Strike Point Research Articles

Surrogate approximation of the Grad–Shafranov free boundary problem via stochastic collocation on sparse grids

In magnetic confinement fusion devices, the equilibrium configuration of a plasma is determined by the balance between the hydrostatic pressure in the fluid and the magnetic forces generated by an array of external coils and the plasma itself. The location of the plasma is not known a priori and must be obtained as the solution to a free boundary problem. The partial differential equation that determines the behavior of the combined magnetic field depends on a set of physical parameters (location of the coils, intensity of the electric currents going through them, magnetic permeability, etc.) that are subject to uncertainty and variability. The confinement region is in turn a function of these stochastic parameters as well. In this work, we consider variations on the current intensities running through the external coils as the dominant source of uncertainty. This leads to a parameter space of dimension equal to the number of coils in the reactor. With the aid of a surrogate function built on a sparse grid in parameter space, a Monte Carlo strategy is used to explore the effect that stochasticity in the parameters has on important features of the plasma boundary such as the location of the x-point, the strike points, and shaping attributes such as triangularity and elongation. The use of the surrogate function reduces the time required for the Monte Carlo simulations by factors that range between 7 and over 30.

Integrated ELM and divertor power flux control using RMPs with low input torque in EAST in support of the ITER research plan

Experiments have been carried out at the EAST tokamak to study ITER-relevant scenario integration issues, related to edge localized mode (ELM) control in H-mode plasmas by the application of three-dimensional (3D) resonant magnetic perturbations (RMPs), which have a large impact on the execution of the ITER research plan. The EAST experiments have successfully demonstrated ELM suppression at normalized torque inputs similar to ITER. The application of RMP fields with high toroidal mode number (n = 4) reduces the impact of ELM control on energy and particle confinement compared to those use lower n (n = 1, 2) RMPs. Injection of successive pellets is found to be effective in increasing the plasma density in ELM-suppressed H-modes and reducing the divertor power without triggering large ELMs at EAST. Access to high recycling and radiative divertor conditions while maintaining ELM suppression has been demonstrated in EAST by the use of gas fuelling and neon impurity seeding. Both approaches have been found to be effective in reducing power fluxes to the divertor strike points in near-separatrix lobes for both n = 2 and n = 4 RMPs. However, reduction of power fluxes in off-separatrix lobes is only effective for n = 4 RMP application, which is consistent with magnetic topology modelling (including plasma response) results showing a shallow penetration into the confined plasma region of field lines connected to these lobes compared to n = 2. The EAST results support the use of high n 3D fields for ELM suppression in ITER high Q DT scenarios since they provide optimum integration features regarding energy and particle confinement, pellet fuelling, radiative divertor operation while eliminating ELM transient power loads and being compatible with low torque input.

SOLPS-ITER modeling of divertor scenarios for EU-DEMO

We developed a first single null divertor scenario for EU-DEMO with the SOLPS-ITER code, including all charge states of D, He and Ar in the simulation and kinetic analysis of the neutral gas, but still leaving out drifts. Our results suggest that a partially detached divertor condition can indeed be obtained, with a corresponding peak heat flux on targets to ≈2 MW m−2, within the expected tolerable steady-state limits. The plasma re-attaches ≈30 cm (measured along the plate) from the low field side strike point deep in the SOL, with a consequent raise in the electron temperature up to ≈16 eV outside the detached region, which requires further analysis to assess a possible role of sputtering, especially considering W self-sputtering. The plasma we developed exhibits Z eff ≈ 1.9 in the core, and a pumping speed a few hundred’s m3 s−1 to maintain steady-state; this points to the need of further studies to better characterize the He accumulation in the core region.

