Flux Trapping Research Articles

Vortex System Dynamics upon Pulsed Magnetization of a HTS

A numerical investigation of the response of a HTS with different numbers of defects to the action of rectangular magnetic field pulses with a varying amplitude is carried out. The time dependences of a magnetic field trapped by the superconductor are calculated at different pulse parameters. The values of the HTS response to pulsed and gradual magnetization and demagnetization of the sample are compared, which reveals that magnetic flux trapping is more efficient under the action of pulses. A feature in the behavior of the vortex lattice acted on by field pulses is established, which relates to correlation between the number of defects and pulse amplitude. Flux trapping is shown to have a maximum dependent on the concentration of defects at each pulse amplitude.

Photosynthetic performance, nutrient status and lipid yield of microalgae Chlorella vulgaris and Chlorococcum humicola under UV-B exposure

The present study was conducted to examine the photosynthetic performance, nutrient status and lipid yield in microalgae Chlorococcum humicola and Chlorella vulgaris under different durations of UV-B exposure (1/2 h, 1 h, 2 h, 3 h and 4 h). Results revealed that UV-B reduces the photosynthetic performance of photosystem II by altering photosynthetic performance index (Pi ABS ), maximum quantum yield (Fv/Fm), net closing rate of reaction centre (Mo), trapping flux (TRo/RC) and effective antenna size with their respective control. Scanning Electron Microscopy (SEM) exhibited variegated structure and increased cell size by ~15–65% which was more pronounced in the case of C. humicola at 4 h of UV-B. The Energy Dispersive Spectroscopy (EDS) data showed that the content of microelements (C, O, Na, and K) in terms of atomic weight % was found to be significantly increased in C. vulgaris while with C. humicola , it was restricted to carbon (C) only. Further, the high antioxidant (ascorbic acid, cysteine and proline) potential and carotenoid/chl a photoprotection response reflects protection against UV-B in the both algae. In the case of lipid, comparative greater increase in cell size of C. humicola correlated with high lipid yield as compare to C. vulgaris at 2 h of UV-B could be employed in the production of biofuel in sustainable manner. Thus, algae C. humicola could be a best alternative feed stock of lipid and biofuel production in the area receiving high solar radiation. • UV-B exposure of 4 h exhibited toxicity in algae C. humicola and C. vulgaris . • UV-B exposure significantly reduces photo system II performance of both algae. • Under 2 h UV-B exposure lipid yield in C. humicola was higher than C. vulgaris . • SEM-EDS revealed altered essential minerals and cell size in algae under UV-B.

Salicylic Acid Induced Photosynthetic Adaptability of Raphanus sativus to Salt Stress is Associated with Antioxidant Capacity

Despite the plethora of published reports on ameliorative effects of exogenously applied salicylic acid (SA) to plants under salt stress, a critical role of SA in redox balance, photosynthetic and electron transport in mediating salt tolerance in plants is still ignored. The present study was aimed to assess the beneficial effects of SA on photosynthetic electron transport in five radish cultivars during salt stress which may translate into protection from salt-induced oxidative damage. Seeds of five radish cultivars (Red Neck Purple, Early Long White, Minnu Radish, Radish 40-day and Gong Swang Radish) were allowed to germinate for five days after which seedlings were sprayed with different concentrations of SA (0, 2 and 5 mM). After 48 h of SA treatment, seedlings were subjected to salt stress (0, 100, and 200 mM NaCl). Salt stress cause reduction in biomass, chlorophyll contents and PSII photochemistry in all five radish cultivars. However, salt stress causes an increase in proline content, lipid peroxidation, ROS content and antioxidant enzymatic activity. Foliar spray of SA downregulated the absorption, trapping and photosynthetic electron transport fluxes while it increased dissipation flux consequently improving photochemistry of most of the radish cultivars under salt stress. This Improved photochemistry and enhanced antioxidant enzymes activity of radish cultivars by SA application resulted in lower ROS generation and membrane damage. Greater accumulation of compatible solutes due to foliar spray of SA might have additional protective effects on photosynthetic machinery by lowering oxidative stress. Moreover, ameliorative effects of SA were cultivar specific. The study suggested that SA could mitigate the detrimental effects of salt stress by regulating physiological and biochemical mechanisms in radish plant.

