Collisional-radiative model for the diagnostics of low pressure inductively coupled krypton plasma

Summary form only given. The physics driving the low and atmospheric pressure discharges have been extensively studied using plasma diagnostics based on optical emission spectroscopy (OES). A popular approach is based on the simulation of emission spectrum, obtained from a suitable population kinetic model accounting the various population and depopulation mechanisms, using specific plasma characteristics as the adjustable parameters¹. The accuracy of such approach highly depends upon the cross sections used in the kinetic-model. We have recently showed the effectiveness of using fully relativistic fine-structure cross sections for the analysis of low pressure argon plasmas². In the present work, we have developed a collisional- radiative (CR) model using our fine-structure relativistic-distorted wave (RDW) cross sections. This model is applied to the study a low pressure inductively coupled (ICP) Kr plasma for which the literature is scarce.Being a heavier element the relativistic effects such as j-j coupling and spin-orbit interactions are expected to play very crucial role in the modelling of Kr plasmas. In the model, we have incorporated 40 fine structure levels in addition to atomic as well as ion ground state. The various processes considered in the model are electron-impact excitation, ionization and their reverse processes through detailed balance principle. The detailed fine-structure electron-impact excitation cross sections have been calculated by using our reliable RDW method3. The required rate coefficients have been calculated from these cross-sections assuming Maxwellian energy distribution. Radially-averaged Kr emission lines from the 2pi →1sj (Paschen notation) were recorded as a function of pressure from 1 to 50mTorr. The electron temperature obtained by the best fit between the measurements and CR model was found to decrease from 6.7 to 2.6eV with the pressure varying from 1 to 50mTorr. These data are in very good ag- eement with Langmuir probe measurements.