The small saturation energy density of excimers requires amplifiers of large cross sections for amplification of short pulses of already medium power. Homogeneous excitation of large volumes of fluorine-based gas mixtures by discharge pumping is a critical interplay of the properties of both pumping and preionization, generally necessitating an intense spatially and temporally controlled x-ray preionization. In the present realization, the stringent intensity requirements of preionization are fulfilled by reducing the pulse duration of the x-ray flash to ∼16 ns and by positioning the x-ray source in the near vicinity of the active volume. It is proven both theoretically and experimentally that by proper choice of the positions of two cylindrical x-ray guns, the spatial distribution of preionization can be tuned to (and around) the optimum distribution. In this way, the spatial distribution of the discharge can also be controlled, giving a practical method to compensate for eventual inhomogenities of the E-field of excitation and to tune the discharge to the desired geometry. In this paper, design considerations and experimental realization of a KrF excimer amplifier of ∼5 × 4 cm2 cross section and a spatially tunable x-ray preionization are presented.