Salvatore Ventre

Resistive wall mode control code maturity: progress and specific examples

Two issues of the resistive wall mode (RWM) control code maturity are addressed: the inclusion of advanced mode damping physics beyond the ideal MHD description, and the possibility of taking into account the influence of 3D features of the conducting structures on the mode stability and control. Examples of formulations and computational results are given, using the MARS-F/K codes and the CarMa code. The MARS-K calculations for a DIII-D plasma shows that the fast ion contributions, which can give additional drift kinetic stabilization in the perturbative approach, also drive an extra unstable branch of mode in the self-consistent kinetic modelling. The CarMa modelling for the ITER steady state advanced plasmas shows about 20% reduction in the RWM growth rate by the volumetric blanket modules. The multi-mode analysis predicts a weak interaction between the n = 0 and the n = 1 RWMs, due to the 3D ITER walls. The CarMa code is also successfully applied to model the realistic feedback experiments in RFX.

Differential vulnerability of retinal layers to early age-related macular degeneration: Evidence by SD-OCT segmentation analysis

PURPOSE We evaluated layer-by-layer retinal thickness in spectral-domain optical coherence tomography (SD-OCT), determined by automated segmentation analysis (ASA) software in healthy and early age-related maculopathy (ARM) eyes. METHODS There were 57 eyes (specifically, 19 healthy eyes under 60 years old, 19 healthy eyes over 60, and 19 ARM eyes) recruited into this cross-sectional study. The mean ages were 36.78 (SD, ±13.82), 69.89 (SD, ±6.14), and 66.10 (SD, ±8.67) years, respectively, in the three study groups. The SD-OCT scans were transferred into a dedicated software program that performed automated segmentation of different retinal layers. RESULTS Automated layer segmentation showed clear boundaries between the following layers: retinal nerve fiber layer (RNFL), ganglion cell layer plus inner plexiform layer (GCL+IPL), inner nuclear layer plus outer plexiform layer (INL+OPL), outer nuclear layer (ONL), and RPE complex. The thickness of the RNFL, ONL, and RPE layers did not show a statistically significant change across the three groups by ANOVA (P = 0.10, P = 0.09, P = 0.15, respectively). The thickness of GCL+IPL and INL+OPL was significantly different across the groups (P < 0.01), being reduced in the ARM eyes compared to healthy eyes, under and over 60 years old. CONCLUSIONS The early morphologic involvement of the GCL+IPL and INL+OPL layers in ARM eyes, as revealed by the ASA, could be related to early anatomic changes described in the inner retina of ARM eyes. This finding may represent a morphologic correlation to the deficits in postreceptoral retinal function in ARM eyes.

Numerical models of volumetric insulating cracks in eddy-current testing with experimental validation

This paper concerns fast electromagnetic modeling of volumetric cracks in conductive materials under eddy-current inspection. The underlying numerical method is described. The model is tested on cracks in aluminum structures employed in aeronautical manufacture. The computational results obtained with the method display satisfactory agreement with the respective experimental and numerical results obtained by representing cracks as nonconductive surfaces.

Coupled Three Dimensional Numerical Calculation of Forces and Stresses on the End Windings of Large Turbo Generators via Integral Formulation

A novel numerical approach to calculate the time evolution of the three dimensional distribution of the magnetic field and forces in the end winding regions of large turbine generators is presented. The proposed approach is based on an integral formulation for nonlinear magnetostatic problems. Its main advantage is the reduction of the discretization to only the conductors and magnetic materials. In this paper the solution of a coupled magnetostructural problem consisting in the calculation of the mechanical stresses and deformations caused by the electrodynamic forces is presented. The analysis is based on a time stepping simulation where the currents are derived from the integration of a lumped parameter model.

Effects of thick blanket modules on the resistive wall modes stability in ITER

In this paper we analyse the effects of three-dimensional ITER conducting structures on resistive wall modes (RWMs) growth rates. In particular, a highly detailed description of the thick ITER blanket modules (BMs) is given, with a volumetric mesh including slits, holes, pockets and an anisotropic resistivity to take into account cooling channels. Also other important details of the vacuum vessel are included, such as the outer triangular support, copper cladding, port extensions. To deal with the resulting huge computational model, a fast/parallel implementation of the CarMa code has been successfully developed and used. Both n = 1 (kink-like instability) and n = 0 (axisymmetric vertical instability) RWM are considered. The computational model is validated, on 2D test cases, by the consistency of fits to the growth rate with no-wall and ideal-wall limits calculated with MARS-F. Considering the full 3D model, the detrimental effect of ports on n = 1 growth rates is essentially counteracted by the beneficial effect of BMs.

A fast 3-D multipole method for eddy-current computation

The adaptive fast multipole method is combined with a three-dimensional (3-D) eddy-current integral formulation using edge-element-based shape functions to reduce the computational complexity and the memory requirements from order N/sup 2/ to nearly order N, where N is the number of edge-related unknowns. The effectiveness of this approach is verified with reference to the analysis of some 3-D problems of practical interest.

Coupling of nonlinear axisymmetric plasma evolution with three-dimensional volumetric conductors

With reference to toroidal fusion devices, we solve axisymmetric nonlinear evolutionary equilibrium equations, describing the plasma behaviour, self-consistently coupled to eddy currents equations, describing surrounding three-dimensional (3D) structures. This formulation allows the analysis of nonlinear plasma quasi-static evolution in the presence of 3D volumetric conductors. Several validations and test cases are presented, suggesting the potential applications of the proposed method to the analysis of various situations of scientific and technical interest for future fusion devices such as ITER and DEMO, like for instance disruptions.

A fast algorithm for solving 3-D eddy current problems with integral formulations

The aim of this paper is to present an efficient technique for the fast solution of three-dimensional eddy currents problems. The method combines Fast Fourier Transform (FFT) on a regular grid for the calculation of long-range interaction, and the standard method for evaluating the short range interaction.

GPU-accelerated analysis of vertical instabilities in ITER including three-dimensional volumetric conducting structures

In this paper, we study the axisymmetric vertical instability of elongated configurations, including the effect of volumetric three-dimensional conducting structures surrounding the plasma. In order to deal with the huge computational models arising from the realistic geometrical description, a GPU-based (graphics processing units) acceleration is pursued. The method is applied to some ITER configurations, for which the open-loop growth rates, the input–output transfer functions and the gain and phase margins are computed.

Interpolating wavelets for the solution of Maxwell equations in the time domain

A wavelet-based approach is presented for solving Maxwell equations. Full benefit is gained from the wavelets in terms of self-adaptativity of the resolution. Using interpolating wavelets allows for a simpler treatment of any operation involving the function, including the imposition of boundary conditions.