Application of multi-species, collisional radiative model to the recombining divertor plasma
- Princeton Plasma Physics Lab., NJ (United States)
Recombination of hydrogen plasma in the divertor volume can be considered as a simple explanation of divertor plasma detachment phenomena experimentally observed on many tokamaks. As will be shown in this report, the presence of co-vibrationally excited molecules significantly enhances the conventional three-body recombination of plasma and expands the plasma temperature and density range responsible for plasma recombination to much higher temperatures and/or lower densities. Elementary atomic and molecular processes relevant for a divertor plasma will be reviewed. The following reaction chains are found to be predominant in the multi-species plasma recombination: (A) Multi-step recombination of a ion and an electron; (B) dissociative attachment of an electron to a molecule with a consequent reaction of mutual neutralization of the negative ion and a proton; (C) atomic to molecular ion conversion with a consequent dissociative recombination of the molecular ion. The chains B and C are incomplete as only the excited atoms are produced and collisional-radiative analysis of H(n > 1) relaxation to the ground state atom must be employed. The set of coupled collisional-radiative models was used to study the kinetics of destruction and production of following particles: H{sub 2}, H{sub 2}{sup +}, H, H{sup -}; taking into account the excitation 2 and CR transitions within the electronic quantum structure of particles. As the molecular reaction rates depend strongly on the vibrational quantum number, v, of the ground state of H{sub 2} and H{sub 2}{sup +} appropriate CR models include the calculation of the cascade of vibrational excitation via e-v, v-T, and E-v processes. We present the effective rate coefficients for plasma recombination due to the processes involving H{sup -} and H{sub 2}{sup +} ions, calculated as a function of plasma density and temperature. A comparison of these coefficients with the three-body ion-electron recombination rate coefficient will be given.
- DOE Contract Number:
- AC02-76CH03073; FG02-91ER54109
- OSTI ID:
- 489476
- Report Number(s):
- CONF-960354--
- Country of Publication:
- United States
- Language:
- English
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