Flux pinning mechanisms and a vortex phase diagram of tin-based inverse opals

Three-dimensional periodic tin structures were synthesized by filling pores in silicon opals with a sphere diameter of 194 nm (Sn190) and 310 nm (Sn300). The samples were examined by the ultra-small-angle x-ray diffraction method, energy dispersive x-ray microanalysis and scanning electron microscopy. It was found that the inverse opal structure consists of tin nanoparticles inscribed in octahedral and tetrahedral pores with diameters of 128 nm and 70 nm for the sample Sn300, and 80 nm and 42 nm for the sample Sn190. The study of the magnetic properties of the samples by SQUID magnetometry showed that magnetization reversal curves exhibit hysteretic behavior. The mechanisms of magnetic flux pinning in the samples depend on the size of the tin nanoparticles. Tin nanoparticles in Sn300 behave like a classical type-I superconductor. The hysteretic behavior of the magnetization reversal curves at low magnetic fields is due to the formation of a network of superconducting contours in Sn300. These superconducting contours effectively trap the magnetic flux. The octahedral tin nanoparticles in Sn190 remain type-I superconductors, but smaller tetrahedral particles behave like type-II superconductors. Type-I and II superconducting particles in Sn190 lead to the coexistence of different mechanisms of flux pinning. These are flux trapping by superconducting contours at low magnetic fields and flux pinning by tetrahedral particles due to the surface barrier at high magnetic fields.

Nano-ZnO priming induces salt tolerance by promoting photosynthetic carbon assimilation in wheat

ABSTRACT High salt seriously reduces plant growth in wheat by depressing photosynthetic carbon assimilation. In this study, wheat plants were firstly primed with nano-ZnO (50 mg L−1), and after 20-day recovery, the plants were then exposed to a 10-day salt stress (200 mM NaCl). The nano-ZnO priming significantly reduced Na concentration and increased leaf water potential under salt stress. In relation to the non-primed plants, the nano-ZnO primed plants possessed more effective oxygen scavenging system as exemplified by the enhanced activities of SOD, APX and CAT, leading to a better maintenance in homeostasis of ROS production under salt stress. The nano-ZnO priming benefited the tolerance of photosynthetic apparatus to subsequent salt stress, which was mainly due to the enhanced trapped energy flux and electron transport flux. The nano-ZnO priming increased the activities of phosphoglucomutase and cytoplasmic invertase, which promoted the sucrose biosynthesis in leaves under salt stress. In addition, the nano-ZnO primed plants had higher shoot dry weight than the non-primed plants under salt stress. Collectively, nano-ZnO priming activated the antioxidant system to depress the oxidative burst and enhanced the efficiency of photosynthetic electron transport and sucrose biosynthesis in leaves under salt stress, hereby improved the salt tolerance in wheat.

Trapping of Magnetic Flux in Bi-2223 Ceramic Superconductors Doped with α-Al2O3 Nanoparticles

By combining experimental results and a simple model, we offer here an explanation for the role played by the low-angle grain boundaries and the doping with α-Al2O3 nanoparticles in the trapping of the magnetic flux in Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Our model correlates the size of the nanoparticles, properties of the superconducting matrix, and the magnetic flux trapped at the intragranular planar defects, the so-called Abrikosov-Josephson vortices. The results indicate that the role played by the doping with α-Al2O3 nanoparticles is to pin the AJ vortices at the grain boundaries with misorientation angles $\theta \sim 10^{\circ }$. We also argue that a similar procedure for identifying conditions for the trapping of the magnetic flux may be applied to other superconducting materials doped with non-magnetic nanoparticles.

