Basic Investigations on the New Acceleration Scheme with Large Amplitude Electron Plasma Waves

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Large amplitude electron plasma waves are excited, when a high power microwave is irradiated to the nonuniform plasma with a static magnetic field. In this scheme, it is aimed to investigate the interactions between an electron beam and electron plasma waves under the effects of VpxB acceleration mechanism. In the fiscal year of 1987, we devoted to the design and construction of new system of experimental apparatus, and in that of 1988, we have performed the experimental investigations. For this purpose, we have made an electron-beam gun with a small size (diameter:3 cm, maximum acceleration voltage:500V, maximum beam current:300mA), which is settled in the overdense region for a resonance absorption of the electromagnetic wave. In the present stage, we have almost finished the experimental work for the first phase, and several new phenomena have been clarified.1. When there is no magnetic field (B=0), precise investigations revealed that the interactions between electron plasma waves and an electron beam occured resonantly at Vp Vb under the controlled conditions and the mechanism for the particle trapping and its conditions are clarified.2. When there is a static magnetic field, the VpxB acceleration scheme is formed and an efficient acceleration of electron beams are observed. In this case, a strong interacton also occurs at Vp Vb and the electron beams are accelerated 2.5-3 times of the initial injection energy.We also constructed to demonstrate a new type electron linear accelerator which does not employ the plasma, but is based on the VpxB acceleration system. The experimental result shows more efficient and stable acceleration of electrons compared with a conventional linear accelerator.