Long pulse production of high current D ion beams in the JT-60 negative ion source

Hanada, Masaya; Kamada, Masaki; Akino, Noboru; Ebisawa, Noboru; Honda, Atsushi; Kawai, Mikito; Kazawa, Minoru; Kikuchi, Katsumi; Komata, Masao; Mogaki, Kazuhiko; et al.

Review of Scientific Instruments, 79(2), p.02A519_1 - 02A519_4, 2008/02

https://doi.org/10.1063/1.2821508

A long pulse production of high-current, high-energy D ion beams was studied in the JT-60U negative ion source that was designed to produce 22 A, 500 keV D ion beams. Prior to the long pulse production, the short pulse beams were produced to examine operational ranges for a stable voltage holding capability and an allowable grid power loading. From a correlation between the voltage holding capability and a light intensity of cathodoluminescence from the insulator made of Fiber Reinforced Plastic insulator, the voltage holding was found to be stable at 340 kV where the light was sufficiently suppressed. The grid power loading for the long pulse operation was also decreased to the allowable level of 1 MW without a significant reduction of the beam power by tuning the extraction voltage (Vext) and the arc power (Parc). These allow the production of 30 A D ion beams at 340 keV from two ion sources at Vacc = 340 kV. The pulse length was extended step by step, and finally reached up to 21 s, where the beam pulse length was limited by the surface temperature of the beam scraper without water cooling. The D ion beams were neutralized to via a gas cell, resulting in a long pulse injection of 3.2 MW D beams for 21 s. This is the first long injection of 20 s in a power range of 3 MW.

Uniform H ion beam extraction in a large negative ion source with a tent-shaped magnetic filter

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

Review of Scientific Instruments, 79(2), p.02C111_1 - 02C111_4, 2008/02

https://doi.org/10.1063/1.2816968

In order to improve the spatial uniformity of negative ion beam, a novel magnetic filter, the tent-shaped filter was applied in the JAEA 10 ampere negative ion source as a replacement to the conventional external magnetic filter. The cusp magnetic field configuration for plasma confinement was changed to form a symmetric cusp field commonly used in many of positive ion sources for high proton yield. This configuration together with the tent filter allows fast electrons emitted from filaments drift azimuthally around the beam axis. This is a major advantage of the current configuration to prevent localization of fast electrons due to B grad B drift in the external filter field. As the result, the standard deviation of H ion beam profile extracted from a wide area of 170 mm 340 mm decreased from 16% with the external filter to 7.9 % with the tent filter. Thus the ion source with the tent filter demonstrated the uniform beam extraction that fulfilled the requirement for ITER NBI.

Acceleration of ampere class H ion beam by MeV accelerator

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

Review of Scientific Instruments, 79(2), p.02C110_1 - 02C110_3, 2008/02

https://doi.org/10.1063/1.2816839

Surface discharge related properties of fiberglass reinforced plastic insulator for use in neutral beam injector of JT-60U

Yamano, Yasushi*; Takahashi, Masahiro*; Kobayashi, Shinichi*; Hanada, Masaya; Ikeda, Yoshitaka

Review of Scientific Instruments, 79(2), p.02A524_1 - 02A524_4, 2008/02

https://doi.org/10.1063/1.2828069

The JT-60U negative-ion-based NBI was designed to have 3-stage electrostatic accelerators with total accelerating voltage of 500kV. In order to hold such high voltage, three Fiberglass Reinforced Plastic (FRP) insulators of 1.8 m inner diameter and 31.5 cm height are used. Currently the hold-off voltage capability of 3-stage FRP insulators has been typically limited to 460 kV without beam acceleration. One of the possible reason is a surface discharges on the FRP insulators. This paper describes measurement results of surface resistivity and volume resistivity under vacuum and atmospheric conditions, secondary electron emission (SEE) characteristics and cathodoluminescence under some keV electron beam irradiation, gas analysis desorbed from the FRP insulator under irradiation of some keV-electron beam were also analyzed.

Effect of energy relaxation of H atoms at the wall on the production profile of H ions in large negative ion sources

Takado, Naoyuki*; Matsushita, Daisuke*; Fujino, Ikuro*; Hatayama, Akiyoshi*; Tobari, Hiroyuki; Inoue, Takashi

Review of Scientific Instruments, 79(2), p.02A503_1 - 02A503_4, 2008/02

https://doi.org/10.1063/1.2802583

Production and transport process of the H atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code was applied to the "JAEA 10 ampere negative ion source" under Cs-seeded condition to obtain a spatial distribution of surface-produced H ions. In this analysis, we focus on the effect of the energy relaxation of the H atoms at the wall on the H ion production from the H atoms. The result indicates that, by considering the energy relaxation of the H atoms at the wall, the production profile of the surface-produced H ion is well reflected in the production profile of the H atom production.

Analysis of electron energy distribution of an arc-discharge H ion source with Monte Carlo simulation

Fujino, Ikuro*; Hatayama, Akiyoshi*; Takado, Naoyuki*; Inoue, Takashi

Review of Scientific Instruments, 79(2), p.02A510_1 - 02A510_3, 2008/02

https://doi.org/10.1063/1.2816966

For optimization and accurate prediction of the amount of H ion production in negative ion source, analysis of electron energy distribution function (EEDF) is necessary. We developed a numerical code which analyzes EEDF in the tandem-type arc discharge source. It is a three-dimensional Monte Carlo simulation code with the effects of cusp, filter, and extraction magnets. Coulomb collision between electrons is treated with Takizuka's model and several inelastic collisions are treated with null-collision method. We applied this code to the JAEA 10 ampere negative ion source. As a result, the order of electron density is in good agreement with experimental results. In addition, the obtained EEDF is qualitatively in good agreement with experimental results.

KEKCB; ECR charge breeder at TRIAC

Imai, Nobuaki*; Jeong, S.-C.*; Oyaizu, Mitsuhiro*; Arai, Shigeaki*; Fuchi, Yoshihide*; Hirayama, Yoshikazu*; Ishiyama, Hironobu*; Miyatake, Hiroari; Tanaka, Masahiko*; Okada, Masayuki*; et al.

no journal, , 

The KEKCB is an ECR ion source for converting singly charged ions to multi-charged ones at Tokai Radioactive Ion Accelerator Complex. By using the KEKCB, singly charged gaseous and non-gaseous ions were successfully converted to the multi-charged ones of A/q 7 with the efficiencies of 7% and 2% respectively. The efficiency was found to be independent of the lifetime of the radioactive nuclei with an order of second. Three collimators placed at the entrance and the exit of the KEKCB defined the beam axis and enabled us to easily handle the beam injection to the KEKCB. Griding and washing the surfaces of aluminum electrode and plasma chamber dramatically reduced the impurity originated from the ECR plasma of the KEKCB.