Improvement of the trapped field of REBCO bulk activated by pulsed field magnetization with a large soft-iron yoke

We study to increase the trapped magnetic field of a REBCO bulk magnet excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used to expose the bulk to the magnetic field for a long time. Although a small yoke 40 mm in diameter was used in our previous study, it was changed to a large yoke 64 mm in diameter in this paper. Accordingly, the pulse width was extended by 13%. When a GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by varying an amplitude of the applied field and temperature in a bulk magnet system using a two-stage GM-type refrigerator with a cooling capacity of 12 W at 20 K, the maximum trapped flux density reached 4.07 T on the center of the bulk surface and 2.56 T on the pole surface at 20 K. Moreover, the total magnetic flux was 3.28 mWb, which was about 13% larger than that of a small yoke. This result suggests that this method is useful in practice because the trapped field can be enhanced only by changing the soft-iron yoke.

Influence of Glacial Meltwater on Summer Biogeochemical Cycles in Scoresby Sund, East Greenland

Greenland fjords receive considerable amounts of glacial meltwater discharge from the Greenland Ice Sheet due to present climate warming. This impacts the hydrography via freshening of the fjord waters and biological processes due to altered nutrient input and the addition of silts. We present the first comprehensive analysis of the summer carbon cycle in the world's largest fjord system situated in southeastern Greenland. During a cruise onboard RV Maria S. Merian in summer 2016, we visited Scoresby Sund and its northernmost branch, Nordvestfjord. In addition to direct measurements of hydrography, biogeochemical parameters and sediment trap fluxes, we derived net community production (NCP) and full water column particulate organic carbon (POC) fluxes, and estimated carbon remineralization from vertical flux attenuation. While the narrow Nordvestfjord is influenced by subglacial and surface meltwater discharge, these meltwater effects on the outer fjord part of Scoresby Sund are weakened due to its enormous width. We found that subglacial and surface meltwater discharge to Nordvestfjord significantly limited NCP to 32 – 36 mmol C m-2 d-1 compared to the outer fjord part of Scoresby Sund (58 – 82 mmol C m-2 d-1) by inhibiting the resupply of nutrients to the surface and by shadowing of silts contained in the meltwater. The POC flux close to the glacier fronts was elevated due to silt-ballasting of settling particles that increases the sinking velocity and thereby reduces the time for remineralization processes within the water column. By contrast, the outer fjord part of Scoresby Sund showed stronger attenuation of particles due to horizontal advection and, hence, more intense remineralization within the water column. Our results imply that glacially influenced parts of Greenland's fjords can be considered as hotspots of carbon export to depth. In a warming climate, this export is likely to be enhanced during glacial melting. Additionally, entrainment of increasingly warmer Atlantic Water might support a higher productivity fjord systems. It therefore seems that future ice-free fjord systems with high input of glacial meltwater may become increasingly important for Arctic carbon sequestration.

Software Tools for Flux Trapping and Magnetic Field Analysis in Superconducting Circuits

We have recently developed and reported methods with which we analyze the effects of external magnetic field and flux trapping on superconducting electronic circuits. Here, we show how the methods can be turned into tools and discuss verification of the analysis results. We present robust and repeatable post-layout verification methods and show examples of magnetic field and flux trapping analysis. This paper makes it possible to analyze the effects of static magnetic fields and trapped flux on circuit operation.

Mapping Flux Trapping in SRF Cavities to Analyze the Impact of Geometry

Mapping Flux Trapping in SRF Cavities to Analyze the Impact of Geometry

Flux Pinning by Columnar Defects Along a-axis in a-axis Oriented YBCO Thin Films

Columnar defects (CDs) along a -axis were installed into an in-plane aligned a -axis-oriented $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{y}$ film by using heavy-ion irradiation, in order to clarify the influence of CDs on flux pinning properties around B || ab . The critical current density J c at B || c significantly decreases after the irradiation, since the CDs act as a channel for flux creep along their length. The magnetic field dependence of J c at B || ab , on the other hand, is weakened by the introduction of CDs. This means that the CDs can trap flux lines at B || ab , whereas naturally growth defects working as effective ab -correlated PCs exist. The trapping angle of CDs along the a -axis is extremely narrow (∼5.8°) in comparison with CDs along the c -axis and is roughly coincides with other ab -correlated PCs. The small trapping angle of CDs along the a -axis is attributed to strong line tension energy of flux lines with elliptical core around B || ab .

