High Power Microwave Generation Research Articles

Guest Editorial The Eighteenth Special Issue on High-Power Microwave and Millimeter-Wave Generation

The field of high-power microwave and millimeter-wave generation continues to be an active area of research and technological development to meet the demand of high peak, average, and prime power needs of government and industrial applications. High-power vacuum electronic devices, producing coherent electromagnetic radiation ranging from tens of centimeters to submillimeter wavelengths, continue to find application in advanced fusion and accelerator device applications, state-of-the-art radar and electronic countermeasures, high data-rate communications, and material processing. Advances in materials, plasmas, cathode technology, and electromagnetic structure design, as well as theory, modeling, and simulation, help to drive this technology to achieve unprecedented peak and average power, more compact size, enhanced waveform agility, greater bandwidth, and higher efficiency.

О допустимой мощности автономного формирователя импульсного электромагнитного поля на основе мощного сверхвысокочастотного генератора.

О допустимой мощности автономного формирователя импульсного электромагнитного поля на основе мощного сверхвысокочастотного генератора.

A New Approach for High-Power Coaxial Magnetron Using Stacked Anode Resonators

A novel design of the ${X}$ -band megawatt-class coaxial magnetron using multiple-anode resonators placed in a stacked configuration is presented. The proposed design enhances the output power of a coaxial magnetron substantially without requiring external circuitry for power combining. The coaxial magnetron design is presented with two different cathode arrangements: one with separate cathodes and the other with connected cathodes. This article presents a new way for the generation of high-power microwaves by combining powers generated by multiple-anode resonators within a coaxial magnetron itself. The proposed coaxial magnetron is analyzed using the particle-in-cell (PIC) simulations. The output power of double-anode resonator magnetron is found to increase about 2.73 times compared with the coaxial magnetron with a single-anode resonator. The peak output power of 5.78 MW with 49.4% efficiency is obtained at 9.2906 GHz when a separate cathode arrangement is used, and both cathodes are excited simultaneously. The circuit efficiency and electronic efficiency are obtained as 83% and 59.5%, respectively. A wide frequency tuning range of 30.5 MHz is obtained, from 9.2840 to 9.3145 GHz. When only one cathode is excited, a different power level can be obtained. The output power can be enhanced further if more than two anode resonators are used in the connected cathode arrangement. The peak output power of 7.8 MW with 52% total efficiency is obtained with three anode resonators. The output performances of both the designs having different cathode arrangements are compared.

Experimental Testing of a 3-D-Printed Metamaterial Slow Wave Structure for High-Power Microwave Generation

A high-power-microwave (HPM) source consisting of a backward wave oscillator (BWO) based on a metamaterial slow wave structure (MTM SWS) is investigated and tested. The MTM SWS is composed of a circular waveguide with periodic loading of two complementary electric split-ring resonator (CeSRR) disks and was designed at the University of California, Irvine, CA, USA (UCI). This SWS has been studied and simulated to quantify its cold structure properties. Moreover, a BWO using the proposed SWS has been simulated using a particle-in-cell solver to evaluate its performance. In the simulations, this BWO has generated 88-MW peak power in a pulse duration on the order of 15 ns with frequency about 2.9 GHz. This SWS was fabricated using 3-D printing and copper plating technology and was tested using the SINUS-6 pulsed electron beam accelerator at the University of New Mexico, Albuquerque, NM, USA (UNM). An output of 22 MW at 3.0 GHz was observed in experiments.

A Multifunctional Long-Lifetime High-Voltage Vacuum Insulator for HPM Generation

A multifunctional, long-lifetime, compact, and coaxial high-voltage (HV) vacuum insulator for Tesla-type generators is proposed for high-power microwave (HPM) generation. This vacuum insulator has two features. First, it is multifunctional since it can not only support the two conductors of the transmission line (TL), supply a vacuum environment for load, but also can eliminate a prepulse from the main pulse, which is realized via a grounded inductor. Second, it has a long lifetime. This feature is realized by optimizing the grounded inductor on the switch side and by grooving on the vacuum side. A 50-cm 700-kV compact coaxial HV vacuum insulator of such kind was designed, which was applied to a 1-MV Tesla-type generator to drive the relativistic backward-wave oscillator (RBWO) for HPM generation. Significantly, it has operated for a lifetime longer than 3 00 000 pulses at a repetition rate of 50 Hz without failure, which verifies the design.

