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[en] A hybrid approach based on rule-based method and Artificial Neural Network (ANN) is proposed for on-line fault diagnosis of nuclear power plant. Rule-based method is used for identifying accident type and ANN is used for accurately estimating some information that is difficult to be diagnosed by rule-based method, such as accident location and severity level. Validity of the proposed method was verified by a simulation experiment in normal operation condition. (authors)

[en] Theoretical and particle simulation methods are used to investigate the transportation processes of intense relativistic electron beam (IREBs) guided by low magnetic field. It is shown that in the foilless diode, a magnetic field of tapered profile along the A-K gap can restrain the radial movement of electrons, and the undulation of radial movement is decreased in waveguide. Electrons movement guided by the magnetic field decreasing gradually along the tapered waveguide are also studied, it is found that the radial undulation of electrons is not enlarged, though the magnetic field decrease along the waveguide. A proper profile can reduce the requirement of the guiding magnetic field, it is advantageous to realize the high power microwave devices packed by permanent magnet. (authors)

[en] An alarm analysis system based on Multi-level Flow Models (MFM) was developed for a PWR NPP. By automatically identifying the primary root causes in complex fault situations, the workload of the operators can be reduced. In addition, because MFM also provides a set of graphical symbols that implies causalities, operators can confirm diagnosis results by semiotic analysis, and hence the understandability of the process of alarm analysis as well as the reliability of maintenance task can be increased. 19 cases of simulation data from RELAP5/MOD2 code were utilized for evaluating the performance of the proposed system. The simulation results show that the proposed alarm analysis system has a good ability to detect and diagnose accidents earlier in time before reactor trip. (authors)

[en] A novel foilless S-band low-impedance transit-time oscillator was designed. The impedance of this oscillator is about 20 Ω. Such an oscillator with coaxial structure has the advantages of low guide magnetic field and quick saturation time, expectantly operating repetitively and in a long-pulse state. As indicated by PIC simulations, the average power of output microwave is about 4.0 GW at the main frequency of 3.175 GHz with the input-diode voltage of 550 kV, the input-diode current of 27.6 kA, and the extra magnetic field of 0.8 T. Based on the simulation results, the power efficiency of microwave is about 26.4%, much better than that of a high-impedance transit-time radiation oscillator at the same input voltage. (authors)

[en] Using external longitudinal magnetic-field to guide dual-beam out of the dual-shift tubes is a key step for the practicality of synchronizing dual-beam produced by a single accelerator. On the basis of the simulation of the confining magnetic-field for the solid dual-beam, the experiment of magnetic-field guiding annular dual-beam was presented. When the diode voltage was 380 kV, dual-beam currents of 5.10 kA and 4.92 kA were obtained. The experimental results indicate that the designed magnetic-field system could confine the annular dual-beam effectively, and the critical confining magnetic-field is about 0.5 T. (authors)

[en] The author estimated the plasma density produced by relativistic electron beam (REB) ionizing neutral gas, using both ionization theory and another method employed often to study energy losses of electron beam transporting through matter in nuclear physics. On experiment, Langmuir probe is employed to measure the plasma density produced by IREB ionizing N₂, and the curve that plasma density varies with gas pressure was obtained. The experimental results indicate that plasma density in low pressure (1-15 Pa) region is in the order of 10¹⁰-10¹¹ cm^-3, which coincides with theoretical estimation, and the method using probe to diagnose plasma produced by IREB ionizing neutral gas was feasible

[en] The diode spurious oscillation in wide-gap klystron amplifier had been studied by using three-dimension high frequency program and particle-in-cell code. A cut-off mode TM₃₁ determined by the space between cathode and diode was found in the diode region, then the diode and diode together form a resonant cavity and a strong electric field was built in the anode-cathode gap, which result in an intense electron beam modulation. According to the simulation results, some improvements were brought forward to optimize the diode structure, and the diode spurious was eliminated ultimately. (authors)

[en] To investigate the feasibility for a helical line to be used as a pulse forming line (PFL), the transmission characteristics of the helical transmission line is studied both theoretically and experimentally. The results indicate that it is feasible to employ a helical line as a long-pulse PFL, and the influence of its dispersion is negligible. Compared with a conventional coaxial PFL, the helical PFL with the same size can produce a longer pulse

[en] By means of a coaxial apparatus, pressurized water breakdown experiments with microsecond charging have been carried out with different surface roughness of electrodes and different ethylene glycol concentrations of ethylene glycol/water mixture. The experimental results about the breakdown stress and the effective time are presented. The breakdown stress is normalized to the situation that the effective time is transformed to 1 μs and analyzed. The conclusions are as follows: (1) the breakdown stress formula is modified to E = 0.561M A^-1/10t_eff^-1/N P^1/8; (2) the coefficient M is significantly increased by surface polishing and ethylene glycol additive; (3) it is accumulative for the capacity of improving electrical breakdown strength for surface polishing, ethylene glycol additive, and pressurization, of which pressurization is the most effective method; (4) the highest stress of 235.5 kV/cm is observed in ethylene glycol/water mixture with an ethylene glycol concentration of 80% at a hydrostatic pressure of 1215.9 kPa and is about one time greater than that in pure water at constant pressure; (5) for pressurization and surface polishing, the primary mechanism to improve the breakdown strength of water dielectric is the increase in the breakdown time delay. Research results indicate great potential in the application of the high power pulse conditioning system of water dielectric