Effectiveness of the Chebyshev Approximation in Magnetic Field Line Tracking

The tracking of magnetic field lines can be very expensive, in terms of computational burden, when the field sources are numerous and have complex geometries, especially when accuracy is a priority, because an evaluation of the field is required in many situations. In some important applications, the computational cost can be significantly reduced by using a suitable approximation of the field in the integrated regions. This paper shows how Chebyshev polynomials are well-suited for field interpolation in magnetic field-line tracking, then discusses the conditions in which they are most appropriate, and quantifies the effectiveness of parallel computing in the approximation procedures

A complex phenotype in a child with familial HDL deficiency due to a novel frameshift mutation in APOA1 gene (apoA-IGuastalla)

Background We describe a kindred with high-density lipoprotein (HDL) deficiency due to APOA1 g ene mutation in which comorbidities affected the phenotypic expression of the disorder. Methods An overweight boy with hypertriglyceridemia (HTG) and HDL deficiency (HDL cholesterol 0.39 mmol/L, apoA-I 40 mg/dL) was investigated. We sequenced the candidate genes for HTG ( LPL, APOC2 , APOA5, GPIHBP1, LMF1 ) and HDL deficiency ( LCAT, ABCA1 and APOA1 ), analyzed HDL subpopulations, measured cholesterol efflux capacity (CEC) of sera and constructed a model of the mutant apoA-I. Results No mutations in HTG-related genes, ABCA1 and LCAT were found. APOA1 sequence showed that the proband, his mother and maternal grandfather were heterozygous of a novel frameshift mutation (c.546_547delGC), which generated a truncated protein (p.[L159Afs*20]) containing 177 amino acids with an abnormal C-terminal tail of 19 amino acids. Trace amounts of this protein were detectable in plasma. Mutation carriers had reduced levels of LpA-I, preβ-HDL and large HDL and no detectable HDL-2 in their plasma; their sera had a reduced CEC specifically the ABCA1-mediated CEC. Metabolic syndrome in the proband explains the extremely low HDL cholesterol level (0.31 mmol/L), which was half of that found in the other carriers. The proband's mother and grandfather, both presenting low plasma low-density lipoprotein cholesterol, were carriers of the β-thalassemic trait, a condition known to be associated with a reduced low-density lipoprotein cholesterol and a reduced prevalence of cardiovascular disease. This trait might have delayed the development of atherosclerosis related to HDL deficiency. Conclusions In these heterozygotes for apoA-I truncation, the metabolic syndrome has deleterious effect on HDL system, whereas β-thalassemia trait may delay the onset of cardiovascular disease

High current and low q95 scenario studies for FAST in the view of ITER and DEMO

The Fusion Advanced Study Torus (FAST) has been proposed as a possible European satellite, in view of ITER and DEMO, in order to: a) explore plasma wall interaction in reactor relevant conditions b) test tools and scenarios for safe and reliable tokamak operation up to the border of stability c) address fusion plasmas with a significant population of fast particles. A new FAST scenario has been designed focusing on low-q operation, at plasma current IP=10 MA, toroidal field BT=8.5T, with a q95=2.3 that would correspond to IP=20 MA in ITER. The flat-top of the discharge can last a couple of seconds (i.e. half the diffusive resistive time and twice the energy confinement time), and is limited by the heating of the toroidal field coils. A preliminary evaluation of the end-of-pulse temperatures and of the electromagnetic forces acting on the central solenoid pack and poloidal field coils has been performed. Moreover, a VDE plasma disruption has been simulated and the maximum total vertical force applied on the vacuum vessel has been estimated

Model for screening of resonant magnetic perturbations by plasma in a realistic tokamak geometry and its impact on divertor strike points

This work addresses the question of the relation between strike-point splitting and magnetic stochasticity at the edge of a poloidally diverted tokamak in the presence of externally imposed magnetic perturbations. More specifically, ad-hoc helical current sheets are introduced in order to mimic a hypothetical screening of the external resonant magnetic perturbations by the plasma. These current sheets, which suppress magnetic islands, are found to reduce the amount of splitting expected at the target, which suggests that screening effects should be observable experimentally. Multiple screening current sheets reinforce each other, i.e. less current relative to the case of only one current sheet is required to screen the perturbation.Comment: Accepted in the Proceedings of the 19th International Conference on Plasma Surface Interactions, to be published in Journal of Nuclear Materials. Version 2: minor formatting and text improvements, more results mentioned in the conclusion and abstrac

