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Gyrotron devices are based on the principle of the relativistic electron cyclotron maser and capable of generating high-power coherent radiation in the millimeter-THz wave range, which are important in imaging, communication, biomedicine. However, traditional particle-in-cell software, simulating the beam-wave interaction of terahertz gyrotron devices, is of huge resource consumption due to massive particles and grid-size dependency of wavelength. Specialized theories need to be developed. In this paper, frequency-domain and time-domain nonlinear theories are introduced. Based on macro-particle assumption and 1-D analytic approximation, the resource consumption is dramatically reduced. The results of two theories coincide with each other. The accuracy of simulation result is demonstrated by comparison with particle-in-cell software. The investigation presented in this paper provides efficient and accurate method to analyze the terahertz gyrotron devices.

A study of electric contact surface treatment to ductile iron has been carried out. This technology was based on the application of the contact resistance heating between the electrode and workpiece. For comparison, the experiments of induction hardening to ductile iron were studied. The microstructure, microhardness, surface residual stress and wear properties were investigated using optical microscope, scanning electron microscope, X-ray diffraction, Vickers microhardness and rolling contact wear tests. Electric contact surface treatment resulted in the formation of fine ledeburite (white bright layer) and martensite in the ductile iron surface, in which the hardness in these areas was higher than that of induction hardened surface. The wear test results showed that the ductile iron surface after electric contact surface treatment had better wear resistance owing to the fine microstructure, high hardness and residual compressive stress.