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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]

Ion cyclotron resonance heating (ICRH), one of the main auxiliary methods, for high-power and long-pulse plasma heating had been developed in Experimental Advanced Superconducting Tokamak (EAST). An impedance matching system, one important part of ICRH, had been developed for high-power injection and transmitter protection by reducing the reflected power from the antenna. The input impedance in the outlet of the stub tuner can be measured by voltage–current probes installed on the coaxial transmission line between the antenna and triple liquid stub tuners, and the optimum liquid levels in the stub tuners can be calculated based on the input impedance. The calculation and adjustment process of the optimum liquid levels are described comprehensively in this article. Finally, impedance matching had been achieved between two shots during EAST experiments. In the near future, a real-time impedance matching system will be developed to prevent large variations of the ICRH antenna impedance and achieve steady-state and long-pulse operation with the ICRH system. [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]

The s- and p-polarization absorbance spectra of Ag nanorod arrays with different heights prepared by oblique angle deposition are studied in detail. For short nanorods, both s- and p-polarization spectra, are dominated by a similar and single resonant peak. For long nanorods, a sharp UV peak dominates the s-polarization spectrum, while a broad vis–near infrared peak dominates the p-polarization spectrum. Three different absorbance peaks located at 293, 360, and 420–720 nm, respectively, have been observed and evolve differently for s- and p-polarization absorbances with the nanorod height. The change of the absorbance as a function of the nanorod height is a reflection of the growth dynamics of the nanorod. The discrete dipole approximation was used to calculate the extinction spectra of Ag nanorod with 80-nm-diameter and different lengths, and the calculated results are qualitatively consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The magnetic properties of columnar Co films on SiO[sub 2] substrates fabricated by oblique-angle incident thermal evaporation at room temperature were systematically examined by multiple techniques, including magnetic force microscopy (MFM), magneto-optical Kerr effect (MOKE), and scanning electron microscopy (SEM). Films with thickness ranging from 50 to 500 nm were deposited at the incident angles θ (with respect to substrate normal) from 0° to 85°. For films with thickness of ∼500 nm, the SEM shows the column tilt angle β increases as the θ angle increases and β < θ. The MFM images show that for 55° < θ < 75°, stripe domains are formed and are nearly parallel to the direction of incident vapor beam. The hysteresis loops obtained from MaKE show that along the direction perpendicular to the incident vapor beam the coercivity H[sub c] stays almost constant for all θ angles and the squareness decreases as the θ increases. This is in contrast to the increase of H[sub c] and the increase of squareness in the direction parallel to the incident vapor beam for θ > 60°. The result implies that for θ > 60°, the axis parallel to the incident beam behaves more like the in-plane easy axis. These magnetic anisotropies are correlated to the angular-dependent columnar structure of Co films. [ABSTRACT FROM AUTHOR]

We study the effect of surface roughness on magnetic domain wall thickness, domain size, and coercivity of thin magnetic films. We show that the roughness increases (decreases) the domain wall thickness and domain size for Bloch walls (Néel walls). The surface roughness affects the domain wall movement and causes the increase of coercivity for Néel walls. The coercivity due to domain rotation for Bloch walls decreases with the increase of roughness. The domain wall thickness, domain size, and coercivity are each related to the demagnetizing factor, which depends on the roughness and type of wall (Bloch wall or Néel wall). The calculated coercivity versus thickness is compared with experimental data of ultrathin Co films, where the thickness dependent roughness parameters are available. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the surface roughness of a computer disk using atomic force microscopy (AFM) and light scattering. Anisotropic rough surfaces and experimental techniques; AFM measurements; Light scattering measurements.

Presents information on a study conducted which examined the characteristics of silicon (Si) random rough surfaces, with focus on physics. Methodology used in the study; Details on the reciprocal space structure of the self-affine rough surface; Information on surface roughness parameters; Limitations in the determination of the roughness of parameters; Results of the study.

