The problem of a steady-state infinitely long plasma cylinder is considered in which nuclear reactions take place. The analysis is restricted to the fully ionized region, but the temperature at the "wall" is sufficiently low, so that nuclear energy is liberated only in the centre. Of all possible nuclear reactions at axis temperature of 108 – 109°K only the D-T reaction is considered (50/50 mixture). The energy is carried away by bremsstrahlung, re-absorption of which is neglected, and by heat conduction to the wall.An externally applied axial magnetic field (between 3 and 10 Tesla at the "wall") perpendicular to the radial temperature gradient gives rise to a large diamagnetic azimuthal current, as a result of which the pressure at the boundary is much lower than in the centre (e.g. 10−1 and 100 atm, respectively). The fuel supply and the ash removal take place through classical diffusion to and from the "wall" through this low-pressure region.The macroscopic equations are solved for a number of values of the parameters involved. No acceptable solution exists if the helium density in the centre is either too low or too high, but it must be higher than the deuterium-tritium density. Solutions with a power production up to 1 GW per metre length and a plasma radius of up to a few metres are found.