Analysis of the H-mode density limit in the ASDEX Upgrade tokamak using bolometry

The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the four phases occur due to a coupling of these two mechanisms. These observations are in line with studies made at AUG with carbon walls, although in those discharges the energy loss was most likely caused by the full detachment of the divertor. The density of the HDL depends only weakly on the plasma current, unlike the Greenwald limit, and can be increased by high heating power, again unlike the Greenwald limit. The triangularity of the plasma has no influence on the density of the HDL, though improves the performance of the plasma, since the onset of the degrading H-mode phase occurs at higher densities. It is explicitly shown that the HDL and also the L-mode density limit are determined by edge parameters. Using pellet fueling, centrally elevated density profiles above the Greenwald limit can be achieved in stable H-modes at a moderate confinement. Future tokamaks will have intrinsic density peaking. Consequently, they will most likely operate in H-modes above the Greenwald limit.Für den Betrieb von zukünftigen Fusionsexperimenten, wie ITER und DEMO, ist das H-Mode-Operationsregime vorgesehen, das sich gegenüber dem L-Mode-Regime durch einen verbesserten Energieeinschluss auszeichnet. Dabei werden hohe Dichten angestrebt um die Fusionsleistung zu maximieren. Bei zu hohen Dichten findet jedoch ein Übergang in das L-Mode-Regime statt. Dieses H-Mode-Dichtelimit (HDL) tritt in der Nähe des Greenwald Limits (GWL) auf, welches eine obere Dichtegrenze für den Betrieb von Tokamaks darstellt. Im Rahmen dieser Doktorarbeit wurde das H-Mode-Dichtelimit am Tokamak ASDEX Upgrade (AUG) im Betrieb mit einer Wolframwand experimentell untersucht. Verschiedene existierende Erklärungsansätze für das Auftreten des HDL, wie zum Beispiel der Einfluss von Strahlungsverlusten, wurden für die durchgeführten Experimente ausgeschlossen. Eine systematische Untersuchung zeigt, dass das HDL durch vier verschiedene, reproduzierbare und quasi-stabile Plasmazustände, die mit ansteigender Plasmadichte aufeinander folgen, charakterisiert wird. Die erste Phase ist eine stabile H-Mode, bei der die Dichte bei konstantem Druck ansteigt. Darauf folgt ein degradierendes H-Mode-Regime, bei dem die zentrale Dichte konstant ist und der Energieeinschluss verschlechtert wird. Die dritten Phase ist der Zusammenbruch des H-Mode-Regimes und somit das eigentliche HDL. Dabei wird der erhöhte H-Mode-Temperaturgradient am Rand abgebaut. In dieser Phase bleibt das gesamte Dichteprofil jedoch konstant. Mit der vierten Phase hat das Plasma das L-Mode-Regime erreicht, bei dem die Dichte bei einem konstanten, niedrigen Energieeinschluss wieder ansteigt. Grenzwerte des radialen elektrischen Feldes und die Leistungsschwelle der H-Mode erklären potentiell den Übergang in die L-Mode, können aber für das Einsetzen des HDL ausgeschlossen werden. Die vier Phasen werden durch eine Kombination von zwei Effekten erklärt: ein Absinken der Ionisationsrate im eingeschlossenen Plasma und ein zusätzlicher, bei hohen Dichten auftretender Energieverlustkanal. Diverse Beobachtungen deuten darauf hin, dass der Verlustkanal durch einen erhöhten konvektiven Transport am Rand des Plasmas entsteht. In dieser Arbeit wurden die vier Phasen auch in AUG Plasmen mit Kohlenstoffwand nachgewiesen. Die Unterschiede zwischen den Beobachtungen bei beiden Wandmaterialien werden auf eine Änderung des Energieverlustkanals zurückgeführt. Dieser Verlustkanal wurde bei Kohlenstoff durch das Ablösen des Plasmas von der Wand erklärt. Dieser Effekt konnte für Wolfram jedoch ausgeschlossen werden. Im Gegensatz zum GWL hängt die Dichte des HDLs im Betrieb mit Wolframwand nur schwach vom Plasmastrom ab. In dieser Arbeit wurde allerdings eine deutliche Abhängigkeit von der Heizleistung nachgewiesen. Die Triangularität des Plasmas hat keine Auswirkung auf die Dichte des HDL, kann aber die Einschlussgüte des Plasmas bei hohen Dichten deutlich erhöhen, da die degradierende Phase später einsetzt. Es wird gezeigt, dass man das HDL und das GWL mit zentral erhöhten Dichteprofilen überschreiten kann. Das beweist, dass beide Limits durch Parameter am Rand bestimmt werden. Hochtemperaturplasmen, wie in ITER und DEMO, werden voraussichtlich intrinsisch zentral erhöhte Dichteprofile haben und sollten entsprechend der vorgestellten Ergebnisse bei Dichten oberhalb des GWL in H-Mode betrieben werden können