Characteristics of Relativistic Microburst Intensity From SAMPEX Observations

AbstractRelativistic electron microbursts are an important electron loss process from the radiation belts into the atmosphere. These precipitation events have been shown to significantly impact the radiation belt fluxes and atmospheric chemistry. In this study we address a lack of knowledge about the relativistic microburst intensity using measurements of 21,746 microbursts from the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX). We find that the relativistic microburst intensity increases as we move inward in L, with a higher proportion of low‐intensity microbursts (<2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region. The mean microburst intensity increases by a factor of 1.7 as the geomagnetic activity level increases and the proportion of high‐intensity relativistic microbursts (>2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region increases as geomagnetic activity increases, consistent with changes in the whistler mode chorus wave activity. Comparisons between relativistic microburst properties and trapped fluxes suggest that the microburst intensities are not limited by the trapped flux present alongside the scattering processes. However, microburst activity appears to correspond to the changing trapped flux; more microbursts occur when the trapped fluxes are enhancing, suggesting that microbursts are linked to processes causing the increased trapped fluxes. Finally, modeling of the impact of a published microburst spectra on a flux tube shows that microbursts are capable of depleting <500‐keV electrons within 1 hr and depleting higher‐energy electrons in 1–23 hr.

Ion Heating by Electromagnetic Ion Cyclotron Waves and Magnetosonic Waves in the Earth's Inner Magnetosphere

AbstractElectromagnetic ion cyclotron (EMIC) waves and magnetosonic waves are commonly observed in the Earth's magnetosphere associated with enhanced ring current activity. Using wave and ion measurements from the Van Allen Probes, we identify clear correlations between the hydrogen‐ and helium‐band EMIC waves with the enhancement of trapped helium and oxygen ion fluxes, respectively. We calculate the diffusion coefficients of different ion species using quasi‐linear theory to understand the effects of resonant scattering by EMIC waves. Our calculations indicate that EMIC waves can cause pitch angle scattering loss of several keV to hundreds of keV ions, and heating of tens of eV to several keV helium and oxygen ions by hydrogen‐ and helium‐band EMIC waves, respectively. Moreover, we found that magnetosonic waves can cause the resonant heating of thermal protons. Our study indicates the importance of energy transfer from the EMIC and magnetosonic waves to ions with different species at thermal energies.

Formation of hot, stable, long-lived field-reversed configuration plasmas on the C-2W device

TAE Technologies’ research is devoted to producing high temperature, stable, long-lived field-reversed configuration (FRC) plasmas by neutral-beam injection (NBI) and edge biasing/control. The newly constructed C-2W experimental device (also called ‘Norman’) is the world’s largest compact-toroid (CT) device, which has several key upgrades from the preceding C-2U device such as higher input power and longer pulse duration of the NBI system as well as installation of inner divertors with upgraded electrode biasing systems. Initial C-2W experiments have successfully demonstrated a robust FRC formation and its translation into the confinement vessel through the newly installed inner divertor with adequate guide magnetic field. They also produced dramatically improved initial FRC states with higher plasma temperatures (Te ~ 250 + eV; total electron and ion temperature >1.5 keV, based on pressure balance) and more trapped flux (up to ~15 mWb, based on rigid-rotor model) inside the FRC immediately after the merger of collided two CTs in the confinement section. As for effective edge control on FRC stabilization, a number of edge biasing schemes have been tried via open field-lines, in which concentric electrodes located in both inner and outer divertors as well as end-on plasma guns are electrically biased independently. As a result of effective outer-divertor electrode biasing alone, FRC plasma is well stabilized and diamagnetism duration has reached up to ~9 ms which is equivalent to C-2U plasma duration. Magnetic field flaring/expansion in both inner and outer divertors plays an important role in creating a thermal insulation on open field-lines to reduce a loss rate of electrons, which leads to improvement of the edge and core FRC confinement properties. An experimental campaign with inner-divertor magnetic-field flaring has just commenced and early result indicates that electron temperature of the merged FRC stays relatively high and increases for a short period of time, presumably by NBI and E × B heating.

