Dual-Frequency, Harmonic, Magnetically Insulated Line Oscillator

Magnetically insulated line oscillators (MILOs) are crossed-field devices which generate a self-induced azimuthal magnetic field via an axial current. This negates the need for external magnets, potentially increasing overall system efficiency at the expense of reduced device efficiency. This article reports the design, simulation, and experimental demonstration of a dual-frequency, harmonic MILO (HMILO), which is composed of two sequential slow wave structures (SWSs) tuned for oscillation at different frequencies, each paired with a set of choke cavities and insulated by the self-generated magnetic field of the common cathode. The two SWSs—designed for operation in
$L$
- and
$S$
-bands at 1 and 2 GHz, respectively—were tested independently before the HMILO experiments. Results for the
$L$
-band MILO (L-MILO) were reported previously by Packard. In the experiments reported here, the isolated
$S$
-band MILO (S-MILO) produced 1.1 ± 0.7 MW of output power at 2.076 ± 0.005 GHz, when supplied with 207 kV and 7.3 kA from the MELBA-C generator. Ultimately, when implementing two separate extractor configurations, the HMILO produced 12.7 ± 7.6 MW at 0.984 ± 0.013 GHz and 3.2 ± 1.5 MW at 2.074 ± 0.003 GHz. These results are compared against simulated performance in the particle-in-cell (PIC) codes CST and improved concurrent electromagnetic PIC (ICEPIC).