Predictive modelling of liquid metal divertor: from COMPASS tokamak towards Upgrade

Following ELMy H-mode experiments with liquid metal divertor target on the COMPASS tokamak, we predict the behavior of a similar target on COMPASS Upgrade, where it will be exposed to surface heat fluxes even higher than those expected in the future EU DEMO attached divertor. We simulate the heat conduction, sputtering, evaporation, excitation and radiation of lithium and tin in the divertor area. Measured high-resolution data from COMPASS tokamak were rescaled towards the Upgrade based on many established scalings. Our simulation then yields the amount of released metal which ranges from 4 mg s−1 upto 12 g s−1 depending mainly on the geometry and Li/Sn choice, quite independently from active cooling or strike point sweeping.

Divertor power loads and scrape off layer width in the large aspect ratio full tungsten tokamak WEST

WEST is a full W tokamak with an extensive set of diagnostics for heat load measurements especially in the lower divertor. It is composed by infrared thermography, thermal measurement with thermocouples and fibre Bragg grating embedded few mm below the surface and flush mounted Langmuir probes. A large database including different magnetic equilibrium and input power is investigated to compare the heat load pattern (location, amplitude of the peak and heat flux decay length) on the inner and outer strike point regions: from the first ohmic diverted plasma (obtained during the second experimental campaign C2 in 2018) up to the high power (8 MW total injected) and high energy (up to 90 MJ injected energy in lower single null configuration) experiments performed in the last experimental campaign (C4 in 2019). Concerning the peak location, a good agreement (<1 cm) is obtained between thermal inversions and flush-mounted LP measurements. The peak heat flux from the whole set of diagnostics is in good agreement and mainly in the ±20% range, while the heat flux decay length reported on the target shows significant discrepancy between diagnostics and location in the machine (±40% range). Despite such discrepancy, heat flux decay length at target is found to scale mainly with the magnetic flux expansion through the variation of the X-point height, as expected. The improved plasma performances achieved during C4 enabled to reach significant heat load in the divertor, up to 6 MW m−2 with 4 MW of additional heating power showing the capability to reach the ITER relevant heat load (10 MW m−2 steady state) with about 7 MW of additional power in L-mode discharge. The heat load distribution is clearly asymmetric with a 3/4 and 1/4 distribution on the outer and inner strike point region respectively for the parallel heat flux.

Modeling of ExB effects on tungsten re-deposition and transport in the DIII-D divertor

Mixed-material DIVIMP–WallDYN modeling, now incorporating ExB drifts, is presented that simultaneously reproduces tungsten (W) erosion and deposition patterns observed during the DIII-D metal rings campaign, in which a toroidally symmetric set of W-coated tiles were installed in the carbon (C) DIII-D divertor. Since most reactor plasma facing component (PFC) designs call for mixed-material environments, including ITER’s W/Be environment, the divertor targets will quickly evolve into reconstituted surfaces of multiple elements. This work identifies controlling physics that affects material migration patterns in the divertor, which impact PFC lifetimes and impurity leakage from the divertor to the core. These simulations indicate that radial and poloidal ExB transport dominates over parallel force balance for high-Z impurities such as W in the divertor region of DIII-D. It is demonstrated that ExB drifts are required to reproduce the experimental observation of non-local W and C co-accumulation in a band ∼7–9 cm outboard of the outer-strike-point (OSP) W source, for attached L-mode conditions in the unfavorable ion grad-B drift direction. In addition, W gross erosion is localized to the region outboard of the OSP, as the formation of C co-deposits suppresses W erosion at the strike point. Time-dependent simulations with scaled ExB impurity drifts (60% of the OEDGE-calculated drift velocity) and W re-erosion quantitatively reproduce these features, including depth-resolved W/C ratios, within a factor of 2 over ∼115 s of accumulated plasma exposure. The location of co-deposition regions is shown to be well-represented by an analytic leakage model, driven largely by poloidal ExB drifts. Qualitative agreement is also found between campaign-integrated W deposition measurements and simulations for the favorable ion grad-B drift direction, the standard mode of operation for most tokamaks. These results imply that a long-term inward radial migration of material from the outer divertor through the private flux region may occur in future devices.

