[en] A novel foilless S-band low-impedance transit-time oscillator was designed. The impedance of this oscillator is about 20 Ω. Such an oscillator with coaxial structure has the advantages of low guide magnetic field and quick saturation time, expectantly operating repetitively and in a long-pulse state. As indicated by PIC simulations, the average power of output microwave is about 4.0 GW at the main frequency of 3.175 GHz with the input-diode voltage of 550 kV, the input-diode current of 27.6 kA, and the extra magnetic field of 0.8 T. Based on the simulation results, the power efficiency of microwave is about 26.4%, much better than that of a high-impedance transit-time radiation oscillator at the same input voltage. (authors)

[en] A novel Ka-band coaxial transit-time oscillator (TTO) with a four-gap buncher is proposed and investigated. Simulation results show that an output power of 1.27 GW and a frequency of 26.18 GHz can be achieved with a diode voltage of 447 kV and a beam current of 7.4 kA. The corresponding power efficiency is 38.5%, and the guiding magnetic field is 0.6 T. Studies and analysis indicate that a buncher with four gaps can modulate the electron beam better than the three-gap buncher in such a Ka-band TTO. Moreover, power efficiency increases with the coupling coefficient between the buncher and the extractor. Further simulation demonstrates that power efficiency can reach higher than 30% with a guiding magnetic field of above 0.5 T. Besides, the power efficiency exceeds 30% in a relatively large range of diode voltage from 375 kV to 495 kV

[en] A relativistic Ku-band coaxial transit-time oscillator has been proposed in our previous work. In the experiments, we find that the asymmetric competition mode in the device limits the microwave power with the increase of the input electric power. For solving such a problem, the methods for analysis and suppression of the asymmetric competition mode in the device are investigated theoretically and experimentally. It is shown that the structure and the material of the collector, the concentricity, and the electron emission uniformity play an important part in the suppression of the asymmetric competition mode in the relativistic Ku-band transit-time oscillator. In the subsequent experiments, the asymmetric mode was suppressed effectively. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 1 GW, frequency of 14.3 GHz close to the simulation one, and efficiency of 20% was generated

[en] An improved Ku-band magnetically insulated transmission line oscillator is proposed and investigated experimentally. In the particle-in-cell simulation, the Ku-band MILO generates the microwave with a power of 1.62 GW and a frequency of 13 GHz at the input voltage of 474 kV. The device is fabricated based on the simulation results, and an experiment system is designed. In the preliminary experiments, output microwave with frequency of 13.02 GHz, power of 150 MW, and pulse width of 17 ns is generated, under the diode voltage of 450 kV. Analysis on the experiment results shows that plasma produced due to the large current hitting to the outside of the collection tank is the essential cause for the low amplitude of the microwave power and short pulse width

[en] A low-impedance transit-time oscillator without foils (LITTO) has been proposed in our previous work. Recently, the experiment is carried out on an intense relativistic electron beam (IREB) generator, which is capable of producing a 50 ns duration electron beam in the voltage range of 0.4-1 MV. With a 600 kV, 24 kA electron beam guided by an external magnetic field of 0.5 T, a radiation power of 2.7 GW at 1.64 GHz has been achieved and the corresponding power conversion efficiency is 18.75%. With the similar voltage and current parameters, the experimental results are reexamined and confirmed by the particle-in-cell (PIC) simulation.

[en] A novel coaxial transit radiation oscillator without external guiding magnetic field is designed to generate high power microwave at Ku-band. By using a coaxial structure, the space-charge potential energy is suppressed significantly, that is good for enhancing efficient beam-wave interaction. In order to improve the transmission stability of the unmagnetized intense relativistic electron beam, a Pierce-like cathode is employed in the novel device. By contrast with conventional relativistic microwave generators, this kind of device has the advantages of high stability, non-guiding magnetic field, and high efficiency. Moreover, with the coaxial design, it is possible to improve the power-handing capacity by increasing the radial dimension of the Ku-band device. With a 550 keV and 7.5 kA electron beam, a 1.25 GW microwave pulse at 12.08 GHz has been obtained in the simulation. The power conversion efficiency is about 30%

[en] An improved foilless Ku-band transit-time oscillator with low guiding magnetic field is proposed and investigated in this paper. With a non-uniform buncher and a coaxial TM₀₂ mode dual-resonant reflector, this improved device can output gigawatt level Ku-band microwave with relatively compact radial dimensions. Besides the above virtue, this novel reflector also has the merits of high TEM reflectance, being more suitable for pre-modulating the electron beam and enhancing the conversion efficiency. Moreover, in order to further increase the conversion efficiency and lower the power saturation time, a depth-tunable coaxial collector and a resonant cavity located before the extractor are employed in our device. Main structure parameters of the device are optimized by particle in cell simulations. The typical simulation result is that, with a 380 kV, 8.2 kA beam guided by a magnetic field of about 0.6 T, 1.15 GW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 37%

[en] The explosively-driven flux compression generators (FCGs) are always used to drive pulse modulators, and high power pulses can be generated on the diodes. In this paper, two dynamically cascaded FCGs were ignited one after another to drive a modulator made up of a pulsed transformer and a pulse forming line (PFL). The two FCGs were controlled by a selftimer with 20 ms interval and the electrical isolation between them was achieved by two fuses. Two pulses with peak power more than 20 GW and pulse interval 20 ms were generated on the diode. The experiment shows that multiple pulses could be obtained by a single modulator if more driving FCGs are used. This method could test the pulsed power apparatus electricity recovery characteristics, which are necessary to build high power and high repetitious frequency accelerators. (authors)

[en] Based on the theoretical analysis of the intense relativistic electron beam propagation in the coaxial drift-tube, a focusing electrode and a coaxial reflector is proposed to lessen the demand of the coaxial Ku-band foilless transit-time oscillator (TTO) for the guiding magnetic field. Moreover, a Ku-band TTO with the focusing electrode and the coaxial reflector is designed and studied by particle in cell simulation. When the diode voltage is 390 kV, the beam current 7.8 kA, and the guiding magnetic field is only 0.3 T, the device can output 820 MW microwave pulse at 14.25 GHz by means of the simulation. However, for the device without them, the output power is only 320 MW. The primary experiments are also carried out. When the guiding magnetic field is 0.3 T, the output power of the device with the focusing electrode and the coaxial reflector is double that of the one without them. The simulation and experimental results prove that the focusing electrode and the coaxial reflector are effective on reducing the guiding magnetic field of the device