Forbidden line emission from highly ionized atoms in tokamak plasmas

Abstract

Collisional excitation rate coefficients and radiative decay rates are interpolated for ions of elements between calcium and krypton and for levels of the 2s22pk, 2s2pk+1, and 2pk+2 configurations, and for the O I, N I, C I, B I, and Be I isoelectronic sequences. With the use of these interpolated atomic data, level populations and relative line intensities can be calculated for ions of these sequences, for levels of the stated configurations. Relative line intensities for transitions between the 2s22pk ground configurations are considered specifically. These transitions are forbidden, e.g., magnetic dipole transitions, and are strong in XUV spectra of tokamak plasmas. The forbidden lines provide important plasma diagnostic information, such as the ion temperature which can be derived from forbidden line profiles. The relative line intensities are presented graphically, in order that they can be used easily by tokamak researchers. Results are given for three values of electron density: 2.5×1013; 1.6×1014; 1015 cm−3, and two values of electron temperature: the ionization equilibrium temperature and twice this temperature. The behavior of the line intensities along the isoelectronic sequences is discussed and the relative importance of excitations into different intermediate levels for populating the upper level of the forbidden line of the B I sequence by cascade is discussed in detail.