A passive and noninvasive diagnostic system based on high-frequency B-dot probes (HFBs) has been designed and developed for the measurement and identification of ion cyclotron emission (ICE) in the Experimental Advanced Superconducting Tokamak (EAST). Details of the hardware components of this system including HFBs, direct current blockers, radio frequency splitters, filters, and power detectors as well as data acquisition systems are presented. A spectrum analyzer is used in addition to the ordinary speed acquisition card for data registration and analysis. The reliability of a HFB based diagnostic system has been well validated during the 2018 spring experiments on the EAST. ICE signals corresponding to fundamental cyclotron frequency of hydrogen ions and harmonics of deuterium ions were observed in experiments where deuterium plasmas were heated with deuterium neutral beams. The field dependence of ICE has been verified by recent experiments with three different background magnetic fields. The observed ratio of the ICE frequency is consistent with the ratio of the magnetic field intensity within measurement errors of a few percent. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Studies the effect of surface roughness on the magnetization reversal of cobalt (Co) films on plasma-etched silicone (Si(100) substrates using thermal evaporation in high vacuum. Measurement of the surface morphologies and magnetic properties of Co films; Suggestion that the magnetization reversal process changed with the surface roughness.

When subjected to a temperature gradient, the liquid film formed on a particle surface in nearcritical vapor may undergo osmotic flow. Such a flow can induce a normal vapor flux onto (away from) the particle surface to compensate the loss (release the excess) of liquid as a result of condensation (evaporation) and produce significant thermophoretic mobility due to the extreme fluid compressibility during the phase change. Based on this principle, we have formulated this unique process and solved for the phoretic mobility by applying the boundary layer method. Unlike the classic mechanisms, this term of phase transition-induced phoretic mobility scales reversely with particle size, which becomes dominant for nanoparticles. [ABSTRACT FROM AUTHOR]

An equivalent model for MgO-based magnetic tunnel junction (MTJ) is used to characterize the frequency behavior of MTJs up to 20 GHz in this paper. From the extracted parasitic factor of MTJ, we found that the parasitic components (beside the junction resistance) significantly yield adverse effect, especially at microwave frequencies. Full parametric studies show that the interfacial capacitance, rather than the geometric capacitance, plays a key role in the drop of efficiency in microwave frequency applications of MTJs. Interfacial resistance engineering is proposed as a solution to improve the parasitic factor, as well as the operation frequency of MTJ. [ABSTRACT FROM AUTHOR]

In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5000 mV/mW. [ABSTRACT FROM AUTHOR]

An ion cyclotron range of frequencies (ICRF) system with power up to 6.0MW and a lower hybrid current drive (LHCD) system up to 4MW have been applied for heating and current drive experiments in Experimental Advanced Superconducting Tokomak (EAST). Significant progress has been made with ICRF heating and LHCD for realizing the H-mode plasma operation in EAST. During 2010 and 2012 experimental campaigns, ICRF heating experiments were carried out at the fixed frequency of 27MHz, achieving effective ions and electrons heating with the H minority heating (H-MH) mode. The H-MH mode produced good plasma performance, and realized H-mode using ICRF power alone in 2012. In 2010, H-modes were generated and sustained by LHCD alone, where lithium coating and gas puffing near the mouth of the LH launcher were applied to improve the LHCD power coupling and penetration into the core plasmas of H-modes. In 2012, the combination of LHCD and ICRH power extended the H-mode duration up to over 30 s. H-modes with various types of edge localized modes (ELMs) have been achieved with HIPB98(y, 2) ranging from 0.7 to over unity. A brief overview of LHCD and ICRF Heating experiment and their application in achieving H-mode operation during these two campaigns will be presented. [ABSTRACT FROM AUTHOR]

A long-pulse high confinement plasma regime known as H-mode is achieved in the Experimental Advanced Superconducting Tokamak (EAST) with a record duration over 30 s, sustained by Lower Hybrid wave Current Drive (LHCD) with advanced lithium wall conditioning and divertor pumping. This long-pulse H-mode plasma regime is characterized by the co-existence of a small Magneto-Hydrodynamic (MHD) instability, i.e., Edge Localized Modes (ELMs) and a continuous quasi-coherent MHD mode at the edge. We find that LHCD provides an intrinsic boundary control for ELMs, leading to a dramatic reduction in the transient power load on the vessel wall, compared to the standard Type I ELMs. LHCD also induces edge plasma ergodization, broadening heat deposition footprints, and the heat transport caused by ergodization can be actively controlled by regulating edge plasma conditions, thus providing a new means for stationary heat flux control. In addition, advanced tokamak scenarios have been newly developed for high-performance longpulse plasma operations in the next EAST experimental campaign. [ABSTRACT FROM AUTHOR]