Efficiency of composted vinasse in the production of basil (Ocimum basilicum L.) under greenhouse conditions

The aim of this study was to determine the effectiveness of vinasse, which is known to be a good source of organic matter and potassium in the production of an aromatic plant. In this context, the vinasse, which is a food industry waste, was composted and applied to the soil alone and mixed with chemical fertilizers in different doses [Only chemical fertilization-control (C), vinasse compost 0.5 t ha-1 (VC-0.5), vinasse compost 0.5 t ha-1 + chemical fertilization 0.5 t ha-1 (VC-0.5+CF), vinasse compost 1 t ha-1 (VC-1), vinasse compost 1 t ha-1 + chemical fertilization 1 t ha-1 (VC-1+CF)] and thus, basil (Ocimum basilicum L.) was produced under greenhouse conditions. Plants were harvested three times in a row when they reached the flowering period. Morphological (number of branches, flower spike height, plant height, fresh weight), agronomic (green herb/drug yield, dry weight) and technological (essential oil ratio, essential oil composition, color value) parameters were examined in the harvested samples. According to the results obtained; while the highest fresh weight, green herb yield and dry weight were obtained by VC+CF, the highest essential oil ratio in the plant was observed in VC. The striking point here is that these results were obtained with 0.5 t ha-1 application rate of the compost. The findings obtained from this study reveal that the compost can be used in basil cultivation together with chemical fertilization.

ELM and inter-ELM heat and particle flux to a secondary divertor in the DIII-D tokamak

DIII-D edge-localized-modes (ELM) discharges with a secondary X-point inside the vessel were used to evaluate the power distribution between the primary and secondary divertors. The magnetic balance, defined by the distance between the primary and secondary separatrices at the outer midplane (dRsep), was varied from −5 mm (lower-single-null, LSN) to +16 mm (upper-single-null, USN). We find that the secondary divertor receives up to 1/3 of the total heat flux (primary + secondary divertors), and it is dominated by the ELM-driven flux. Both the radially-integrated and the peak heat flux to the secondary divertor decay below ∼50% of the maximum as dRsep is varied from −5 to +6 mm, but the integrated heat flux decay flattens out and it would take dRsep above ∼25 mm to reduce the ELM heat flux to the secondary divertor below 10% of the one deposited to a well-defined SN. Both the secondary inner strike point (ISP) and outer strike point receive heat flux during ELMs. The peak heat flux is comparable in both strike points for dRsep < 10 mm, but the ISP receives less than 15% of the total flux. This is experimental evidence that the secondary inner divertor region receives significant ELM flux which should be taken into account for the design of future generation tokamaks.

Computation of Lightning Current from Electric Field Based on Laplace Transform and Deconvolution Method

A method for computation of the lightning channel base current from the corresponding vertical component of lightning electric field was presented. The algorithm was developed by applying Laplace transform. The lightning current was estimated from its deconvolution with a special transfer function. The transfer function includes information about geometry and physical properties of entire lightning impulse generation system. The method was verified for a Heidler-type base current and a MTLL model of its propagation within the lightning channel. Research was done for close, middle, and far distance to the lightning strike point. Optimum performance was obtained for the middle distance of several kilometers where the electrostatic, induction, and radiation components of the transfer function were of the same range. An analysis was done for input electric field with and without noise superimposed on its time domain waveform. Relative uncertainties for the electric field and calculated lightning channel base current were similar each other. The presented approach can substantially increase a number of lightning current parameters which can be identified on the basis of its electric field signature. This method can be applied by the lightning location systems using preprocessing which increases the timing efficiency of the transfer function estimation.

Assessment of filtered cameras for quantitative 2D analysis of divertor conditions during detachment in JET L-mode plasmas

Estimates for 2D distributions of electron temperature, , electron density, , and atomic deuterium density, , in the JET divertor volume have been inferred from deuterium Balmer line intensity ratios obtained from tomographic reconstructions of divertor camera measurements. This enables also investigation of ionization, , and recombination, , rates. The analysis shows a decrease of to 0.5–1.0 throughout the outer divertor during detachment in low-confinement (L-mode) plasmas. Simultaneously, the high- region and the distribution in the outer divertor are observed to elongate and shift from the outer strike point towards the X-point. The observations are in qualitative agreement and follow the same sequence with modelling predictions of EDGE2D-EIRENE simulations of a density scan. While the method was found to provide good representation of the evolution of volumetric recombination during detachment, in agreement with the simulations, the movement of the ionization front upstream could not be followed due to lack of spatial overlap between the ionization region and the necessary emission distributions. Consequently, the representation of the ionization conditions and the particle balance in the detached outer divertor are compromised.

