High Current Negative Ion Source Research Articles

Influence of surface produced negative ions on sheath structure

Surface production of negative ion is a dominating process in a high current negative ion source. In presence of surface produced negative ions, the plasma sheath near a metallic plane is modified and has been analysed in this report. The multivalued nature of electric potential at the sheath edge in electronegative plasma, determined by Bohm criterion is pursued in presence of surface produced negative ions.

Status of BINP proton tandem accelerator

The status of a unique 2.0MeV, 10mA proton tandem accelerator with vacuum insulation is presented. The accelerator is intended to be used in facilities generating resonant gamma rays for explosives detection and epithermal neutrons for boron neutron-capture therapy of brain tumors. A magnetically coupled DC voltage multiplier derived from an industrial ELV-type electron accelerator is used as a high voltage source for the accelerator. A dc high current negative ion source has been developed for injection into the tandem. In the tandem accelerator there is set of nested potential electrodes with openings which form a channel for accelerating the negative hydrogen ion beam and subsequently accelerating the proton beam after stripping in the gas target. The electrodes are connected to a high voltage feedthrough insulator to which required potentials are applied from the high voltage power supply by means of a resistor voltage divider. In the paper the first experimental results obtained with the vacuum insulated tandem accelerator are also given.

Optimization of plasma grid material in cesium-seeded volume negative-ion sources

In cesium-seeded hydrogen negative-ion sources, surface production on the plasma grid plays an important role in negative ion production. To enhance the surface, it is required to use material that would give a lower work function when Cs is absorbed on the surface. In a semicylindrical and cesium-seeded volume negative-ion source, eight materials (W, Cu, Mo, V, Cr, Ni, Ag, and Au) were tested as candidates for the plasma grid material. To avoid deposition of the cathode material on these materials, a filament-free plasma source was used, to fire the microwave (2.45 GHz) discharge in the Kamaboko source. The material surface was examined by measuring the photoelectron current by laser irradiation. It was observed that the discharge enhanced the photoelectron current when the material was biased negatively to the plasma potential during discharge. In the present experiment, Ni, Au, and Ag surfaces with a Cs layer showed a higher photoelectron current than the others. This was 1.5 times larger than that of Cu and W used as a plasma grid and filament in conventional high current negative ion sources. It is expected that higher negative-ion production efficiency would be obtained by using Ni, Ag, and Au as the plasma grid material, if deposition of filament materials is avoided on the surface.

Development of high power ion sources for fusion (invited)

Recent progress and development activities regarding high power ion sources for fusion researches are reviewed. High power positive ion sources, which have progressed in the 1980s, played important roles in fusion research. Most of the ion sources developed for major neutral beam injection (NBI) systems are a large area magnetic multipole type with tungsten cathode, and produce tens of amperes of positive hydrogen/deuterium/tritium ion beams at the energy around 100 keV. The NBI systems based on these ion sources delivered tens of MW neutral beams to the plasmas, and contributed to produce high temperature plasmas in the break-even condition in the tokamak type fusion devices. Meanwhile, R and D of high current negative ion sources were carried out for a high energy NBI system to be utilized not only for plasma heating, but also for the steady state operation and stable plasma control in the fusion burning plasmas. In the 1990s, rapid progress of high current negative ion sources has been made. Particularly, a cesiated magnetic filter source with high plasma confinement has, for the first time, produced a multi-ampere negative ion beam stably in the conditions required for the negative-ion-based NBI systems, namely high negative ion current density, low operating pressure, low extracted electron current, and good beamlet optics. Based on this progress, a 500 keV 10 MW NBI system has been developed for JT-60U at the Japan Atomic Energy Research Institute, and construction of a 180 keV 15 MW NBI system is carried on at the National Institute for Fusion Science in Japan. The same type of negative ion source is applied to the design of a 1 MeV NBI system for the International Thermonuclear Experimental Reactor (ITER).

