Search

An X-band Cerenkov-type high power microwave (HPM) oscillator driven by a sheet electron beam is proposed and designed in this paper. In order to improve the efficiency of simulation optimization, a research method is proposed in which the large caliber coaxial Cerenkov-type HPM oscillator is taken as an initial model, which is equivalent to that of the planar slow-wave structure (SWS) by using the similarity between the planar SWS and the large caliber coaxial SWS. In addition, the effectiveness of the equivalent method is verified from the geometric structure, the field distribution of the operating mode, dispersion characteristics, and the preliminary particle simulation results of two devices. Based on the results of an X-band large caliber coaxial Cerenkov-type HPM oscillator, an X-band Cerenkov-type HPM oscillator driven by a sheet electron beam is investigated by the 3D particle-in-cell code. The simulation results show that the power conversion efficiency can reach 26.1% at the frequency of 11.9 GHz with the output power of 0.3 GW, while the sheet electron beam has the energy of 486 kV and it carries the current of 2.4 kA conducted by the magnetic field of 2.5 T. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel Ku-band coaxial transit-time oscillator (TTO) with Pierce-like cathode is proposed in this paper. TTO has the characteristics of low space-charge effect and short interaction distance. Combining with these features, we design a novel Pierce-like cathode to lower the demand for the guiding magnetic field. The guiding magnetic field intensity is reduced to about 0.32T by loading the Pierce-like cathode, but the magnetic field intensity is not a stable value, it fluctuates at 0.32T because of the properties of permanent magnet. To achieve the light and small goals of TTO, we design a novel permanent magnet structure with NdFeB. Based on the research, the typical simulation result is that when the diode voltage is 440kV, the beam current is 11kA, the guiding magnetic field is about 0.32T, the device can output 1.46GW microwave pulse at 14.2GHz. The power conversion efficiency is about 30%. [ABSTRACT FROM AUTHOR]

In this article, a self-breakdown repetitive gap switch based on the graphite electrodes with surface modified by TiC is investigated to improve the scattering of the breakdown voltage. The self-breakdown repetitive gap switch was experimentally studied with the graphite electrodes and two kinds of TiC modified graphite electrodes (hereinafter referred to as TiC-I electrodes and TiC-II electrodes). Results show that the scatterings of the breakdown voltages of the graphite, TiC-I and TiC-II electrodes were 2.49%, 1.80%, and 1.54%, respectively. Compared with the graphite electrodes, the mass losses of TiC-I and TiC-II electrodes are reduced by 50% and 68%. The influence of electrode surface morphology on the switch stability is analyzed based on the mechanism of switch conduction process. Compared with the graphite electrodes, the electric field amplification coefficients of TiC-I and TiC-II electrodes are more evenly distributed, which leads to the more evenly distributed field emission current density. Thus, the breakdown areas of TiC-I and TiC-II electrodes are smaller and the gas breakdown processes are more stable than those of the graphite electrodes, resulting in smaller scattering of the breakdown voltage. The method that decreases the scattering of the breakdown voltage and reduces the mass loss of the electrodes by modifying graphite electrodes surface can greatly improve the stability of the switch, which is of significance to the application of the switch in the compact, long time stable operation of high-power pulse power devices. [ABSTRACT FROM AUTHOR]

In this paper, a compact rep-rate GW pulsed power generator is developed. First, its three key subsystems are theoretically analyzed, engineering designed, and experimentally investigated, respectively. The emphases are put on these four problems: the theoretical analysis of the voltage distribution across the conical secondary windings of the high-coupling transformer, the investigation of the high energy storage density dielectric used in the pulse forming line, the choice of the gas flow velocity of the gas blowing system, and theoretical analysis of the passive stability of the pulsed power generator operated in rep-rate mode. Second, the developed pulsed power generator is described in detail. It has a 0.2-m diameter, a 1.0-m length, and a 20-\Omega wave impedance. Across a 100-\Omega resistive dummy load, it can steadily operate at a 300-kV output voltage in 50-Hz rep-rate and 250 kV in 150 Hz without gas blowing system. The average power is \sim1~kW. Finally, the pulsed power generator is applied to drive a relativistic backward-wave oscillator, generating a high-power microwave with peak output power of 200 MW and duration (full-width at half-maximum) of 5 ns in 150-Hz rep-rate. These efforts set a good foundation for the development of a compact rep-rate pulsed power generator and show a promising application for the future. [ABSTRACT FROM AUTHOR]

