Geophysics for Mineral Exploration

This Special Issue contains ten papers which focus on emerging geophysical techniques for mineral exploration, novel modeling, and interpretation methods, including joint inversions of multi physics data, and challenging case studies. The papers cover a wide range of mineral deposits, including banded iron formations, epithermal gold–silver–copper–iron–molybdenum deposits, iron-oxide–copper–gold deposits, and prospecting forgroundwater resources

Annual report 2006 // Institute of Safety Research

[no abstract available

Annual report 2006 // Institute of Safety Research

[no abstract available

Compact Stars in the QCD Phase Diagram

The book edition of the Universe Special Issue “Compact Stars in the QCD Phase Diagram” is devoted to the overarching aspects shared between heavy-ion collisions and compact star astrophysics in investigating the hadron-to-quark matter phase transition in the equation of state of strongly interacting matter in different regions of the phase diagram of QCD. It comprises 22 review and research articles that, together, will serve as a useful guide in educating both young and senior scientists in this emerging field that represents an intersection of the communities of strongly interacting matter theory, heavy-ion collision physics and compact star astrophysics

Realistic multi-machine tokamak profile simulations and numerical ramp-down optimization using the RAPTOR code

Predictive modelling of plasma profiles is an essential part of ongoing research in tokamak plasmas, required for a successful realization of future fusion reactors. This thesis focuses on upgrading the RAPTOR code to extend the area of its applicability for plasma modelling and scenario development. RAPTOR is a light and fast simulator, solving radial transport equations, developed for plasma real-time control. This thesis also demonstrates new strategy for ramp-down optimization. The RAPTOR transport model has been extended to take into account the influence of the time-varying plasma equilibrium geometry and background kinetic profiles on the evolution of the predicted plasma profiles. It allows to get more realistic predictions of the plasma state in case of rapid changes in the plasma shape and equilibrium. Also transport equations for the ion temperature and plasma particles (electrons and ions) have been implemented in the code. Benchmarks have been performed with more sophisticated transport ASTRA and CRONOS codes and with prescribed data for the particle transport in ITER. With successful benchmarks, we confirm that the new transport equations are solved correctly. A new ad-hoc transport model based on constant gradients for core and pedestal regions, that is suitable for simulations of transition between H (high) and L (low confinement) modes, has been implemented into RAPTOR. This model assumes ``stiffness'' of the plasma profiles in the core region, reflecting their relatively weak reaction to changes in the heat flux. Only few transport model parameters have to be prescribed. They are validated with predictive simulations of the time evolution of plasma profiles for TCV, ASDEX Upgrade and JET plasmas. We demonstrate the capabilities of RAPTOR for fast and realistic predictions of plasma state over the entire plasma discharges, i.e. from ramp-up to ramp-down. We have defined characteristic gradients in the ``stiff'' region for each machine and L/H confinement modes and have obtained a very good agreement with experimental measurements. We have also demonstrated several special cases, where the obtained set of the transport parameters does not work, and proposed possible solutions of the problems. An optimization procedure for the plasma ramp-down phase has been developed during this work. Nondisruptive termination scenarios are necessary for safe operation of ITER, since it can withstand only a limited amount of plasma disruptions. Automatic optimization algorithms can be applied for searching the optimal ramp-down trajectory. With RAPTOR, optimization results are obtained in a reasonable time (hours). We define the goal of the optimization as ramping down the plasma current as fast as possible while avoiding any disruptions caused by reaching physical or technical limits. Physical constraints are relevant for most tokamaks, others are technical and related to the specific tokamaks. We show how different goals and constraints can easily be included or updated in order to simulate a new machine. A proper plasma shaping during the current ramp-down can reduce significantly the plasma internal inductance, improving its vertical stability. Specific heating scenarios allow to reduce the drop in βpol during H-L transition, which is important for plasma MHD stability. Results of numerical and experimental ramp-down studies for TCV, AUG and JET plasmas are presented

Optics in Our Time

Optics, Lasers, Photonics, Optical Devices; Quantum Optics; Popular Science in Physics; History and Philosophical Foundations of Physic

