Response Of Plasma Facing Components In Tokamaks Due To Intense Energy Deposition Using Particle-In-Cell(pic) Methods

Damage to plasma-facing components (PFC) due to various plasma instabilities is still a major concern for the successful development of fusion energy and represents a significant research obstacle in the community. It is of great importance to fully understand the behavior and lifetime expectancy of PFC under both low energy cycles during normal events and highly energetic events as disruptions, Edge-Localized Modes (ELM), Vertical Displacement Events (VDE), and Run-away electron (RE). The consequences of these high energetic dumps with energy fluxes ranging from 10 MJ/m2 up to 200 MJ/m2 applied in very short periods (0.1 to 5 ms) can be catastrophic both for safety and economic reasons. Those phenomena can cause a) large temperature increase in the target material b) consequent melting, evaporation and erosion losses due to the extremely high heat fluxes c) possible structural damage and permanent degradation of the entire bulk material with probable burnout of the coolant tubes; d) plasma contamination, transport of target material into the chamber far from where it was originally picked. The modeling of off-normal events such as Disruptions and ELMs requires the simultaneous solution of three main problems along time: a) the heat transfer in the plasma facing component b) the interaction of the produced vapor from the surface with the incoming plasma particles c) the transport of the radiation produced in the vapor-plasma cloud. In addition the moving boundaries problem has to be considered and solved at the material surface. Considering the carbon divertor as target, the moving boundaries are two since for the given conditions, carbon doesn\u27t melt: the plasma front and the moving eroded material surface. The current solution methods for this problem use finite differences and moving coordinates system based on the Crank-Nicholson method and Alternating Directions Implicit Method (ADI). Currently Particle-In-Cell (PIC) methods are widely used for solving complex dynamics problems involving distorted plasma hydrodynamic problems and plasma physics. The PIC method solves the hydrodynamic equations solving all field equations tracking at the same time sample particles or pseudo-particles (representative of the much more numerous real ones) as the move under the influence of diffusion or magnetic force. The superior behavior of the PIC techniques over the more classical Lagrangian finite difference methods stands in the fact that detailed information about the particles are available at all times as well as mass and momentum transport values are constantly provided. This allows with a relative small number of particles to well describe the behavior of plasma even in presence of highly distorted flows without losing accuracy. The radiation transport equation is solved at each time step calculating for each cell the opacity and emissivity coefficients. Photon radiation continuum and line fluxes are also calculated per the entire domain and provide useful information for the entire energetic calculation of the system which in the end provides the total values of erosion and lifetime of the target material. In this thesis, a new code named HEIGHTS-PIC code has been created and modified using a new approach of the PIC technique to solve the three physics problems involved integrating each of them as a continuum providing insight on the plasma behavior, evolution along time and physical understanding of the very complex phenomena taking place. The results produced with the models are compared with the well-known and benchmarked HEIGHTS package and also with existing experimental results especially produced in Russia at the TRINITI facility. Comparisons with LASER experiments are also discussed

The Evidence for the Accelerating Universe: Endorsement and Robust Consistency

The 2011 Nobel Prize in Physics was awarded to researchers from the Supernova Cosmology Project and the High-z Supernova Search Team for the discovery of the accelerating expansion of the universe. In this paper, I provide a historical analysis of the supernova cosmology evidence put forward by these teams for the accelerating universe, in terms of an iterative model of scientific progress developed by Hasok Chang in the context of his study of the development of measurement standards. I argue, using the key concept of epistemic iteration, that the iterative model adequately accounts for evidence production in experimental science as well. In order to apply Chang’s model to the experimental evidence for the accelerating universe, I introduce the concept of endorsement as a particular mode of progress, and argue that supernova scientists produced an endorsed measurement system to claim evidence for their discovery. Furthermore, I show that the credibility of the evidence was not based on a particular measurement, rather, what proved to be decisive was the “robust consistency” of many individual results

Biogeographical Analysis of Abyssal Bottom Habitats: Using an Abiotic Province Scheme and Metazoan Occurrence Databases.

M.A. Thesis. University of Hawaiʻi at Mānoa 2017

Studio di un indicatore per la valutazione del rischio delprogetto nella metodologia dell’analisi costi benefici - Proposed risk indicators in the cost-benefit analisys methodology

Cost-benefit analysis allows to assess in advance the performance of investment projects through the calculation of appropriate indices, such as the NPV, the IRR, the B/C ratio. Performance indicators are, however, affected by the uncertainty inherent in the exercise of forecasting the future values of the physical and economic parameters generated by the project. Probability distribution of the expected values of each performance indicator can be determined, e.g., through Montecarlo simulations of the CBA model. Derived from the simulated probability distribution, the paper, starting from the definition of the loss function in the statistical decision theory, proposes a set of risk indicators (Index of absolute risk, Index of internal relative risk, Index of generalized relative risk), which include a "weight" function that models the level of aversion against the expected loss of the performance indices by the person who will bear the project risk.risk analysis, risk adversion, Montecarlo simulation, cost benefit analysis - rischio, avversione al rischio, simulazione Montecarlo, analisi costi benefici