Creación de espacios de aprendizaje y enseñanza para la investigación transformadora y transdisciplinar : el Laboratorio de Innovación Transformadora

Para lograr una transición hacia el desarrollo sostenible son fundamentales la ciencia y la educación, especialmente la educación superior. Se necesitan formatos educativos para capacitar a los estudiantes en la realización de investigaciones transformadoras. Con base en la investigación transdisciplinaria y transformadora en laboratorios del mundo real y estudios del futuro, desarrollamos un módulo de aprendizaje y enseñanza integral: el Laboratorio de Innovación Transformadora (lit). El laboratorio desarrolla cinco competencias clave y tres tipos de conocimiento necesarios para impulsar innovaciones en sostenibilidad socialmente robustas. En este artículo se presentan las principales características de este formato vivencial y reflexivo, además de un manual para facilitar el laboratorio. También se comparten y discuten los aprendizajes centrales de la implementación de este formato en programas de estudio existentes a partir de dos pruebas realizadas en dos universidades alemanas

Estimating humus reproduction of bioenergy crops

Der landwirtschaftliche Anbau von Energiepflanzen in Deutschland nimmt heute bereits einen relevanten Anteil des Ackerlandes in Anspruch und ist weiter im Wachsen begriffen. Für die ökologische Nachhaltigkeitsbewertung ist in diesem Zusammenhang u.a. zu prüfen, welchen Einfluss Energiepflanzenproduktionssysteme auf die Humusbilanzen der Anbauflächen ausüben. Validierte Koeffi­zienten für die Bewertung von Energiepflanzenproduk­tionssystemen in der Humusbilanz stehen allerdings heute noch nicht zur Verfügung. Problematisch ist hier, dass bei der Methode des VDLUFA als aktueller Standardmethode für die Humusbilanzierung in Deutschland die Festlegung neuer Koeffizienten nur über Analogieschluss von bereits bewerteten Kulturen möglich, eine reproduzierbare Parametrisierung jedoch methodenbedingt ausgeschlossen ist. Im vorliegenden Artikel werden daher reproduzierbare Humusbilanzkoeffizienten für Produk­tionssysteme verschiedener Energiepflanzen mit dem Modellansatz HU-MOD berechnet. Mit dem Modell berechnete Humusreproduktionskoeffizienten für Fruchtarten können prinzipiell auch für die Humusbilanzierung nach VDLUFA verwendet werden. Eine Modellevaluation zur Prüfung der Anwendbarkeit bei Energiepflanzenproduktionssystemen wurde anhand von Daten aus der Literatur für Zea mais und Miscanthus × giganteus erfolgreich vorgenommen. Mit dem Modell wurden mäßig bis stark negative Humusbilanzkoeffizienten für alle bewerteten Energiepflanzenproduktionssysteme, mit Ausnahme von Miscanthus × giganteus, berechnet. Die ermittelten Koeffizienten liegen dabei insgesamt in einem plausiblen Bereich, der durch Kalibrierung des Modells für die Bewertung von Zea mais und Miscanthus × giganteus bestätigt wurde. Dennoch muss festgestellt werden, dass die aktuelle Datenlage zur ober- und unterirdischen Biomasseproduk­tion in Energiepflanzen-Produktionssystemen sowie zu Anfall und Umsatz von Ernte- und Wurzelrückständen noch sehr schwach und für die Kalibrierung von Mo­dellen zur Bewertung von Einflüssen auf die organische Bodensubstanz insgesamt unzureichend ist. Weiterhin liegen nur für wenige Kulturen Ergebnisse vor, die eine Validierung entsprechender Modellergebnisse zulassen. Für die Nachhaltigkeitsanalyse des Energiepflanzenanbaus und die Umsetzung von § 17 BBodSchG besteht daher dringender Forschungsbedarf.    The production of bioenergy crops is increasing in Germany, and today these crops already occupy a relevant share of the total arable land. For environmental impact assessment, the humus balance of bioenergy crop production systems is one important figure. However, the necessary humus balance coefficients are not available for these crops until now. One problem in generating these coefficients for the actual German standard method for humus balancing (VDLUFA, 2004) is that the included coefficients have been derived from long-term field experiments, but a reproducible procedure for the calculation of new coefficients has not been specified. Therefore, we present results from modeling humus reproduction of different bioenergy crops with the HU-MOD approach. The model in principal allows for the calculation of balance coefficients for the VDLUFA (2004) method. Model performance in the assessment of bioenergy crops is tested based on literature data on Zea mais and Miscanthus × giganteus. According to the HU-MOD model, all bioenergy crops under assessment exhibit considerably negative humus reproduction, with Miscanthus × gigan­teus as an exception. Calculated humus reproduction is in a plausible magnitude, as supported by the calibrated model application with Zea mais and Miscanthus × giganteus. However, the parametrization of the humus balance model is hindered by a very limited availability of data, especially with regard to below ground biomass. Further, the data base for validations of the new coefficients is extremely insufficient, indicating the strong demand for more efforts in data supply.   &nbsp

