In recent years, vacuum has attracted attention as an excellent insulating medium and is used in many high voltage and high electric field equipment. To improve the performance and reliability of the equipment, it is essential to improve the electric strength, and more advanced insulation technology is required. In a previous study, it was reported that apertures and the number of apertures affected the property of electron emission on electrodes with millimeter-sized apertures. Besides, micro-sized pits have been observed on electrode surface after chemical polishing and electric breakdown. However, it is not clear that how these micro-sized pits affect electron emission, whether they cause vacuum breakdown, or not. Therefore, the purpose of this study was to investigate the effect of micro-sized pits on electron emission. In this study, voltage-current measurement, and breakdown tests were conducted in vacuum using electrodes with and without micro-sized pits (5 µm square side). In addition, electric field simulations of electrodes with micro- or millimeter-sized pit were performed. From these results, it is considered that micro-sized pits have little effect on field electron emission and it is suggested that the micro-sized pits appeared after breakdown are probably generated by other physical processes following the breakdown.

Electron linacs based on superconducting radio frequency (SRF) technology are gaining attention as a highly efficient and high-power electron beam (EB) source for variety of applications. We also intend to apply the SRF technology for wastewater purification and radioactive isotope production that requires high-power EBs. Development of an electron source with high average current suitable for the SRF electron linac has been started. The objective of this work is to generate a pulsed EB with a high repetition rate, same as either the SRF accelerating frequency (1.3 GHz) or its subharmonic frequency. As even a small beam loss can quench SRF cavities, the EB produced by an electron gun should be of small emittance and sufficiently short pulses. Using simulation codes, the current dependence of the beam properties has numerically investigated based on the electron gun configuration at Research Center for Electron Photon Science (ELPH). At present, we are conducting studies to optimize and improve the electron gun including the grid pulser with design and development of the SRF linac. In addition, an electron gun test stand is currently under construction to experimentally evaluate the EB produced by the electron gun system. In this paper, we will present the results of numerical studies for the electron gun system.

Reducing the surface optical loss and broadening the spectral response range is an effective method to improve the power conversion efficiency of the multi-junction solar cells. We simulated the different HLHL (high/low/high/low index) antireflection coatings (ARCs) for the triple-junction solar cells based on an optical transfer matrix. From the ARC optimization results, the total effective reflectivity (R_e) of ZnS/MgF₂/ZnS/MgF₂ is the lowest among HLHL ARCs, which is 1.34%, best R_e at the region of interest appeared to be 5.03% for the top solar cell, 1.20% for the middle solar cell, and 0.93% for the bottom solar cell. Moreover, the effects of thickness, refractive index, and incident angle on the performance of the ZnS/MgF₂/ZnS/MgF₂ ARC were analyzed. It was found that the thickness of each film decreases when it deviates from the optimal theoretical value, and the appropriate reduction of MgF₂ refractive index can reduce total R_e. The ZnS/MgF₂/ZnS/MgF₂ ARC exhibits remarkable antireflection properties over a broad wavelength and a wide angular range. The experimental results showed that the reflectance spectrum of ZnS/MgF₂/ZnS/MgF₂ is basically consistent with the theoretical curve.

This paper presents the results of experimental studies of the structural characteristics of the epitaxial layers of GaAs_1−x−yZnSe_xGe_y solid solutions grown from a bismuth solution-melt on GaAs substrates with (100) crystallographic orientation. The grown epitaxial film of the GaAs_1−x−yZnSe_xGe_y solid solution is a single crystal with a sphalerite-like structure with the (100) orientation corresponding to the substrate orientation. It is shown that ZnSe molecules partially replace GaAs molecules in defect-capable regions of the (100) matrix crystal lattice at the high-potential sites.

Mode transitions in reactive sputtering of metal (Ti, V) oxides are studied. Under a controlled Ar gas pressure at a flow rate of 10 sccm, direct current sputtering plasma was generated. The oxygen flow rate Q and discharge power P were changed in two ways (Q was varied at fixed P, and vice versa), and the mode transitions were monitored using the state jump in the discharge voltage. When the transition points (P, Q) were plotted as two-dimensional (2D) maps, the metal-to-oxide and oxide-to-metal transition points were found to be located on two corresponding straight lines that passed through the origin, irrespective of how the parameters were varied. The origin of this behavior is discussed and ascribed to the linear relationship between the input power and the sputter etching rate of the target. These results also suggest that the metal-mode, hysteresis, and oxide-mode regions of the 2D map can be determined by a few pilot experiments. By depositing vanadium oxide films under conditions in the oxide-mode region, near its boundary, films with very similar optical properties could be obtained.