We present a report on a program to develop a high‐power X‐band magnicon amplifier for linear accelerator applications. The goal of the program is to generate 50 MW at 11.4 GHz with 50% efficiency, using a 200 A, 500 keV electron beam produced by a cold‐cathode diode on the NRL Long‐Pulse Accelerator Facility. The initial experiment, designed to study the gain from the first (driven) deflection cavity to a second (passive) deflection cavity, is under way.