Impact of externally applied 3D fields on plasma rotation and correlation to particle losses

El modo de alto confinamiento (H-mode) está considerado como el modo de operación óptimo para futuros dispositivos de fusión nuclear. El H-mode viene acompañado de inestabilidades que provocan la expulsión de partículas y energía, y deterioran el confinamiento del plasma. Aunque dichas inestabilidades son tolerables en los dispositivos actuales, el desarrollo de t´ecnicas para su control es fundamental de cara a garantizar la integridad de futuros reactores. La aplicación de perturbaciones magnéticas externas es una de las herramientas más extendidas para la mitigación e incluso completa supresión de dichas inestabilidades. Estas perturbaciones alteran la simetría del campo magnético que confina al plasma. La respuesta del plasma a dichas perturbaciones es una línea de investigación muy activa actualmente. El objetivo de este trabajo es el estudio detallado de dos descargas de baja colisionalidad, llevadas a cabo en el tokamak ASDEX Upgrade. Durante estas descargas se aplican perturbaciones magnéticas externas para estudiar la respuesta del plasma. El estudio está centrado en el análisis de la evolución temporal acoplada de la rotación toroidal de las impurezas, pérdida de iones rápidos y densidad. Los resultados obtenidos revelan fuertes correlaciones entre estos para´metros. Las interdependencias entre las magnitudes dependen de (1) la caracterización de la población de iones rápidos sujeta a pérdidas y (2) la posición radial en la que se miden rotación y densidad. Se han observado fuertes cambios en el patrón de correlaciones asociados a las diferencias en las órbitas de los iones rápidos; y la intensificación de la correlación hacia el borde del plasma. Bajo determinadas circunstancias, se produce un cambio en el sentido de giro de la rotación toroidal de las impurezas en el borde del plasma, i.e. las impurezas en el borde y en el centro giran en sentido contrario. Ello también conlleva un cambio en el patrón de la correlación.The high-confinement mode (H-mode) is considered to be the baseline operational scenario for future nuclear fusion devices. The H-mode is accompanied by instabilities that cause cyclic ejection of particles and energy, thus deteriorating the confinement of the plasma. Although these instabilities are tolerable in current experiments, the development of techniques for their control is crucial to guarantee the integrity of future devices. The application of external 3D magnetic fields is one of the most efficient techniques to achieve the mitigation and even full suppression of these instabilities. These magnetic perturbations break the symmetry of the magnetic field. The impact of the perturbations on the plasma is currently a very active research line. The objective of this thesis is a detailed analysis of two low collisionality discharges, which were carried out in the ASDEX Upgrade tokamak experiment. In these two discharges static magnetic perturbations were applied to study plasma response. The study is focused on the observation of the coupled evolution of the toroidal impurity rotation, fast-ion losses and electron density. The results reveal strong correlations between the parameters. The interdependencies between the parameters depend on (1) the type of fast-ion population which is subject to losses and (2) the radial position at which rotation and density are measured. A strong change in the correlation pattern is associated with changes in the orbit topology of the fast-ions. The correlation towards the plasma edge becomes more intense. Under certain circumstances, a change in the correlation pattern at the edge is connected to an impurity toroidal rotation reversal, i.e. a spin-up of the impurities in opposite direction to the plasma core.Universidad de Sevilla. Máster Universitario en Física Nuclea

Analysis of supercritical carbon dioxide Brayton cycles for a helium-cooled pebble bed blanket DEMO-like fusion power plant

Article number 112860Nuclear fusion is expected to be a clean and almost-unlimited power source in the near future. The first net power demonstration plant (DEMO) is planned to start operation in 2050. The supercritical carbon dioxide (S-CO2) Brayton cycle is an excellent candidate for integration with a fusion power plant, such as DEMO, because of its high efficiency at intermediate temperatures and low interaction of coolant with tritium. This work analyses a set of S-CO2 Brayton cycle layouts for its integration in a DEMO-like fusion power plant, considering the specific requirements and heat availability characteristics. A framework has been developed to integrate the PROCESS code and the numerical solver EES to study the thermal and economic aspects of integrating the different S-CO2 cycle layouts. In total, 14 layouts have been studied and grouped into a more conservative (DEMO1, pulsed operation) and more advanced (DEMO2, steady-state operation) fusion reactors. The PROCESS code has been used to obtain the DEMO 2018 Baseline, which defines the available power from each heat source and their boundary conditions. This code has also been used to assess the cost of the optimal layout. Thermal storage has been added to the DEMO1 scenario to avoid standby times that could negatively affect the cycle equipment lifetime and efficiency. Besides, these boundary conditions have been extended to account for possible technical improvements by the time of its construction in the DEMO2 scenario. A sensitivity analysis of the most characteristic parameters of the cycles shows a strong dependence on the turbine inlet temperature for all layouts, which is constrained by the reactor material limits. The cycle efficiency (electric power produced before consumptions non-related to the cycle) has been selected as the figure of merit for the optimisation. The results show a 38% cycle efficiency for DEMO1 and 56% for DEMO2 scenarios. These efficiencies drop to 20% and 38% values, respectively, when the reactor and cooling loop power consumptions are considered. These values are obtained for current fusion reactor conceptual designs. The economic analysis shows the economic viability of DEMO2 scenarios.Ministerio de Ciencia e Innovación (España) FPU17/06273Horizonte 2020 (Unión Europea) 708257Horizonte 2020 (Unión Europea) 80516

