An experimental test bed has been used to extensively investigate the operating characteristics of various types of cathode and anode in an x‐ray preionizer. The temporal development, intensity, and uniformity of x‐ray beams generated by a carbon fiber cold cathode and corona plasma cathode were measured and compared. Electron densities of >108cm−3in N2(1 atm) and >109cm−3in Ar (1 atm) could be generated. Factors affecting the high repetition rate operation of both cathodes were examined. The effect of transmitting target material and thickness on x‐ray output were investigated.