300 research outputs found
Topology during magnetic reconnection events in RFX-mod
No full textThis paper is devoted to the characterization of magnetohydrodynamics (MHD) tearing modes causing plasma–wall interaction (PWI) in the
Reversed-Field eXperiment (RFX-mod) reversed-field pinch (RFP) device. We study an example of a magnetic reconnection event in a high
plasma current discharge. The PWI is measured via a fast camera looking at the graphite-covered inner wall, showing two separated footprints of neutral carbon radiation. A first, simple analysis shows that the phase-locking of m=1 tearing modes is the principal cause of
enhanced PWI, as it is well documented in literature. Many modes contribute to the phase-locking, actually more than those measured with
the magnetic sensors. A more refined analysis is based on calculation of the Connection Length to the wall and of the loss time of Maxwellian
ions via the Hamiltonian guiding center code ORBIT. This analysis confirms the importance of the m=1 phase-locking as a loss channel of
high-energy particles, which is the mechanism that dominates the PWI pattern, but an additional role of the m=0, n=7 mode is
highlighted, which is a new result for the RFP. The PWI mediated by the m=0 islands is milder, which is a good outlook for the RFX-mod2
upgraded device, currently in the assembly phase
Additive manufacturing of inorganic components using a geopolymer and binder jetting
No full textA large volume binder jetting printer was employed to fabricate prism-shaped geopolymer components. A two parts system was used, comprising: 1) a highly alkaline solution, which was jetted on a powder bed containing aggregates (sand particles), and 2) a reactive solid component (pure metakaolin or metakaolin plus fast setting cement), present in the powder bed. In order to be able to generate appropriate, defect-free powder layers and suitably discharge the powders from the hopper feeding the layer forming system, a granulation approach was employed. The jetted alkaline solution effectively reacted with the metakaolin powders present in the granules, forming a geopolymer. Printed geopolymer parts, fabricated with the addition of 30 wt% metakaolin, possessed a compressive strength of ~20 MPa, even with ~30 vol% of residual porosity, and no significant variation in the compressive strength was observed after leaving the printed parts submerged in water for 1 week
Towards reliability-based design of rockfall hybrid barriers and attenuators: A focus on the resistances
No full textThe conventional design approach for geotechnical structures presented in Eurocode 7 (EC7) shows limitations when dealing with rockfalls. To overcome these limitations, we propose the application of Reliability Based Design (RBD), which describes the relationship between the actions and the system's resistance through the definition of a reliability index. In this work, particular attention has been given to innovative rockfall protection structures such as hybrid barriers and/or attenuators. Considering the applicability of RDB approach, the paper focuses on the response of these structures to the impact of the block and their absorption capacity at different stress levels. In this context, numerical modelling represents a powerful solution to reproduce the behaviour of these structures subjected to dynamic impacts at different Kinetic Energy levels
Cold Consolidation of Pharmaceutical Waste Glass Powders Through Alkali Activation and Binder Jet 3D Printing
No full textThe recent COVID-19 emergency has led to an impressive increase in the production of pharmaceutical vials. This has led to a parallel increase in the amounts of waste glass; manufacturers typically recover material from faulty containers by crushing, giving origin to an unrecyclable fraction. Coarse fragments are effectively reused as feedstock for glass melting; on the contrary, fine powders (<100 microns), contaminated by metal and ceramic particles due to the same crushing operations, are landfilled. Landfilling is also suggested for pharmaceutical containers after medical use. This study aims at proposing new opportunities for the recycling of fine glass particles, according to recent findings concerning alkali activation of pharmaceutical glass, combined with novel processing, i.e., binder jetting printing. It has already been shown that pharmaceutical glass, immersed in low-molarity alkaline solution (not exceeding 2.5 M NaOH), undergoes surface dissolution and hydration; cold consolidation is later achieved, upon drying at 40–60 °C, by a condensation reaction occurring at hydrated layers of adjacent particles. Binder jetting printing does not realize a full liquid immersion of the glass powders, as the attacking solution is selectively sprayed on a powder bed. Here, we discuss the tuning of key parameters, such as the molarity of the attacking solution (from 2.5 to 10 M) and the granulometry of the waste glass, to obtain stable printed blocks. In particular, the stability depends on the formation of bridges between adjacent particles consisting of strong T-O bonds (Si-O-Si, Al-O-Si, B-O-Si), while degradation products (concentrating Na ions) remain as a secondary phase, solubilized by immersion in boiling water. Such stability is achieved by operating at 5 M NaOH
Ion and electron local transport inside Single Helicity islands in the Reversed Field Pinch
No full textThe ion and electron diffusion coefficients inside the helical magnetic core in a single helicity reversed field pinch (RFP) toroidal plasma have been numerical determined by a Monte Carlo test particle approach. A new algorithm aimed at approximating with polyhedra the magnetic surfaces obtained with Poincaré cross sections has been developed. Stationary simulations of test ion and electron transport have been performed: they allow the determination of the average diffusion coefficients inside the helical core both for ions and electrons, which are much lower than those found in standard multiple helicity plasmas. Results are discussed and compared with those found in previous RFP simulations. The technique may be relevant also for stellarator and tokamak studies
Analyse de la structure génétique des populations du mildiou de la vigne (Plasmopara viticola)
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