Direct ion orbit loss near the plasma edge of a divertor tokamak in the presence of a radial electric field

The loss region in the initial velocity space of the direct orbit loss ions near the plasma edge of tokamaks with the divertor configuration is studied analytically. The results of this analysis are compared with the numerical results of the loss region in the JET case obtained by Chankin and McCracken (1993). The results agree with each other semiquantitatively in several cases involving the presence of a radial electric field. A measure of the direct ion orbit loss Gamma is calculated from the given loss region in the initial velocity space for JET, JT-60U and ITER. When the initial position of an ion is located in the outside torus (r>R_x, where R_x is the radius at the null X point), the dependence of Gamma on the radial electric field shows the existence of a local maximum and a local minimum in the negative region of the radial electric field