Development of high current negative ion source

The development of high current negative ion sources has been intensively continued for application to fusion research, especially neutral beam injection. Recently, the research and development of hydrogen negative ion sources has made rapid progress. Negative ion beam current has been remarkably enhanced by seeding cesium in a magnetically filtered multicusp plasma source. As a result, a negative ion beam current of more than 16 A is obtained at an energy of 120 keV. According to studies of negative ion sources during the last decade a design principle for volume production multi-cusp negative sources has been mostly approved. The present status of the development of high current negative ion sources is briefly reviewed. The performance and the characteristics of a negative ion source are discussed. Emphasis is placed on the important issues and optimized condition: low operating pressure, the relation between the plasma parameters and the extracted beam current, the optimum Cs seeding conditions, the beam extraction characteristics of the negative ion source and the suppression of electron current extracted with the negative ions. The optimum condition is described by considering the physical principle of the negative ion sources and the physical and technological consideration of the design of the negative ion sources are given.

Negative-ion implantation technique

Negative-ion implantation is a promising technique for charging-free implantation for the forthcoming ULSI fabrication, in which the water charging by positive-ion implantation will become a troublesome problem even with an electron shower. The negative-ion implantation technique remarkably ameliorates such a charging problem since the incoming negative charge of implanted negative ions is easily balanced by the outgoing negative charge of a part of secondary electrons. Thus, the surface charging voltage is maintained to within about ± 10 V for isolated conducting materials and insulators, and is free from space and time fluctuations. A high-current negative-ion source and a medium current negative-ion implanter developed for this technique are described with the design concepts. In addition, the fundamental measurements of interactions between the negative-ion beam and the gas/solid are also described.

High current negative ion sources (invited)

A brief historical survey is presented of the origin of negative ion sources and their application for tandem accelerators and for fusion. Present-day volume-production sources and surface-production negative ion sources are described.

Current status of development of ion sources in Japan from a standpoint of materials science (invited)

The current status of development of novel ion sources for materials science in Japan is reviewed. Several types of microwave ion sources which permit a reactive gas discharge have been developed for the production of high intensity and low-charge-state ion beams. The plasma cathode technique, as an electron source, provides conventional ion sources with a long lifetime. Metal ion sources which can deliver a pure metal ion beam have been developed, extracting metal ions from a high temperature discharge chamber of large volume or a porous tip surface. A new principle metal ion source by use of a metal cluster, which consists of hundreds to thousands of metal atoms, has been developed. High current negative ion sources have been developed for both light and heavy ions, resulting from in-depth investigation of negative ion production mechanisms.

Development of a high current negative ion source for fusion application.

Negative ion based neutral beam injector is one of the most attractive heating system in future fusion reactors. In realizing the system, the crucial device which has to be developed is a high intensity negative ion source. Significant progress has been made on the negative ion source in these years. Among them, a few ampere negative ion beam were produced stably, while the divergence of negative ion beams becomes to be as low as<10 mrad. We consider these results are demonstrating the potential of the negative ion source for the heating device in future reactors.

Measurement of the quantum efficiency of noble-gas scintillators for x-rays: A E Kiss and N Patla,Brit J Appl Phys, Ser 2, 1 (5), 1968, 617–624.

Negative-ion implantation is a promising technique for charging-free implantation for the forthcoming ULSI fabrication, in which the water charging by positive-ion implantation will become a troublesome problem even with an electron shower. The negative-ion implantation technique remarkably ameliorates such a charging problem since the incoming negative charge of implanted negative ions is easily balanced by the outgoing negative charge of a part of secondary electrons. Thus, the surface charging voltage is maintained to within about ± 10 V for isolated conducting materials and insulators, and is free from space and time fluctuations. A high-current negative-ion source and a medium current negative-ion implanter developed for this technique are described with the design concepts. In addition, the fundamental measurements of interactions between the negative-ion beam and the gas/solid are also described.