[en] Lithium application in a liquid-lithium thermonuclear reactor pursues three main goals: tritium breeding, blanket cooling and the first wall steam protection against the direct contact with thermonuclear plasma. To acquire data on the protective properties of the boundary lithium plasma one should investigate into the helical instability of arc discharge in lithium plasma. The obtained data enable to conclude that under experiment the helical instability of arc discharge may evolve within the limits of rather restricted range of plasma parameters