RF window which serves as a barrier between the vacuum and air sides is a very important device for RF cavity of cyclotron. But the performances of a basic RF window are not good in impedance matching characteristics and service life. In this paper, two kinds of RF window are developed to improve performances from three candidate designs as impedance matching optimization, thermal consideration during RF operation, and multipactor effect analysis. The multiple comparisons indicate that one of the designed RF windows is far better than the others, and a low-power test has verified its impedance matching characteristic. This optimal RF window may be widely used in other low energy cyclotron and similar devices.

We report comprehensive angle-resolved photoemission investigations on the electronic structures and nematicity of the parent compounds of the iron-based superconductors including CeFeAsO, BaFe₂As₂, NaFeAs, FeSe and undoped FeSe/SrTiO₃ films with 1, 2 and 20 layers. While the electronic structure near the Brillouin zone center Γ varies dramatically among different materials, the electronic structure near the Brillouin zone corners (M points), as well as their temperature dependence, are rather similar. The electronic structure near the zone corners is dominated by the electronic nematicity that gives rise to a band splitting of the d_xz and d_yz bands below the nematic transition temperature. A clear relation is observed between the band splitting magnitude and the onset temperature of nematicity. Our results may shed light on the origin of nematicity, its effect on the electronic structures, and its relation with superconductivity in the iron-based superconductors.

A coupling model for the waves in ion cyclotron resonance frequency (ICRF) in tokamak plasmas is described. The simulation is performed based on the finite element method. A cold plasma dielectric tensor is used. A perfectly matched layer (PML) is applied to describe the ICRF wave single-pass absorption in the core plasma. The selection of PML characteristic parameters is optimized in a wide wave frequency range and validated for plane waves and ICRF waves. The dependencies of the coupling resistance on the plasma-antenna gap, average plasma density, and plasma profiles are given. The simulation results are in good agreement with the experimental results.