We present results of the investigation of different types of cathodes operating in an electron diode powered by a high-voltage generator (300 kV, 250 ns, 84 Ω, ⩽5 Hz). The cathodes which have the same emitting area of 100 cm2 are made of metal–ceramic, carbon fibers, carbon fabric, velvet, or corduroy. We also tested carbon fibers and carbon fabric cathodes coated by CsI. It was shown that for all types of cathodes the electron emission occurs from the plasma which is formed as a result of a flashover of separate emitting centers. The amount of the emitting centers and the time delay in the electron emission were found to depend strongly on the accelerating electric field growth rate. Experimental data concerning the uniformity of the light emission from the cathode surface and divergence of the generated electron beams are presented. Data related to the general parameters of the diode, namely its impedance, power, and energy are given as well. For all the cathodes investigated the observed diode impedance indicated the existence of a quasistationary cathode plasma boundary for electron current density ⩽20 A/cm2. We present the dependencies of the average emitted electron current density and of the time delay in the electron emission on the number of generator shots. We also present data of the vacuum deterioration as a result of the tested cathodes operation. The obtained data are discussed within the framework of plasma formation as a result of cathode surface flashover.
The article presents a source producing high-power ultrawideband
electromagnetic pulses. The source includes a generator of
monopolar pulses, a bipolar pulse former, and a combined
ultrawideband transmitting antenna. Monopolar 150-kV, 4.5-ns
pulses are transformed into bipolar 120-kV, 1-ns pulses, which
are emitted by the antenna. The pulse repetition rate of the
setup is up to 100 Hz. The peak power of the source is 170 MW
as measured with a TEM-type receiving antenna having 0.2–2
GHz passband. The pattern width of the transmitting antenna
at a half-level of peak power is 90° and 105° for the
H- and E-planes, respectively. The electric field strength measured
4 m from the transmitting antenna in the direction of the main
radiation maximum is 34 kV/m.
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