Investigation Of Current Research Articles

Numerical investigation of electron cyclotron and electron Bernstein wave current drive in EXL-50U spherical torus.

Numerical investigation of electron cyclotron and electron Bernstein wave current drive in EXL-50U spherical torus.

Thermal rectification through the topological states of asymmetrical length armchair graphene nanoribbons heterostructures with vacancies

We present a theoretical investigation of electron heat current in asymmetrical length armchair graphene nanoribbon (AGNR) heterostructures with vacancies, focusing on the topological states (TSs). In particular, we examine the 9-7-9 AGNR heterostructures where the TSs are well-isolated from the conduction and valence subbands. This isolation effectively mitigates thermal noise of subbands arising from temperature fluctuations during charge transport. Moreover, when the TSs exhibit an orbital off-set, intriguing electron heat rectification phenomena are observed, primarily attributed to inter-TS electron Coulomb interactions. To enhance the heat rectification ratio (η Q ), we manipulate the coupling strengths between the heat sources and the TSs by introducing asymmetrical lengths in the 9-AGNRs. This approach offers control over the rectification properties, enabling significant enhancements. Additionally, we introduce vacancies strategically positioned between the heat sources and the TSs to suppress phonon heat current. This arrangement effectively reduces the overall phonon heat current, while leaving the TSs unaffected. Our findings provide valuable insights into the behavior of electron heat current in AGNR heterostructures, highlighting the role of topological states, inter-TS electron Coulomb interactions, and the impact of structural modifications such as asymmetrical lengths and vacancy positioning. These results pave the way for the design and optimization of graphene-based devices with improved thermal management and efficient control of electron heat transport.

Investigation of electron cyclotron wave absorption and current drive in CFETR hybrid scenario plasmas

The investigation of electron cyclotron (EC) wave absorption and current drive has been performed for the China Fusion Engineering Test Reactor (CFETR) hybrid scenarios using the TORAY code. To achieve the physics goal of the EC system in CFETR, a total of four wave frequency values and nine locations of launching antennas have been considered, and the injection poloidal and toroidal angles have been scanned systematically. The electron cyclotron current drive (ECCD) efficiency of the 170 GHz EC system is quite low due to the wave-particle interactions being located at the low-field side. To optimize the ECCD efficiency, the wave frequency is increased up to 221–250 GHz, which leads to the power being deposited at the high-field side. The off-axis ECCD efficiency can be significantly enhanced by launching EC waves from the top window and injecting them towards the high-field side. The optimized ECCD efficiency at ρ = 0.32 and at ρ = 0.4 is 2.9 and 2.2 times that of 170 GHz, respectively.

Investigation of electron cyclotron current drive efficiency on the J-TEXT tokamak

Electron cyclotron current drive (ECCD) efficiency research is of great importance for the neoclassical tearing mode (NTM) stabilization. Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD power threshold reduction. ECCD efficiency has been investigated on the J-TEXT tokamak. The electron cyclotron wave (ECW) power scan was performed to obtain the current drive efficiency. The current drive efficiency is derived to be approximately η 0 = (0.06–0.16) × 1019 A m−2 W−1 on the J-TEXT tokamak. The effect of the residual toroidal electric field has been included in the determination of the current drive efficiency, which will enhance the ECCD efficiency. At the plasma current of I p = 100 kA and electron density of n e = 1.5 × 1019 m−3, the ratio of Spitzer conductivity between omhic (OH) and ECCD phases is considered and the experimental data have been corrected. The correction results show that the current drive efficiency η 1 caused by the fast electron hot conductivity decreases by approximately 79%. It can be estimated that the driven current is approximately 24 kA at 300 kW ECW power.