Investigation of asymmetric mode competition in a relativistic backward wave oscillator

The relativistic backward wave oscillator (RBWO) is one of the most important high-power microwave generators. Its stability and reliability must be further improved to meet the demands of key applications. The factors that limit its performance are varied but include radio frequency breakdown and mode competition. Based on a C-band RBWO, the mode competition was carefully analyzed and the effects on the performance of the RBWO were revealed. As shown in the studies, for an axisymmetric system, asymmetric mode competition probably still exists. Therefore, a three-dimensional particle-in-cell model was configured to investigate the mode competition. The theoretical and experimental results confirmed that the competing mode for a C-band RBWO was EH21. Changing the gap between the cathode and anode was found to be effective for suppressing the asymmetric mode.

Cylindrical cavity design and particle-tracking simulation in cyclotron auto-resonance accelerator

The Cyclotron Auto-Resonance Accelerator (CARA) is a novel concept of accelerating continuous-wave (CW) charged-particle beams. This type of accelerator has applications in environment improvement area and generation of high-power microwaves. In CARA, the CW electron beam follows a gyrating trajectory while undergoing the interaction with a rotating TE11-mode RF field and tapered static magnetic field. The cylindrical cavity operating at TE11p-mode is adapted to accelerate electron beam. The cavity size is optimized to obtain a beam with designed energy, then a design method of the TE11p-mode acceleration cavity is described here. Moreover, regardless of space charge effect, several particle-tracking simulations of CARAs are showed.

High Power Microwave Generation by Double-Anode Virtual Cathode Oscillator

High Power Microwave Generation by Double-Anode Virtual Cathode Oscillator

Investigation on Dynamic Properties of Amorphous Magnetic Core Stimulated by Different Driving Voltages

Amorphous magnetic core has been widely used in pulsed power technology with applications including plasma science research, high-power microwave generation, and material surface treatment. For different applications, dynamic properties of the magnetic core will vary with stimulated magnetic field which determines by magnetization time and waveform of the driving voltage. In this paper, toroidal amorphous magnetic core ( $\Phi ~540$ – $740\times25$ mm) was investigated theoretically, numerically, and experimentally. Specifically, the circuit is analyzed. A high-voltage test stand, which can generate different driving voltages with same components, was designed and developed in our laboratory. Dynamic properties, including magnetic induction change, coercive force and losses, were studied under three different typical waveforms with the same magnetic flux. Driving voltages of the pulses were 12, 12, and 6 kV and the magnetization rates were 0.6, 1.2, and 0.6 T/ $\mu \text{s}$ , respectively. Experimental results show reasonable agreement with the numerical analysis.

Development of a GW-Level Solid-State Long Pulse Generator

Solid-state pulsed power systems are characterized by high repeatability, high reliability, long lifetime, free maintenance, and easy usage. Such systems with moderate peak power (100-MW level) are widely applied in the high average power region; however, many issues are still to be researched to obtain GW-level peak power. In this paper, a high power solid-state pulse generator delivering a GW-level quasi-rectangle pulse is developed to investigate the electrical characteristics of the generator: 1) the system design is accomplished based on a reasonable setting of a power compression ratio combining semiconductor switches and magnetic switches and verified via circuit simulation; 2) key technologies such as serially connected thyristor switches, magnetic pulse compressor (MPC), Blumlein type low impedance pulse forming network (LIPFN), and induction voltage adder (IVA) are investigated for subsystem construction; and 3) at present, the experimental results achieved on a dummy load are a peak pulsed power of 5.2 GW, a pulsewidth of 170 ns, a repetitive rate of 20 Hz, and an operation time of 5 s with good waveform repeatability. The generator can be potentially applied for high power microwave (HPM) generation, X-ray sources, and industrial applications such as material surface treatment and pulse electric field (PEF) sterilization.

