Low Flux Density Research Articles

Tungsten erosion by unipolar arcing in DIII-D

Unipolar arcing was an important mechanism of metal surface erosion during the recently conducted Metal Rings Campaign in DIII-D when two toroidally continuous tile rings with 5 cm wide W-coated TZM inserts were installed in graphite tiles in the lower divertor, one on the floor and one on the shelf. Most of the arc damage occurred on the shelf ring. The total amount of W removed by arcing from the affected ∼4% of the shelf ring area was estimated ∼0.8 × 1021 at., about half of the total amount of W eroded and redeposited outside the inserts (1.8 ± 0.9)×1021 at. The rings were exposed for a total of ∼480 discharges, an equivalent of plasma time on W surfaces (with MA) ∼103 s. Arcing was monitored in situ with WI (400.9 nm) filtered camera and photomultipliers and showed that: (i) arcing only occurred during ELMs and disruptions, (ii) arcing rate was much lower on the floor than on the shelf ring, and (iii) arcing had a low cut off power flux density about 2 MW m−2. About half of arc tracks had large pitch angle and probably were produced during disruptions. Such tracks were only found on the shelf. Moderate toroidal variation of the arc track density and W erosion with nearly n = 1 pattern has been measured.

Astronomical and Meteorological Conditions of a Solar System Operation

Acquisition and processing of as much solar energy for heating and electricity generation in Poland and in the world is a very important objective in the policy of alternative energy sources. The main problem with the reception of solar energy by solar collectors is vary energy supply at different times of day and year and low flux density of radiation. The term of solar radiation one mean transmission or emission of energy in the form of electromagnetic waves. The radiation emitted from the surface of the sun spreads out in all directions in space, reaches the Earth’s surface in only partly, especially the solar collectors. The most important parameters characterizing solar radiation are daily, monthly and annual sum of solar radiation. Its express the amount of solar energy which falls on a unit area at a given time. Number of hours of sunshine during the day are dependent on two key factors. The first one is the time from the sunrise to sunset, which strongly depends on the date and latitude. The second factor is the weather (clouds), influences solar radiation, radiation in touch with clouds is absorbed and dissipated. This publication shows the impact on the energy yield of the flat collector installation and astronomical conditions (angle of inclination and declination of solar), and climate. The calculations of determining the astronomical conditions of the place where the installation is located ware analyzed. The solar installation is located in Rzeszow (Poland) and the plate collector placed on the roof of building. Based on specific methodology for selected days the calculation of the elevation angle of the Sun, hourly angle, the sun azimuth and angle of incidence of the radiation on any plane were set. The results are shown in diagrams. The effect of cloud cover on the acquisition of solar energy by the collector is also shown.

Field distribution of magnetograms from simulations of active region formation

Context. The evolution of the photospheric magnetic field distributions (probability densities) has previously been derived for a set of active regions. Photospheric field distributions are a consequence of physical processes that are difficult to determine from observations alone. Aims. We analyse simulated magnetograms from numerical simulations, which model the emergence and decay of active regions. These simulations have different experimental set-ups and include different physical processes, allowing us to investigate the relative importance of convection, magnetic buoyancy, magnetic twist, and braiding for flux emergence. Methods. We specifically studied the photospheric field distributions (probability densities found with a kernel density estimation analysis) and compared the results with those found from observations. Results. Simulations including convection most accurately reproduce the observed evolution of the photospheric field distributions during active region evolution. Conclusions. This indicates that convection may play an important role during the decay phase and also during the formation of active regions, particularly for low flux density values.

