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Ϫϱ t ABSTRACT: In this paper, the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) algorithm for a two-dimensional (2D) TE wave is extended to a full three-dimensional (3D) wave. The weakly conditional stability is verified by numerical simulation results. Numeri-

In this paper, UNIPIC code, a new member in the family of fully electromagnetic particle-in-cell (PIC) codes for simulations of high power microwave (HPM) generation, is introduced. In the UNIPIC code, the electromagnetic fields are updated using the second-order, finite-difference time-domain (FDTD) method, and the particles are moved using the relativistic Newton–Lorentz force equation. The convolutional perfectly matched layer method is used to truncate the open boundaries of HPM devices. To model curved surfaces and avoid the time step reduction in the conformal-path FDTD method, CP weakly conditional-stable FDTD (WCS FDTD) method which combines the WCS FDTD and CP-FDTD methods, is implemented. UNIPIC is two-and-a-half dimensional, is written in the object-oriented C++ language, and can be run on a variety of platforms including WINDOWS, LINUX, and UNIX. Users can use the graphical user’s interface to create the geometric structures of the simulated HPM devices, or input the old structures created before. Numerical experiments on some typical HPM devices by using the UNIPIC code are given. The results are compared to those obtained from some well-known PIC codes, which agree well with each other.

With the development of high power microwave (HPM) technology, the power and pulse duration of the HPM source increase substantially, the breakdown of the dielectric window of the HPM source feed has been becoming the major factor of limiting the transmission and radiation of HPM. This paper presents an electrostatic particle-in-cell and Monte Carlo collisions method for simulating the breakdown on HPM dielectric surface and establishes a physical model of HPM dielectric surface breakdown involving outgassing. The breakdown process including the main physical mechanisms, such as the field emission, multipactor, outgassing, and collision of gas ionization, is simulated. The influence of outgassing on the dielectric window breakdown is studied by simulating the breakdown with different outgassing speeds. The similarity between the dc and HPM dielectric surface breakdown is discussed.

High power vacuum electronic devices of millimeter wave to terahertz regime are attracting extensive interests due to their potential applications in science and technologies. In this paper, the design and experimental results of a powerful compact oversized surface wave oscillator (SWO) in Y-band are presented. The cylindrical slow wave structure (SWS) with rectangular corrugations and large diameter about 6.8 times the radiation wavelength is proposed to support the surface wave interacting with annular relativistic electron beam. By choosing appropriate beam parameters, the beam-wave interaction takes place near the π-point of TM01 mode dispersion curve, giving high coupling impedance and temporal growth rate compared with higher TM0n modes. The fundamental mode operation of the device is verified by the particle-in-cell (PIC) simulation results, which also indicate its capability of tens of megawatts power output in the Y-band. Finally, a compact experimental setup is completed to validate our design. Measurement results show that a terahertz pulse with frequency in the range of 0.319–0.349 THz, duration of about 2 ns and radiation power of about 2.1 MW has been generated.

In this paper using fixed point methods we establish some existence theorems of positive (nontrivial) solutions for integral boundary value problems of nonlinear Hadamard fractional differential equations.

Electrocatalytic production of hydrogen peroxide (H2O2) by 2e- oxygen reduction (ORR) is a clean on-site method. Although doped carbon materials have been widely used in hydrogen peroxide research, few studies...

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