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The Ion Cyclotron Range of Frequency (ICRF) heating system of the China Fusion Engineering Test Reactor (CFETR) is intended to provide plasma heating with a minimum power output of 20 MW, which demands the Radio Frequency (RF) window to possess a higher performance requirement. This paper presents the design of an RF window for the CFETR ICRF heating system and focuses primarily on the design and confirmation of its electromagnetic performance. The RF window can be effectively matched in the operating frequency range and has an S11 of under −59 dB. The geometry of the cone type ceramics was optimized to reduce the surface tangential electric field distribution. An analysis of the electric field distribution of the RF window at 50 kV indicates that the pressure side was below 2.3 kV/mm and the vacuum side was below 1.3 kV/mm. Furthermore, a transmission line test bench with an open-terminated setup was constructed to conduct withstand voltage tests on the mockup, and the results showed that the mockup could withstand 62 kV for 2 s and 47 kV for 120 s. [ABSTRACT FROM AUTHOR]

The pitch height–dependent optical extinction spectra and the electric field enhancement of helical and multiring nanostructures are studied by the discrete dipole approximation method. For light incident along the axis of the helix, with the increase of the pitch height, the plasmon peak wavelengths redshift monotonically and the electric coupling between two adjacent pitches weakens. The plasmon peak can also be tuned by changing the polarization of the incident light, particularly by circularly polarized light. In most cases, the maximum electric field is distributed near the surface of the helix. As a comparison, since multiring structures do not have helicity, the extinction spectra are polarization independent and the maximum electrical fields always distribute on the top ring. These results show that the optical properties of helical structures are different when irradiated by left or right circular polarized light. Understanding and manipulating pitch height allow one to tune the plasmon peak and rearrange the electric field enhancement distribution of helical nanostructures. [ABSTRACT FROM AUTHOR]

We use the discrete dipole approximation method to investigate the length-dependent optical extinction spectra and the E-field enhancement of Ag nanorods with different topologic shapes, such as cylindrical, needlelike, periodic, L, and Y shapes. Comparing to nanorods with a simple shape (cylinder and needle), irregular nanorods show many distinct plasmon resonances over a large spectral range. The main plasmon peaks are redshifted with the increase of the lengths and enhanced E-field distribution at those wavelengths depends strongly on the shapes of the nanorods. More hot spots are observed for the nanorods with more defects (i.e., periodic, L, and Y shapes) and the maximum E fields are in the same order of magnitude for cylindrical nanorods and depends on the polarization and propagation directions of the excitation light. The polarization dependent extinction spectra of nanorods with different shapes have also been calculated and are shown to be dependent on the symmetry of the nanorod structure. With specific incident direction, by changing the incident polarization angle, the maximum E field of L- and Y-shaped nanorods can vary in location and magnitude. These results show that defects or imperfections in Ag nanorod structures could drastically change the optical properties, generate extra hot spots for surface enhanced spectroscopy, and have different enhanced field distribution for future plasmonic applications. [ABSTRACT FROM AUTHOR]

Lower hybrid wave (LHW)-plasma coupling experiments in HT-7 [J. K. Xie and HT-7 Group, Proceedings of the 16th International Conference on Fusion Energy, Montreal, 1996 (IAEA, Trieste, 1997), Vol. 1, p. 685] were carried out by means of puffing gas (CD4 and D2) just around the antenna. Both experiments show that wave-plasma coupling is improved by the gas puffing. The maximum distance between the plasma and the antenna is limited to about 8 cm due to the plasma disruption. The variation in the lined averaged density in the different channels gives a possible evidence of the mechanism of the ionization of neutral gas. The effect of the gas flow rate on the wave-plasma coupling shows that an optimized gas flow rate is necessary for good coupling, being consistent with simulation through Brambilla theory qualitatively. Experiments with puffing D2 show that the improved coupling results from the global density increase and the local gas puffing. Langmuir probe measurements indicate that the gas puffing effectively increases the density and decreases the temperature in scrape of layer. Studies show that the ionization of the puffed gas is affected by both LHW electric field and plasma temperature. Comparison of D2 and CD4 puffing shows that D2 improves coupling better with less effect on core density. [ABSTRACT FROM AUTHOR]

Using the discrete dipole approximation method, two visible extinction peaks are found for Ag nanohelixes. Both of them redshift periodically in an approximate half pitch with the helix height and redshift linearly with the helix diameter and pitch height. At the two absorbance peaks, an integer number of E-field maxima occur along the helix. These field maxima could be treated as results of collective electron oscillations by periodic effective dipoles within a half pitch along the helix. The wavelengths of the absorbance peaks are found to scale with the effective dipole length, which is consistent with the periodic structure of the helix. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role. [ABSTRACT FROM AUTHOR]