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

A Dual-Frequency High-Power Microwave Generator

We propose a novel dual-frequency high-power microwave generator consisting of both an axial generator and a radial one stretching from the middle of the tube head of the former. As a high-voltage pulse is injected into the diode system, a cathode with two blades generates two relativistic electron beams that separately travel through the axial and radial diodes. Therefore, both the subsources are driven by the relativistic beams and generate intense microwave pulses simultaneously. An axial relativistic backward-wave oscillator and a radial transit-time oscillator are designed and combined to realize this purpose. Particle-in-cell simulation shows that when the diode voltage is 505 kV, microwaves with powers of 0.95 and 1 GW are generated in the axial and radial subsources, with frequencies of 15.2 and 9.5 GHz, respectively. An equivalent efficiency of over 35% is achieved with an axial magnetic field of 0.86 T and a radial magnetic field of 0.5 T.

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

Announcing the Eighteenth Special Issue of IEEE Transactions on Plasma Science on High-Power Microwave and Millimeter Wave Generation, 2020

Initial Test of Optoelectronic High Power Microwave Generation From 6H-SiC Photoconductive Switch

High-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. This letter presents a design and initial test of an optoelectronic class B push-pull microwave power amplifier (MPA) using two 6H-SiC photoconductive switches. The initial tests have been conducted with bias voltage of ±2.4 kV, at 80 kW peak laser pulse power, demonstrating that the SiC PCSS working in linear mode can produce microwaves. Then, circuit simulation is conducted to study the factors affecting the electrical efficiency, such as the quantum efficiency, the peak laser pulse power, and the bias voltage. It is speculated that the MPA could output 1 mW microwave power and achieve electrical efficiency of more than 60% with a bias voltage of 15 kV, quantum efficiency of 0.2, and peak laser pulse power of 100 kW.

A compact solid-state high voltage pulse generator.

In this paper, a compact solid-state high voltage pulse generator, composed of a pulse transformer and a magnetic pulse compressor, is investigated numerically and experimentally. The generator can achieve pulses with a peak voltage over several tens of kilovolts and a rise-time in the microsecond level, which can be widely used in plasma physics research, high power microwave generation, and material treatment. Specifically, PSpice software is used to analyze the performance of the generator. Then, the generator was constructed in our laboratory. The experimental results illustrate that when the charging voltage of the generator was changing from 10 kV to 14 kV, typical pulses with a peak voltage ranging from 67 kV to 95 kV and rise-time between 10 µs and 12 µs were obtained on a dummy load. The generator can continually work over 10 min with a repetitive rate of 20 Hz, and until now, it has been successfully achieving over 1 × 106 high voltage pulses. Experiments show reasonable agreement with numerical analysis.

Guest Editorial The 17th Special Issue on High Power Microwave Generation

The publication of this 17th Special Issue on High Power Microwave (HPM) Generation continues a series first published in December 1985. Since the first volume, the entire HPM field has undergone tremendous changes and advances. While initially being work done in government institutions, research now spans the range of academic institutions, corporate research groups, and government laboratories from across the world. The subject areas addressed have evolved, as well. In 1985, the topics spanned five categories: 1) gyrotrons and cyclotron-resonance devices; 2) free-electron lasers; 3) virtual-cathode and reflex oscillators; 4) Cerenkov radiation generators; and 5) magnetrons, klystrons, and backward-wave oscillators. These areas still remain active areas of research interest, now augmented by the rapid advance of particle-in-cell codes and electromagnetic solvers as tools to model and help understand HPM devices.

