UNM operates the “classic,” 1.58/2.11/4.11 A6 RM with radial output driven by the MARX generator of the PulseRad110A accelerator (Fig. 1) [1]. The operational parameters and the output characteristics of the A6 RM are monitored with the Tektronix DPO 71254C scope: Ch1 - Cathode voltage by a voltage divider, Ch2 - Discharge current by a Rogowski coil, Ch3 - Output power density by an electric field probe and a crystal detector, and Ch4 - Electric field oscillations by a “cut” WR284 waveguide(Fig. 2) whose frequency spectrum (Fig. 3(d)) is calculated by the DPO 71254C scope internally. Typical oscillograms, Ch1- Ch4, obtained at magnetic field ~3.75 kG and MARX charging voltage ±33 kV, which results in the “peak: accelerating voltage of the MARX generator $6 \times(2 \times 33 \text{kV}) \sim 400 \text{kV}$, are shown at Fig. 3

The University of New Mexico (UNM) operates the “classic” 1.58/2.11/4.11 six-cavity (A6) high-voltage or relativistic magnetron (RM) driven by the PULSERAD110A pulsed power generator. The A6 RM operation, similar to any other RM, is controlled by the crossed (i) internal radial electric field, $E_{r}$, created by the cathode voltage drop, $V_{d}$, between the cathode and the anode or slowwave structure (SWS) of the A6 RM, and (ii) the external magnetic field, $B_{z}$. The measurements of the UNM A6 RM output characteristics are performed by scanning $B_{z}$ vs $V_{d}$ to define the range of $V_{d}$ within the magnetron operational domain, $V_{d}\left(B_{z}\right)$, between the Hull cutoff and the Buneman-Hartree synchronous voltages, where the “classic” A6 RM can operate in its “intrinsic” $\boldsymbol{2} \boldsymbol{\pi}$-mode at frequency $\sim 4.6 \mathrm{GHz}$. The performed $B_{z}$ vs $V_{d}$ scan also allows for calibration of the cathode voltage $V_{d}$ against the magnetic field $B_{z}$.

The experimental measurements of electron beam cur-rent-voltage (I-V) characteristics on the SINUS-6 accelerator are performed by analyzing (i) the electron-beam current produced by explosive emission cathodes of different types in a magnetically-insu-lated coaxial diode (MICD) of the SINUS-6 accelerator, and (ii) an accelerating voltage applied to the cathodes. The direct comparison of experimentally measured I-V characteristics with analytical cal-culations and numerical particle-in-cell (PIC) simulations of the MICD of the SINUS-6 accelerator is presented. The results of the comparison are analyzed, and the following steps in this work are discussed.

The University of New Mexico (UNM) developed an A6 relativistic magnetron (RM) that may operate in two basic configurations of output power extraction from resonant cavities of the magnetron: (i) radial output with microwave power extraction from one of six resonant cavities into a rectangular horn antenna, and (ii) axial output microwave power extraction from all six resonant cavities smoothly tapered in the axial direction onto a conical horn antenna. In both configurations, the magnetron is driven by the PULSERAD-110A electron beam accelerator that is able to provide 100’s of kV of accelerating voltage and several kA of electron-beam current during tens of ns of output pulsed power with its internal output impedance ~35 Ω. While driven by kV/kA pulsed power, the A6 RM is able to provide 100’s of MW of output microwave power either in the 2π-mode, whose “cold” operational frequency is ~4.6 GHz, or in the π-mode, whose “cold” operational frequency is ~2.3 GHz, with a standard solid cylindrical “cold” explosive-emission cathode. Results of UNM’s latest experimental measurements of output microwave power from an A6 RM with radial output demonstrated ~350 MW of high-power microwave (HPM) power at frequency ~4.675 GHz (2π-mode) during ~25 ns of output HPM pulse.

Experimental results are presented for a high power backward wave oscillator (BWO). An overmoded slow wave structure (SWS) with a relativistic hollow electron beam was used to increase the interaction impedance and to avoid RF breakdown. The results of experiments with this overmoded (D/λ ≈ 8) SWS successfully produced high power radiation at 78.5 GHz. The rectangular corrugation SWS can be fabricated more easily compared to a sinusoidal one. In order to select a higher order mode as the operating mode, a mode selection technique was utilized. In this work, the experimental results were compared with calculations performed using the MAGIC PIC code; the measured data are shown to agree favorably with simulations.