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%.

Application of CPML to truncate the open boundaries of cylindrical waveguides in 2.5-dimensional problems

In order to solve the problem of truncating the open boundaries of cylindrical waveguides used in the simulation of high power microwave （HPM） sources, this paper studies the convolutional PML （CPML） in the cylindrical coordinate system. The electromagnetic field＇s FDTD equations and the expressions of axis boundary conditions are presented. Numerical experiments are conducted to validate the equations and axis boundary conditions. The performance of CPML is simulated when it is used to truncate the cylindrical waveguides excited by the sources with different frequencies and modes in the 2.5-dimensional problems. Numerical results show that the maximum relative errors are all less than -90 dB. The CPML method is introduced in the 2.5-dimensional electromagnetic PIC software, and the relativistic backward wave oscillator is simulated by using this method. The results show that the property of CPML is much better than that of the Mur-type absorbing boundary condition when they are used to truncate the open boundaries of waveguides. The CPML is especially suitable for truncating the open boundaries of the dispersive waveguide devices in the simulation of HPM sources.