Generation and Control of Ultrafast Circular Photon Drag Current in Multilayer PtSe2 Revealed Via Terahertz Emission

AbstractThe generation and control of ultrafast photocurrents on the surface of transition‐metal dichalcogenides (TMDs) are essential for the development of advanced optoelectronic devices. A detailed understanding of the mechanism of ultrafast photocurrent generation is primarily needed to design functional devices. Here, it is reported that ultrafast photocurrents in multilayer PtSe2 are induced by the photon drag effect with high conversion efficiency. Particularly, under circularly polarized laser excitation, anisotropic in‐plane photon drag currents are generated, leading to the elliptically polarized terahertz (THz) radiation directly controlled by the helicity of the pump beam. Furthermore, a new model called “THz emission by the circular ac Hall effect” (TECacHE) is proposed to unveil the carrier transport process. It is observed that the origins of elliptically polarized THz emission controlled by helicity involve the pure circular photon drag current and the retardation induced by the Lorentz force. Besides, ultrafast ternary encoding is proposed and demonstrated by polarized THz emission. The results not only provide a new contactless detection model to study surface ultrafast photocurrents but also afford a fundamental investigation of the circular photon drag current in layered TMDs for THz telecommunication devices.

Investigation and direct observation of sidewall leakage current of InGaN-Based green micro-light-emitting diodes.

Electrical and optical characteristics of InGaN-based green micro-light-emitting diodes (µLEDs) with different active areas are investigated; results are as follows. Reverse and forward leakage currents of µLED increase as emission area is reduced owing to the non-radiative recombination process at the sidewall defects; this is more prominent in smaller µLED because of larger surface-to-volume ratio. Leakage currents of µLEDs deteriorate the carrier injection to light-emitting quantum wells, thereby degrading their external quantum efficiency. Reverse leakage current originate primarily from sidewall edges of the smallest device. Therefore, aggressive suppression of sidewall defects of µLEDs is essential for low-power and downscaled µLEDs.

Investigation of the surface leakage current of the nBn InGaAsSb infrared photodetector by using photoreflectance spectroscopy

The surface leakage current of the nBn infrared detector based on InGaAsSb/AlGaSb heterostructure was studied by using photoreflectance spectroscopy (PR). The Franz-Keldysh oscillations (FKOs) in PR spectra showed that the minority carriers (electrons) mainly affect the surface electric field in the nbn structures. The results show that the electric field increases due to the photovoltaic effect as the temperature increases. However, the increased ratio of the electric field at low temperature is lower than that of high temperature. At low temperatures, when the temperature drops, the generation-recombination (G-R) associated with dark current is eliminated, and the surface electric field variation becomes lower. By increasing the temperature and dark current, the electric field changes more. In addition, the unipolar barrier photodiode exhibits no surface leakage current at low temperatures without blocking the bulk currents.

Cold Atmospheric Pressure Plasma Jet Operated in Ar and He: From Basic Plasma Properties to Vacuum Ultraviolet, Electric Field and Safety Thresholds Measurements in Plasma Medicine

Application desired functionality as well as operation expenses of cold atmospheric pressure plasma (CAP) devices scale with properties like gas selection. The present contribution provides a comparative investigation for a CAP system operated in argon or helium at different operation voltages and distance to the surface. Comparison of power dissipation, electrical field strength and optical emission spectroscopy from vacuum ultraviolet over visible up to near infrared ((V)UV-VIS-NIR) spectral range is carried out. This study is extended to safety relevant investigation of patient leakage current, induced surface temperature and species density for ozone (O3) and nitrogen oxides (NOx). It is found that in identical operation conditions (applied voltage, distance to surface and gas flow rate) the dissipated plasma power is about equal (up to 10 W), but the electrical field strength differs, having peak values of 320 kV/m for Ar and up to 300 kV/m for He. However, only for Ar CAP could we measure O3 up to 2 ppm and NOx up to 7 ppm. The surface temperature and leakage values of both systems showed different slopes, with the biggest surprise being a constant leakage current over distance for argon. These findings may open a new direction in the plasma source development for Plasma Medicine.

