Atomistic Simulations of Divertor-Plasma Interactions in Fusion Reactors

The world's energy demand and harmful green-house gas emissions are continuously increasing, while the fossil fuel reservoir may soon end. Currently, there is no clear alternative to the traditional energy production methods for a safe and clean future. Fusion could be part of the solution offering a green-house gas free, virtually endless, safe and large scale energy production. A major challenge for fusion is, however, to produce more energy than needed to achieve and maintain the fusion reaction. The most feasible fusion reaction is based on two hydrogen isotopes: deuterium and tritium, which fuse to produce a helium atom and a neutron. For these atoms to fuse, they must overcome the repulsive interaction between them, requiring extreme temperatures. Thus, the particles ionize forming gas plasma. On Earth, this condition can only be met by isolating the plasma from its environment, for instance, by using closed magnetic fields to form a torus-like shaped plasma, also known as tokamak. However, the plasma particles will interact with the reactor walls as their confinement is never perfect, the exhausted plasma must leave the reactor and impurities are introduced in the plasma boundary to control its characteristics. The plasma-wall interactions are especially intense at the divertor, where the plasma is designed to touch the wall. Understanding these processes is essential to develop safe, long-lasting materials and to avoid contaminating the plasma fuel. The main candidates as first wall materials in future fusion reactors are beryllium for the main wall, and tungsten and carbon for the divertor. Also, the materials may mix due to wall erosion, transport of the eroded particles and their deposition in a new location. Plasma-wall interactions can be studied in current experimental reactors or in linear plasma devices. However, this work is often insufficient to understand the underlying mechanisms. Further, the effects of plasma-wall interactions in materials develop in a wide range of time and length scales. Multi scale modelling is a tool that allows to overcome these challenges, improving the predictions for future fusion reactors. In this thesis, the plasma wall interactions taking place in a fusion reactors divertor have been studied by computational means. The interaction of pure and mixed divertor materials, with plasma and impurity particles were modelled. The work was mainly based on atomistic scale calculations, and a Kinetic Monte Carlo algorithm has also been developed to extend the results to macroscopic scales, enabling a direct comparison with experiments. First, deuterium irradiation of various W-C composites has been modelled, focusing on deuterium implantation, variations of the substrate composition and C erosion mechanisms. Carbon was preferentially eroded, varying the substrate's composition throughout the irradiation. The presence of carbon also affected the D implantation characteristics. As carbon became less likely to be an ITER first wall material, the present work focused on the tungsten-beryllium-deuterium system. The tungsten-beryllium mixing showed a strong dependence on irradiation energy and angle. Further, the presence of Be led to higher fuel implantation and W erosion was suppressed by mixed layer formation. The obtained yields were compared to Binary Collision Approximation results, in order to improve the description of the latter method. Furthermore, an unexpected and possibly harmful phenomenon has been addressed in this thesis: porous nano-morphology formation in tungsten by helium plasma exposure. First, the main characteristics and active mechanisms in the system were identified by atomistic simulations. Then, the porous morphology growth was modelled by implementing these processes in a Kinetic Monte Carlo code, resulting in rates that agreed with experimental findings. A morphology growth model was derived where the time dependence is driven by the evolution of the surface roughness, which is a stochastic process and thus evolves as the square root of time.Världens energibehov och utsläppen av skadliga växthusgaser stiger hela tiden, medan reserverna av fossila bränslen sinar. För tillfället finns det inget klart alternativ till de traditionella energiproduktionsmetoderna för en säker och ren framtid. Fusion kan vara en del av lösningen, tack vare en växthusgasfri, i praktiken outsinlig, säker och storskalig energiproduktion. En stor utmaning för fusion är att producera mer än den energi som krävs för att skapa och upprätthålla fusionsreaktionen. Den mest genomförbara fusionsreaktion bygger på två väteisotoper: deuterium och tritium, som genom fusion blir en helium atom och en neutron. För att dess atomer skall fusionera är de tvungna att överkomma den frånstötande kraften mellan dem, vilket kräver extrema temperaturer. Därmed joniseras partiklarna och det bildas ett gasplasma. På jorden kan detta ske endast genom att separera plasmat från omgivningen, t.ex. genom att använda slutna magnetiska fält för att skapa ett torusformat plasma. Separationen är dock aldrig perfekt och partiklarna i plasmat kommer att växelverka med reaktorväggarna. Plasma-vägg växelverkan är speciellt kraftig vid divertorn, somn är designad att möta plasmat. Det är kritiskt att förstå dessa processer för att utveckla säkra och långlivade material och undvika förorening av bränslet i plasmat. Plasma-vägg växelverkan kan undersökas i befintliga experimentella reaktorer eller i linjära plasmamaskiner. Det experimentella arbetet är dock ofta otillräckligt då det gäller att förstå de underliggande mekanismerna. Vidare uppstår effekterna i material av plasma-vägg växelverkan på en bred tids- och längdskala. Multiskalsmodellering är ett verktyg som överkommer dessa utmaningar och förbättrar antagandena för framtida fusionsreaktorer. I denna avhandling undersöks plasma-vägg växelverkningarna som tar plats i divertorn i en fusionsreaktor genom datorberäkningar. Växelverkan mellan rena och blandade divertormaterial och plasma, samt orenheter, har modellerats. Studien är främst baserad på beräkningar på atomskala. En kinetisk Monte Carlo algoritm har utvecklats för att förlänga resultaten till makroskopiska skalor, vilket tillåter en direkt jämförelse med experiment