Design and implementation of a prototype infrared video bolometer (IRVB) in MAST Upgrade

A prototype infrared video bolometer (IRVB) was successfully deployed in the Mega Ampere Spherical Tokamak Upgrade (MAST Upgrade or MAST-U), the first deployment of such a diagnostic in a spherical tokamak. The IRVB was designed to study the radiation around the lower x-point, another first in tokamaks, and has the potential to estimate emissivity profiles with spatial resolution beyond what is achievable with resistive bolometry. The system was fully characterized prior to installation on MAST-U, and the results are summarized here. After installation, it was verified that the actual measurement geometry in the tokamak qualitatively matches the design; this is a particularly difficult process for bolometers and was done using specific features of the plasma itself. The installed IRVB measurements are consistent both with observations from other diagnostics, including magnetic reconstruction, visible light cameras, and resistive bolometry, as well as with the IRVB-designed view. Early results show that with conventional divertor geometry and only intrinsic impurities (for example, C and He), the progression of radiative detachment follows a similar path to that observed for large aspect ratio tokamaks: The peak of the radiation moves along the separatrix from the targets to the x-point and high-field side midplane with a toroidally symmetric structure that can eventually lead to strong effects on the core plasma inside the separatrix

A descriptive analysis of relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke

<p>Abstract</p> <p>Background</p> <p>The aims of the present study were to examine relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke, as assessed by urinary cotinine-to-creatinine ratio (CCR), and to describe the CCR over seven days among infants at home.</p> <p>Methods</p> <p>A convenience sample of 27 households was drawn. Each household had to have at least one daily tobacco smoker and one child up to three years of age. Over a seven-day period, urine samples were obtained from the child daily. To examine relations between parents' self-reported smoking and infants' daily CCR, generalized estimating equation (GEE) analysis was used.</p> <p>Results</p> <p>The data revealed that infants from households with indoor smoking had higher CCRs than infants in households with outdoor smoking. CCRs were higher in girls than in boys. Older infants had lower CCRs than younger infants. Smoking outside the home versus inside the home, infant's gender, and infants' age accounted for 68% of the variance in CCR in a GEE data analysis model. No increase or decrease of CCR over time was found.</p> <p>Conclusion</p> <p>The findings suggest that parents' self-reported smoking indoors at home versus outdoors is predictive of CCR among infants three and younger. Higher CCR concentrations in girls' urine need further examination. Furthermore, significant fluctuations in daily CCR were not apparent in infants over a seven-day time period.</p

