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Journal Articles

Coulomb coupling and heating of charged particle beams in the presence of dispersion

Okamoto, Hiromi*; Sugimoto, Hiroshi*; Yuri, Yosuke

Journal of Plasma and Fusion Research SERIES, Vol.8, p.950 - 954, 2009/09

Journal Articles

Development of negative ion based neutral beam injector toward JT-60SA

Tanaka, Yutaka; Hanada, Masaya; Kobayashi, Kaoru; Kamada, Masaki; Kisaki, Masashi

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1547 - 1550, 2009/09

This paper reports recent R&D results on negative ion-based NBI system for JT-60 Super Advanced where 10 MW neutral beams is designed to be injected for 100 seconds. There are major two issues to realize such as a high-power and long-pulse injection, i.e., the improvement of voltage holding capability and the reduction of the grid power loading of the JT-60U negative ion source with three acceleration stages. As the first step for improving voltage holding capability, the breakdown location has been examined on site of JT-60U by measuring the lights emitted from spark gaps that are installed outside of the ion source in parallel with acceleration stages. To reduce the grid power to an allowable level, outward deflection of outmost beamlets, due to space charge of the inner beamlets, was suppressed by distorting the acceleration electric field at the edge of the grids. This allowed to reduce the highest grid power loading to acceptable level of 5 %.

Journal Articles

Development of the microfission chamber for fusion power diagnostics on ITER

Ishikawa, Masao; Kondoh, Takashi; Nishitani, Takeo; Kusama, Yoshinori

Journal of Plasma and Fusion Research SERIES, Vol.8, p.334 - 337, 2009/09

Microfission chambers (MFCs) are one of the most important diagnostics to measure total neutron source strength in ITER. The MFCs will be installed behind blanket modules upper outboard and lower outboard in the vacuum vessel. Double coaxial mineral insulated (MI) cables as signal cables are also installed form the MFCs to the upper port. It is very difficult to install the MI cables together with the MFC because of the security regulation. In this design work, a new type of MFC, which can be separable from the MI cable, has been designed. On the other hand, steaming neutrons along the gap between two blanket modules can affect the absolute measurement of total neutron source strength. The effects of streaming neutrons tat the installation position are investigated by a neutron Monte Carlo calculation using MCNP version 5 code. The result suggests that the effect of streaming neutrons should be taken into account if the MFCs are installed at the distance less than 20 cm from the gap.

Journal Articles

Toroidal rotation profiles under the influence of fast-ion losses due to toroidal field ripple

Honda, Mitsuru; Takizuka, Tomonori; Fukuyama, Atsushi*; Yoshida, Maiko; Ozeki, Takahisa

Journal of Plasma and Fusion Research SERIES, Vol.8, p.316 - 320, 2009/09

Characteristics of toroidal rotation profiles in tokamak plasmas are studied under the influence of fast-ion losses due to a toroidal field (TF) ripple by using a one-dimensional multi-fluid transport code, TASK/TX. When a neutral beam (NB) is injected into a plasma, a part of fast ions is lost due to the effect of the TF ripple. The radial current then flows inward in the bulk plasma to keep quasi-neutrality and it exerts a torque on the plasma in the direction opposite to the plasma current. A parametric survey of the toroidal rotation driven by this torque is conducted to quantify the sensitivity to various externally-controllable sources such as a co-tangential NBI power. In the case of a larger ripple amplitude, it is observed that the counter-toroidal rotation develops near the periphery of the plasma as an increase in the co-NBI input power while the co-toroidal rotation velocity on the magnetic axis reaches a maximum value at a certain NBI power. This torque can be mitigated by increasing a gas puff rate. An increase in the plasma current also leads to the reduction in the counter rotation induced by ripple.

Journal Articles

Observation of UV harmonics from a thin-foil target in the high-intensity laser-driven proton generation

Sagisaka, Akito; Pirozhkov, A. S.; Ma, J.-L.; Mori, Michiaki; Yogo, Akifumi; Ogura, Koichi; Orimo, Satoshi; Nishiuchi, Mamiko; Kiriyama, Hiromitsu; Kanazawa, Shuhei; et al.

Journal of Plasma and Fusion Research SERIES, Vol.8, p.464 - 467, 2009/09

We measure the UV harmonics from a thin-foil target by changing the laser pulse duration in the high-energy proton generation. The maximum proton energies are around 1 MeV. In the case of the $$sim$$500 fs, the peaks of UV harmonics up to fourth-order clearly appear. The spectra are broadened and shifted at the pulse durations of $$sim$$100 fs and $$sim$$30 fs.

Journal Articles

Uniform negative ion beam extraction in a cesium-seeded large negative ion source with a tent magnetic filter

Tobari, Hiroyuki; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Kashiwagi, Mieko; Watanabe, Kazuhiro; Umeda, Naotaka; Sakamoto, Keishi

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1530 - 1533, 2009/09

We applied a tent-shaped magnetic filter combined with a symmetry line-cusp field with a Cesium seeding for the surface production of negative ions. Uniform hydrogen plasma was produced without any localization of primary electrons under low-pressure condition. The negative ion beam extracted from a wide area of 34 cm $$times$$ 17 cm showed spatial deviation of only 7.9%. It was concluded that incident uniform flux of positive ions and/or atoms flux on the surface of the plasma grid was achieved with the tent filter, which enhanced the surface production of negative ions.