Loss and Noise Analysis of Transformer ComprisingGrooved Grain-Oriented Silicon Steel

For the reduction of transformer noise and efficient use of energy, we developed a domain-refined highly grain-oriented silicon steel with a linearly grooved surface by an electrolytic etching method. The steel showed very low iron loss even after a high-temperature annealing process, such as stress relief annealing, while magnetic flux density at 800 A/m, which is one of the very fundamental evaluation criteria for grain-oriented silicon steel, was lower than that without grooves. In light of our previous study, steels with a low flux density are disadvantageous for lowering transformer noise, but there have been no reports on the detailed noise property of this grooved grain-oriented silicon steel. In this paper, we investigated transformer noise as well as the transformer loss for the first time by fabricating three model transformers, each of which comprised one of the following grain-oriented electrical steels: grooved grain-oriented silicon steel having flux density of 1.90 T at 800 A/m, non-grooved grain-oriented silicon steel having flux density of 1.93 T at 800 A/m, and non-grooved grain-oriented silicon steel having flux density of 1.90 T at 800 A/m. As a result, transformer loss exhibited a tendency similar to the loss of a single sheet, and the grooved grain-oriented silicon steel showed the lowest loss. As for noise, even with the lower flux density, the grooved grain-oriented silicon steel showed a very low noise level equivalent to that of the non-grooved grain-oriented silicon steel with the high flux density, while the non-grooved grain-oriented silicon steel with the low flux density showed the largest noise level. From the results of magnetostriction measurements and dynamic domain observation by a newly developed method, it was found that the grooves had little influence on the generation of magnetic domains, which increased magnetostriction and transformer noise. Thus, we confirmed that low noise and low loss properties of the transformer were both realized by the application of the grooved silicon steel.

The Kok effect in Vicia faba cannot be explained solely by changes in chloroplastic CO2 concentration.

The Kok effect - an abrupt decline in quantum yield (QY) of net CO2 assimilation at low photosynthetic photon flux density (PPFD) - is widely used to estimate respiration in the light (R), which assumes the effect is caused by light suppression of R. A recent report suggested much of the Kok effect can be explained by declining chloroplastic CO2 concentration (cc ) at low PPFD. Several predictions arise from the hypothesis that the Kok effect is caused by declining cc , and we tested these predictions in Vicia faba. We measured CO2 exchange at low PPFD, in 2% and 21% oxygen, in developing and mature leaves, which differed greatly in R in darkness. Our results contradicted each of the predictions based on the cc effect: QY exceeded the theoretical maximum value for photosynthetic CO2 uptake; QY was larger in 21% than 2% oxygen; and the change in QY at the Kok effect breakpoint was unaffected by oxygen. Our results strongly suggest the Kok effect arises largely from a progressive decline in R with PPFD that includes both oxygen-sensitive and -insensitive components. We suggest an improved Kok method that accounts for high cc at low PPFD.

Elevated CO2 Improves Vegetative Growth of Water-stressed Zea mays L. Under Low Photosynthetic Photon Flux Density

Elevated CO2 Improves Vegetative Growth of Water-stressed Zea mays L. Under Low Photosynthetic Photon Flux Density

Effect of combined static magnetic field and cold water shock treatment on the physicochemical properties of cucumbers

Based on the mechanism of temperature shock treatment and electromagnetic effect for food preservation, this paper developed a novel food preservation method by combining static magnetic field with low magnetic flux density and low-temperature water shock to process the fresh postharvest vegetable. Compared with the single cold-water shock treatment (CST, Tw = 2 °C, τ = 40 min), the static magnetic field and cold-water shock treatment (SMCT, B = 70 Gs, Tw = 2 °C, τ = 40 min) caused an increase of cooling-rate of cucumbers' tissues during treatment. Weight loss of SMCT was also lower than that of CST during storage. Furthermore, decay incidence and color difference of SMCT were about 40.2% and 10.6% lower than that of CST. Activities of catalase and superoxide dismutase for SMCT were higher than that of CST, which caused a reduction of malondialdehyde. Experimental results confirmed that SMCT had a positive influence on pre-cooling, preservation quality and physicochemical properties of cucumbers.

Initial growth and microstructure feature of Ag films prepared by very-high-frequency magnetron sputtering**Project supported by the National Natural Science Foundation of China (Grant Nos. 11675118 and 11275136).