Investigation of the low-frequency stray current induced corrosion on reinforced concrete infrastructure in high-speed rail transit power supply system

High-speed electrified rail transit (HSERT) has been developed intensely worldwide. However, the reinforced concrete infrastructure (RCI), especially for the deck of viaducts, has the risk of stray current (SC) induced corrosion. The present research is dedicated to revealing the mechanism of low-frequency SC (LSC) induced corrosion and providing a scientific basis to ensure serviceability, sustainability and cycle-life performance design of RCI. Considering the spatial distribution and time consumption of oxygen as well as pore saturation of RCI, the mathematical model of LSC induced corrosion is established. Based on the fluctuations of oxygen concentration, the quasi-steady state is proposed. And the corrosion behaviors of RCI with different pore saturation subjected to LSC are compared systematically. The results of mathematical model are verified by the measurement of half-cell potential.

Investigation of the critical current of an industrial 2G HTS wire with a modified composition stoichiometry based on Gd in strong magnetic fields

Investigation of the critical current of an industrial 2G HTS wire with a modified composition stoichiometry based on Gd in strong magnetic fields

An investigation of variable welding current on impact strength of metal inert gas welded specimen

Metal Inert Gas (MIG) welding is one of the most commonly used welding process for joining different grades and alloys of steel. Its productivity and quality depends upon many factors like arc voltage, current, weld speed and heat generated during welding. There have been many studies performed on impact of welding parameters on mechanical strength during MIG welding. In this particular study, an attempt has been made to investigate the effect of varying welding current with constant voltage on the impact strength of the weld bead of similar and different material. The objective of this is to design a V- joint and evaluate the strength of the similar and dissimilar metal pieces on different current and constant voltage conditions. The materials used in this study are mild steel and stainless steel. The method used for the impact testing is IZOD test.

Maximal current of a pulsed constricted arc discharge operating in the forevacuum plasma electron source

The paper presents results of investigation of maximal current of the pulsed constricted arc discharge generating emission plasma in the forevacuum plasma electron source. Distinctive feature of the forevacuum plasma electron source is the absence of pressure differential between region of formation of emission plasma and the region of acceleration and propagation of electron beam. Therefore, the operating conditions of the constricted arc in the forevacuum plasma source are significantly different from the conditions in the plasma electron sources generating electron beams at pressure 10–3–10–1 Pa. The constriction of the positive column of the arc discharge provides, as it known, to reduce influence of instability and chaotic behavior of the cathode spot of the arc on the formation of emission plasma. In the investigated pressure range 3–20.5 Pa, the maximal current of the constricted arc discharge has been limited either by extinction of the arc or by initiation of the cathode spots on the constricting electrode and transition of the arc operation to the cascade mode. Increase of gas pressure and the use of working gas with larger ionization cross section (e.g. argon) have provided increase of the maximal arc current. The increase in the constricting channel diameter has provided the increase of maximal current and provided lower minimal gas pressure, at which stable operation of the constricted arc ensured. The decrease of length of the constricting channel has provided noticeable increase in the maximal arc current only at gas pressure more than 12 Pa.

Helicon wave heating and current drive in toroidal plasmas

Investigation of helicon wave heating and current drive (CD) in toroidal plasma has been carried out with the ray-tracing code GENRAY. The wave trajectories, profiles of power deposition and driven-currents are presented. It is shown that increasing the poloidal launch angle does not change the absorption rate of the wave, but moves the peak of the wave deposition toward the plasma core. Wave frequencies in the range of our interest (460 MHz ∼ 480 MHz) do not change the absorption of the wave. Under low parameter plasmas, we find that both the peak position and magnitude of the wave power deposition are dependent on the launched parallel refractive index n||. With increasing the refractive index, the driving efficiency first increases and then decreases. The parallel refractive index figure of merit for mid-plane launching in HL-2M configuration is 3.2. With high plasma parameters, both the position and magnitude of the driving current are weakly dependent on n||. The magnitude of the driven current is determined by both the absorption rate and the value of ξe, which is related to n||. It is also demonstrated that driven current increases with increase of the core plasma temperature and decrease of the core plasma density. The plasma ohmic current seems do not significantly affect the helicon CD efficiency, but moves the driven current toward the plasma core region and narrows the width of the driven current profile. In addition, the preliminary calculations including scrape-off-layer (SOL) suggest that the power absorption rate loss in SOL is about 5%–20%. These results provide a reference and theoretical basis for the design and construction of HL-2M helicon wave system.

