Excitation and ionization of neutral Cr and Mo, and the application to impurity influx

The atomic physics required to study impurity influx from a localized surface is examined and then applied to chromium and molybdenum. To this end, we have calculated term energies and oscillator strengths for the a S-7 --> y, z P-7(o) and a S-5 --> y, z P-5(o) transitions in neutral Cr and Mo in a multiconfiguration Hartree-Fock approximation. We have calculated excitation cross sections for these dipole transitions and for the a 7S --> a 5S, y, z P-5(o) transitions, which couple the ground to the metastable system, in a close-coupling approximation using the non-relativistic R-matrix method. Pseudo-resonances were removed from the latter transitions using a novel transformation and reduction method which eliminates those linear combinations of (N+1)-electron bound states that are not required by orthogonality. We have calculated the direct ionization cross sections from the ground (7S) and metastable (5S) terms in a distorted-wave approximation, and And significant near-threshold sensitivity to the effective potentials used. We have incorporated this primary atomic data into the Atomic Data and Analysis Structure (ADAS) and solved the quasi steady-state generalized collisional-radiative population rate equations. We present results for the number of ionization events per observed photon, the SXB ratio, over a wide range of electron temperatures-and densities. The SXB ratio can be used to directly relate spectroscopic emissivity measurements to impurity flux from a localized surface such as the target plates in a magnetic fusion divertor.