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Journal Articles

Spatial structure of volume recombination in JT-60U detached divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Sawada, Keiji*; Takizuka, Tomonori; Kawashima, Hisato; Shimizu, Katsuhiro; Asakura, Nobuyuki

Plasma and Fusion Research (Internet), 4, p.025_1 - 025_7, 2009/08

The volume recombination in detached divertor plasmas is a key process to reduce the ion flux to the divertor plates. Two-dimensional measurement is one of the ways to investigate a spatial structure of the volume recombination. In this work, the deuterium Balmer-series lines from a detached divertor plasma were observed two-dimensionally with a spatial resolution of 1 cm and were reconstructed into two-dimensional emissivities with a tomography technique. The ratio of the D$$_{beta}$$ to the D$$_{alpha}$$ emissivity was compared to that calculated by the collisional-radiative model. This ratio could not be explained only by the excitation of D by electron impact, indicating that the volume recombination contributed to the D$$_{beta}$$ emission. This is the case for the region above the inner strike point with 8 cm and 4 cm, respectively, in the r- and the z-direction on the poloidal cross-section.

Journal Articles

Particle control in long-pulse H-mode discharges of JT-60U

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Takenaga, Hidenobu; Oyama, Naoyuki; Kawashima, Hisato; Fujimoto, Kayoko

Nuclear Fusion, 48(8), p.085002_1 - 085002_8, 2008/08

 Times Cited Count:12 Percentile:47.3(Physics, Fluids & Plasmas)

Particle control is one of the key issues for steady-state operation in fusion reactors. In short discharges, the first wall absorbs hydrogen particles and it works as a pump (wall pumping). The wall pumping is effective to control the plasma density. However, in future tokamak devices, wall retention increases in a long discharge. Then, it is expected that the wall retention is saturated and the wall pumping does not work. Therefore, for steady-state operation, particle control by active divertor pumping without the wall pumping should be established. In JT-60U, long-pulse high-density H-mode plasmas have been sustained by divertor pumping under global wall saturation. The energy confinement and ELM activity can be sustained, while wall pumping does not work and even outgas appears. The outgas is attributed to increase in the divertor-plate temperature. On the other hand, wall pumping continues for longer than 20 s in high-density (ne $$sim$$ 0.8 nGW) discharges with an X-point MARFE and detached divertor plasma. X-point MARFEs have also been controlled by the divertor pumping. As a result, the electron density control by the divertor pumping and the gas puffing is effective under the wall saturation. However, it should be noted that the wall-pumping rate changes to maintain the electron density against the control. The change in the wall pumping suggests dynamic equilibrium between particle flux and desorption as an important wall-pumping mechanism.

Journal Articles

Volume recombination of C$$^{4+}$$ in detached divertor plasmas of JT-60U

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Shimizu, Katsuhiro; Konoshima, Shigeru; Fujimoto, Kayoko; Kawashima, Hisato; Higashijima, Satoru

Nuclear Fusion, 47(11), p.1458 - 1467, 2007/11

 Times Cited Count:20 Percentile:60.65(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Modification of tomography technique for two-dimensional spectroscopic measurement in JT-60U divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Sawada, Keiji*; Takizuka, Tomonori; Shimizu, Katsuhiro; Kawashima, Hisato; Asakura, Nobuyuki

Plasma and Fusion Research (Internet), 2, p.S1121_1 - S1121_4, 2007/11

Understanding deuterium particle behavior in the divertor plasma is necessary to study the ionizing and recombining plasmas. Two-dimensional spectroscopic measurement of deuterium emission is useful to understand deuterium particle behavior in divertor plasmas. The information of the ionization and recombination can be obtained by measurement of deuterium Balmer-series lines. A wide-spectral-band spectrometer with a CCD detector was used to observe deuterium Balmer-series lines with two-dimensional spatial distribution in the JT-60U divertor region. From the measurement, we can obtain a two-dimensional distribution of D$$_{beta}$$ and D$$_{gamma}$$ using a computer tomography technique. The D$$_{beta}$$ emission was strong above the strike point in the inner divertor and around the strike point in the outer divertor. The D$$_{gamma}$$ emission was strong above the strike point in the inner divertor.

