[en] The change of the electron beam distribution function due to the wave excited by the beam density modulation is observed, in relation to the suppression of electron waves in a beam-plasma system. (Auth.)

[en] Four or five longitudinal electron waves of axial beam modes are excited simultaneously in a bounded electron beam-plasma system. They are accompanied with an ion-acoustic wave of an axial mode under appropriate plasma conditions. This ion-acoustic wave can not be excited directly by beam-plasma interaction, where upsilonsub(b)/upsilonsub(te)>=3. When a beam density is modulated by an external r.f.signal whose frequency is close to any one of frequencies of electron waves excited spontaneously, all of the electron waves and the ion-acoustic wave are suppressed simultaneously. It is verified experimentally that quenching of the ion-acoustic wave is not brought about directly by the beam modulation, but by the damping of the electron wave which constitutes an energy source of the ion-acoustic wave. (author)

[en] Published in summary form only

[en] The destruction mechanism of the amplitude oscillation in the system of a cold beam and a weakly collisional plasma is examined numerically. The excitation of the neighboring waves depends not only on the beam strength but also on the beam velocity upsilonsub(b)/upsilonsub(t). Even if s is large, the system becomes stable for the excitation of the neighboring waves with large upsilonsub(b)upsilonsub(t). Consequently, collisional effects become more important for the destruction process because either of the collisional and the neighboring wave effects competes with another in playing a decisive role for the destruction of amplitude oscillations. (author)

[en] In order to study the mechanism of H^- production due to volume processes and the dependence of H^- production on plasma parameters, a comprehensive model is presented. The model considers important processes for the production of both H^- and positive ions. A set of particle balance equations in a steady-state hydrogen plasma are solved simultaneously. The calculated results have confirmed that H^- ions are generated by dissociative attachment to highly vibrationally excited hydrogen molecules (vibrational level upsilon''=5-10) and these molecules are produced by electrons with energies in excess of 30 eV. (author)

No abstract available

[en] Interaction between two waves is investigated numerically for the unbounded and the bounded electron beam-plasma systems, with reference to the control of wave spectrum and the suppression of the wave due to pre-modulation of the beam. In the case of the unbounded system, deformation of the beam distribution function is occurred in relation to suppression of one wave by the other wave. While, in the case of the bounded system, occurrence of deformation depends on whether reflected beams are present or not. When injected beams are reflected at the other end, two wave interaction occurs under the constant wave energy. On the other hand, when injected beams are absorbed at the other end, suppression of one wave due to the other wave is accompanied with additional broadening of the beam distribution function. (author)

[en] Suppression of the beam-excited electron wave in a bounded system is investigated in connection with the beam distribution function. Wave suppression has two different processes depending on whether injected beams are reflected at the other end or not. In the absence of reflected beam electrons, deformation of the beam distribution function is observed in relation to the suppression of the electron wave. However, when beam electrons are reflected, the external wave suppresses the electron wave but distribution function shows no appreciable change. By using the method of partial simulation, interaction between two waves in the bounded system including nonlinear motions of beam electrons is studied numerically. Qualitative agreement between experimental and numerical results is obtained. (author)

[en] The development of powerful D/sup -/ ion sources is essential for neutral beam injectors, with beam energies considerably in excess of 150 keV, for the next generation of fusion reactors. Since some experiments with low-pressure hydrogen discharges have observed unexpectedly high H/sup -/ ion densities (i.e. more than 30% of the ions may be H/sup -/), such discharges are currently being studied for the development of negative ion sources. Recently, the authors have reconfirmed numerically that H/sup -/ ions are generated by dissociative attachment to highly vibrationally excited molecules H/sub 2//sup */ (vibrational level v'' =5-10) and these molecules are produced by fast electrons e/sub f/ with energies in excess of 30 eV. Previously, they also obtained that wall effects, i.e. recombination of H at the wall, play an important role in determining the ratio of positive ion species in hydrogen plasmas. The purpose of this paper is to clarify the wall effects on volume production of H/sup -/ ions and to investigate the dependence of H/sup -/ production on plasma parameters

[en] The purpose of this work is to clarify the dependence of H/sup -/ ion production on plasma parameters, i.e. the electron density n/sub e/, the electron temperature T/sub e/, the pressure of hydrogen gas rho and the system scale length V/A(V and A are the volume and the surface area of the discharge vessel), and the wall parameters for neutral particles