Characterizing the plasma-induced thermal loads on a 200 kW light-ion helicon plasma source via infra-red thermography

The light-ion helicon plasma source of the Proto-MPEX linear plasma device has been recently upgraded to enable pulsed (0.5–1 s) operation up to 200 kW. The main objective of this work is to report on the plasma-induced surface heat fluxes incident on the helicon window during high power operation (60–150 kW net power) for the purpose of the design of the upcoming material plasma exposure eXperiment (MPEX). The IR imaging system and associated physics models for the extraction of surface heat fluxes are presented. Experimental results demonstrate that the control of the plasma strike point via magnetic flux mapping and the use of dedicated limiters is effective at reducing the heat loads on the dielectric window. Moreover, it is found that the flux mapping must create a gap between the plasma and the dielectric window of at least the plasma radial decay length. Extrapolated to 200 kW net RF power, this mode of operation can reduce the power lost to the dielectric window by 33%. The results presented have direct application to the design of high-powered helicon plasma sources that operate in a steady state. Examples include linear divertor simulators such as MPEX, electric thrusters, negative ion sources for NBI and linear plasma–material interaction test stands.

Synchronized Tissue Acquisition Techniques for Novel Biomarker Discovery: Are You Ready to Waltz?

Synchronized Tissue Acquisition Techniques for Novel Biomarker Discovery: Are You Ready to Waltz?

The idiosyncratic characteristics of Turkish REITs: evidence from financial ratios

PurposeThis paper aims to determine the specific financial ratio's effects on market value and return of assets for Turkish real estate investment trusts (REITs) traded at Istanbul Stock Exchange (ISE). The paper intends to define liquidity ratios, financial structure ratios, return ratios and stock performance ratios related to market value and return of asset.Design/methodology/approachThe study includes 17 REITs traded in ISE. The period of study is specified as the year from 2009 to 2018. Panel data analysis is applied in this study. Dependent variables are current market value and return of assets, independent variables are 12 financial ratios, which are considered to explain the model significantly. These ratios will be calculated from audited year-end balance sheets for specific periods throughout at least ten years as time series. Two different models and hypotheses have been established to identify the financial ratios that affect the market value and return of assets for REITs.FindingsAccording to the results, long-term financial loans/total assets, return of equity and working capital ratio are negatively correlated with market value, while market value/book value and total assets are correlated positively. On the other hand, market value/book value ratio, price/earning ratio, long-term financial loans/total assets and earnings per share are correlated with return of assets. REITs have high levels of financial leverage, especially in foreign currency. The striking point is that REITs hardly ever do not use financial derivatives to hedge their position again currency and interest rate risk. This approach makes the financial structures of REITs vulnerable and fragile against market volatility.Originality/valueIn Turkey, as an example of an emerging market, financial borrowing does not increase the return rates and market value for REITs due to market's idiosyncratic properties. This finding provides substantial insight into how the debt and equity allocation of Turkish REITs should be structured. Also, it has been observed that forward-looking expectations are considered more than the current situation in the market.