Journal Articles

Particle control under wall saturation in long-pulse high-density H-mode plasmas of JT-60U

Kubo, Hirotaka; Nakano, Tomohide; Asakura, Nobuyuki; Takenaga, Hidenobu; Tsuzuki, Kazuhiro; Oyama, Naoyuki; Kawashima, Hisato; Shimizu, Katsuhiro; Urano, Hajime; Fujimoto, Kayoko; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

no abstracts in English

Journal Articles

Radiation processes of impurities and hydrogen in detached divertor plasmas of JT-60U

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Shimizu, Katsuhiro; Konoshima, Shigeru; Fujimoto, Kayoko; Kawashima, Hisato; Higashijima, Satoru

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Volume recombination of C$$^{4+}$$ and $$e^{-}$$ into C$$^{3+}$$ is observed for the first time in detached plasmas with MARFE. It is found that the recombination flux of C$$^{4+}$$ to C$$^{3+}$$ is comparable to the ionization flux of C$$^{3+}$$ to C$$^{4+}$$, and that the recombination zone is above an X-point and beneath the ionization zone. This result suggests that this volume recombination predominantly produces C$$^{3+}$$ ions, which contribute 60-80 % to the total radiation power in the divertor plasma.

Journal Articles

Two-dimensional spectroscopic measurement of hydrogen emission in JT-60U divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Kawashima, Hisato; Shimizu, Katsuhiro; Asakura, Nobuyuki

Fusion Science and Technology, 51(2T), p.247 - 249, 2007/02

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Report on 9th Workshop on Plasma Physics by Young Scientist

Suzuki, Takahiro; Urano, Hajime; Fujimoto, Kayoko

Purazuma, Kaku Yugo Gakkai-Shi, 82(6), P. 391, 2006/06

no abstracts in English

Oral presentation

Visualization of hydrogen atom distribution in JT-60U divertor plasma with a computer tomography technique

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Konoshima, Shigeru; Ishikawa, Masao; Asakura, Nobuyuki; Shimizu, Katsuhiro

no journal, , 

no abstracts in English

Oral presentation

Measurement of density of highly-charged heavy ions from optically forbidden lines in JT-60U plasmas

Nakano, Tomohide; Tsuzuki, Kazuhiro; Kubo, Hirotaka; Shimizu, Katsuhiro; Asakura, Nobuyuki; Fujimoto, Kayoko

no journal, , 

no abstracts in English

Oral presentation

Measurement of two-dimensional atom distribution in JT-60U divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Shimizu, Katsuhiro; Asakura, Nobuyuki

no journal, , 

no abstracts in English

Oral presentation

Report of new diagnostics in JT-60U

Kawano, Yasunori; Sakamoto, Yoshiteru; Suzuki, Takahiro; Fujimoto, Kayoko

no journal, , 

no abstracts in English

Oral presentation

Temporal evolution of electron temperature and density during ELM in JT-60 divertor plasma

Nakano, Tomohide; Asakura, Nobuyuki; Ono, Noriyasu*; Kajita, Shin*; Kawashima, Hisato; Kubo, Hirotaka; Shimizu, Katsuhiro; Fujimoto, Kayoko

no journal, , 

no abstracts in English

Oral presentation

Two-dimensional measurement of ionizing and recombining plasmas in JT-60U detached divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Shimizu, Katsuhiro; Sawada, Keiji*; Kawashima, Hisato; Asakura, Nobuyuki

no journal, , 

no abstracts in English

Oral presentation

Evaluation of the electron distribution function for detached plasma in JT-60U

Uehara, Kazuya; Asakura, Nobuyuki; Sadamoto, Yoshiro*; Kawashima, Hisato; Kubo, Hirotaka; Nakano, Tomohide; Takenaga, Hidenobu; Fujimoto, Kayoko; Amemiya, Hiroshi*; Saito, Yoshifumi*

no journal, , 

The temperature and energy of electrons are important issues when energy and particle fluxes to the divertor are evaluated. To do this, we have analyzed the electron energy distribution function by differentiating the probe current with respect to the probe voltage numerically, where probe current has been measured in the divertor plasma of JT-60U. We have evaluated the electron temperature and the shape of the distribution function when the X point MARFE and the plasma detachment are formed.