Diffuse Auroral Electron and Ion Precipitation Effects on RCM-E Comparisons With Satellite Data During the 17 March 2013 Storm.

Effects of scattering of electrons from whistler chorus waves and of ions due to field line curvature on diffuse precipitating particle fluxes and ionospheric conductance during the large 17 March 2013 storm are examined using the self-consistent Rice Convection Model Equilibrium (RCM-E) model. Electrons are found to dominate the diffuse precipitating particle integrated energy flux, with large fluxes from ~21:00 magnetic local time (MLT) eastward to ~11:00 MLT during the storm main phase. Simulated proton and oxygen ion precipitation due to field line curvature scattering is sporadic and localized, occurring where model magnetic field lines are significantly stretched on the night side at equatorial geocentric radial distances r 0 ≳8 R E and/or at r 0 ~5.5 to 6.5 R E from dusk to midnight where the partial ring current field has perturbed the magnetic field. The precipitating protons likewise contribute sporadically to the storm time Hall and Pedersen conductance in localized regions whereas the precipitating electrons are the dominate storm time contributor to enhanced Hall and Pedersen conductance at auroral magnetic latitudes on the night and morning side. The RCM-E model can reproduce general features of the Van Allen Probe/MagEIS observed trapped electron differential flux spectrograms over energies of ~37 to 150 keV. The simulations with a parameterized electron loss model also reproduce reasonably well the storm time Defense Meteorological Satellite Program integrated electron energy flux at 850 km at satellite crossings from predawn to midmorning. However, model-data agreement is not as good from dusk to premidnight where there are large uncertainties in the electron loss model.

Magneto-resistivity and magnetization investigations of YBCO superconductor added by nano-wires and nano-particles of titanium oxide

We study in this work the influence of titanium oxide (TiO2) nano-wires (NWs) and nano-particles (NPs) addition on the flux trapping potential of YBa2Cu3Oy (YBCO for brevity). Samples were characterized using various techniques, including X-rays diffraction, scanning electron microscopy, temperature dependence of resistivity under magnetic field and magnetization measurements. Three kinds of YBCO + x TiO2 samples with x = 0.0 and 0.1 wt% were synthetized via the solid-state reaction route. The activation energy U0, the coherence length ξ(0), the upper critical field Hc2(0) and irreversibly field Hirr are estimated and discussed in the relation to TiO2 addition effect. The derived parameters are increased for samples containing 0.1 wt% of TiO2 nano-entities and are more enhanced in Y–Ti NPs sample. It results therefore, that suitable amount of TiO2 nano-particles addition can be useful tool for the manufacture of a promising YBCO compound for practical applications.

Influence of crystalline structure on rf dissipation in superconducting niobium

Bulk niobium is the most common material used in the fabrication of rf superconducting cavities for accelerators. Predicting and reducing the rf surface dissipation in these cavity structures is mandatory, since it has a tremendous cost impact on the large accelerator projects. In this paper the author hopes to demonstrate that sources of dissipation usually attributed to external causes (mainly flux trapping during cooldown and hydrides precipitates) are related to the same type of crystalline defects that affect the local superconducting properties and can be at the source of early vortex penetration at the surface. We also want to show how these types of defects can explain some of the discrepancies observed from other laboratories in niobium cavity doping experiments. Understanding the origin and the role of these defects could provide direction for improving material specifications as well as improving fabrication control from sheet material to completed cavity. In particular, we will demonstrate that dislocation entanglements, due to the fabrication damage layer, have the strongest impact for the pinning behavior of trapped flux, as well as hydrogen segregation in cavity niobium. The author wishes to present to the superconducting radio frequency (SRF) accelerator community the synthesis of experimental results scattered in the literature, completed with some personal results. The results of this effort provide a new perspective on recently published work in the domain of SRF cavity doping and sensitivity to trapped flux during cooldown. I will also try to draw whenever possible, some conclusions about other types of superconductors used for SRF applications including $\mathrm{Nb}/\mathrm{Cu}$ thin films and to discuss their possible change of behavior with field or frequency. I will concentrate on surface and material science aspects since the experimental results on rf cavities have already been treated elsewhere.

