A flash x‐ray source has been fabricated to examine the plasma‐driven shutter for the Nova Fusion Laser System at the Lawrence Livermore National Laboratory. This source has a 20‐ns pulse width and 1.5‐ and 4.5‐keV x rays. It has been used to characterize plasma moving at 1–5 cm/&mgr;s with areal densities down to 0.1 mg/cm2and a spatial resolution of 2.5 &mgr;m. By using this x‐ray source to diagnose the Nova plasma shutter, the authors were able to discover and cure sources of plasma nonuniformity and empirically select the foil dimensions and the current required for Nova.