Oral presentation

Status of diagnostics development in JAEA

Kawano, Yasunori; Kondoh, Takashi; Hatae, Takaki; Ishikawa, Masao; Fujimoto, Kayoko; Asakura, Nobuyuki

no journal, , 

In the international thermonuclear experimental reactor (ITER), a lot of plasma diagnostic system will be employed for generation, control, and understanding of burning plasmas. Here, contribution from the knowledge and techniques which are obtained at existing tokamaks to ITER diagnostics is important. In this talk, recent progress of diagnostics development in JT-60U is presented. The contents are as follows: (1) development of high power and high repetition rate single mode CO$$_{2}$$ laser for collective Thomson scattering, (2) development of Thomson scattering diagnostic with application of Fourier transform spectrometer, (3) fast measurement of neutron emission profile using digital signal processing, (4) computer tomography for divertor plasma spectroscopy, and (5) dust measurement using fast TV camera

Oral presentation

Radiation processes of impurities in detached divertor plasmas of JT-60U

Nakano, Tomohide; Asakura, Nobuyuki; Shimizu, Katsuhiro; Konoshima, Shigeru; Fujimoto, Kayoko; Kawashima, Hisato; Higashijima, Satoru

no journal, , 

WeThe intensity ratios of 9 C IV lines from the C IV emission peak were analyzed with a collisional-radiative model. From the analysis, it was found that the lowly-excited levels ($$n le 4$$) were predominantly populated by the excitation from the ground state of $$mbox{C}^{3+}$$ by an electron impact with an electron temperature of 10 eV and an electron density of $$5 times 10^{20} mbox{m}^{-3}$$, while the highly-excited levels ($$n ge 6$$) by the volume recombination of $$mbox{C}^{4+}$$ and an electron with an electron temperature of 3 eV. With these parameters and the absolute intensity of C IV ($$mbox{3s}^2mbox{S}-mbox{3p}^2mbox{P}$$) and C IV ($$n=6-7$$) lines, the radiation power due to the excitation and the recombination process were determined to be, respectively, 40% and 0.5% of the total radiation power measured by a bolometer. Further, it was found that the $$mbox{C}^{4+}$$ recombination flux was comparable to the $$mbox{C}^{2+}$$ ionization flux.

Oral presentation

Recent studies of heat and particle loadings in long pulse discharges and influence on PWI in JT-60U

Asakura, Nobuyuki; Nakano, Tomohide; Kawashima, Hisato; Masaki, Kei; Fujimoto, Kayoko; Ono, Noriyasu*; Tanabe, Tetsuo*

no journal, , 

ELMy H-mode plasmas have been recently operated during long duration under the wall saturated condition in JT-60U. Investigation of the heat and particle handling and PSI studies such as erosion and deposition of carbon have been progressed. Deuterium gas balance has been studied in short term, and it was found that globally saturated condition of PFCs is caused mostly by an increase in wall temperature near the divertor. Increase in the divertor pumping was investigated to demonstrate particle control under the globally saturated condition. Erosion and deposition of the carbon target has been analyzed at the divertor tiles after the experiment campaigns. Deposition pattern and its rate on the tile surface were similar to those at other tokamaks such as JET. On the other hand, deposition depth of the tile edge was relatively smaller, which suggests difference of tile arrangement. Deuterium co-deposition was found to be smaller. Influence of operation temperature is discussed.

Oral presentation

Two-dimensional structure of volume recombination in JT-60U detached divertor plasmas

Fujimoto, Kayoko; Nakano, Tomohide; Kubo, Hirotaka; Sawada, Keiji*; Takizuka, Tomonori; Kawashima, Hisato; Shimizu, Katsuhiro; Asakura, Nobuyuki

no journal, , 

The volume recombination in detached divertor plasmas is a key process to reduce the ion flux to the divertor plates. The deuterium Balmer-series lines (D$$alpha$$, D$$beta$$, ..., D$$theta$$) from a detached divertor plasma were observed two-dimensionally with a spatial resolution of about 1 cm and were reconstructed with a tomography technique. The ratio of the D$$beta$$ to the D$$alpha$$ emissivity was compared to that calculated by the collisional-radiative model. This ratio could not be explained only by the excitation of D by electron impact, indicating that the volume recombination contributed to the D$$beta$$ emission. This is the case for the region above the inner strike point with about 8 cm and 4 cm, respectively, in the r- and the z-direction on the poloidal cross-section. In this region, from the ratios of the D$$alpha$$, D$$beta$$, ..., D$$theta$$ emissivities, the electron density and temperature were evaluated to be about 1$$times$$10$$^{20}$$ m$$^{-3}$$ and less than 0.3 eV, respectively.

Oral presentation

Radiation process of carbon ions in JT-60U detached divertor plasmas

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Fujimoto, Kayoko; Shimizu, Katsuhiro; Konoshima, Shigeru; Kawashima, Hisato; Higashijima, Satoru

no journal, , 

no abstracts in English

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