In space phenomena and in laboratory experiments plasmas are usually non-stationary and non-uniform. Chemical composition may be rather complicated and the distribution of atoms over ionization degrees and quantum states is usually non-equilibrium. Moreover, the velocity distribution of free particles may be also non-equilibrium, i.e. non-Maxwellian. Our model, designed for spectroscopy of such complicated plasmas, is as follows.
Plasmas are approximated by means of the 3D sequence of Lagrangian cells affected by collective radiation field and the radiation of external sources (lasers, backlighters, hot surfaces, or external plasmas). The external radiation is included in the boundary condition to the equation of radiative transfer, which is integrated self-consistently with non-stationary collisional-radiative rate equations for each cell. During the integration, besides a computation of space-average direction-average intensity of radiation in each cell (needed for computation of probabilities of photoinduced transitions) the code simulates signals of spectroscopic equipment (spectrometers, PCDs, bolometers, pinhole cameras, etc.) in particular experiment.
The code has three operation modes. In most general mode the code operates as atomic-kinetics and radiative-transfer subroutines of magnetohydrodynamics (MHD) code. However, in this mode the computations last for months and we performed them only once for 2D simulation of gas-puff z-pinch. In the second mode the code operates as a post-processor of MHD code. In the third, most simple, mode plasma of interest is approximated by a few cells, which follow prescribed scenario. This scenario may be a simplified version of MHD simulation or some idea to be checked quickly.
Radiation transport and density effects in non-equilibrium plasmas
Modified on: 2012-12-20