Characteristics of the 20kV, 1.5A Neutral Beam Injection System

For a fusion reaction to be feasible, it is necessary to heat plasmas to a very high temperature. One of the most promising ways for heating plasmas is to inject high energy neutral particles to the magnetically confined plasmas and to convert their kinetic energy to the thermal energy through collisions. In order to investigate various problems associated with this neutral beam injection method, a 20kV, 1.5A neutral beam injector has been designed and constructed. By using this injection system, the effect of a gas injection to the ion source was investigated, and it was shown that the accurate control of the gas injection pressure was necessary to attain the stable ion beam extractions. The effect of the anode size on the arc discharge characteristics in an ion source was also obtained experimentally. The beam profiles were measured by a calorimeter and the good beam convergence was shown to be obtrained by the present system. Since the plasma produced in the ion source contained molecular ions, the low energy particles existed in the ion beam. The energy of the extracted ion beam was analysed by using the deflection magnet, and the variations of low energy ion fractions with arc descharge currents were also clarified