Research progresses on Cherenkov and transit-time high-power microwave sources at NUDT

Research progresses on Cherenkov and transit-time high-power microwave(HPM)sources in National University of Defense Technology(NUDT)of China are presented.The research issues are focused on the following aspects.The pulse-shortening phenomenon in O-type Cerenkov HPM devices is suppressed.The compact coaxial relativistic backward-wave oscillators(RBWOs)at low bands are developed.The power efficiency in M-Type HPM tubes without guiding magnetic field increased.The power capacities and power efficiencies in the triaxial klystron amplifier(TKA)and relativistic transit-time oscillator(TTO)at higher frequencies increased.In experiments,some exciting results were obtained.The X-band source generated 2 GW microwave power with a pulse duration of 110 ns in 30 Hz repetition mode.Both L-and P-band compact RBWOs generated over 2 GW microwave power with a power efficiency of over 30%.There is approximately a 75% decline of the volume compared with that of conventional RBWO under the same power capacity conditions.A 1.755 GHz MILO produced 3.1 GW microwave power with power efficiency of 10.4%.A 9.37 GHz TKA produced the 240 MW microwave power with the gain of 34 dB.A 14.3 GHz TTO produced 1 GW microwave power with power efficiency of 20%.

Effects of Organic Fertilizers Made from Distiller＇s Grains on the Growth and Development of Flue-cured Tobacco

Pot experiments were conducted to study the effects of different organic fertilizers made from distiller＇s grains on the physiological characteristics and growth of flue-cured tobacco. The results showed that the agronomic traits and biomass of flue-cured tobacco in the three treatments were higher than that of the control group,and the mixed application of different organic fertilizers made from distiller＇s grains and compound fertilizer could promote the growth and development of flue-cured tobacco significantly.

Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.

Spectral-interferometry-based diff-iteration for high-precision micro-dispersion measurement

Precise measurement of micro-dispersion for optical devices(optical fiber,lenses,etc.)holds paramount significance across domains such as optical fiber communication and dispersion interference ranging.However,due to its complex system,complicated process,and low reliability,the traditional dispersion measurement methods(interference,phase shift,or time delay methods)are not suitable for the accurate measurement of micro-dispersion in a wide spectral range.Here,we propose a spectral-interferometry-based diff-iteration(SiDi)method for achieving accurate wide-band micro-dispersion measurements.Using an optical frequency comb,based on the phase demodulation of the dispersion interference spectrum,we employ the carefully designed SiDi method to solve the dispersion curve at any position and any order.Our approach is proficient in precisely measuring micro-dispersion across a broadband spectrum,without the need for cumbersome wavelength scanning processes or reliance on complex high-repetition-rate combs,while enabling adjustable resolution.The efficacy of the proposed method is validated through simulations and experiments.We employed a chip-scaled soliton microcomb(SMC)to compute the dispersion curves of a 14 m single-mode fiber(SMF)and a 0.05 m glass.Compared to a laser interferometer or the theoretical value given by manufacturers,the average relative error of refractive index measurement for single-mode fiber(SMF)reaches 2.8×10^(-6) and for glass reaches 3.8×10^(-6).The approach ensures high precision,while maintaining a simple system structure,with realizing adjustable resolution,thereby propelling the practical implementation of precise measurement and control-dispersion.