Anomalous losses of energetic particles in fusion plasmas

The confinement of energetic particles (EP) in nuclear fusion devices is studied in the presence of an oscillating electrostatic potential and an axi-symmetric magnetic equilibrium. Despite the poloidal and toroidal symmetries, radial transport is observed. The transport leads to an algebraic decaying loss time, which is at odds with diffusive transport that predicts a faster exponential decay. A dynamical explanation of the observed anomalous loss time decay is presented. It is shown that transport is characterized by Lévy flights that lead to super-diffusive poloidal transport and asym-metric non-Gaussian (Lévy) probability distribution functions of displacements. The anomalous scaling exponents are shown to be consistent with the Continuous Time Random Walk (CTRW) theory. The results imply that EP might efficiently slowed down by the thermal population before leaving the system. Also, the asymmetric transport can potentially lead to a net torque

On seed island generation and the non-linear self-consistent interaction of the tearing mode with electromagnetic gyro-kinetic turbulence

The multi-scale interaction of self-consistently driven magnetic islands with electromagnetic turbulence is studied within the three dimensional, toroidal gyro-kinetic framework. It can be seen that, even in the presence of electromagnetic turbulence the linear structure of the mode is retained. Turbulent fluctuations do not destroy the growing island early in its development, which then maintains a coherent form as it grows. The island is seeded by the electromagnetic turbulence fluctuations, which provide an initial island structure through nonlinear interactions and which grows at a rate significantly faster than the linear tearing growth rate. These island structures saturate at a width that is approximately $\rho_{i}$ in size. In the presence of turbulence the island then grows at the linear rate even though the island is significantly wider than the resonant layer width, a regime where the island is expected to grow at a significantly reduced non-linear rate. A large degree of stochastisation around the separatrix, and an almost complete break down of the X-point is seen. This significantly reduces the effective island width.Comment: Joint Varenna - Lausanne International Worksho

Síntesis de alil y vinilsilil alcoholes para la reacción de prins

En este Trabajo de Fin de Grado se estudian las posibilidades de síntesis de diferentes vinil- y alilsilil alcoholes y la posterior ciclopropanación del doble enlace de la molécula. Para llevarlo a cabo se ha partido siempre del fenildimetilalilsilano 1, previamente sintetizado, y se han utilizado diferentes aldehídos para observar la eficiencia de estas reacciones en función de la naturaleza de los aldehídos empleados y de las condiciones de reacción. Una vez obtenidos los alcoholes se procedió a la ciclopropanación del doble enlace mediante la reacción de Simmons- Smith para observar el alcance de la misma y su posible optimización.In this dissertation, I studied the synthetic possibilities of vinyl- and allylsilyl alcohols and the subsequent cyclopropanation of the double bond of the product. To carry out this study, the starting point has always been the phenyldimethylallylsilane 1, previously synthesized, and the use of different aldehydes in order to study the efficiency of these reactions depending on the aldehydes and their reaction conditions. Once the alcohols were obtained, I proceeded to the cyclopropanation of the double bond by means of the Simmons-Smith reaction, to observe the scope of the reaction and its possible optimization.Grado en Químic

Physics informed Neural Networks applied to the description of wave-particle resonance in kinetic simulations of fusion plasmas

The Vlasov-Poisson system is employed in its reduced form version (1D1V) as a test bed for the applicability of Physics Informed Neural Network (PINN) to the wave-particle resonance. Two examples are explored: the Landau damping and the bump-on-tail instability. PINN is first tested as a compression method for the solution of the Vlasov-Poisson system and compared to the standard neural networks. Second, the application of PINN to solving the Vlasov-Poisson system is also presented with the special emphasis on the integral part, which motivates the implementation of a PINN variant, called Integrable PINN (I-PINN), based on the automatic-differentiation to solve the partial differential equation and on the automatic-integration to solve the integral equation

A 5D gyrokinetic full-f global semi-lagrangian code for flux-driven ion turbulence simulations

International audienceThis paper addresses non-linear gyrokinetic simulations of ion temperature gradient (ITG) turbulence in tokamak plasmas. The electrostatic Gysela code is one of the few international 5D gyrokinetic codes able to perform global, full-f and flux-driven simulations. Its has also the numerical originality of being based on a semi-Lagrangian (SL) method. This reference paper for the Gysela code presents a complete description of its multi-ion species version including: (i) numerical scheme, (ii) high level of parallelism up to 500k cores and (iii) conservation law properties

Stable Deuterium-Tritium plasmas with improved confinement in the presence of energetic-ion instabilities

Providing stable and clean energy sources is a necessity for the increasing demands of humanity. Energy produced by Deuterium (D) and Tritium (T) fusion reactions, in particular in tokamaks, is a promising path towards that goal. However, there is little experience with plasmas formed by D-T mixtures, since most of the experiments are currently performed in pure D. After more than 20 years, the Joint European Torus (JET) has carried out new D-T experiments with the aim of exploring some of the unique characteristics expected in future fusion reactors, such as the presence of highly energetic ions in low plasma rotation conditions. A new stable, high confinement and impurity-free D-T regime, with reduction of energy losses with respect to D, has been found. Multiscale physics mechanisms critically determine the thermal confinement. These crucial achievements importantly contribute to the establishment of fusion energy generation as an alternative to fossil fuels

Identifying Reduced-Form Relations with Panel Data

The literature that tests for U-shaped relationships using panel data, such as those between pollution and income or inequality and growth, reports widely divergent (parametric and non-parametric) empirical findings. We explain why lack of identification lies at the root of these differences. To deal with this lack of identification, we propose an identification strategy that explicitly distinguishes between what can be identified on the basis of the data and what is a consequence of subjective choices due to a lack of identification. We apply our methodology to the pollution-income relationship of both CO2- and SO2-emissions. Interestingly, our approach yields estimates of both income (scale) and time (composition and/or technology) effects for these reduced-form relationships that are insensitive to the required subjective choices and consistent with theoretical predictions