The initial growth and microstructure feature of Ag films formation were investigated, which were prepared by using the very-high-frequency (VHF) (60 MHz) magnetron sputtering. Because of the moderate energy and very low flux density of ions impinging on the substrate, the evolutions of initial growth for Ag films formation were well controlled by varying the sputtering power. It was found that the initial growth of Ag films followed the island (Volmer—Weber, VW) growth mode, but before the island nucleation, the adsorption of Ag nanoparticles and the formation of Ag clusters dominated the growth. Therefore, the whole initial stages of Ag films formation included the adsorption of nanoparticles, the formation of clusters, the nucleation by the nanoparticles and clusters simultaneously, the islands formation, and the coalescence of islands.

The eMERGE Survey – I: Very Large Array 5.5 GHz observations of the GOODS-North Field

We present new observations of the GOODS-N field obtained at 5.5 GHz with the Karl G. Jansky Very Large Array (VLA). The central region of the field was imaged to a median r.m.s. of 3 microJy/beam with a resolution of 0.5 arcsec. From a 14-arcmin diameter region we extracted a sample of 94 radio sources with signal-to-noise ratio greater than 5. Near-IR identifications are available for about 88 percent of the radio sources. We used different multi-band diagnostics to separate active galactic nuclei (AGN), both radiatively efficient and inefficient, from star-forming galaxies. From our analysis, we find that about 80 percent of our radio-selected sample is AGN-dominated, with the fraction raising to 92 percent when considering only the radio sources with redshift >1.5. This large fraction of AGN-dominated radio sources at very low flux densities (the median flux density at 5.5 GHz is 42 microJy), where star-forming galaxies are expected to dominate, is somewhat surprising and at odds with other results. Our interpretation is that both the frequency and angular resolution of our radio observations strongly select against radio sources whose brightness distribution is diffuse on scale of several kpc. Indeed, we find that the median angular sizes of the AGN-dominated sources is around 0.2-0.3 arcsec against 0.8 arcsec for star-forming galaxies. This highlights the key role that high frequency radio observations can play in pinpointing AGN-driven radio emission at microJy levels. This work is part of the eMERGE legacy project.

Heat transfer in boiling of refrigerant R-21 in a downward flow in an assembly of minichannels

The paper presents the results of an experimental study of heat transfer in boiling of refrigerant R-21 in a downward flow in a vertical assembly of minichannels of a plate-fin heat exchanger. Characteristic regimes of vapor-liquid flow and heat transfer coefficients have been obtained for the case of plain fins in the ranges of low mass velocities and heat fluxes that are typical of the industry but poorly studied. The obtained data show no significant dependence of the heat transfer coefficient on the heat flux density and mass velocity, which may be explained by the decisive effect of the evaporation of thin liquid film on the heat transfer at low heat flux density.

Analysis of Inductance According to the Applied Current in Spoke-Type PMSM and Suggestion of Driving Mode

The spoke-type permanent magnet synchronous motor (PMSM) is a motor built using nonrare earth elements, which feature low flux density. It has a flux concentrated structure of permanent magnet arrangement to improve power density. Further, the torque in the spoke-type PMSM is composed of a magnetic torque component from the permanent magnets and a reluctance torque arising from the inductance difference between the d - and q -axis. This paper analyzed the d - and q -axes inductances that affect the reluctance torque depending on the magnitude of the applied current and the current phase angle of the spoke-type PMSM at base speed. We also derived the variation of the d - and q - axis inductances, which is shown at the operation speed region. Accordingly, the variation of the current phase angle for generating the maximum output power is analyzed. Based on the above results, we predicted the variation in the driving mode of the spoke-type PMSM, and subsequently verified the prediction experimentally.

