Collisional recombination in nonideal plasmas
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AL, NONLINEAR, AND SOFT MATTER PHYSICS
Collisional Recombination in Nonideal Plasmas A. V. Lankin Joint Institute for High Temperatures, Russian Academy of Sciences, ul. Izhorskaya 13/19, Moscow, 125412 Russia Moscow Institute of Physics and Technology, Institutskii per. 9, Dolgoprudnyi, Moscow oblast, 141700 Russia e-mail: [email protected] Received June 28, 2007
Abstract—We suggest a model that allows one to consider the kinetics of collisional recombination in a nonideal plasma and to calculate its rate by the molecular dynamics method. We have found that the dependence of the collisional recombination rate on the plasma coupling parameter differs significantly from the extrapolation of the three-body recombination rate to the nonideal region. The recombination rate in a strongly coupled plasma has been found to decrease with increasing coupling parameter. We have established that the effect of plasma nonideality increases with ion charge. The recombination kinetics is shown to depend significantly on how the ions are arranged in the medium. Collisional recombination transforms into three-body one as the coupling parameter of the medium decreases. PACS numbers: 52.65.Yy, 52.27.Gr, 52.20.-j DOI: 10.1134/S1063776108110186
1. INTRODUCTION The plasma used in many applications is nonideal [1, 2]. Allowance for the recombination process is also important for describing the processes in a nonideal plasma produced, for example, in clusters by intense laser radiation; collisional recombination should play a major role in this case [3, 4]. In [4], the recombination rate was estimated by extrapolating the three-body recombination rate [5] in an ideal plasma to the nonideal region. In [3], the approximation from [6] was also used to estimate this rate. The effect of the coupling parameter Γ = (4πne/3)1/3e2/kT (ne is the electron concentration and e is the electron charge) on the recombination rate was considered in various approximations in [6–11]. In [6], the recombination rate was calculated by analyzing the Fokker– Planck drift of electrons in energy in a nonideal plasma. Based on this approximation, the authors of [6] conclude that the recombination rate decreases significantly in a nonideal plasma. Although this qualitative conclusion is corroborated in other papers, the quantitative estimates of the recombination rate in [6] cannot be considered satisfactory, since the stability loss for some of the highly excited levels is disregarded in this paper. As was shown in [7, 8], this should affect strongly the recombination process in plasma. The plasma microfields should play an important role in the recombination process. The structure of the microfields in a nonideal plasma was investigated in [12]. A detailed allowance for the effect of electric and magnetic fields on the recombination process was made in [9], where the recombination via highly excited levels was shown to be strongly suppressed when these are
taken into account in the region of a strongly coupled plasma (Γ > 1). It should be noted that some of the p
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