A hydrophobic front surface in Janus catalytic motors could introduce two effects to the motion kinetics: a partially slippery surface and a change in catalytic reaction rate. Experimentally, the hydrophobic Janus motors have been observed to move appreciably faster than the hydrophilic ones for large size motors with high fuel concentrations. Numerical investigation and experimental data reveal that the slippery surface has an insignificant effect on motor kinetics compared to an enhanced catalytic reaction rate, which could result from the water depletion layer around the hydrophobic surface and the strong hydrophobic interaction between the generated O2 and the hydrophobic surface. [ABSTRACT FROM AUTHOR]

Using a 2 MW 2.45 GHz lower hybrid wave (LHW) system installed in experimental advanced superconducting tokamak, we have systematically carried out LHW-plasma coupling and lower hybrid current drive experiments in both divertor (double null and lower single null) and limiter plasma configuration with plasma current (Ip) ∼ 250 kA and central line averaged density (ne) ∼ 1.0-1.3 × 1019 m-3 recently. Results show that the reflection coefficient (RC) first is flat up to some distance between plasma and LHW grill, and then increases with the distance. Studies indicate that with the same plasma parameters, the best coupling is obtained in the limiter case (with plasma leaning on the inner wall), followed by the lower single null, and the one with the worst coupling is the double null configuration, explained by different magnetic connection length. The RCs in the different poloidal rows show that they have different coupling characteristics, possibly due to local magnetic connection length. Current drive efficiency has been investigated by a least squares fit with N//peak=2.1, where N//peak is the peak value of parallel refractive index of the launched wave. Results show that there is no obvious difference in the current drive efficiency between double null and lower single null cases, whereas the efficiency is somewhat small in the limiter configuration. This is in agreement with the ray tracing/Fokker-Planck code simulation by LUKE/C3PO and can be interpreted by the power spectrum up-shift factor in different plasma configurations. A transformer recharge is realized with ∼0.8 MW LHW power and the energy conversion efficiency from LHW to poloidal field energy is about 2%. [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 an oblique angle deposition technique, an array of well-aligned and tilted TiO2 nanorods has been fabricated by electron-beam evaporation method. The as-deposited TiO2 nanorod array is amorphous and porous with fibrous fine structures on the surface of individual nanorods. After annealing, the amorphous TiO2 crystallizes gradually into an anatase phase with annealing temperature and duration, but no visible change occurs in the porous morphology and surface fine structures even when annealed at 500 °C for 5 h. The annealing under O2 flow causes the optical band gap of TiO2 to increase from 3.32 to 3.39 eV, due to the decrease in oxygen defect concentration. The photocatalytic activity of the annealed TiO2 sample is doubled compared with that of the as-deposited sample. The enhanced specific surface area by the porosity and fine structures of obliquely deposited TiO2 nanorod array is very promising for the applications such as chemical sensor, photovoltaic solar cell, and photocatalyst material for environmental protection. [ABSTRACT FROM AUTHOR]

Using oblique angle coevaporation, the authors have successfully incorporated Ag nanoparticles into MgF2 porous films. The size of the embedded Ag nanoparticles and the porosity of MgF2 host increase with increasing vapor incident angle, resulting in a redshift in the plasmon resonant wavelength of the Ag nanoparticles. The optical properties of the composite films also depend on the ratio of MgF2 and Ag, the film thickness, and the host porosity. This method can be used to fine-tune the plasmon absorbance peaks of metal-insulator composite thin films, and have potential applications in optical devices and chemical and biological sensing. [ABSTRACT FROM AUTHOR]

The structural and optical properties of WO3 nanorods prepared by oblique angle depositions were studied and compared with WO3 thin films. The x-ray diffraction analysis revealed that both the thin films and nanorods annealed at temperatures of 400 and 500 °C had an orthorhombic structure, while only the thin films showed a monoclinic phase when annealed at 300 °C. The band gap energies of the thin films and nanorods all decreased with increasing annealing temperature. The polarized optical absorbance spectra of the as-deposited nanorod samples initially showed anisotropy, but after annealing at temperatures above 400 °C, they became isotropic. This is believed to result from the changes in morphology, crystal structure, and orientation of the nanorod arrays after annealing. [ABSTRACT FROM AUTHOR]