Experimental investigation of lower hybrid current drive induced plasma rotation on the experimental advanced superconducting tokamak

Rotation and its shear can reduce the magnetohydrodynamic instabilities and enhance the confinement. The LHCD has been proposed as a possible means of rotation driving on a future fusion reactor. Exploring the mechanisms of LHCD rotation driving on the current tokamaks can provide important reference for future reactors. On EAST, it was previously shown that 2.45 GHz LHCD can drive plasma toroidal rotation and the change of edge plasma rotation leads the co-current core rotation to increase. At higher frequency, 4.6 GHz lower hybrid wave can more effectively drive co-current plasma toroidal rotation. On EAST, at the lower current, the effects of different LHCD power on plasma toroidal rotation are analyzed. Higher power LHCD has a better driving efficiency. The effect of safety factor (<i>q</i>) profile on toroidal rotation is also presented. The LHCD can change the profile of safety factor due to current drive. It is found that when the power exceeds 1.4MW, the <i>q</i> profile remains unchanged and the rotation changes only very slightly with LHCD power, suggesting that the current profile is closely related to rotation. In order to further analyze the dynamic process of plasma toroidal rotation driven by lower hybrid current drive on EAST, the toroidal momentum transport due to LHCD is deduced by using the modulated LHCD power injection. Based on the momentum balance equation, the toroidal momentum diffusion coefficient (<i>χ</i><i><sub>φ</sub></i>) and the toroidal momentum pinch coefficient (<i>V</i><sub>pinch</sub>) are obtained by the method of separation of variables and Fourier analysis for the region where the external momentum source can be ignored. It is found that the momentum diffusion coefficient (<i>χ</i><sub><i>φ</i></sub>) and momentum pinch coefficient (<i>V</i><sub>pinch</sub>) tend to increase from the core to the outer region. This is consistent with the characteristic that the toroidal rotation velocity first changes in the outer region and then propagates to the core when the toroidal rotation is driven by LHCD.

Experimental Study on Superconducting Level Sensors in Liquid Helium

An approach for experimental investigation of the optimum sensor current of a superconducting level sensor is established and is then used for the investigation of the same of a NbTi and a MgB2/SS level sensors in liquid helium. On comparing the experimental results with that of the computational model established earlier, to simulate the operation of a superconducting level sensor, it was found that both agree closely. This shows the validity of the computational model for the characterization of a superconducting level sensor. Further on, the operation of these level sensors in a two-current method was studied. The results showed a higher heat load and level measurement time. However, it indicated an opportunity of retaining the linearity of the voltage versus liquid level curve even under high boil-off rate inside the cryostat. To scrutinize these findings, the NbTi level sensor operation in liquid helium was studied up to a boil-off rate of 5.77 g/s. It was observed that the sensor operation was not affected; however, the two-current method showed a more accurate level measurement compared to the one-current method.

A Mathematical Model for the Characterization of Superconducting Level Sensors

An automated level control in cryogenic systems requires a precise and continuous level measurement. If properly characterized, superconducting level sensors are a viable option for the same. The operation of a superconducting level sensor is based on the difference in the heat transfer from the sensor wire to the liquid and the gaseous phases of the cryogen. The higher heat transfer in the liquid phase results in a superconductive status, whereas the lower heat transfer in the gaseous phase results in a normal conductive status with a voltage drop corresponding to the length of the wire in the gaseous phase. Hence, it demands a judicious selection of the sensor and the operational parameters such as the current input, for an accurate level measurement as well as the reduction of the liquid boil off. In this paper, to simulate the operation of a superconducting level sensor, a model has been developed by taking the steady-state heat balance along the sensor wire. It is then used for the investigation of the sensor current, voltage output at various liquid levels, and temperature profile of the sensor wires of NbTi and MgB 2 /SS level sensors in LHe. Furthermore, design guidelines have been proposed for an MgB 2 /SS superconducting level sensor for LH 2 level measurement. The parameters considered for the analysis are the sensor wire diameter and the active length. In addition, the effect of an external resistor on the sensor operation is also studied.