Study and control of turbulent transport in the Boundary Plasma region of the TJ-II stellarator and the JET tokamak

Mención Internacional en el título de doctorThermonuclear fusion has been proposed as a sustainable, clean and safe energy source to meet the energy demands of the future. There are, however, still several challenges that need to be overcome in order to realize a viable fusion power plant. One of the great challenges is the integration of physics and technology optimization. Performance of magnetic fusion reactors is limited by heat and particle losses. The heat and particle losses are understood to be governed by the non-linear interplay of turbulence and plasma flows but uncertainty remains on e.g. physics of the sudden transitions between confinement regimes, isotopic scaling of confinement, non-linear saturation mechanisms of plasma turbulence, power exhausts and plasma-wall interaction. This thesis investigates the interplay of flows and turbulence in the TJ-II stellarator and the influence of magnetic configuration on plasma-wall interaction in the JET tokamak. A deep understanding of the mechanisms leading to turbulence self-regulation via Zonal Flows (ZFs) is of paramount importance. In this sense, the assessment of Long Range Correlations (LRC) in the plasma edge, by the use of Langmuir probe systems, have been proven to be a powerful strategy to study the interaction between ZFs and turbulence. Improvements in the experimental strategy to characterize LRC have been applied to study the interplay between neoclassical radial electric fields and ZFs and the transition to improved confinement regimes in the TJ-II stellarator. Experimental studies reveal the role of neoclassical radial electric fields to control the amplitude of Zonal Flows resulting in the development of both long (neoclassical) and short (due to Zonal Flows) radial electric field scales with important implication in the physics understanding of transport self-regulation mechanisms. A comprehensive description of the influence of plasma scenarios on the radial width of ZFs is given here, with a special focus on its dependence with heating and isotope scaling. For the first time, the characterization of low frequency fluctuating ZFs and mean radial electric fields has been experimentally studied during the L-H transition in Hydrogen and Deuterium plasmas in the stellarator TJ-II. No evidence of isotope effect on the L-H transition dynamics was observed. These observations emphasize the critical role of both zero frequency (equilibrium) and low frequency varying large-scale flows for stabilizing turbulence during the triggering of the L-H transition in magnetically confined toroidal plasmas and show that there are different paths to reach the L-H transition with impact on the conditions to access the H-mode regime. In addition to the relevance of studies carried out in stellarators, experimental validation of relevant plasma scenarios in large tokamaks constitute the fundamental test bench for future burning fusion reactors such as ITER. For example in the last years it has been shown that, in the JET tokamak, with the new ITER-like wall, global plasma confinement is strongly linked to the divertor magnetic topology, which influences the Boundary Plasma and the Plasma Wall Interaction. In this Thesis we show a study on how the neutral fluxes are affected by the divertor magnetic configuration and, as a consequence, how the SOL plasma changes. We also present a detailed preliminary analysis of the dynamic behavior of Ion and Neutral fluxes during the ELM-cycle. The results point to the Recycling coefficient, which varies significantly within this short time-scale, something that could have important implications in the understanding of the H-mode performance.El aprovechamiento de la energía de la fusión termonuclear se ha propuesto como un método limpio y sostenible para hacer frente a las demandas energéticas futuras. Sin embargo, actualmente todavía se deben superar retos científicos y técnicos para hacer viable la operación de un reactor nuclear de fusión. Uno de los mayores retos es el entendimiento de la física del plasma que tiene lugar en los reactores de fusión así como la optimización tecnológica de los propios reactores. El rendimiento de los futuros reactores de fusión está limitado por las pérdidas de partículas y de calor. Ambos fenómenos están gobernados por la interacción no lineal entre la turbulencia del plasma y los flujos a gran