Study of a dense (~1021 m-3) plasma heating by a relativistic electron beam and confinement of the plasma in multimirror magnetic field is carried out at the GOL-3 facility. The high-resolution spectral system in the visible region is used for investigation of plasma parameters.

The analysis of the shape of D spectral line shows that wings of this line are determined by the Doppler broadening from atoms being in the hot plasma core at high-temperature operation regime. A survey spectrometer with spatial and time resolution was used in addition to high-resolution spectrometer for detail study of this regime. Results of radial distribution measurements of D line radiation show the presence of neutral deuterium in the hot plasma core. Ion temperature of the hot plasma achieves 2 keV.

The evolution of radial distribution of D line radiation, diagnostics features and results on ion temperature dynamics in the hot plasma core are presented in the paper.