Investigation of current IV Team construction development in Chinese medicine hospitals in Beijing

Objective To investigate present intravenous infusion team (IV Team) construction developing situation and problems during management in Chinese medicine hospital in Beijing, so as to put forward improvement measures for IV regulations and management in Chinese medicine hospitals, and provide reasonable suggestions. Methods The group sampling methods was used in September 2016, and self-design questionnaire was investigated in 33 Chinese medicine hospitals in Beijing region for the construction of IV Team, IV development and their issues and strategies. Results IV Teams were built in 17 hospitals (51.5%) ; multidisciplinary members formed IV Team in 2 hospitals (6.1%) ; 22 hospitals (66.7%) had IV nurse specialist. The usage rate of PICC、ultrasound-guided PICC placement were both low (both 36.4%) . PICC maintaining outpatient clinic rate was low (18.2%) and high rate of IV infusion (78.8%) , high rate of administrating vaso-stimulant drugs (75.8%) , high rate of steel needle etc. There were some problems about IV Team construction and management, including the lacking standard regulations (60.6%; the shortage of facilities for IV injection (63.6%) ; construction, management, fee charging and staff (45.5%) etc. Conclusions IV Team construction has been primary established and developed well in Beijing, but problems still exist in construction of professional teams, safety problems on Chinese Medicine IV infusion, no standard regulations, and unperfected facilities for administration. Key words: Nursing management; Intravenous infusion team; Chinese medicine hospital

Passivation of multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors

We study the effect of surface passivation on pseudomorphic multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors. A combination of ozone oxidation to form GeOx and GeSnOx on the surface of the diodes followed by atomic layer deposition of Al2O3 for protection of these native oxides provides reduced dark current. With a temperature-dependent investigation of dark current, we calculate the activation energy to be 0.26 eV at a bias of −0.1 V and 0.05 eV at −1 V for the sample passivated by this ozone method. Based on these activation energy results, we find that the current is less dominated by bulk tunneling at lower reverse bias values; hence, the effect of surface passivation is more noticeable with nearly an order-of-magnitude improvement in dark current for the ozone-passivated sample compared to control devices without the ozone treatment at a voltage of −0.1 V. Passivation also results in a significant enhancement of the responsivity, particularly for shorter wavelengths, with 26% higher responsivity at 1100 nm and 16% higher performance at 1300 nm.

Study of the Influence of Helical Bending Strain and Perpendicular Self-Field on Critical Current Degradation for Multilayer YBCO Tapes

An experimental investigation of the critical current (I c ) degradation of multilayer twisted yttrium barium copper oxide (YBCO) tapes in self-field was performed. The influence of the number of tape layers (N) and twist pitch (P) on critical current was researched. The results showed that the influence of helical bending strain and perpendicular self-field on critical current degradation was a comprehensive process. No critical current degradation was found when there was just one layer and the twist pitch was over 20 mm. However, the situation would change when the number of tape layers increased. The critical current degradation would increase with increase in helical bending strain or perpendicular self-field. The critical current degradation can reach a maximum of 24.6% when the helical bending strain was 0.23% and the number of tape layers was 5. A mathematic formula was set up to express the comprehensive influence of helical bending strain and perpendicular self-field on critical current degradation. The results can provide an important theoretical foundation for the application of high temperature superconducting tapes and the design of YBCO cables.

Features of the effect of the supply current on the operation mode of an oscillator based on an IMPATT diode taking into account the reflected signal

A theoretical investigation of the IMPATT diode supply current on the operation mode of a generator is out. As additional parameters affecting the operation mode, the coefficients of signal reflection from the inhomogeneity in the output transmission line and the delay time of this signal have been analyzed. It is shown that the following modes of synchronization may appear at various relations between these parameters: with an instability of the amplitude, multifrequency mode, dynamic chaos mode, single-frequency mode, and oscillation suppression mode. Based on the solution to the autogenerator equation, the possible operation modes of a generator based on the IMPATT diode were analyzed. The results make it possible to assess the range of parameters where a negative effect upon the operation mode of the oscillator will be absent and the ranges of the oscillator’s parameters when the mode of dynamic chaos can be obtained.