This article reports the observation of intense x‐ray emission by a nonequilibrium energetic electron flow that can be produced when an explosive formed‐ferrite filament is used as a plasma initiator in a high vacuum of 10−5–10−3Torr. Exposure dose measurements and pinhole photographs for the x‐ray emission have shown that x rays originate linearly along a 14.5‐cm filament with a high exposure dose level of 50 mR(mili‐roentgen)/pulse at 6.5 keV, the predominant x‐ray energy. The x‐ray emission characteristics are described in terms of the time‐resolved and ‐integrated observations in order to infer the x‐ray emission mechanism in which an interaction between energetic electron flow and a cloud of ions or neutral atoms thermally produced from the filament has to be taken into account in the close vicinity of the filament.