escala, conocidos como Flujos Zonales. Por otra parte, la física de las transiciones espontáneas entre regímenes de diferente nivel de confinamiento, el efecto isotópico y sus implicaciones, los mecanismos de saturación no lineal de la turbulencia así como la evacuación de los flujos de calor y la física de la interacción entre el plasma y la pared necesita todavía ser entendida. Esta tesis describe la investigación empírica de la interacción entre las diferentes escalas de turbulencia de plasma en el stellarator TJ-II y la influencia de la configuración magnética en la física de la interacción plasma-pared en el tokamak JET. A este efecto, se han utilizado dos diagnósticos: las sondas electrostáticas (conocidas como sondas de Langmuir) y espectroscopía rápida en el espectro visible. Es de suma importancia la comprensión profunda de los mecanismos que conducen a la autorregulación de la turbulencia por la acción de los Flujos Zonales (ZF). En este sentido, se ha demostrado que la evaluación de las correlaciones de largo alcance (LRC) en el borde del plasma, mediante el uso de los sistemas de sondas de Langmuir, es una estrategia poderosa para estudiar la interacción entre ZF y la turbulencia. Las mejoras en la estrategia experimental para caracterizar LRC se han aplicado para estudiar la interacción entre los campos eléctricos radiales neoclásicos ZF durante la transición a regímenes de confinamiento mejorados en el stellarator TJ-II. Los estudios experimentales llevados a cabo revelan el papel de los campos eléctricos radiales neoclásicos en el control de la amplitud de los flujos zonales que resultan en el desarrollo de escalas de campos eléctricos radiales largos (neoclásicos) y cortos (debidos a los flujos zonales), con una importante implicación en la comprensión física de los mecanismos de auto-regulación transporte radial. Aquí se proporciona una descripción completa de la influencia de los escenarios de plasma en el ancho radial de las ZF, con un enfoque especial en su dependencia con el calentamiento y la masa isotópica. Por primera vez, la caracterización de estas fluctuaciones globales de baja frecuencia y campos eléctricos radiales se ha estudiado experimentalmente durante la transición L-H en plasmas de hidrógeno y deuterio en el stellarador TJ-II. No se observó evidencia de efecto isótopo en la dinámica de transición L-H. Estas observaciones enfatizan el papel crítico del campo eléctrico neoclásico (o de equilibrio) y los flujos a gran escala de baja frecuencia para estabilizar la turbulencia durante el inicio de la transición L-H en plasmas toroidales confinados magnéticamente. Esto muestra que existen diferentes caminos para alcanzar la transición de LH con impacto sobre las condiciones de acceso al régimen de confinamiento mejorado. Además de la relevancia de los estudios realizados en stellarators, la validación experimental de escenarios relevantes de plasma en grandes tokamaks constituye el banco de pruebas fundamental para futuros reactores de fusión como ITER. Por ejemplo, en los últimos años se ha demostrado que, en el tokamak JET, con la nueva pared, que es idéntica a la que estará instalada en ITER, el confinamiento global del plasma está fuertemente vinculado a la topología del divertor, lo que influye en la física y en las características del borde del plasma y de la interacción plasma-pared. En esta tesis, mostramos un estudio sobre cómo los flujos de partículas neutras se ven afectados por la configuración magnética del divertor y, en consecuencia, cómo cambia la parte más externa del plasma, en la que las líneas de campo no están cerradas sobre sí mismas, sino que se cierran a través de los elementos metálicos del dispositivo, conocida como “Scrape-Off Layer”. También presentamos un análisis preliminar detallado del comportamiento dinámico de los flujos de iones y neutros durante las inestabilidades de tipo ELM. Los resultados apuntan al coeficiente de reciclado, que varía significativamente dentro de esta breve escala de tiempo, algo que podría tener implicaciones importantes en la comprensión del rendimiento en modo de alto confinamiento.Este trabajo se ha realizado en el marco del proyecto ENE2012-38620-C02-01 (referencia BES-2013-065215), del Ministerio de Ciencia, Innovación y Universidades (MICINN).Programa Oficial de Doctorado en Plasmas y Fusión Nuclear por la Universidad Carlos III de MadridPresidente: Luis Conde López.- Secretario: Isabel García Cortés.- Vocal: Alexander Vladimirovich Melniko