Laser-driven heavy ion acceleration

The rapid neutron capture process (r-process) is responsible for the generation of about half of the heavy elements beyond iron in the Universe. While knowledge about its long-debated astrophysical sites converged recently by the first multi-modal observation of neutron-star mergers by the LIGO-Virgo collaboration in 2017, the nuclear properties of the involved isotopes, especially around the waiting point at the magic neutron number N = 126, still remain inaccessible using conventional accelerator techniques. As a consequence, Habs et al. proposed about one decade ago the fission-fusion reaction mechanism, which offers the potential to produce neutron-rich r-process isotopes close to this waiting point at N = 126 applying ultra-dense, laser-accelerated bunches of heavy, fissile ions in the mass range of A ≥ 200 with kinetic energies around 7 MeV/u. Only two publications had reported on the measurement of laser-accelerated heavy ions in the relevant energy range at the beginning of this work, with maximum kinetic energies of 2 MeV/u. This dissertation presents the results from two experimental campaigns dedicated to advance the knowledge about laser-driven gold ion acceleration and to generate an ion bunch which meets the energy requirements of the fission-fusion reaction mechanism. In both experiments, the heavy ion energies have been successfully pushed towards higher limits, finally resulting in the detection of laser-accelerated heavy ions with energies beyond the fission-fusion threshold of 7 MeV/u. A radiative target cleaning has been implemented in order to reduce the contribution of hydrocarbon contaminants on the gold foil surfaces to the laser-accelerated heavy ion bunches. A Thomson parabola spectrometer has been designed with parameters that ideally support the detection of heavy ions. With that diagnostics, individual gold ion charge states could be resolved for the first time, showing a remarkable target thickness dependency, which cannot be explained with the common ionization mechanisms in a straight-forward way. Thus, the data presented in this thesis is highly valuable as input for future theoretical considerations on the ionization processes of heavy ions in laser-generated plasmas.Der schnelle Neutroneneinfangprozess (r-Prozess) ist verantwortlich für die Erzeugung von ungefähr der Hälfte aller Elemente im Universum mit einer höheren Masse als Eisen. Während sich seit der ersten multimodalen Beobachtung einer Neutronensternverschmelzung durch die LIGO-Virgo-Kollaboration im Jahr 2017 die Erkenntnisse über die vieldiskutierten astrophysikalischen Schauplätze des r-Prozesses unlängst verdichteten, bleiben die nuklearen Eigenschaften der beteiligten Isotope, insbesondere um den Wartepunkt bei der magischen Neutronenzahl von N = 126, noch immer unzugänglich für die konventionelle Beschleunigertechnologie. In Folge dessen entwickelten Habs et al. vor etwa einem Jahrzehnt die Idee des 'Fission-Fusion'-Reaktionsmechanismus, welche das Potenzial birgt, neutronenreiche r-Prozess-Isotope in der Nähe dieses Wartepunkts bei N = 126 mittels ultradichter, laserbeschleunigter Pulse schwerer, spaltbarer Ionen im Massenbereich von A ≥ 200 und mit kinetischen Energien um 7 MeV/u zu erzeugen. Zum Beginn dieser Arbeit lagen lediglich zwei Veröffentlichungen vor, die über die Messung laserbeschleunigter Schwerionen im relevanten Energiebereich berichteten, mit kinetischen Energien von maximal 2 MeV/u. Diese Dissertation präsentiert die Ergebnisse zweier Experimentierkampagnen, die darauf abzielten, das Wissen über lasergetriebene Goldionenbeschleunigung zu erweitern und Ionenpulse zu erzeugen, welche die energetischen Voraussetzungen des 'Fission-Fusion'-Reaktionsmechanismus erfüllen. In beiden Experimenten wurden die Schwerionenenergien erfolgreich nach oben getrieben, was schlussendlich in der Detektion von laserbeschleunigten Schwerionen mit Energien jenseits des 'Fission-Fusion'-Schwellenwerts von etwa 7 MeV/u resultierte. Um den Beitrag von Kohlenwasserstoffverunreinigungen auf den Goldfolienoberflächen zu den laserbeschleunigten Schwerionenpulse zu reduzieren, wurde eine Targetreinigung mittels optischer Laserstrahlung implementiert. Für die Messung von Schwerionen wurde ein Thomson-Parabel-Spektrometer konstruiert, dessen Parameter ideal auf diesen Zweck abgestimmt wurden. Mit Hilfe dieser Diagnostik konnten zum ersten Mal einzelne Goldladungszustände aufgelöst werden, wodurch eine bemerkenswerte Abhängigkeit von der Targetdicke ans Licht kam, die nicht auf einfache Art und Weise durch die gewöhnlichen Ionisationsmechanismen erklärt werden können. Die Daten aus dieser Doktorarbeit stellen daher einen sehr wertvollen Beitrag für künftige theoretische Betrachtungen der Ionisationsprozesse von Schwerionen in lasererzeugten Plasmen dar

Level-k reasoning and time pressure in the 11–20 money request game

AbstractArad and Rubinstein (2012a) have designed a novel game to study level-k reasoning experimentally. Just like them, we find that the depth of reasoning is very limited and clearly different from that in equilibrium play. We show that such behavior is even robust to repetitions; hence there is, at best, little learning. However, under time pressure, behavior is, perhaps coincidentally, closer to that in equilibrium play. We argue that time pressure evokes intuitive reasoning and reduces the focal attraction of choosing higher (and per se more profitable) numbers in the game