Analysis of evolving capillary transition, gravitational fingering, and dissolution trapping of CO2 in deep saline aquifers during continuous injection of supercritical CO2

Dissolution trapping of supercritical CO2 (ScCO2) in deep saline aquifers undergoes different stages such as ScCO2 mixing with brine, buoyant convection and slumping of CO2 rich brine. The effects of permeability and capillarity on these stages were previously studied for (i) uniformly injected ScCO2 at the top of the aquifer and (ii) spreading from a finite initial patch of CO2 or after short injection duration of CO2. In this paper we discuss the results of continuous injection of CO2 from a well that is screened inside the aquifer between caprock at the top and bedrock at the bottom. For this case, the injection pressure significantly influences the spreading of CO2 plumes. The injection pressure decreases with time for constant mass injection flux of ScCO2 (m˙). Injected ScCO2 flows upward and spreads laterally below the caprock. An evolving capillary transition zone is one of the main features of this study. Below the capillary transition zone, the diffusive boundary layer of dissolved CO2 becomes unstable depending on the injection pressure (PScCO2), permeability (k) and capillary entry pressure (Pc0). The evolution of ScCO2 and dissolved CO2 plume and injection pressure history are directly proportional to m˙/k. The evolution rate and the onset time of gravitational instability are inversely proportional to k. For very small and large m˙/k ratio, gravitational instability may not occur. Higher permeability yields more effective CO2 dissolution trapping and dissolution flux increases after onset of convection. For continuous injection case, the plume tip position varies as the power law of time tn where 0.6 < n < 0.85 where t is in years and plume tip position is in meter.

The effect of size and aspect ratio on the trapped field properties of single grain, Y–Ba–Cu–O bulk superconductors

Bulk, single grain (RE)Ba2Cu3O7−δ [(RE)BCO, where RE is a rare earth element or yttrium] high temperature superconductors exhibit significant potential for use in a variety of engineering applications due to their ability to trap large magnetic fields, which can be up to ten times greater than those generated by conventional, iron-based magnets. Limitations on the maximum size to which single grains can be grown, however, are a major obstacle to the further development of these materials. Indeed, multiple samples are often required to achieve the required superconducting properties in particular applications. The geometry of bulk (RE)BCO single grain samples plays an important role in determining the superconducting properties of a given technical arrangement. In order to gain a better understanding of the full application potential of bulk single grain superconductors, three relatively long, cylindrical YBCO single grains of different diameters were fabricated and their trapped field and total trapped flux measured at 77 K as a function of sample height. The effects of size and aspect ratio of YBCO single grains on these key applied properties have been investigated experimentally and the results compared qualitatively with the predictions of an established theoretical model. Conclusions based on the trapped field measurements on a variety of single grain samples are presented in this study and the possibilities of using assemblies of smaller samples for engineering devices, in particular, are discussed.

Stable Levitation of Superconducting Myxines of Galathea Plasma Traps

Designing magnetic systems of Galathea plasma traps on the basis of levitating superconducting magnetic coils requires searching for their stable levitating states. For this purpose, proceeding from the property of superconductors to preserve the trapped magnetic flux, the potential energy of a system of several coaxial superconducting rings (one of the rings is fixed) with given trapped magnetic fluxes is obtained as an analytic function of the coordinates of the free rings along the system axis and angular deviations of their axes from the common axis of the system in a uniform gravity field in the thin-ring approximation. Computations demonstrate that, under certain values of physical parameters (the trapped magnetic flux and the dimensions and masses of the rings), this dependence has local minima, which correspond to stable equilibrium states of the levitating rings. For high-temperature superconducting (HTSC) rings and short-circuited HTSC coils manufactured for experiments on levitation, equilibrium states are found in different cases by calculating the aforementioned dependence of the potential energy. In the case where the magnetic fluxes trapped by the rings have the same signs, the calculated equilibrium levitating states of an HTSC ring in the field of a short-circuited HTSC coil (or an HTSC ring), namely, states that are stable against vertical displacements and angular deviations of the axis from the vertical, are implemented experimentally.