Dynamics of the pedestal transport during edge localized mode cycles at ASDEX Upgrade

The dynamic behaviour of the ion and electron energy, particle and momentum transport measured during type-I edge localized mode (ELM) cycles at ASDEX Upgrade is presented. Fast measurements of the ion and electron temperature profiles revelead that the ion and electron energy transport recover on different timescales, with the electrons recovering on a slower timescale (Cavedon et al 2017 Plasma Phys. Control. Fusion 59 105007). The dominant mechanism for the additional energy transport in the electron channel that could cause the delay in the electron temperature gradient (VTe) recovery is attributed to the depletion of energy caused by the ELM. The local sources and sinks for the electron channel in the steep gradient region are much smaller compared to the energy flux arriving from the pedestal top, indicating that the core plasma may dictate the local dynamics of the VTe recovery during the ELM cycle. A model for the edge momentum transport based on toroidal torque balance that takes into account the existence of poloidal impurity asymmetries has been developed. The analysis of the profile evolution during the ELM cycle shows that the model captures the dynamics of the rotation both before the ELM crash and during the recovery phase.European Commission (Euratom) Grant agreement No. 633053H2020 Marie-Sklodowska Curie programme (grant agreement No. 708257)European Union’s Horizon 2020 (grant agreement No. 805162

Experimental study of the impact of ion orbit losses on the edge radial electric field at the ASDEX Upgrade tokamak

Spanish Ministry of Science, Innovation and Universities (grant FPU17/06273)EUROfusion Consortium 63305

Upgrade of the edge Charge Exchange Recombination Spectroscopy system at the High Field Side of ASDEX Upgrade

The upgrade of the high field side (HFS) edge charge exchange recombination spectroscopy (CXRS) system of ASDEX Upgrade is presented. This diagnostic provides temperature, rotation and radiance measurements of impurity species by taking advantage of the gas puff based CXRS technique (GP-CXRS). The system is formed by a fast piezoelectric valve, that injects thermal neutrals into the plasma, and two optical heads. The localized gas injection together with properly aligned lines of sights (LOS) lead to a high spatial resolution of 5–19 mm. Fast gas puff modulation allows a precise subtraction of the passive part of the signal. The existing poloidal optical head has been replaced with a new one to increase the radial resolution. The number of lines of sight (LOS) of the poloidal optical head has been increased from 8 to 16 covering around 7 cm of the plasma edge at the HFS. The same radial range is also viewed by a toroidal optical head. The neutral deposition, needed to calculate the impurity density profile, has been modelled using the FIDASIM code. A realistic gas puff geometry has been implemented in the code. The first measurements of impurity temperature, rotation and radiance utilizing the upgraded diagnostic are presented.Universidad de Sevilla PPITUS 2017EUROfusion Consortium 633053H2020 Marie-Skłodowska Curie programme (Grant No. 708257)Spanish Ministry of Economy and Competitiveness (Grant No. FJCI-201422139

Poloidal impurity asymmetry studies using the upgraded high field side edge CXRS diagnostic at ASDEX Upgrade

EUROfusion Consortium 63305

Progress towards a quiescent, high confinement regime for the all-metal ASDEX Upgrade tokamak

EUROfusion Consortium 633053European Union’s Horizon 2020 80516

Characterization of edge poloidal impurity asymmetries at ASDEX Upgrade

EUROfusion Consortium 63305

Determination of the background neutral density from passive Balmer alpha CX emission at the ASDEX Upgrade tokamak

EUROfusion Consortium 63305

In-out charge exchange measurements and 3D modelling of diagnostic thermal neutrals to study edge poloidal impurity asymmetries

A new method was developed to model the neutral population produced by the gas puff based charge exchange recombination spectroscopy systems at ASDEX Upgrade (AUG). With this method, the edge impurity density on the high field side (HFS) and low field side (LFS) can be obtained without the need to apply a neutral beam injection system. The neutral penetration needed for the calculation of the impurity density is obtained with a new gas puff module implemented in the FIDASIM code. The LFS impurity density profile evaluated with the new gas puff module matches the impurity density calculated with standard beam-based charge exchange diagnostics. Impurity temperature, rotation and density profiles at the HFS and LFS of an AUG H-mode discharge are presented. Edge impurity toroidal and poloidal flows show asymmetric structures. The impurity density asymmetries obtained with the new gas puff module are consistent with the observed flow structure