Growth and structural properties of silicon on Ag films prepared by 40.68 MHz very-high-frequency magnetron sputtering

The growth of silicon on Ag films via 40.68 MHz very-high-frequency (VHF) magnetron sputtering was investigated. The energy distribution and flux density of the ions on the substrate were also measured. The results showed that 40.68 MHz magnetron sputtering can produce ions with higher energy and lower flux density. The impact of these ions onto the grown surface promotes the growth of silicon, which is related to the crystalline nature and microstructure of the underlayer of the Ag films, and there is large particle growth of silicon on Ag films with a preferred orientation of (111), and two-dimensional growth of silicon on Ag films with a better face-centered cubic structure.

Thermal-Mechanical Noise in Resonant Thin-Film Magnetoelectric Sensors

Thin-film magnetoelectric sensors, i.e., composites of magnetostrictive and piezoelectric materials, are able to measure very low magnetic flux densities in the picotesla range. In order to further improve the limit of detection it is of high importance to understand and quantify the relevant noise sources. In this paper, a common model for the deflection noise in vibrational structures is applied to the cantilever structure of resonant magnetoelectric sensors. By means of deflection and noise measurements the existence of thermal-mechanical noise even in sensor structures with a size in the centimeter range is proven. Based on these findings a noise equivalent circuit is suggested which allows not only the distinction between the impact of different sensor-intrinsic noise sources and also the involvement of the preamplifier noise. We found that the thermal-mechanical noise is the dominant noise source if direct signal detection is performed at the first bending resonance frequency of the sensor. However, this kind of noise is not the limiting influence when applying magnetic frequency-conversion techniques.

CO2 fixation and lipid accumulation in biofilms of the aerial microalga Coccomyxa sp. KGU-D001 (Trebouxiophyceae)

This study compares lipid accumulation by immobilized aerial microalga Coccomyxa sp. KGU-D001 (Trebouxiophyceae) in biofilms and in aqueous suspended cultivation. Under direct exposure to normal air (low CO2) and light conditions, triacylglycerol (TAG) synthesis was significantly stimulated in algal biofilms on wet cotton wool. The TAG accumulation increased with decreasing thickness of the biofilm. This trend was attributed to CO2 fixation by photosynthesis of the biofilm cells, which increases the cellular accumulation of TAG. In a 17-μm-thick biofilm cultivated for 7 days, the total fatty acid (FA) content reached 27% of the cell dry weight. Under these conditions, approximately 60% of the fixed cellular carbon was presumed to be invested in TAG synthesis through free FAs. The CO2 fixation rate was almost maximized at relatively low photon flux density (25 μmol photons m−2 s−1). CO2-gas fixing algal biofilm systems can realize novel non-suspended cultivations, called artificial leaves, and thus present as strong candidates for biodiesel production in the near future.

Performance Evaluation of Interior Permanent Magnet Motors Using Thin Electrical Steels

This work investigates the impact of thin electrical steel laminations on the performance of interior permanent magnet (IPM) motors for electric vehicle tractions. Three different electrical steel grades are used in IPM motor designs and the performance is evaluated by simulation. It is found that thin laminations can improve the efficiency of the IPM motor, but the output torque could be slightly reduced due to low saturation flux density. Therefore, direct replacement of core materials for the same motor design may not be suitable. This paper presents the considerations for the design of IPM motors using thin laminations. The motor performance, including torque, efficiency, and constant power speed range is evaluated. A process is developed for the design of high performance IPM motors using thin laminations. Experimental studies are conducted to validate the simulations and designs.

A New Magnetizer for Measuring the Two-Dimensional Magnetic Properties of Nanocrystalline Alloys at High Frequencies

Nanocrystalline alloys are used extensively in high-frequency electromagnetic applications for their low magnetic losses and high saturation flux densities. To characterize their vector magnetic properties over a broad frequency range, a new magnetizer with a compact flux density-field B-H sensor was developed for two-dimensional testing up to 10 kHz.

