A theoretical analysis of neutral beam probe for measuring ion temperature of a plasma

The parameters of high temperature plasma can be measured by analyzing the energy spectra of the fast neutral particles emerging from the plasma column. This technique involves two methods, i.e. the passive and the active methods. However, it is difficult to measure the parameters of the central part of large and dense plasma by the passive method because slow neutrals are hardly able to reach the central part of the plasma when the plasma becomes considerably large and dense. Instead, the active or the neutral beam probe method can be used, in which well-collimated beam of fast neutral particles is injected into plasma. In this paper, a theoretical basis of the neutral beam probe for measuring the local ion temperature of plasma is given. In the paper, general theory, and its application to the central test volume of plasma are described, and the numerical results for some typical plasma are shown. It is concluded that the beam probe of fast hydrogen atoms can be used to measure the local ion temperature of plasma, and for the plasma of tokamak of current and next generations, it is desirable to choose the beam energy in the range from 10 keV to 30 keV. It is pointed out that the method of least squares can be applied to determine the local ion temperature from the measured data. (Wakatsuki, Y.)