Global ground strike point characteristics in negative downward lightning flashes – Part 2: Algorithm validation

Abstract. At present the lightning flash density is a key input parameter for assessing the risk of occurrence of a lightning strike in a particular region of interest. Since it is known that flashes tend to have more than one ground termination point on average, the use of ground strike point densities as opposed to flash densities is more appropriate. Lightning location systems (LLSs) do not directly provide ground strike point densities. However, ingesting their observations into an algorithm that groups strokes into respective ground strike points results in the sought-after density value. The aim of this study is to assess the ability of three distinct ground strike point algorithms to correctly determine the observed ground-truth strike points. The output of the algorithms is tested against a large set of ground-truth observations taken from different regions around the world, including Austria, Brazil, France, Spain, South Africa and the United States of America. These observations are linked to the observations made by a local LLS in order to retrieve the necessary parameters of each lightning discharge, which serve as input for the algorithms. Median values of the separation distance between the first stroke in the flash and subsequent ground strike points are found to vary between 1.3 and 2.75 km. It follows that all three of the algorithms perform well, with success rates of up to about 90 % to retrieve the correct type of the strokes in the flash, i.e., whether the stroke creates a new termination point or follows a pre-existing channel. The most important factor that influences the algorithms' performance is the accuracy by which the strokes are located by the LLS. Additionally, it is shown that the strokes' peak current plays an important role, whereby strokes with a larger absolute peak current have a higher probability of being correctly classified compared to the weaker strokes.

Global ground strike point characteristics in negative downward lightning flashes – Part 1: Observations

Abstract. Information about lightning properties is important in order to advance the current understanding of lightning, whereby the characteristics of ground strike points (GSPs) are in particular helpful to improving the risk estimation for lightning protection. Lightning properties of a total of 1174 negative downward lightning flashes are analyzed. The high-speed video recordings are taken in different regions, including Austria, Brazil, South Africa and the USA, and are analyzed in terms of flash multiplicity, duration, interstroke intervals and ground strike point properties. According to our knowledge this is the first simultaneous analysis of GSP properties in different regions of the world applying a common methodology. Although the results vary among the data sets, the analysis reveals that a third of the flashes are single-stroke events, while the overall mean number of strokes per flash equals 3.67. From the video imagery an average of 1.56 GSPs per flash is derived, with about 60 % of the multiple-stroke flashes striking the ground in more than one place. It follows that a ground contact point is struck 2.35 times on average. Multiple-stroke flashes last on average 371 ms, whereas the geometric mean (GM) interstroke interval value preceding strokes producing a new GSP is about 18 % greater than the GM value preceding subsequent strokes following a pre-existing lightning channel. In addition, a positive correlation between the duration and multiplicity of the flash is presented. The characteristics of the subset of flashes exhibiting multiple GSPs is further examined. It follows that strokes with a stroke order of 2 create a new GSP in 60 % of the cases, while this percentage quickly drops for higher-order strokes. Further, the possibility of forming a new lightning channel to ground in terms of the number of strokes that conditioned the previous lightning channel shows that approximately 88 % developed after the occurrence of only one stroke. Investigating the time intervals in the other 12 % of the cases when two or more strokes re-used the previous lightning channel showed that the average interstroke time interval preceding a new lightning channel is found to be more than twice the time difference between strokes that follow the previous lightning channel.

Red meat allergy in patients with IgE antibodies specific for galactose-alpha-1.3-galactose; A case series from Turkey

Study aimGalactose-α-1,3-galactose (alpha-Gal) syndrome is a delayed-type hypersensitivity reaction that occurs after consumption of mammalian meat and mammalian products. Our aim was to analyze patients in our population with alpha-Gal syndrome and to present their results. Materials and methodsOur study included 18 patients exhibiting allergic symptoms after consumption of mammalian meat and mammalian products between 2018 and 2019. Retrospective examination of these patients’ files enabled us to examine the duration of onset of their allergic symptoms, the extent of their allergies, and their familial history, blood type, and comorbidities, as well as the existence of atopy, their place of residence and their skin test results. ResultsWhile 14 out of 18 patients included in the study have ongoing meat allergy, 4 of them recovered from their allergy. All patients were living in the countryside and had a history of contact with ticks during the hazelnut harvest. The median age was 37.44±11.55 years. Time to onset of symptoms after consumption of red meat was 2.68±2.58hours. Skin prick tests with cetuximab were positive for 8 of 9 patients agreeing to advanced research, while the patient with a negative test result was in the group that recovered from meat allergy. We nevertheless detected that serum galactose-alpha-1,3-galactose-specific IgE values were positive for all 9 patients. ConclusionThe most striking point in our study was that most of our patients were female and that all patients reported a history of contact with ticks at hazelnut harvest.

