TWO ELECTRON CAPTURE PROCESSES IN PLASMAS CONTAINING MULTIPLY CHARGED IONS

Abstract
It has recently been recognized that the electron transfer processes between the multicharged ions and neutral species in a crucial way influence the ionization equillibriun, energy balance, radiation and transport properties of many laboratory and astrophysical high-temperature plasmas^1-3. Such a role of these processes is a result of their extremely large cross sections (σ~10^-14cm² ; σ~z^q, q = 1-2) and the fact that highly excited states of the product ions are preferencially created by them. In Tokamak-type thermonuclear plasmas, additionally heated by neutral beams, the multicharged impurity ions play a detrimental role, which even may prevent reaching the fusion burning conditions¹. The important neutral species, which undergo charge-changing collisions with multicharged ions in the outer layers gf the Tokamak plasma, are D, T and He. Almost equally important role plays the electron transfer collisions between multicharged ions and neutrals in the expanding laser produced plasmas². In such plasmas, the above mentioned processes serve as an efficient mechanism for creation of inverted population of the electronic levels of the product ions. The radiative decay of these levels is responsible for the EUV enission from laser produced plasmas.