Alfvén cascade eigenmodes above the TAE-frequency and localization of Alfvén modes in D- 3 He plasmas on JET

Various types of Alfvén Eigenmodes (AEs) have been destabilized by fast ions over a broad frequency range from ~80 kHz to ~700 kHz in a series of JET experiments in mixed D-3He plasmas heated with the three-ion ICRF scenario [M. Nocente et al., Nucl. Fusion 60, 124006 (2020)]. In this paper, we identify the radial localization of AEs using an X-mode reflectometer, a multiline interferometer and soft X-ray diagnostics. The analysis is focused on the most representative example of these measurements in JET pulse #95691, where two different types of Alfvén cascade (AC) eigenmodes were observed. These modes originate from the presence of a local minimum of the safety factor qmin. In addition to ACs with frequencies below the frequency of toroidal Alfvén eigenmodes (TAEs), ACs with frequencies above the TAE frequency were destabilized by energetic ions. Both low- (f ≈80-180 kHz) and high-frequency (f ≈ 330-450 kHz) ACs were localized in the central regions of the plasma. The characteristics of the high-frequency ACs are investigated in detail numerically using HELENA, CSCAS and MISHKA codes. The resonant conditions for the mode excitation are found to be determined by passing ions of rather high energy of several hundred keV and similar to those established in JT-60U with negative-ion-based NBI [M. Takechi et al., Phys. Plasmas 12, 082509 (2005)]. The computed radial mode structure is found to be consistent with the experimental measurements. In contrast to low-frequency ACs observed most often, the frequency of the high-frequency ACs decreases with time as the value of qmin decreases. This feature is in a qualitative agreement with the analytical model of the high-frequency ACs in [B.N. Breizman et al., Phys. Plasmas 10 3649 (2003)]. The high-frequency AC could be highly relevant for future ITER and fusion reactor plasmas dominated by ~ MeV energetic ions, including a significant population of passing fast ions.

A novel Image Security Protection Method Based on DCT Compression Theory and Hyper-chaotic Mapping

This paper studies the current situation of image compression encryption and analyzes the influence of low frequency (DC coefficient) and high frequency (AC coefficient) on image structure in DCT transformation. Based on this, a novel image security protection method based on DCT compression theory and hyper-chaotic mapping is proposed. First, the position of the pixel of the original image is disturbed, and converts the image from spatial domain into frequency domain by the two-dimensional DCT transformation and quantization. Second, change the pixel values by modifying the values of the sign bit of AC coefficient and DC coefficient. At last, the encrypted image is obtained by carrying out inverse quantization, inverse transformation and reverse operation by bit.

DualRing

We present DualRing, a novel ring-form input device that can capture the state and movement of the user's hand and fingers. With two IMU rings attached to the user's thumb and index finger, DualRing can sense not only the absolute hand gesture relative to the ground but also the relative pose and movement among hand segments. To enable natural thumb-to-finger interaction, we develop a high-frequency AC circuit for on-body contact detection. Based on the sensing information of DualRing, we outline the interaction space and divide it into three sub-spaces: within-hand interaction, hand-to-surface interaction, and hand-to-object interaction. By analyzing the accuracy and performance of our system, we demonstrate the informational advantage of DualRing in sensing comprehensive hand gestures compared with single-ring-based solutions. Through the user study, we discovered the interaction space enabled by DualRing is favored by users for its usability, efficiency, and novelty.

High frequency AC electric glow discharge visualization technology and application in big diameter hypersonic low-density wind tunnel

In order to visualize the rarefied flow field in a Φ1m hypersonic low-density wind tunnel, an electric glow discharge technique based on high frequency excited power has been developed. Firstly, finite element simulation analysis has been carried out, and it is concluded that the breakdown voltage can be reduced by using high frequency power supply; then an electric glow discharge apparatus has been fabricated, and the discharge images were compared with simulations; besides, a clear flow field around HB-1 standard model has been observed using this technology; finally, the influence of glow discharge on the flow field, as well as the differences between direct current and high frequency electric glow discharges is discussed at the end of this paper.