A Novel Ferrite SMDS Spoke-Type BLDC Motor for PV Bore-Well Submersible Water Pumps

Photovoltaic (PV) powered submersible electric water pumps are becoming popular in remote rural areas, due to the nonavailability of grid connectivity. However, the initial cost of a PV system is high. Permanent magnet (PM) brushless dc (BLDC) motors are efficient compared to existing induction motors, which reduce the cost of PV array. However, steep increase in the cost of rare-earth magnets like NdFeB and SmCo makes the use of PM motor uneconomical for PV systems. Thus, the design of PM motors with ferrite magnets is gaining interest. These magnets have low remanence flux density and are brittle. Thus, flux concentration rotor topologies are desirable. The conventional spoke-type (ST) rotor is one such topology. However, flux leakage is one of its prime concerns. To negotiate this, a novel “semi-modular dual-stack” ST BLDC motor along with its parametric aided three-dimensional finite element method analysis is proposed for a PV-based 100 mm deep bore-well submersible water pump. The motor features minimum flux leakage irrespective of rotor bridge width. In addition, a lumped parameter thermal network is modeled for quick estimation of the winding temperature rise. A prototype motor is fabricated to ascertain the results obtained from simulations, and the experimental results are presented.

Low-pressure plasma-enhanced behavior of thermionic converters

High-pressure plasmas have historically been used in thermionic energy converters both to reduce the electrode workfunctions and to mitigate the space-charge effect. The behavior of such devices has been studied extensively, but low-pressure thermionic converters are far less understood. Advances in nanotechnology, such as the possibility to intercalate nanomaterials-based electrodes with alkali metals in order to reduce workfunction, may alleviate the need for high gas pressures; low-pressure devices may thus play a significant role in future if they can address the space-charge problem. Here, we develop the physics of low-pressure thermionic converters by solving the Vlasov-Poisson system of equations self-consistently. We demonstrate that various possibilities arise due to intricate interactions between the spatially varying electron and ion concentrations, leading to phenomena such as plasma oscillations at higher ion fluxes. We show that even a relatively low ion flux density (∼5×10−4 times the flux density of electrons) reduces space-charge significantly and increases the electron current density by a factor of 7. We further extend the model by including electron and ion emission from both the cathode and anode electrodes.

Development of a 60 kHz, 180 kW, Over 85% Efficiency Inductive Power Transfer System for a Tram

Conventional contact-based train power transfer systems have high maintenance costs and safety issues and cause noise and additional aerodynamic drag. Instead of the conventional system, a loosely coupled online wireless power transfer (WPT) system for a train is proposed in this paper. The operating frequency of the proposed design is 60 kHz to ensure a low flux density and a high-efficiency system with a large air gap. In addition, a new transmitter track and pick-up geometry for 60 kHz operation are designed using finite element analysis (FEA). The proposed design is evaluated theoretically and experimentally. By using the simulated results, a new 180 kW, 15 m test-bed for a tram is constructed. The total power transfer efficiency is greater than 85% at the rated output power, and the loss distribution in the system is identified. Electromagnetic field (EMF) radiation and the voltage induction at the rail are measured for safety evaluation. The measured EMF satisfied international guidelines.

Effects of cold rolling on magnetic minor hysteresis loops of duplex stainless steels

We have investigated scaling properties of magnetic minor hysteresis loops for duplex stainless steels with 60% ferrite and 40% austenitic phases, subjected to cold rolling up to 97% reduction. While the Steinmetz law, which is a scaling relation between maximum flux density and hysteresis loss and is generally valid for ferromagnetic steels, fails, that between remanent flux density and hysteresis loss exhibits a power law in the wide low and medium flux density regime, associated with a scaling exponent of . Further, the coefficient drops after rolling reduction of 10%, and then increases with reduction, whereas coercivity monotonically increases. Considering microstructural observations, the coefficient seems to also reflect morphology of the ferritic and austenitic phases in addition to the density of dislocations.