoshi, Kiyonori; Ikegami, Kiyoshi*; et al.

Review of Scientific Instruments, 87(2), p.02B128_1 - 02B128_3, 2016/02

BB2015-1473.pdf:4.28MB

 Times Cited Count:3 Percentile:72.41(Instruments & Instrumentation)

A numerical model of plasma transport and electromagnetic field in the J-PARC RF ion source has been developed to understand relation between antenna coil heat loadings and plasma production/transport processes. From the calculation, the local plasma density increase is observed in the region close to the antenna coil. The magnetic field line with absolute magnetic flux density 30-120 Gauss results in the magnetization of electron which leads to high local ionization rate. The results suggest that modification of magnetic configuration can be made to reduce plasma heat flux onto the antenna.

Journal Articles

22A beam production of the uniform negative ions in the JT-60 negative ion source

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Grisham, L. R.*; Hatayama, Akiyoshi*; Shibata, Takanori*; Yamamoto, Takashi*; Akino, Noboru; Endo, Yasuei; et al.

Fusion Engineering and Design, 96-97, p.616 - 619, 2015/10

 Times Cited Count:9 Percentile:23.46(Nuclear Science & Technology)

In JT-60 Super Advanced for the fusion experiment, 22A, 100s negative ions are designed to be extracted from the world largest ion extraction area of 450 mm $$times$$ 1100 mm. One of the key issues for producing such as high current beams is to improve non-uniform production of the negative ions. In order to improve the uniformity of the negative ions, a tent-shaped magnetic filter has newly been developed and tested for JT-60SA negative ion source. The original tent-shaped filter significantly improved the logitudunal uniformity of the extracted H$$^{-}$$ ion beams. The logitudinal uniform areas within a $$pm$$10 deviation of the beam intensity were improved from 45% to 70% of the ion extraction area. However, this improvement degrades a horizontal uniformity. For this, the uniform areas was no more than 55% of the total ion extraction area. In order to improve the horizontal uniformity, the filter strength has been reduced from 660 Gasus$$cdot$$cm to 400 Gasus$$cdot$$cm. This reduction improved the horizontal uniform area from 75% to 90% without degrading the logitudinal uniformity. This resulted in the improvement of the uniform area from 45% of the total ion extraction areas. This improvement of the uniform area leads to the production of a 22A H$$^{-}$$ ion beam from 450 mm $$times$$ 1100 mm with a small amount increase of electron current of 10%. The obtained beam current fulfills the requirement for JT-60SA.

Journal Articles

Progress of divertor simulation research toward the realization of detached plasma using a large tandem mirror device

Nakashima, Yosuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Oki, Kensuke*; Sakamoto, Mizuki*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; Imai, Tsuyoshi*; et al.

Journal of Nuclear Materials, 463, p.537 - 540, 2015/08

 Times Cited Count:17 Percentile:7.69(Materials Science, Multidisciplinary)

Journal Articles

Development of divertor simulation research in the GAMMA 10/PDX tandem mirror

Nakashima, Yosuke*; Sakamoto, Mizuki*; Yoshikawa, Masayuki*; Oki, Kensuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

Journal Articles

Analysis of electron temperature distribution by kinetic modeling of electron energy distribution function in JAEA 10 ampere negative ion source

Shibata, Takanori; Terasaki, Ryo*; Kashiwagi, Mieko; Inoue, Takashi; Dairaku, Masayuki; Taniguchi, Masaki; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; et al.

AIP Conference Proceedings 1515, p.177 - 186, 2013/02

 Times Cited Count:8 Percentile:4.33

In the neutral beam injector in JT-60SA, one of issues is that negative ion beam is partially intercepted at acceleration grids due to a spatial non-uniformity of negative ion production on large extraction area (0.9$$times$$0.45m$$^{2}$$). Previous experiments showed that fast electrons emitted from filament cathodes are transported in a longitudinal direction by $$mathbf{B} times textrm{grad} mathbf{B}$$ drift and the spatial distribution of electron temperature ($$T_e$$) strongly relates with the non-uniformity. In this study, a three-dimensional electron transport analysis has been developed. Electron temperature in the analysis agreed well with measurements in JAEA 10A ion source. This study clarified that the bias of $$T_e$$ distribution are caused by the following reasons; (1) fast electrons drifted in the longitudinal direction survives near the end wall with energy up to $$E$$ = 25-60 eV and (2) they produces thermal electrons by collision with plasma particles there.