Significant progress has been made on the HT-7 superconducting tokamak (R = 1.22 m, a = 0.27 m) in the past year toward obtaining advanced operating modes in steady state. By combining ion Bernstein wave and lower hybrid current drive edge-localized-mode-free limiter H-mode discharges with H[SUB89] ∼ 2, β[SUBN]*H[SUB89]>3 have been obtained that lasted for 53 τ[SUBE]. A well-boronized wall prevented further impurity accumulation and the large pumping kept the recycling at a very low level. The density was kept almost constant with the feedback control. The noninductive driven current fraction is about 60% and bootstrap fraction is about 18%. The central electron temperature is about 2.6 keV and density above 2 × 10[SUP19]m[SUP-3]. With reduced plasma parameters of central Te ∼ 1.5 keV and n[SUBe0] ∼ 2 × 10[SUP19]m[SUP-3], H[SUB89] ∼ 1.45, β[SUBN] ∼ 1.1, the improved confinement phase lasts for more than 100 τ[SUBE] with the noninductive driven current fraction ∼ 70%. [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]

By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. A hydride shell is not formed during the hydrogenation. [ABSTRACT FROM AUTHOR]

A bubble propulsion model based on catalyzed hydrogen peroxide decomposition and momentum change via O2 bubbles detaching from the catalytic surface is proposed to explain the autonomous motion of catalytic nanomotors. The propelling force closely depends upon the surface tension of the liquid as well as the bulk concentration of hydrogen peroxide, and the model predictions are supported by the experimental data of Pt-coated spherical silica microbead motors. [ABSTRACT FROM AUTHOR]

The “hot spots” mechanism is a common wisdom for surface enhanced Raman scattering (SERS). We argue that this is true when the hot spots are directly exposed to the detector. For complex SERS substrates with layered structures such as nanorod arrays, the structure and the layer absorbance both play important roles, which make the effect of hot spots less significant. Using a numerical calculation of the local electric field distribution of an Ag nanorod array substrate, we demonstrate that the layer absorbance must be considered in order to obtain polarization-dependent SERS intensity that is consistent with experimental data. [ABSTRACT FROM AUTHOR]

We have investigated the surface enhanced Raman scattering (SERS) from Au nanocombs and nanorods under different excitation conditions. The SERS intensity from nanocombs is always larger than that from nanorods, but the polarized SERS dependence is similar for the two nanostructures. These results agree quantitatively well with the local E-field calculations, and the nanospine in the nanocomb increases the local E-field over all surfaces of the nanocomb structure. The combination of experimental and numerical results predicts that the Raman enhancement at 633 nm excitation is estimated to be from seven to eight times that at 785 nm excitation. [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]

We experimentally show the viability of isolating and micropositioning ZnO-based nanostructures in an electrodynamic trap to investigate their intrinsic optical nature under atmospheric conditions. An electrospray technique is used to spray a dilute solution of ZnO tetrapods (in methanol) into an electrodynamic “endcap” trap. Subsequent tuning of trapping parameters, as the methanol evaporates, leads to the stable confinement of a single ZnO tetrapod in free space. Using this method, we trap a single ZnO tetrapod structure, manipulate its position, and study its lasing characteristics. [ABSTRACT FROM AUTHOR]

A simple torsion balance is designed to directly determine the force generated by catalytic nanomotor nanorods. A 1 cm1 silicon substrate coated with ∼3.1×108 nanomotors was attached to a balancing weight and submerged into different concentrations of hydrogen peroxide. The force generated through the catalytic reaction leads to a measurable torque applied to the torsion balance. The force is on the order of 10-14-10-13 N per individual nanomotor and has a linear concentration dependence with a slope of 4.82×10-14 N per percentage of hydrogen peroxide in agreement with previous studies. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide [Mg(OH)2] thin layers were formed by a chemical reaction between Mg nanoblades and water. Infrared (IR) spectroscopy showed a OH bond-stretching vibrational mode at 3699 cm-1. The assignment was verified by reactions with heavy water, producing OD bonds with the expected isotopic frequency shift. An asymmetric Fano line shape was observed for the OH layer on metallic Mg, while a symmetric Lorentzian (or Bright–Wigner) profile was observed for the OH layer on insulating MgH2. The results indicate that the OH layer on the Mg nanoblades is so thin that the vibrational mode couples to the free-electron continuum of Mg metal. [ABSTRACT FROM AUTHOR]