Copper nanowire–carbon nanotube hierarchical structure for enhanced field emission

Field emitters have found ample variety of applications from field emission displays to high power microwave generators. Though a myriad of materials have been considered for emitter application, carbon nanotubes (CNT) are prominent to offer outstanding field emission characteristics, owing to its nano-dimensions and excellent electrical transport properties. While nano-apex of CNTs aids in achieving high field enhancement factor, its high electrical conductivity ensures minimum resistance to electron flow. Next-generation field emitters demand to show high emission current, at a lower applied electric field, which can be achieved by a three-dimensional (3-D) emitter structure. In this research work, a 3-D hierarchical field emitter structure was synthesized involving carbon nanotubes (CNT) on copper nanowires (Cu NW). Field emission characterization of this hierarchical structure in DC bias showed a low turn-on field of 1.8–2.1 V/µm and maximum current density of 1.84 mA/cm2. CuNW–CNT emitter also demonstrated a remarkable emission stability of nearly 8 h which is very significant for practical applications. Properties of the field emitter CuNW–CNT hierarchical emitter was correlated with its morphology.

High power microwave plasma discharge

High-power microwave (HPM) has broad applications in scientific research, civil and military community. HPM has the character of peak power of tens of Giga-Watt and the pulse width from tens of to hundreds of nanosecond. The intense electromagnetic breakdowns in the HPM generation, transmission and radiation systems, seriously limit the HPM systematic power capacity, and become the bottle neck of the HPM technology-development and the international technical challenge. In this paper, the recent developments of intense electromagnetic breakdown at vacuum and air sides of output window and on metal surfaces are reviewed and discussed. To understand the breakdown mechanism at window, several multipactor dynamic models are developed, especially involving electron-neutral collision and ionization in the desorbed gas layer, analytically obtaining the influence of desorption gas on multipactor saturation, and space charge field and potential distribution above dielectric surface formed by multipactor and plasma. By diagnosing the time- and space-evolution optical emissions, the mechanisms of nano-second microwave-driven discharges near the dielectric/vacuum and dielectric/air interface were discussed. For breakdown at the dielectric/vacuum interface, multipactor and plasma developing in a thin layer of several millimeters above interface, revealing intense ionization concentrated in a desorbed high-pressure layer. For breakdown at the dielectric/air interface, nonlinear positive feedback of formation of a space-charge microwave sheath near the dielectric surface, accelerated by the normal components of the microwave field, significantly enhances the local-field amplitude and hence ionization near the dielectric surface. The mechanism and methods of using magnetic field satisfying specific amplitude and direction perpendicular to E rf x E dc to suppress microwave multipactor were theoretically studied and experimental demonstrated. The methods of the external resonant magnetic field have been demonstrated by proof-of principle S-band large power experiments to significantly improve the power capacity by 9 times. The Halbach-like magnets to generate the transverse homogeneous B-field in a large scale was designed to suppress multipactor, and the window breakdown threshold was significantly enhanced at multi-Giga-watt. The methods of periodic surface profiles on suppressing microwave multipactor were discussed. The three-dimensional periodic ripple profile with each unit of rotational symmetric surface is proposed and theoretically and experimentally demonstrated to suppress multipactor for arbitrary electromagnetic mode with any polarization. In theoretical aspect, basic physics courses are described qualitatively, the basic models of secondary electron multipator, gas desorption and plasma avalance are established, but lack of quantitive results and experimental diagnostic of plasma energy and density. The physical and chemical methods of periodici surface, resonant magnet, and surface fluorination are successfully used in suppressing breakdown and improving the power capacity, but there is distance away from practical application.

RF Breakdown of the Resonant Reflector in a Relativistic Backward Wave Oscillator

Radio frequency (RF) breakdown can result in pulse shortening and severely limits the performance of high-power microwave (HPM) generators. In this paper, the initial stage of RF breakdown in HPM generators with a strong external guiding magnetic field has been carefully analyzed. It is thought that the initial breakdown process involves electron emission induced by an intense local field, electron acceleration in the electric field, and electron bombardment on the structure’s surfaces. Strong external guiding magnetic fields play a key role in the RF breakdown process of HPM generators. They concentrate the impact energy and make it more destructive. To suppress RF breakdown, feasible solutions include lowering the local field strength, decreasing the energy of the field-emitted electrons obtained from the RF field, reducing the deposited energy density, and improving the material’s resistance to electron bombardment.