Journal Articles

Development of polarization interferometer for Thomson scattering diagnostics in JT-60U

Hatae, Takaki; Howard, J.*; Ebizuka, Noboru*; Hirano, Yoichi*; Koguchi, Haruhisa*; Kitamura, Shigeru; Sakuma, Takeshi; Hamano, Takashi

Journal of Plasma and Fusion Research SERIES, Vol.8, p.680 - 684, 2009/09

A polarization interferometer based on the Fourier transform spectroscopy for the Thomson scattering diagnostics is being developed to evaluate the validity. At the first stage, a dual channel polarization interferometer utilizing a fixed-thickness birefringent plate is developed, and the target $$T_{e}$$ and $$n_{e}$$ ranges were $$<$$ 1 keV and $$>$$ 5$$times$$10$$^{18}$$ m$$^{-3}$$, respectively. The electron temperature is successfully measured by the dual channel polarization interferometer in TPE-RX reversed field pinch machine, for the first time. The temperature of the polarization interferometer nearly agrees with that of the filter polychromator. At the second stage, we are developing a multichannel polarization interferometer employing a Wallaston prism to cover wider range of electron temperature. Interferograms of three kinds of light sources are measured by the multichannel polarization interferometer, and those spectra are reconstructed by Fourier transform. In the measurement of a blackbody radiation source using the multichannel polarization interferometer, both ideal and measured spectra agree within 8%.

Journal Articles

Numerical modelling of high energy ion transport in tokamak plasmas

Hamamatsu, Kiyotaka

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1134 - 1137, 2009/09

no abstracts in English

Journal Articles

Integrated modeling for control of advanced tokamak plasma

Ozeki, Takahisa; Hayashi, Nobuhiko; Honda, Mitsuru; Aiba, Nobuyuki; Hamamatsu, Kiyotaka; Shimizu, Katsuhiro; Kawashima, Hisato; Hoshino, Kazuo; Takizuka, Tomonori; Tokuda, Shinji

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1138 - 1142, 2009/09

Journal Articles

Transport of heavy hydrocarbon and its redeposition on plasma facing walls

Oya, Kaoru*; Inai, Kensuke*; Kikuhara, Yasuyuki*; Nakano, Tomohide; Kawata, Jun*; Kawazome, Hayato*; Ueda, Yoshio*; Tanabe, Tetsuo*

Journal of Plasma and Fusion Research SERIES, Vol.8, p.419 - 424, 2009/09

Redeposition of C$$_{2}$$H$$_{4}$$ and C$$_{2}$$H$$_{6}$$ chemically eroded from carbon walls is simulated by EDDY code incorporated with the reflection on a hydrogenated and amorphized carbon surface. The redeposition rate for heavy hydrocarbons is drastically decreased by introduction of the reflection. The redeposition patterns on the surface are enlarged by the reflection, but it is narrower for the heavy hydrocarbons than for CH$$_{4}$$. The photon emissions of C$$_{2}$$ from C$$_{2}$$H$$_{4}$$ (C$$_{2}$$H$$_{6}$$) decay faster than that of CH from CH$$_{4}$$ in high-temperature ($$>$$10 eV) plasmas, which reproduces the difference of the decay of the CD and C$$_{2}$$ light intensities observed in the vicinity of the outer diverter plates of JT-60U. For such temperatures, the inverse photon-efficiency, which is defined as the ratio of the number of the launching hydrocarbons to the photoemission events of CH and C$$_{2}$$, is in good agreement with the values observed in JT-60U experiments.

Journal Articles

Conjugate variable method for applying to MHD stability analysis

Tokuda, Shinji

Journal of Plasma and Fusion Research SERIES, Vol.8, p.1176 - 1178, 2009/09

The conjugate variable method is discussed in order that the Hamilton-Lie perturbation theory becomes applicable to ordinary differential equations that appear in plasma physics. The method is used to the analysis of charged particle motion in a magnetic field, and to the reduced MHD (MagnetoHydroDynamic) equations to derive a canonical 1-form of them. The 1-form thus obtained provides the initial step for the application of the Hamilton-Lie perturbation theory.

Journal Articles

Measurement of DT and DD neutrons with a TOF spectrometer for determination of fuel ion density ratio in ITER

Okada, Koichi*; Kondo, Keitaro; Ochiai, Kentaro; Sato, Satoshi; Konno, Chikara; Okamoto, Atsushi*; Kobuchi, Takashi*; Kitajima, Sumio*; Sasao, Mamiko*

Journal of Plasma and Fusion Research SERIES, Vol.8, p.666 - 669, 2009/09

Measurement of fuel ion density ratio, $$n$$$$_{rm D}$$/$$n$$$$_{rm T}$$, is required for burning control on ITER. The measured $$n$$$$_{rm D}$$/$$n$$$$_{rm T}$$ ratio must be fed back in real time. A neutron measurement system to measure $$n$$$$_{rm D}$$/$$n$$$$_{rm T}$$ should be operable at high counting rate. It is estimated that the number of emitted DT neutrons is 200 times higher than that of DD neutrons under the condition of ITER standard operation. A neutron measurement system was developed using a DT/DD generator, where DT neutrons are dominant and DD neutrons are contaminated slightly in the neutron beam. The measurement instrument was a TOF spectrometer. Signals originating from each neutron must be distinguished in order to measure the fuel ratio. We developed a circuit system with discrimination windows to distinguish each signal pulse, and DT and DD neutrons were measured separately and simultaneously with this system. The experimental result indicates a possibility that this system is suitable for measurement of fuel ion density ratio on ITER.

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