Modeling of ion extraction from a laser-produced plasma by a nonuniform electrostatic field

In terms of the particle-in-cell (PIC) method, the approximation of heavy negatively charged particles (HNP) is developed and used to calculate the parameters of ion extraction from a plasma produced by selective laser ionization of atomic vapor. The approximation is based on the assumption that the mobility of plasma electrons is infinite and that there is an ion sheath in the plasma, in this version of the PIC method, the plasma electrons are replaced by HNPs, whose mass substantially exceeds the electron mass. The parameters of the HNPs are chosen such that the charge distribution in a plasma with varying potential is equilibrium. For this purpose, an artificial friction is introduced for HNPs. The ion motion is assumed to be the motion of real particles in a self-consistent field. The HNP approximation allows fast calculation of the ion current in a nonuniform electrostatic field without taking into account the plasma potential. This approximation is used to model the extraction of ions from plasma in two types of electrostatic extractors most suitable for atomic vapor laser isotope separation.