The Effect of Water Absorption in Ceramic Coatings on High Frequency ac Resistance

Thermally sprayed ceramic coatings can be used for wear protection as well as thermal and electrical insulation. When exposed to environments with high humidity, the water absorption of the ceramic coating has a tremendous impact on the electrical insulation. In thermally sprayed ceramic coatings, water can easily be absorbed by the porous microstructure of the coating. A general result of the water absorption is the reduction of the dc resistivity. However, in the high frequency regime of ac loads, contrary results were observed for sealed Al2O3 coatings on steel substrates. Specimens exposed to high air humidity have shown an increased ac resistance compared to dry specimens if frequencies above 1 MHz are considered. To analyse this phenomenon, a novel measurement technique was developed to investigate the influence of the water absorption of detached ceramic coatings on the ac resistivity at high frequencies. Moreover, the water absorption of the ceramic is measured gravimetrically. To ensure the results are also applicable to ceramic coatings on substrates, the morphology of the coating was analysed using electron microscopy and compared to reference specimens deposited on steel substrates from [1].

Integrated methodology to calculate nonsinusoidal AC systems of high frequency

During the research and development of fundamentally new AC systems of high frequency, the authors identified the problems of the calculations and modeling of the operating modes of such systems according to the method of Yu.M. Osipova. Application of the method gives results that are significantly different from the experimental ones. The aim of the study is to improve the methodology considering the features of high-frequency electrical systems, their topology, and components. The research has been carried out based on a mathematical model of an electrical system of high frequency, which includes a power supply, matching transformers, cable lines and a load. The power supply is modeled in a simplified form with the internal resistance of the transistors. An analytical technique for calculating and modeling high-frequency AC systems has been developed. Analytical expressions are presented to calculate the characteristics and parameters of the high frequency system components. Recommendations on automation of the developed technique using MATLAB, Python or Simulink are presented.Comparison of the results of calculation and the experiment is carried out to confirm the reliability. The results of the research work can be used for modeling and calculating high frequency alternating current systems to determine the current load, voltage levels, analyze overvoltages and emergency modes.

Development and Research of Power Electronic Converters for Adjustable Transformers

The Thesis is devoted to research of for injection transformer (IT) electronic control methods for IT which are based on high-frequency AC pulse regulation in electrical circuits with the purpose to change AC electrical parameters (amplitude, rms value, phase shift) in IT control circuits. As such pulse control methods of AC systems have been rarely studied, the work pays more attention to the in-depth study of these methods, developing both calculation methods based on the basic harmonic determination of modulated AC and AC and their effect on the electrical load circuit operating parameters. In this way unipolar, bipolar and interphase modulation systems using bi-directional electronic semiconductor switches have been studied. A calculation methodology for the LC filtering system of modulated voltage signals has been developed which is based on the above-mentioned basic harmonic influence method. The transmission of such modulated regulatory influence signals through the IT system and the possibilities to provide an extended influence on the possibility of changes in IT load parameters are also considered. The paper discusses the possibilities to create new modulation-based electronic control and conversion systems for various AC applications, such as single-phase-two-phase and single-phase-three-phase voltage splitting systems. All the proposed technical solutions have been tested with computer models, and the results agree well with the theoretical calculations, which allows us to consider that the technical proposals are applicable in practice.

Study and Implementation of Partial Resonant High-Frequency AC-Link Inverter Operating in Soft-Switching Condition

In this paper, a high-frequency AC-link DC–AC converter is presented with detailed analysis. This converter is used as an interface between a dc power source and a grid. The studied converter is a universal power converter which consists of two bridges separated by an AC-link; each bridge is connected to a source or it feeds a load. The link of this converter contains a parallel pair inductance-capacitor. The inductance is used to stock/supply energy and for the link capacitor, it allows to perform soft switching during turning on/turning off of the switches. The studied converter has considerable advantages compared to the other topologies. Its fundamental properties are, especially, the compactness, reliability and efficiency which it ensures. Also, it guarantees longer lifetime and the possibility to transfer power in the two power flow directions. In this talk, the principles of the ac-link inverter operation are clearly explained in this paper. Simulation results, under MATLAB/SIMULINK, are shown to validate the correct operation and the efficiency of the proposed converter topology. The control algorithm is, also, experimentally implemented using a dSPACE 1104 control board.