Compact High Power Microwave Source Research Articles

PIC simulations of a frequency agile multicavity relativistic magnetron using irregular ring metamaterials driven by a transparent cathode

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility.

Mode control by rearrangement of the slow wave structure in a 12-cavity relativistic magnetron with diffraction output using single-stepped cavities driven by a transparent cathode

We present the design of an agile slow wave structure for a “crab-like” A12 relativistic magnetron with diffraction output using single-stepped cavities. By regrouping the interaction region as three sets of four cavities, the TE31 operating mode is generated at 2.60 GHz with 1.0 GW output power for an applied voltage of U = 350 kV and a magnetic field of B = 0.34 T. By regrouping the interaction region as four sets of three cavities, the TE41 operating mode is generated at 2.82 GHz with 1.0 GW output power for an applied voltage of U = 355 kV and a magnetic field of B = 0.36 T. Furthermore, by regrouping the interaction region as six sets of two cavities, the TE31 mode and the TE21 mode are generated. When an applied voltage of U = 350 kV and a magnetic field of B = 0.33 T are used, its output power can be as high as 1.0 GW for the TE31 mode operating at 2.5 GHz. In addition, when an applied voltage of U = 350 kV and a magnetic field of B = 0.42 T are used, its output power can be as high as 1.0 GW with operating mode TE21 at 2.62 GHz. It was found that the rearrangement of the slow wave structure can control the operating mode and, at the same time, lower the operating condition of the beam/wave interaction compared to the traditional 12-cavity relativistic magnetron. The result suggests that this configuration is favorable for mode switching through mechanical rearrangement of the slow wave structure. This work seeks to design a compact high power microwave source for a narrowband directed microwave beam that is suitable for mode switching investigations.

A Frequency-Agile Relativistic Magnetron With Axial Tuning

A frequency-agile relativistic magnetron with axial tuning is presented. To achieve axial tuning, reentrant cavity which has two radial parts connected by a coupling hole had been introduced. Resonant frequency of this cavity configuration can be tuned by adjusting the axial length of each coupling hole without any variation of other parameters. Multi-antenna output technique had been integrated with the reentrant cavity chain to obtain high conversion efficiency in the whole tuning range. Simulation results showed that this tube had a tuning range between 1.23 GHz to 1.70 GHz, corresponding to relative bandwidth of 32% about a center frequency of 1.465 GHz. In this tuning range, the maximum output power is 1.81 GW at 1.605 GHz, corresponding to an efficiency of 54.5%. This axial tuning RM is a promising compact high power microwave source with wide tuning range.

A “crab-like” A6 relativistic magnetron with diffraction output driven by a transparent cathode

We present the design of an A6 relativistic magnetron with diffraction output (MDO) which looks like a crab and we named it the “crab-like” A6 MDO. This article shows that the crab-like A6 MDO driven by a transparent cathode can radiate the TE11 mode with an output power of about 1 GW when an optimized applied voltage of U=440 kV and magnetic field of B=0.43 T are used. Its electronic efficiency, as obtained using UNIPIC particle-in-cell (PIC) simulations, can be as high as 44% in S-band. The UNIPIC PIC code used in simulations also demonstrates that the crab-like A6 MDO can radiate both two electron spokes in the TE21 mode with an operating frequency of 2.1 GHz and four electron spokes in the TE21 mode with an operating frequency of 2.5 GHz when different magnetic field amplitudes are used for an applied voltage of U=400 kV. This result suggests that this configuration is favorable for mode switching. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for mode switching investigations.

High Repetition-Rate Operation of a Compact Buncher for Microwaves

Recently, we have designed and built a new microwave tube; it has been given the name “Arletron.” It works in S-band, and we describe in this paper its operation. A 200-keV 1-kA annular electron beam (e-beam) is strongly bunched in a simple assembly of two pillbox cavities. The bunching occurs at the frequency of the -mode resonance of the system. An extracting cavity, inserted just downstream from the buncher, has been used to extract and to convert the kinetic energy of the beam into an RF wave that is then radiated by a conical antenna. The Arletron is a short and compact high-power microwave source whose repetition rate depends on the pulsed power system; operation at 100 Hz has been routinely achieved. The e-beam does not intercept grids or electrodes before being collected. MAGIC simulations predict that an Arletron can be, in principle, operated from S-band to C-band (2-6 GHz). Although a magnetic field is needed to propagate the beam, it is low enough to be produced by permanent magnets.