Casimir Energy in Deconstruction and the Cosmological Constant

We demonstrate that by employing the correspondence between gauge theories in geometric and in deconstructed extra dimensions, it is possible to transfer the methods for calculating finite Casimir energy densities in higher dimensions to the four-dimensional deconstruction setup. By this means, one obtains an unambiguous and well-defined prescription to determine finite vacuum energy contributions of four-dimensional quantum fields which have a higher-dimensional correspondence. Thereby, large kink masses lead to an exponentially suppressed Casimir effect. For a specific model we hence arrive at a small and positive contribution to the cosmological constant in agreement with observations.Comment: 38 pages, 5 figures, minor changes in the text, results unchanged, figure added, reference adde

Radial basis function interpolation for black-box multi-physics simulations

Interpolation based on radial basis functions (RBF) is a standard data map- ping method used in multi-physics coupling. It works on scattered data without requiring additional mesh topology or neighborhood information of support points. However, sys- tem matrices of the equations for the coefficients tend to be ill-conditioned. In this work, we illustrate the problem by a simple example and discuss possible remedies. Furthermore, we investigate the numerical performance of this method on uniform and non-uniform meshes with a particular focus on the coupling of black-box components where typically no information about the underlying discretization can be extracted. Radial basis func- tion interpolation usually uses an enhancement of the radial basis functions by a global polynomial in order to properly capture constant components and linear trends in the given data. We present a method that determines this polynomial independent from the radial basis function ansatz, which substantially improves the condition number of the remaining RBF system. Furthermore, we show that a rescaling approach can be used to either increase the accuracy or improve the condition number even further by choosing radial basis functions with a smaller support radius. The results represent an intermediate state with the aim to be integrated into the multi-physics coupling library preCICE

The Scalability-Efficiency/Maintainability-Portability Trade-off in Simulation Software Engineering: Examples and a Preliminary Systematic Literature Review

Large-scale simulations play a central role in science and the industry. Several challenges occur when building simulation software, because simulations require complex software developed in a dynamic construction process. That is why simulation software engineering (SSE) is emerging lately as a research focus. The dichotomous trade-off between scalability and efficiency (SE) on the one hand and maintainability and portability (MP) on the other hand is one of the core challenges. We report on the SE/MP trade-off in the context of an ongoing systematic literature review (SLR). After characterizing the issue of the SE/MP trade-off using two examples from our own research, we (1) review the 33 identified articles that assess the trade-off, (2) summarize the proposed solutions for the trade-off, and (3) discuss the findings for SSE and future work. Overall, we see evidence for the SE/MP trade-off and first solution approaches. However, a strong empirical foundation has yet to be established; general quantitative metrics and methods supporting software developers in addressing the trade-off have to be developed. We foresee considerable future work in SSE across scientific communities.Comment: 9 pages, 2 figures. Accepted for presentation at the Fourth International Workshop on Software Engineering for High Performance Computing in Computational Science and Engineering (SEHPCCSE 2016

A comparison of various quasi-newton schemes for partitioned fluid-structure interaction

During the last 5 years, quasi-Newton schemes have proven to be a robust and efficient way to couple partitioned fluid-structure interaction. We showed in previous work that they also allow to perform a parallel coupling. Bogaers et al. introduced a new variant based on a multi-vector update [14]. This variant renders a tuning of the reuse of old information unnecessary as all old iterations are implicitly covered in a Jacobian update. In this work, we compare this multi-vector variant in an inverse formulation to the classical IQN-ILS algorithm for serial as well as parallel coupling

Afterpulse Measurements of R7081 Photomultipliers for the Double Chooz Experiment

We present the results of afterpulse measurements performed as qualification test for 473 inner detector photomultipliers of the Double Chooz experiment. The measurements include the determination of a total afterpulse occurrence probability as well as an average time distribution of these pulses. Additionally, more detailed measurements with different light sources and simultaneous charge and timing measurements were performed with a few photomultipliers to allow a more detailed understanding of the effect. The results of all measurements are presented and discussed

What drives risk perception? A global survey with financial professionals and laypeople

Contains fulltext : 209823.pdf (preprint version ) (Open Access)01 juli 202026 p

Towards a framework for impact assessment for mission-oriented innovation policies. A formative toolbox approach

Mission-oriented policies (MOIP) have become important means to foster transformative change in many countries. Yet, approaches for assessing these policies' impacts are still in their infancy, not least due to the complexity of MOIP. To address this gap, we propose a toolbox approach that supports policy-makers during policy design and implementation, and allows for an identification of potential impacts by a theory-based approach. To disentangle the complexity of missions, we first conceptualize MOIPs as multiple translation processes from mission formulation and design to implementation. Each translation step shapes the policies' impacts. Based on this framework, we develop a set of specific analytical tools that are intended to support the process of bringing missions into realization, but also help to assess whether missions contribute to the postulated goals. These tools include a mapping of the socio-technical systems, a typology to explore the transformative ambition of missions, a process to develop impact pathways, an inventory of policy instruments to support the mission design, and indicators to measure mission progress along the developed pathways. Finally, we propose several analytical questions to explore the context for the development of potential impacts