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Your search keyword '"Oohara, Wataru"' showing total 19 results
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19 results on '"Oohara, Wataru"'

1. Development of hydrogen ionic plasma source with superimposed positive-ion beam.

Author

Oohara, Wataru and Fujii, Masashi

Subjects
*HYDROGEN plasmas, *MAGNETIC flux density, *PLASMA density, *PLASMA sources, *ELECTRON plasma
Abstract

A hydrogen ionic plasma source has been developed that is with a low residual electron presence (<0.01) using an aluminum plasma grid for negative hydrogen ion production and a control grid for electron removal. The ionic plasma density increases when a positive-ion beam is superimposed on a hydrogen plasma and irradiated onto the Al plasma grid. Even though the ionic plasma is formed in a region with high-deflection magnetic flux density, a collapse phenomenon can occur downstream of the region under certain electrode voltage conditions, causing electrons to appear and forming an electron plasma. Under electrode voltage conditions that prevent the collapse, the nine ionic plasmas, each passing through extraction apertures with a diameter of 1.3 cm, are combined to form the ionic plasma with a diameter of approximately 6 cm and a density on the order of 10 9 cm−3. [ABSTRACT FROM AUTHOR]

Published
2024
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2. Plasma production by helicon waves with single mode number in low magnetic fields

Author

Sato, Genta, Oohara, Wataru, and Hatakeyama, Rikizo

Subjects
Physics - Plasma Physics
Abstract

Radio-frequency discharges are performed in low magnetic fields (0-10 mT) using three types of helicon-wave exciting antennas with the azimuthal mode number of $|m|$ = 1. The most pronounced peak of plasma density is generated in the case of phased helical antenna at only a few mT, where the helicon wave with $|m| = 1$ is purely excited and propagates. An analysis based on the dispersion relation well explains the density-peak phenomenon in terms of the correspondence between the antenna one-wavelength and the helicon wavelength. The $m=+1$ helicon wave propagates even in high magnetic fields where the density peaks are not observed, but the $m=-1$ helicon wave disappers. It is expected theoretically that the $m=-1$ helicon wave shows cutoff behavior in a low density region, [M. Kramer, Phys. Plasmas 6, 1052 (1999)], and the cutoff of $m=-1$ helicon wave experimentally observed coincides with the calculated one., Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)

Published
2004

3. Fluctuation-phase relation between positive and negative ions on pair-plasma electrostatic waves

Author

Oohara, Wataru, Date, Daisuke, and Hatakeyama, Rikizo

Subjects
Physics - Plasma Physics
Abstract

Three kinds of electrostatic modes are experimentally observed to propagate along magnetic-field lines for the first time in the pair-ion plasma consisting of only positive and negative fullerene ions with an equal mass. It is found that phase lags between the density fluctuations of positive and negative ions vary from 0 to $\pi$ depending on the frequency and is fixed at $\pi$ in the cases of ion acoustic and ion plasma waves, respectively. In addition, a new mode with the phase lag about $\pi$ appears in an intermediate-frequency band between the acoustic and plasma waves., Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)

Published
2004

6. Analysis of the Cesium Distribution in the JT-60SA Negative Ion Sources for Steady Long-Pulse Operation

Author

Yoshida, Masafumi, Oohara, Wataru, Ichikawa, Masahiro, Hiratsuka, Junichi, mae quinones Saquilayan, Glynnis, Umeda, Naotaka, Kojima, Atsushi, Kashiwagi, Mieko, Masahiro, Ichikawa, Junichi, Hiratsuka, Naotaka, Umeda, Atsushi, Kojima, and Mieko, Kashiwagi

Abstract

To realize stable negative ion beams for 100 s required in the neutral beam injector of JT-60SA, a physical model to control cesium (Cs) distribution inside the negative ion source has been developed in order to maintain the stable negative ion production at the plasma grid (PG) surface with Cs. In this work, to quantitatively evaluate Cs coverage on the PG, a three-dimensional Cs transportation code was introduced to consider the spatial Cs distribution in the source. The spatial temperature distribution of the chamber wall was also introduced in this model. As a result, the reasonable variation of the Cs coverage for 100 s was obtained, compared to that in the initial model. Based on the modified model, the operational temperature of the chamber wall was proposed to be less than 60 ℃ to suppress the desorption of Cs in the chamber wall and to sustain the stable negative ion production. In addition, it was also suggested that a slightly higher wall temperature before the operation leads to a decrease in the amount of Cs stored at the chamber wall, resulting in suppression of Cs consumption in the ion source.

Published
2020

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