PLASMA SHAPE AND FUELING DEPENDENCE ON THE SMALL ELMS REGIME IN TCV AND AUG

A series of experiments has been conducted at AUG and TCV to disentangle the role of fueling, plasma triangularity and closeness to a double null (DN) configuration for the onset of the small ELM regime. At AUG, the role of the SOL density has been revisited. Indeed, it turns out that a large density SOL is not a sufficient condition to achieve the type-II (small) ELM regime. This has been demonstrated with a constant gas fueled plasma close to DN which has been progressively shifted down, relaxing therefore the closeness to DN at constant. As the plasma is moved down, Type-I ELMs are progressively restored, finally being the unique ELM regime. It is observed that not only the pedestal top profiles are unchanged, but also the SOL profiles remained unaffected by transition from Type-II to Type-I ELMs. We conclude that the separatrix density is not the unique key parameter and it is hypothesized that the local magnetic shear, modified by the closeness to DN, could play an important role. A small ELM regime with good confinement has been achieved at TCV, a full carbon machine featuring an open divertor. A systematic scan in the fueling rate has been done for both medium and high triangularity shapes. For the latter case, a configuration close to a DN configuration, the stored energy and the pedestal top pressure increase by 5% and 30% respectively compared to the medium triangularity case. For both shapes, as the D2 fueling is increased, the Type-I ELM frequency decreases and small ELMs are observed in between large ones. Finally for the high triangularity, at the maximum fueling rate, the large ELMs are fully suppressed and only the small ELMs remain. As observed in JET and AUG, the pedestal pressure degrades with increasing fueling, up to 40% for the high triangularity scenario, although the stored energy remains almost unchanged. It is also observed that, for both shapes, the density at the separatrix increases with the fueling rate, reaching ne,sep/nG ~0.3 at ne,av/nG~0.75. The small ELM regime at TCV is associated with a coherent mode at about 30 kHz seen by the magnetic probes located at the outboard midplane. The outer target heat loads from IR tomography are reduced by more than a factor of 5 when transiting towards the small ELM regime

Transformative innovation lab : handbook to facilitate students' real-world laboratory projects to promote transformative and transdisciplinary competencies

Science and education are central fields and a lever for sustainable development. With the newly developed student teaching and learning format "Transformative Innovation Lab" - TIL for short - students are to be enabled to conduct independent transformative research. To this end, the researchers, under the direction of the Wuppertal Institute, developed and tested the new learning concept in the project "Development, testing and dissemination of new qualification offers for 'change agents' for transformative learning using the real-world laboratory approach" (EEVA). The detailed results and numerous implementation tips have been published in a practical handbook aimed at academic teaching staff and other multipliers

Creating learning and teaching spaces for transformative and transdisciplinary research : the Transformative Innovation Lab

For achieving a transition towards sustainable development, central importance is attached to science and education, and especially higher education. Suitable formats are needed for empowering students to perform transformative research. On the basis of transdisciplinary and transformative real-world laboratory research and futures studies, we develop encompassing learning and teaching module: the Transformative Innovation Lab (til). The lab builds on insights into five key competencies and three types of knowledge needed for developing socially robust sustainability innovations. In this paper, the main features of this experiential and reflexive format are presented and linked to a handbook for facilitating the lab. Central learnings for implementing the format in existing study programmes from two test runs at two German universities are shared and discussed

Design principles for advancing higher education sustainability learning through transformative research

A growing number of transformative research practices that redefine the role of science in engaging with local - mostly urban - transformation processes have emerged in recent decades. However, while education is considered a key driver for sustainability transformations, higher education has been slow to develop and implement dedicated, appropriate and effective transformative education programmes and learning modules. In this paper, we present a framework of design principles for transformative learning modules in higher education. These principles are derived from two growing discourses: higher education sustainability learning, and transdisciplinary and transformative research - both of which are centrally anchored in the field of sustainable development and sustainability science. The principles presented provide guidance for course leaders in higher education to create learning modules aimed at enabling students to become engaged in transdisciplinary and transformative research that fosters sustainability transitions in local and urban contexts. We use the Transformative Innovation Lab (TIL) - a learning course developed and tested at two German universities - as an example of how the design principles can be applied. The module, which runs over two semesters, supports Masters students in their process of developing real-world laboratories and exploring urban sustainability transitions through collaborative experimentation with local practice partners. We discuss the factors that enable and limit the implementation of transformative learning modules and outline aspects of the novel roles adopted by lecturers in transformative teaching environments. Moreover, we highlight the need for both institutional change and transformative teaching formats that go beyond transformative research as key for driving universities to take responsibility for collaboratively fostering sustainability transitions in their local contexts