Multi-Scale Modelling to Relate Beryllium Surface Temperature, Deuterium Concentration and Erosion in Fusion Reactor Environment

Peer reviewe

Promoting adherence to psychopharmacological treatment among prisoners with mental health problems: Follow-up of a randomized controlled trial

This study presents follow-up results regarding a treatment adherence programme (TAP) for prisoners, the initial effectiveness of which we previously evaluated in a randomized controlled trial. Here we used an experimental design with two randomized groups and assessment at four time points: baseline (pre-intervention), at 3 months (post-intervention), and at 6 and 9 months after baseline. Participants were 151 prisoners with mental health problems (Mage = 41.85, SD = 10.31) who were randomly assigned to either the TAP or treatment as usual (TAU). Prisoners who completed the TAP showed a greater improvement in treatment adherence at 3 and 9 months, compared with those who received TAU. There were no significant differences between the groups in subjective well-being under medication. The availability of an easy-to-apply, universal programme that is able to promote treatment adherence in the prison context could make a positive contribution to the general health of inmates

Global scaling of the heat transport in fusion plasmas

A global heat flux model based on a fractional derivative of plasma pressure is proposed for the heat transport in fusion plasmas. The degree of the fractional derivative of the heat flux, a, is defined through the power balance analysis of the steady state. The model was used to obtain the experimental values of a for a large database of the Joint European Torus (JET) carbon-wall as well as ITER like-wall plasmas. The fractional degrees of the electron heat flux are found to be alpha < 2, for all the selected pulses in the database, suggesting a deviation from the diffusive paradigm. Moreover, the results show that as the volume integrated input power is increased, the fractional degree of the electron heat flux converges to alpha similar to 0.8, indicating a global scaling between the net heating and the pressure profile in the high-power JET plasmas. The model is expected to provide insight into the proper kinetic description for the fusion plasmas and improve the accuracy of the heat transport predictions.Peer reviewe

Atomistic Simulations Of Deuterium Irradiation On Iron-based Alloys In Future Fusion Reactors

Peer reviewe

A Social-Emotional Learning Program for Suicide Prevention through Animal-Assisted Intervention

The aim of the study was to carry out a pilot implementation and evaluation of the OverCome-AAI program, a pioneering program for the prevention of suicidal behavior through animal-assisted interventions for young people with high risk factors for suicidal behavior. The study sample consisted of 30 adolescents (11 boys and 19 girls) aged between 14 and 17 years (Mean age = 15.50, SD = 1.60) from the Basque Country (Northern Spain). After the intervention, subjects presented reductions in suicidal ideation, suicide plans, and non-suicidal self-harm, as well as a greater predisposition to seek help. A reduction in the intensity of mental pain was also found, although no differences were observed in indicators of hopelessness and depression. The preliminary results obtained in this pilot study suggest that the OverCome-AAI program may be effective in reducing suicidal behavior and non-suicidal self-harm in young people in residential care who present high risk factors for suicide.This research was funded by the call for research grants at the UPV/EHU 2017, grant number (US18/05), Agintzari Sociedad Cooperativa de Iniciativa Social, and by the call for research grants at the Basque Government, grant number (IT892-16)

Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed three-ion scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of He-3 ions to high energies in dedicated hydrogendeuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast He-3 ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, He-3-rich solar flares.Peer reviewe

Eskultura-praktika bat garatzeko erabilitako kogenerazio prozesua

96 p. : il.Este libro recoje proyecto ha sido desarrollado por 12 profesores del Dpto. de Escultura de la Facultad de Bellas Artes UPV/EHU. en un proceso de investigación plástico desde el área de la cerámica y la escultura, con aplicaciones en nuestra práctica profesional como docentes, con el objetivo que nos permita profundizar en los recursos expresivos de los tiempos del material, indagar en la capacidad transformadora de un objeto dado y proponer protocolos de uso de las formas, las representaciones y las estructuras, generando nuevas aportaciones conformadoras y modificadoras. Planteamos como método el concepto “deriva”, el cual presenta acepciones singulares en cada contexto; en nuestro caso elegimos “Tomar una cosa una dirección nueva”. Se puede entender la Deriva como Intervalo, Intervalo como Distancia, como intersticio... El intervalo facilita el desplazamiento de la obra de arte y de los procesos creativos, y consideramos que la cerámica asume principios desde el horizonte conceptual del arte actual, donde los significados vuelven a fundamentar la práctica. Hemos trabajado formando 4 grupos, generando una plataforma de investigación artística secuenciada, organizada a través de las superposiciones y discontinuidades entre los diferentes componentes del equipo, trabajando escalonadamente con una misma idea (la deriva como actitud). Se ha obtenido como resultado una estrategia de métodos activos que nos permiten transferir conocimientos del saber de la práctica artística colaborativa hacia el entorno educativo.Este libro es uno de los objetivos correspondientes al proyecto desarrollado dentro de la ayuda de iniciación a la incorporación en la investigación concedida en 2012 con el código NUPV12/19 y cuyo director es Juan Antonio Gómez Rui

Mutational spectrum in a worldwide study of 29,700 families with BRCA1 or BRCA2 mutations.

The prevalence and spectrum of germline mutations in BRCA1 and BRCA2 have been reported in single populations, with the majority of reports focused on White in Europe and North America. The Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA) has assembled data on 18,435 families with BRCA1 mutations and 11,351 families with BRCA2 mutations ascertained from 69 centers in 49 countries on six continents. This study comprehensively describes the characteristics of the 1,650 unique BRCA1 and 1,731 unique BRCA2 deleterious (disease-associated) mutations identified in the CIMBA database. We observed substantial variation in mutation type and frequency by geographical region and race/ethnicity. In addition to known founder mutations, mutations of relatively high frequency were identified in specific racial/ethnic or geographic groups that may reflect founder mutations and which could be used in targeted (panel) first pass genotyping for specific populations. Knowledge of the population-specific mutational spectrum in BRCA1 and BRCA2 could inform efficient strategies for genetic testing and may justify a more broad-based oncogenetic testing in some populations

RF Sheath-Enhanced Plasma Surface Interaction Studies using Beryllium Optical Emission Spectroscopy in JET ITER-Like Wall

A dedicated study on JET-ILW, deploying two types of ICRH antennas and spectroscopic observation spots at two outboard, beryllium limiters, has provided insight on long-range (up to 6m) RFenhanced plasma-surface interactions (RF-PSI) due to near-antenna electric fields. To aid in the interpretation of optical emission measurements of these effects, the antenna near-fields are computed using the TOPICA code, specifically run for the ITER-like antenna (ILA); similar modelling already existed for the standard JET antennas (A2). In the experiment, both antennas were operated in current drive mode, as RF-PSI tends to be higher in this phasing and at similar power (∼0.5 MW). When sweeping the edge magnetic field pitch angle, peaked RF-PSI effects, in the form of 2-4 fold increase in the local Be source,are consistently measured with the observation spots magnetically connect to regions of TOPICAL-calculated high near-fields, particularly at the near-antenna limiters. It is also found that similar RF-PSI effects are produced by the two types of antenna on similarly distant limiters. Although this mapping of calculated near-fields to enhanced RF-PSI gives only qualitative interpretion of the data, the present dataset is expected to provide a sound experimental basis for emerging RF sheath simulation model validation