A6 magnetron operation analysis: Experimental verification of the Buneman-Hartree threshold on the magnetron operational domain

The Buneman-Hartree (BH) threshold condition defines the exact phase synchronism, inside the magnetron interaction space – between the anode and the cathode of the magnetron, where the electron cloud rotates in the crossed external radial electric E and axial magnetic B fields with azimuthal drift velocity, v_q. The BH condition is achieved when the electron drift velocity equals/synchronous to/with the azimuthal phase velocity, v_ph, of the desired for a magnetron operation electromagnetic wave, v_q=v_ph, that depends on the frequency and the mode (electric field pattern) of the wave. For the “classic” “1.58/2.11/4.11” A6 relativistic magnetron (RM) geometry, the BH condition of the 2π-mode, whose operational frequency is ~4.7 GHz, is defined at, for example, ~220 kV at 0.5 T, ~270 kV at 0.6 T, ~320 kV at 0.7 T, and so on. The University of New Mexico (UNM) operates the A6 RM driven by the PULSERAD-110A Marx Generator (MG) that can provide 100’s of kV of accelerating voltage and several kA of electron-beam current during tens of ns of output pulsed power and 100’s of MW of output microwave power in the 2π-mode. Experimental verification of the BH condition for the A6 RM operating in the 2π-mode is performed by varying axial magnetic field B at several fixed charging voltages U of the PULSERAD-110A MG defining the radial electric field E. The BH condition is achieved in the experiment at the maximum magnetic field B whereby the 2π-mode of the A6 RM may still be detected. Results of the experiments are analyzed and discussed.