ELECTRON-IMPACT EXCITATION AND IONIZATION OF AR+ FOR THE DETERMINATION OF IMPURITY INFLUX IN TOKAMAKS

Electron-impact excitation for Ar+ is studied using close-coupling R-m atrix theory in LS coupling. Both 28-state and 40-state close-coupling approximations are employed and cross sections and effective collisio n strengths for selected excitation transitions are compared. In addit ion, ionization rate coefficients for Ar+ are determined using distort ed-wave theory and compared with experiment. Finally, these data, alon g with experimental and theoretical radiative rates, are entered into a collisional-radiative modelling program-(atomic data and analysis st ructure) to obtain SXB ratios for the radiative transitions 3p(4)(P-3) 4p(4)D --> 3p(4)(P-3)4s(4)P and 3p(4)(P-3)4p(2)D --> 3p(4)(P-3)4s(2)P. These SXB ratios allow one to relate spectroscopic emissivity measure ments to impurity influx from a localized source. In the present studi es, we modelled the impurity influx when only the ground term contribu tes to the ionization of Ar+ and showed that the SXB ratio correspondi ng to the radiative transition between the doublet terms is less sensi tive to electron density and more reliable than the SXB ratio correspo nding to the radiative transition between the quartet terms. Additiona l collisional-radiative modelling studies of impurity influx when the ground and metastable states contribute to the ionization of Ar+ are a lso proposed.