Experimental study of the influence of gas puff locations on H-mode boundary plasmas with argon seeding on EAST

To investigate the optimal scenario of impurity seeding to obtain divertor plasma detachment for target protection, experiments with Ar&D2 seeding from two different poloidal locations, the upper outer (UO) divertor target and lower outer (LO) target, were carried out on EAST. Partial energy detachment (the electron temperature near the strike point T e,spt ⩽ 10 eV) were obtained with Ar&D2 mixture puffing from the UO target and, for the first time, from the LO target into H-mode plasmas in the upper single null (USN) configuration. The peak heat flux q t on the UO target was significantly reduced (by ∼80%). The rollover of ion flux density j s did not appear probably due to insufficient momentum loss, which is independent of the puff locations. The poloidal asymmetries of particle and heat fluxes on the targets have also been investigated. The UO-dominant asymmetry of particle flux was reversed, while the UO-dominant asymmetry of heat flux was mitigated but not reversed. The plasma confinement dropped by only 14% and 8.2% in the LO-puff case and UO-puff case, respectively, during detachment. The high level of C may contributed greatly to the higher radiation in the bulk plasma region and the greater decline in W MHD in the LO-puff case.

Effects of a coherent mode on the redistribution of divertor particle flux in HL-2A H-mode plasmas

The effects of a coherent mode (CM) at a frequency of f = 13–16 kHz on the redistribution of divertor particle flux have been studied in HL-2A H-mode plasmas using multiple diagnostics. The experimental results demonstrate that a CM localized at the middle of the pedestal results in outward particle transport, limiting the growth of the pedestal density gradient in the recovery phase of the pedestal, leading to a substantial increase in the localized particle flux striking the outer divertor target, which clearly deviates from the primary peak at the strike point. These observations indicate that the CM might play a crucial role in redistributing the divertor particle flux, which is important for understanding and controlling the divertor heat flux in future fusion-relevant devices.

Insulin Resistance as a Common Link Between Current Alzheimer's Disease Hypotheses.

Almost 115 years ago, Alois Alzheimer described Alzheimer's disease (AD) for the first time. Since then, many hypotheses have been proposed. However, AD remains a severe health public problem. The current medical approaches for AD are limited to symptomatic interventions and the complexity of this disease has led to a failure rate of approximately 99.6%in AD clinical trials. In fact, no new drug has been approved for AD treatment since 2003. These failures indicate that we are failing in mimicking this disease in experimental models. Although most studies have focused on the amyloid cascade hypothesis of AD, the literature has made clear that AD is rather a multifactorial disorder. Therefore, the persistence in a single theory has resulted in lost opportunities. In this review, we aim to present the striking points of the long scientific path followed since the description of the first AD case and the main AD hypotheses discussed over the last decades. We also propose insulin resistance as a common link between many other hypotheses.

Evaluation of lightning location using measured induced voltage obtained from distribution power networks

Lightning location is a significant issue in the protection of transmission lines, renewable energy sources, and electrical equipment. In this article, a new technique for the determination of lightning striking points is been proposed. This method is depending on measured values of lightning-induced voltage obtained from distribution power lines in the vicinity of the lightning channel. The proposed method considers lightning location as well as lightning current wave shape at the channel base. It was validated using a number of measured return stroke currents, and the outcomes are debated accordingly. All electromagnetic field components were taken into consideration in the proposed method, and lightning current wave shape was determined in contrast with the other, widely used methods. Evaluated lightning current wave shapes, based on local measured data, can be used to examine and improve existing protection schemes in renewable energy generation farms, transmission lines, and other power sites. Moreover, lightning maps and ground flash density can be obtained from the evaluated lighting location data to be used in lightning risk assessment studies.