Generation of microwave pulses with a carrier frequency of 3.8 GHz and a length of 75 ns by a relativistic Cherenkov microwave oscillator without a guiding magnetic field

In the experiment with an electron energy of $\approx$ 500 keV, the long-pulse ($\sim$300 $T$, where $T$ is the oscillation period) the generation regime of a relativistic Cherenkov microwave oscillator without a guiding magnetic field at a carrier frequency of 3.8 GHz has been obtained. A high-power microwave radiation pulse length of $\sim$75 ns, a peak generation power of 210 $\pm$ 30 MW, and a power conversion efficiency of 9 $\pm$ 2% were attained.