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Examines development of large-scaled hydrogen negative ion source. Negative ion based neutral beam injector in the large helical device fusion machine; Negative ion acceleration; Electron suppression; Beam steering; Measurement of neutralization efficiency.

Discusses the suppression of accelerated electrons in a high-current large negative ion source. Design of the external filter type large negative ion source; Grid configuration of the accelerator; Thermal load measurement by water calorimetry; Improvement of the acceleration efficiency; Negative-ion related current loss.

Describes the operation of a high-power large negative ion source for a long pulse duration using a three-grid single-state accelerator. Shape of the extraction grid; Achievement of a stable long-pulse arc discharge with an arc power of 100 kilowatt; Measurement of the neutralization efficiency of the accelerated negative ion power density.

Reports on the development of large high current hydrogen negative ion sources for the negative ion based neutral beam injector of the Large Helical Device at the National Institute of Fusion in Japan. Optimization of 1/3 scale negative ion source; Electron density and electron temperature of the driver region; Beam extraction and acceleration characteristics.

Describes the development of an intense negative hydrogen ion source with an external magnetic filter produced by a pair of permanent magnet rows located at 35.4 centimeter separation. Generation of a strong cusp magnetic field for improvement of the plasma confinement; Focus on the structure of the ion source and the experimental results.

Investigates a negative hydrogen ion source using a localized virtual magnetic filter of type I in the plasma electrode. Ion source and the local filter arrangement; Arrangement of the multi-pole magnetic field; Characteristics of the cesium seeded operation.

Examines cesium recovery from the polluted layers by additional discharges in the 1/3 scale hydrogen negative ion source for LHD-NBI system. Mechanism of recovery; Ejection of cesium from the underlying enriched layer by the arc and its transport to the surface.

Reports on the operation of a large vacuum-immersed negative hydrogen ion source on the negative-ion-based neutral beam teststand. Features of the ion source; Density of the plasma in the downstream space; Comparison of the characteristics of two magnetic filters under similar operating conditions.

To develop the powerful negative-ion-based neutral beam injection system for the large helical device, a 1/3 scaled H[sup -] source has been tested, which is immersed in the vacuum vessel. Intrinsic features of the vacuum-immersed large H[sup -] source are described. Plasma density of higher than about 10[sup 12] e/cm³ is produced. During the beam extraction, it was found that a beam-induced thin plasma exists in the vacuum vessel. In order to get a long pulse beam, this plasma was shielded and then the beam conditioning was completed up to the total beam energy of 70 kev for 100 ms, with the arc power up to about 50 kW. It is confirmed that H[sup -] current scaling as wall as the plasma parameters would be similar to the scaling which is achieved by the previous 1/3 source. [ABSTRACT FROM AUTHOR]

The characteristics of a large negative-ion source with external filter is investigated for the neutral-beam injection system in a large helical device. The magnetic cusp field is set up at almost the same strength as that in our well optimized 1/3 ion source with rod-type magnetic filter. An H[sup -] ion current of 5.2 A is extracted from the ion source with Cs seeding. The H[sup -] current corresponds to 19.7 mA/cm², and the value is comparable to the current density obtained using the 1/3 scaled ion source with a rod-type magnetic, filter at the same extraction voltage. In low operating pressure, the ion source with the external filter has a better performance on the extraction of H[sup -] ions. [ABSTRACT FROM AUTHOR]

A large vacuum-immersed negative-ion source has been investigated for the development of the neutral beam injection system in a large helical device. The structure of the vacuum-immersed source is compact and light because it is free from atmospheric pressure. Therefore, this is very advantageous for a large-scaled ion source. Moreover, since the grids of the accelerator are supported by post insulators, enhanced pumping of gaps between grids is expected, leading to a reduction of stripping loss of negative ions. The gas pressure distribution between grids was calculated and the stripping loss of H[sup -] ions was estimated and the effectiveness of the vacuum-immersed source structure was confirmed. The gas temperature effect of the gas pressure distribution is also considered by using a Monte Carlo code. [ABSTRACT FROM AUTHOR]

The multiampere negative hydrogen ion source has been developed in National Institute for Fusion Science (NIFS). The ion source is a volume-production type multicusp one with an extraction area of 25 × 25 cm². It is found that high density negative hydrogen ions of more than 1 × 10[sup 12] cm[sup -3] are produced in the center of the arc chamber with a double magnetic filter configuration. A supply of a small amount of cesium vapor into the arc chamber has greatly enhanced the H[sup -] ion current and reduced the operation pressure. The H[sup -] ion current of 3.3 A has been extracted from a Cs-seeded plasma at the pressure of 0.9 Pa. [ABSTRACT FROM AUTHOR]

Presents the compact cesium (Cs) coating system which was used for the direct deposition of Cs atoms and ions onto the inner surface of a third scale hydrogen negative ion source for the large helical device-neutral beam injection system. Beam current evolution after Cs depositions; Effect of temperature on hydrogen current.