Abstract <p>Hot dense plasma is formed in a thin skin layer of a massive conductor (rod) with a nanosecond rise time of megaampere current through it. With a current rise time of about or less than 1 ns, the initial active resistance of the skin layer of a metal rod with a diameter of 1–2 mm, as well as the plasma formed on its surface with a temperature of about 100 eV is fractions of an Ohm per 1 cm of length, which, with a rod length of 1–3 cm, provides a terawatt power of Joule heating and generated soft X-ray radiation at a current level of several megaamperes. Fast switching of the current to the load (to the rod) is realized by preliminary short-circuiting the load with injected plasma, thin foil or a radial wire array. The current is switched to the load during the movement of the short-circuiting plasma accelerated by the Lorentz force. This paper presents the results of experiments on the fast explosion of the surface of aluminum rods with a diameter of 0.3–3.0 mm in a configuration with plasma injection into the load region. It is shown that the generation of a powerful soft X-ray pulse is maintained with an increase in the rod diameter to at least 3 mm.</p>