Thermal ionization of helium in the quantum mechanical representation of Feynman path integrals

The method of Feynman path integrals is used to calculate the degree of ionization in a thermodynamically equilibrium, dense helium plasma. A quantum statistical calculation which is based on the “first principles” and in which the permutation symmetry and electron spin variable are explicitly taken into account is carried out for a helium atom that is in thermal and mechanical contact with a plasma at a temperature from 30000 to 400000 K. Numerical integration over virtual paths is performed by the Monte Carlo method. When the temperature and density are varied, the amount of singly charged ions in a plasma varies nonmonotonically, reaching a maximum at a temperature of about 70 000 K and a pressure of 100 MPa. Radial profiles of the electron density around a helium nucleus are obtained, as well as contour lines of the degree of ionization in the p-T plane of the plasma states. The role of fluctuations is investigated. It is shown that the fluctuations of the local electron density near a helium ion have a radical effect on the values of the ionization-recombination equilibrium constants.