A Parametrical Determination of the Influence Region of Holes in Electromagnetic Devices by the Compensation Theorem

In the optimal design of electromagnetic devices, the robustness is a critical aspect. In the modern robust optimization procedures, the evaluation of suitable partial derivatives is required at each step of the search process; the estimate of the sensitivity is required also in non robust optimizations if the robustness of the final design with respect to a number of independent parameters must be assessed. On the other hand, the tolerance analysis is a widely adopted tool in the analysis of electromagnetic devices, whose main aim is to assess the impact of some independent uncertain parameters (e.g. geometrical dimensions or materials properties) on a device performance as, for example, the electromagnetic field in a volume of interest. Similar considerations apply when a general property in nominal design, such as symmetry, is lost due to non symmetrical deformations. In both cases - robust design and tolerance analysis - if assuming a linear behavior of the system, the classical compensation theorem can reveal to be a quite powerful tool

Analysis of Stress Induced by Plasma Disruption on Vacuum Vessel through Multi-physics Modeling.

The analysis of the stresses induced on the vacuum vessel (VV) of a Tokamak and its internal components by the plasma instabilities, such as plasma disruptions, also following a Vertical Displacement Event (VDE) is one of the major concern in the Tokamak design. So the availability of a fast simulation tool for evaluating different design options, also able to perform parametric analysis, is highly attractive to define the project requirements and to verify the conceptual design. To respond to this wish, a methodology based on the multi-physics modeling capability offered by the Comsol® software platform was developed. It consists in coupled simulations based on the data sharing between two 2D axisymmetric model, everyone coupled with a corresponding 3D model, shifted each other of 10 degrees. In the 2D axisymmetric model of every couple, the magnetic and electric fields generated by the plasma VDE and disruption, are calculated imposing the plasma time evolution as input. In the corresponding 3D model only the mechanical structures are present and on them the Electric and Magnetic fields are extruded, determining so the induced currents diffusion in the passive conductors. Then the resulting Lorentz's forces are imposed as body loads on the mechanical structures, so a linear stress analysis can be carried out after the constraints assignment. The same procedure is followed with the second couple of 2D/3D models for check purposes, comparing some proper physical quantities, such as the total induced current flowing on the VV. In this paper the methodology is presented by reporting the simulation of a double null plasma VDE, lasting c.a. 100 ms, followed by a full 5.5 MA plasma current quench in about 40 ms

Electromagnetic analysis with Equivalent Models of Complex Conducting Structures

Complex conducting structures, whenever they are not the focus of interest of the electromagnetic analysis, are approximated by means of equivalent simplified models. Composite materials can be treated as homogeneous anisotropic media. Complex 3D structures can be approximated by means of 2D axisymmetric models or lumped parameter systems. The material properties or the parameters of the equivalent models are determined in such a way as to preserve the interaction with the remaining structures. Upper and lower bounds are established for electromagnetic quantities of interest for plates with circular holes and quasi-axisymmetric structures in fusion device

EX-VESSEL MAGNETIC MEASUREMENTS IN JET: A CRITICAL ASSESSMENT OF THE COLLAR PROBE

The paper reviews a set of magnetic probes which was installed in JET in order to improve the field measurements in the proximity of the iron, and focuses in particular on one of them. The set consists of six Limb probes, attached to the upper horizontal iron yokes, and one Collar Probe, inserted in the collar region of the iron structure. The probes include pick-up coils, flux loops, Hall sensors, and a temperature sensor. The data provided by the system are regularly acquired and recorded within the set of JET Pulse Files. They can be used in studies implying measurement of the stray field due to the residual magnetization, as well as for all the modeling activities involving 3D studies, in particular resistive wall mode studies, more accurate modeling for the vertical stabilization, interactions between NBI and magnetic field. In addition, the experience gained with Hall transducers is considered valuable in view of their potential use in ITER. Unlike the limb probes, the collar probe did not pass the functional commissioning, due to an unexpected discrepancy between the signals from Hall sensors and pick-up coils. The analysis illustrated in the paper shows that a critical assessment of the local configuration and a suitable magnetic modeling solve the issue of the observed discordance, by putting it in relation with a local geometrical effect due to the peculiar shape of the ferromagnetic collar teeth. The improvement of magnetic models targeted to the prediction of signals produced by magnetic sensors is important, also considering that a large number of magnetic probes in ITER will be located close to the ferromagnetic inserts