be 1. The ion density changes with time, so the ion density calculated from equation (1) is integrated temporally and spatially to obtain the number of ions by the next equation: Here the polar coordinates are set at the centre of the target as shown in Fig. 5, and the ion density at r=L, 0=0° is a standard value. In equation (2) the sampling is done at constant intervals At(~l //sec) and the integration with time is done by the summation of each value. The values of and Vt are the ion density and the expansion velocity of the zth group of ions. The is the coefficient of the angle dependence of the expansion plasma. Experimental results show that as shown in Fig. 6. The kinetic energy of each ions group is given by mv, 2m,/2 (m is the mass of an ion), therefore the kinetic energy of the expansion ions Ep is obtained from the next eauation.
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