Journal Articles

Study of negative hydrogen ion beam optics using the 2D PIC method

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.22 - 30, 2013/02

 Times Cited Count:8 Percentile:4.33

We have developed the integrated 2D PIC code for the analysis of the negative ion beam optics, in which an overall region from the source plasma to the accelerator is modeled. Thus, the negative ion trajectory can be solved self-consistently without any assumption of the plasma meniscus form initially. This code can reproduce the negative ion beam halo observed in an actual negative ion beam. It is confirmed that the surface produced negative ions which are extracted near the edge of the meniscus can be one of the reasons for the beam halo: these negative ions are over-focused due to the curvature of the meniscus. The negative ions are not focused by the electrostatic lens, and consequently become the beam halo.

Journal Articles

Study of plasma meniscus formation and beam halo in negative hydrogen ion sources

Okuda, Shin*; Miyamoto, Kenji*; Fukuyama, Toshishige*; Nishioka, Shu*; Hatayama, Akiyoshi*; Fukano, Azusa*; Hanada, Masaya; Kojima, Atsushi

AIP Conference Proceedings 1515, p.107 - 113, 2013/02

 Times Cited Count:9 Percentile:3.53

A meniscus of plasma-beam boundary in H$$^{-}$$ ion sources largely affects the extracted H$$^{-}$$ ion beam optics. Recently it is shown that the beam halo is mainly caused by the meniscus, i.e. ion emissive surface, close to the plasma grid (PG) where its curvature is large. The purpose of this study is to clarify the effect of H$$^{-}$$ surface production rate on plasma meniscus and beam halo formation with PIC (particle-in-cell) modeling. It is shown that the plasma meniscus and beam halo formation is strongly dependent on the amount of surface produced H$$^{-}$$ ions.

Journal Articles

Study of beam optics and beam halo by integrated modeling of negative ion beams from plasma meniscus formation to beam acceleration

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya; Kojima, Atsushi

Applied Physics Letters, 102(2), p.023512_1 - 023512_4, 2013/01

 Times Cited Count:18 Percentile:30.68(Physics, Applied)

To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.

Journal Articles

In-vessel tritium

Ueda, Yoshio*; Oya, Kaoru*; Ashikawa, Naoko*; Ito, Atsushi*; Ono, Tadayoshi*; Kato, Daiji*; Kawashima, Hisato; Kawamura, Gakushi*; Kenmotsu, Takahiro*; Saito, Seiki*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 88(9), p.484 - 502, 2012/09

no abstracts in English

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:84.78(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

Numerical analysis of surface produced H$$^{-}$$ ions by using two-dimensional particle-in-cell method

Miyamoto, Kenji*; Okuda, Shin*; Hatayama, Akiyoshi*; Hanada, Masaya

Review of Scientific Instruments, 83(2), p.02A723_1 - 02A723_4, 2012/02

 Times Cited Count:8 Percentile:55.01(Instruments & Instrumentation)

The modeling and analysis of a negative ion source is proceeding by using a 2D particle-in-cell simulation. The effect of the H$$^{-}$$ ion production on the plasma grid (PG) surface is investigated. It is shown that with the increase of H$$^{-}$$ ions per time step, the H$$^{-}$$ ion current density is enhanced, while the electron current density decreases with increasing the H$$^{-}$$ production rate on the PG surface. Theseresults agree well with the experimental results observed in typical negative ion sources. Moreover, it is found that plasma quasi-neutrality is held mainly by both H$$^{+}$$ and H$$^{-}$$ ions in the bulk plasma.

Journal Articles

Inward pinch of high-Z impurity in a rotating tokamak plasma; Effects of atomic processes, radial electric field and Coulomb collisions

Hoshino, Kazuo; Toma, Mitsunori*; Shimizu, Katsuhiro; Nakano, Tomohide; Hatayama, Akiyoshi*; Takizuka, Tomonori

Nuclear Fusion, 51(8), p.083027_1 - 083027_6, 2011/08

 Times Cited Count:4 Percentile:76.56(Physics, Fluids & Plasmas)

Journal Articles

Inward pinch of high-Z impurity due to atomic processes in a rotating tokamak plasma and the effect of radial electric field

Hoshino, Kazuo; Toma, Mitsunori*; Shimizu, Katsuhiro; Nakano, Tomohide; Hatayama, Akiyoshi*; Takizuka, Tomonori

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 6 Pages, 2011/03

The transport of high-Z impurity in a toroidally rotating tokamak plasma is investigated analytically and numerically. It is shown that the inward pinch is driven by the atomic processes in co- and ctr- rotating plasmas. This inward pinch is enhanced by the radial electric field. It is derived that the negative and positive radial electric fields cause the inward pinch and the outward movement (unpinch) of the high-Z impurity, respectively, under the influence of Coulomb collisions with the rotating background plasma. In the ctr-rotation case, the inward pinch becomes significant with increasing toroidal rotation velocity, because the directions of the both pinches are inward. On the other hand, in the co-rotation case, these pinches have opposite directions. Therefore, the unpinch due to the positive radial electric field is decreased by the inward pinch due to the atomic processes. These tendencies are consistent with the tungsten accumulation observed in the JT-60U.

