Liu Guozhi

Theoretical Study of a Plasma-Filled Relativistic Cerenkov Generator With Coaxial Slow-Wave Structure

The linear and nonlinear theory of a plasma-filled relativistic Cherenkov generator with coaxial slow-wave structure (SWS) is developed. Linear analysis includes the space-charge limiting current, dispersion relations, dispersion curves, and coupling impedance. In nonlinear theory, the electron beam space-charge effect, nonsynchronous interaction, and complex reflection coefficients of the electromagnetic wave at the boundaries of the SWS are taken into account. With the assumption of quasi steady state, the self-consistent equations are numerically calculated using the fourth-order Runge-Kutta method. The effects of the relative phase between inner and outer corrugations, phase and amplitude of the complex reflection coefficient at the boundaries of the SWS, and plasma density on device efficiency are discussed. Efficiencies of up to 37% without plasma and about 50% with plasma density of np = 3-7 times 1011 cm-3 are obtained.

A New Reflector Designed for Efficiency Enhancement of CRBWO

A new reflector consisting of the inner and outer conductors is introduced into the coaxial relativistic backward wave oscillator for the first time through optimizing the distribution of the electric field and distance between the reflector and the slow wave structure. The improved reflector can excite the superposition of the axial electric fields to benefit the electron premodulation. The improved reflector is investigated by the particle-in-cell numerical simulation. A result of 43% power efficiency, 1.0-GW power, and 7.3-GHz operation frequency is obtained under the diode voltage 530 kV and current 4.4 kA.

Comparative research on three types of coaxial slow wave structures

This paper studies three types of coaxial slow wave structures (SWSs): (1) with ripples on both the inner and outer conductors; (2) with ripples on the outer conductor and smooth on the inner one; and (3) with ripples on the inner conductor and smooth on the outer one. The frequencies, coupling impedances, time growth rates and beam-wave interaction efficiencies of the three types of coaxial SWSs are obtained by theoretical analysis. Moreover, the relativistic Cerenkov generators (RCGs) with the three types of coaxial SWSs are simulated with a fully electromagnetic particle-in-cell code, and the results verify the theoretical analysis. It is proved that the RCG with double-rippled coaxial SWS has the highest conversion efficiency and the shortest starting time.

A study of high power microwave air breakdown

This paper presents the results of research on microwave breakdown in air, it includes the experimental study and the theoretical analysis. The experimental study has been done in a waveguide with a frequency of 9.37GHz, the peak power up to 200kW, pulse width from 0.3 to 2.0μs. The repetition rate of microwave source is from single pulse to 970 pulse per second. The process of the breakdown of repetition pulse has also been recorded for a burst of ten pulses. A theoretical model for breakdown threshold is presented also. The theoretical are in good agreement with the experimental ones.

Simulation Studies of a Relativistic Klystron With Strong Input Power

As one of the potential high-power microwave devices on the level of gigawatts, relativistic klystron amplifier (RKA) can be used for power combination to further improve the radiation microwave power. Because of self-excited oscillation of the intense relativistic electron beam, the frequency and phase characteristics of general relativistic klystron devices are independent with the driven microwave pulse. In order to obtain frequency and phase locking, a method of improving the input power is put forward to inhibit these parasitic oscillations. This paper reports a particle-in-cell simulation study of the RKAs characteristics under the condition of strong power feeding. By making use of the 500-keV 6-kA electron beam, the simulation results show that strong input power can inhibit the parasitical oscillations in cavity and modulate the beam very well with only one cavity. About 5.4-kA modulation current and a microwave with power of 1.4 GW, bandwidth of 5%, and efficiency of 50% are obtained. The new amplifier driven by the strong input power proves to be a potential device to attain high amplitude stability, high efficiency, high spectral purity, wide bandwidth, and low level of phase and amplitude noise.

Theoretical investigation of an electron beam propagating through a wide gap cavity

This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations are obtained to describe the modulation of the beam current and kinetic energy. A relativistic klystron amplifier (RKA) model is introduced, which uses an inductively-loaded wide gap cavity as an input cavity. And a numerical code is developed for the extended model based on the equations, from which some relations about the modulated current and modulated energy are numerically given.

Space-charge limiting current in spherical cathode diodes

The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the non-relativistic situation are presented in this paper. The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface. The generated space-charge limiting current is deduced. In the case of a pin-shaped-cathode diode, the space-charge limiting current is also obtained, indicating that the current is independent of the geometric parameters of the diode. Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that, for pin-arrayed cathodes, the distance between pins should be in the range from 1.2D to 1.5D, where D is the distance between the two electrodes.

Growth rate of the Coaxial Slow Wave Structure

The growth rate of the Coaxial Slow Wave Structure is studied through a simple method employing the relativistic Newtons equation, the driving Maxwell equations and the linear assumption of the small signals. In addition, effects of the electron kinetic energy and the beam current on the growth rate are investigated preliminarily.

Optimal Matching of Magnetic Pulse Compressor

Energy transmission efficiency in the magnetic pulse generators varies with saturated time of magnetic switch. An optimal matching time exists and depends on the compression ratio, under which, the energy transmission efficiency can reach approximate 100%. The equation of required magnetic core volume is obtained by taken into account the optimal matching mode. It indicates that a great reduction on the volume is feasible under the optimal matching mode. The circuit simulation code-PSPICE is also introduced to simulate a 3-stage magnetic pulse compressor, and the results are in accordance with those of equivalent circuit analyses.

Effect of longitudinal applied magnetic field on the self-pinched critical current in intense electron beam diode

The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numerical simulations. The results shows that an applied longitudinal magnetic field tends to increase the self-pinched critical current. Without the effect of anode plasma, the maximal diode current approximately equals the self-pinched critical current with the longitudinal magnetic field applied; when self-pinched occurs, the diode current approaches the self-pinched critical current.