Definition of collisional-radiative rate coefficients in plasma

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:489434

Braams, B J ^[1]

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1. New York Univ., NY (United States)

The Collisional-Radiative (CR) model for atomic rate coefficients was introduced in connection with hydrogen and hydrogenic ions, and has been employed since by many authors to define effective rate coefficients for ionization and recombination in cases where collisional processes on excited states axe important. In such cases a fine-level description of the plasma would use as unknowns the densities in each possible excited state of any charge state of any plasma constituent, and would explicitly consider all possible transitions between such excited states; all this coupled to spatial transport and boundary conditions. In practice the transport description of plasma has to be done on a coarser level in which the unknowns represent just densities in each charge state, while the population in excited states is assumed to be in some sense in an equilibrium defined by the charge state densities. The traditional CR model uses as the unknowns in the reduced description the densities in the ground state associated with any charge state. It is assumed that the transition matrix in the fine description has a particular block structure, in which excited states of charge state i, say, are coupled only to other excited states of that same charge state, to the ground state of charge state i, and to the ground state of charge state i + 1. In this case, under the assumption that transport processes and source processes are slow compared to the transitions among excited states, the excited state population at charge state i is expressed in terms of the population densities of the ground states of levels i and i + 1, and this assumption allows to define effective ionization and recombination coefficients for transitions between ground states, thus eliminating the excited states from the description.

• DOE Contract Number: FG02-86ER53223
• OSTI ID: 489434
• Report Number(s): CONF-960354--
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
HYDROGEN
ION-ATOM COLLISIONS
IONIZATION
PLASMA
RECOMBINATION