Fundamentally different responses of a LiTaO 3 thin film detector are observed when it is subjected to short microwave pulses as the pulse intensity is altered over a wide range. We start from weak microwave pulses which lead to only trivial pyroelectric peak response. However, when the microwave pulses become intense, the normally expected pyroelectric signal seems to be suppressed and the sign of the voltage signal can even be completely changed. Analysis indicates that while the traditional pyroelectric model, which is a linear model and works fine for our data in the small regime, it does not work anymore in the large signal regime. Since the small-signal model is the key foundation of electromagnetic-wave sensors based on pyroelectric effects, such as pyroelectric infrared detecters, the observation in this work suggests that one should be cautious when using these devices in intense fields. In addition, the evolution of detector signal with respect to excitation strength suggests that the main polarisation process is changed in the large signal regime. This is of fundamental importance to the understanding on how crystalline solids interact with intense microwaves. Possible causes of the nonlinear behaviour is discussed. [ABSTRACT FROM AUTHOR]

The radial transit time oscillator (RTTO) is promising to realize high power output of millimeter-waves. Although the radial structure can enhance the power capacity, less cavities and small radial dimension make it difficult to improve the power capacity in RTTOs, especially in the extraction cavity. A one-gap extraction cavity in the Ka-band RTTO is proposed in this paper to improve the power capacity. Without electrons, taking the TM011 cavity as an example, the radial reversal resonant electric field can intersect with radial electrons. By choosing the sizes of the cavity, the synchronization of the electrons and the electric field can be realized to achieve effective energy exchange. In particle-in-cell simulation, the RTTO with the TM011 extraction cavity can output 1.0 GW high power microwaves (HPMs) at 31.2 GHz, and the beam-wave conversion efficiency is 31.6%. The maximum electric field in the TM011 cavity is only 800 kV/cm, which is less than one third that in the TM010 extraction cavities. In addition, the TM012 extraction cavity is employed to improve the efficiency to 35.4%. At the same time, because of the increase in the output power, the maximum radial electric field in the TM012 cavity increases to 850 kV/cm. Therefore, the one-gap extraction cavity can realize multiple energy exchanges to get high beam-wave conversion efficiency and enhance the power capacity in the extraction cavity significantly. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetic pulse compressors, based on magnetic switches, are considered as competitive candidates for high-voltage pulse generation. It is generally believed that the lack of operating-parameter tunability of these devices is currently one of the crucial factors limiting their applications. In this paper, an adjustable high-power magnetic pulse compressor, which is deemed as the key component of a power supply system, is investigated theoretically and experimentally. Dominant parameters of the compressor, including the compression ratio, the saturation time, and the peak voltage, can be regulated, which is beneficial for widening the application areas of power supply systems. Specifically, the prepulse of the magnetic pulse compressor is studied as one of the key parameters. A two-stage magnetic pulse compressor was then setup and when the charging time of the primary source was alternated between 19 and 25 μs, pulses with rise-time of 1 μs were achieved with good repeatability. This in turn verified the tunable capacity of the device. When applied in a solid-state high-voltage pulse generator, the pulse compressor successfully enabled the generation of intense electron-beam with peak power over 5 GW, peak voltage of 380 kV, pulse width over 170 ns, and repetitive rate of 20 Hz. The device has been successfully used for research on plasma science and for driving the sources of high-power microwaves where the requirements on the device often vary substantially. In the latter application, based on the high reliability of the solid-state pulse generator, optical diagnosis has been conducted of the plasma expansion characteristics of the magnetically insulated coaxial diodes cathode, in order to analysis the mechanism of the pulse shortening phenomenon. Experimental results show reasonable agreements with the analyses. [ABSTRACT FROM AUTHOR]

Magnetic switches could improve the stability, reliability, repetition rate, and life of pulsed power systems, based on which, a high power, low impedance, and long pulse generator has been investigated numerically and experimentally. The generator accomplishes the power compression and the pulse forming at a relatively low voltage level, consisting of a core-type pulse transformer, a two-stage magnetic compression unit, a low impedance pulse forming network, and magnetic type main switches. A full circuit model was developed using PSPICE software to analyze key factors that influence output characteristics of the generator. Key subsystems were manufactured and experimental research was carried out on the whole system. Preliminary results achieved with a dummy load of 2.5 $\Omega$ show that the output pulse power is about 2.0 GW and the pulsewidth is about 170 ns, which are in reasonable agreement with the numerical analysis. [ABSTRACT FROM PUBLISHER]