Journal Articles

3D modeling of the electron energy distribution function in negative hydrogen ion sources

Terasaki, Ryo*; Fujino, Ikuro*; Hatayama, Akiyoshi*; Mizuno, Takatoshi; Inoue, Takashi

Review of Scientific Instruments, 81(2), p.02A703_1 - 02A703_3, 2010/02

 Times Cited Count:19 Percentile:31.08(Instruments & Instrumentation)

In order to develop the large H$$^{-}$$ ion source for future fusion reactors, the uniform production of H$$^{-}$$ ions is one of the important issues. Recently, it has been shown experimentally in JAEA 10A negative ion source that the non-uniformity of the electron energy distribution function (EEDF) inside the source and the resultant non-uniformity of the H$$^{-}$$ production strongly affect the H$$^{-}$$ beam optics. Therefore, modeling of the EEDF and analysis of the spatial non-uniformity of the EEDF is necessary to optimize H$$^{-}$$ ion source and the beam optics. For this purpose, we are developing the 3D3V Monte Carlo modeling of the EEDF in realistic 3D geometry. The code reproduces the spatial non-uniformity of the EEDF observed in the experiments. Our developing code is a powerful tool for the design of the next generation sources.

Journal Articles

Tritium science and technology for fusion reactor, 3; Theory and code development for evaluation of tritium retention and exhaust in fusion reactor

Oya, Kaoru*; Inai, Kensuke*; Shimizu, Katsuhiro; Takizuka, Tomonori; Kawashima, Hisato; Hoshino, Kazuo; Hatayama, Akiyoshi*; Toma, Mitsunori*; Tomita, Yukihiro*; Kawamura, Gakushi*; et al.

Purazuma, Kaku Yugo Gakkai-Shi, 85(10), p.695 - 703, 2009/10

no abstracts in English

Journal Articles

Numerical analysis of incident angle of heavy metal impurity to plasma facing components by IMPGYRO

Hoshino, Kazuo; Toma, Mitsunori*; Furubayashi, Masahiko*; Hatayama, Akiyoshi*; Inai, Kensuke*; Oya, Kaoru*

Journal of Nuclear Materials, 390-391, p.168 - 171, 2009/06

 Times Cited Count:4 Percentile:65.4(Materials Science, Multidisciplinary)

The self-sputtering yield and the reflection yield are important for a prediction of the tungsten impurity content penetrating into the main plasma in future fusion reactors. These yields greatly depend on the incident angle of impurities to the plasma facing components. The IMPGYRO code is applied to the analysis of the angle distribution of incident impurities and the effect of the incident angle and energy on the sputtering and reflection yields. The incident angle distribution is divided into several peaks corresponding to charge states. This is caused by the different acceleration for each charge state by the sheath. In the attached plasma case, the sheath increases the self-sputtering yield. This is due to the change of the incident angle by the sheath rather than the change of the incident energy. On the other hand, in the detached plasma case, the significant effects of the sheath on the sputtering yield and the reflection yield is not seen.

Journal Articles

What is really happening between the plasma edge and the wall?, 2; Defence from the plasma attack

Hatayama, Akiyoshi*; Takizuka, Tomonori

Nippon Genshiryoku Gakkai-Shi, 50(7), p.443 - 447, 2008/07

no abstracts in English

Journal Articles

What is really happening between the plasma edge and the wall?, 1; Physics modeling

Hatayama, Akiyoshi*; Takizuka, Tomonori

Nippon Genshiryoku Gakkai-Shi, 50(6), p.380 - 382, 2008/06

no abstracts in English

JAEA Reports

Spatial uniformity of negative ion beam in magnetically filtered hydrogen negative ion source; Effect of the H$$^{-}$$ ion production and transport processes on the H$$^{-}$$ ion beam intensity profile in the Cs-seeded negative ion source (Joint research)

Takato, Naoyuki; Tobari, Hiroyuki; Inoue, Takashi; Hanada, Masaya; Seki, Takayoshi*; Kato, Kyohei*; Hatayama, Akiyoshi*; Sakamoto, Keishi

JAEA-Research 2008-031, 44 Pages, 2008/03

JAEA-Research-2008-031.pdf:4.05MB

The origin of the H$$^{-}$$ ion beam non-uniformity under the Cesium seeded condition was studied in the JAEA 10 Ampere negative ion source by measuring the profiles of the beam intensity and plasma parameters. The numerical analyses, such as the trace of particles (the electron, the H$$^{0}$$ atom and the H$$^{-}$$ ion) trajectories using the Monte Carlo method, were also applied to consider the experimental results.

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