Irradiation programme HFR phase IIb - SPICE. Impact testing on up to 16.3 dpa irradiated RAFM steels. Final report for task TW2-TTMS 001b-D05

Bestrahlungsprogramm HFR Phase IIb – SPICE: Kerbschlagbiegeuntersuchungen an bis 16.3 dpa bestrahlten RAFM Stählen Die Untersuchung des bestrahlungsinduzierten Versprödungsverhaltens von niedrigaktivierbaren ferritisch-martensitischen (RAFM) Stählen bildet das Ziel der vorliegenden Arbeit. Die Neutronenbestrahlung bei verschiedenen Bestrahlungstemperaturen (250-450 °C) bis zu einer Schädigung von 16,3 dpa (nominell) wurde im Hoch Fluss Reaktor („High Flux Reactor“) Petten im Rahmen des HFR Phase IIb (SPICE) Bestrahlungsprogramms durchgeführt. Die Kerbschlageigenschaften wurden an miniaturisierten Charpy-V Proben (des KLST Typs) mittels der instrumentierten Kerbschlagbiegeversuche ermittelt. Der Hauptschwerpunkt des Bestrahlungsprogramms liegt in der Untersuchung des Einflusses der Neutronenbestrahlung auf die mechanischen Eigenschaften von einem europäischen RAFM Referenzstahl für die Erste Wand des Demonstrationsreaktors (DEMO), EUROFER97, bei zwei verschiedenen Wärmebehandlungen. Die mechanischen Eigenschaften von EUROFER97 wurden mit denen von internationalen Referenzmaterialien (F82H-mod, OPTIFER-Ia, GA3X und MANET-I), welche im SPICE Projekt untersucht wurden, verglichen. Die Bestrahlungsresistenz von bis 16,3 dpa bei 250-450 °C bestrahltem EUROFER97 ist vergleichbar mit der von besten Referenz-Strukturmaterialien. Es wurde für alle untersuchten RAFM Stähle eine erhebliche Tieftemperaturversprödung (Tirr ≤ 300 °C) beobachtet. Die Wärmebehandlung von EUROFER97 bei höherer Austenisierungstemperatur führt zur wesentlichen Verbesserung des Versprödungsverhaltens bei niedrigen Bestrahlungstemperaturen (Tirr ≤ 350 °C). Bei Tirr ≥ 350 °C liegen die Sprödbruchübergangstemperaturen (DBTT) von untersuchten niedrigaktivierbaren Stählen unterhalb von -20 °C und damit weit unterhalb der Anwendungstemperatur. Die Analyse des Verfestigungs- vs. Versprödungs- Verhaltens deutet auf die verfestigungsdominierte Versprödung unterhalb von Tirr ≤ 350 °C mit 0,17≤ C100 ≤ 0,53 °C/MPa. Oxiddispersionsgehärteter ODS EUROFER Stahl mit 0,5 wt.% Y2O3 wurde bei ausgewählten Temperaturen bestrahlt. Bereits im unbestrahlten Zustand zeigte ODS EUROFER keine be- friedigende Kerbschlagbiegeeigenschaften, gekennzeichnet durch eine niedrige USE = 2,54 J und durch eine große DBTT = 135 °C. Die Zunahme von USE für Bestrahlungstemperaturen unterhalb von Tirr ≤ 350°C deutet außerdem auf ein nicht optimiertes Herstellungsverfahren. Bei Tirr = 250 °C ist die bestrahlungsinduzierte Verschiebung der Übergangstemperatur vergleichbar mit der vom EUROFER97. Bei höheren Bestrahlungstemperaturen zeigt hingegen ODS EUROFER größere Versprödung im Vergleich zum Referenzmetall. Die Rolle des Heliums in der Materialversprödung wurde an EUROFER97 basierten Stählen untersucht, welche mit verschiedenem Bor Gehalt (0,008-0,112 wt.%) dotiert wurden. Bor dotierte Proben zeigen zunehmende Versprödung und Abnahme der Zähigkeit mit der Zunahme des generierten Helium Gehalts. Bis zu einem Helium Gehalt von 84 appm ist bei Tirr = 250 °C Helium induzierte Versprödung auf Helium induzierte Verfestigung zurückzuführen. Höhere Helium Konzentrationen führten zu weiteren Versprödungsmechanismen zusätzlich zur Helium induzierten Verfestigung

Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities

A simple model is introduced to describe conductance measurements between a scanning tunneling microscope (STM) tip and a noble metal surface with adsorbed transition metal atoms which display the Kondo effect. The model assumes a realistic parameterization of the potential created by the surface and a d3z2-r2 orbital for the description of the adsorbate. Fano lineshapes associated with the Kondo resonance are found to be sensitive to details of the adsorbate-substrate interaction. For instance, bringing the adsorbate closer to the surface leads to more asymmetric lineshapes while their dependence on the tip distance is weak. We find that it is important to use a realistic surface potential, to properly include the tunnelling matrix elements to the tip and to use substrate states which are orthogonal to the adsorbate and tip states. An application of our model to Co adsorbed on Cu explains the difference in the lineshapes observed between Cu(100) and Cu(111) surfaces.Comment: 11 pages, 8 eps figure

Propylene Carbonate Reexamined: Mode-Coupling β\beta Scaling without Factorisation ?

The dynamic susceptibility of propylene carbonate in the moderately viscous regime above $T_{\rm c}$ is reinvestigated by incoherent neutron and depolarised light scattering, and compared to dielectric loss and solvation response. Depending on the strength of $\alpha$ relaxation, a more or less extended $\beta$ scaling regime is found. Mode-coupling fits yield consistently $\lambda=0.72$ and $T_{\rm c}=182$K, although different positions of the susceptibility minimum indicate that not all observables have reached the universal asymptotics

Universal and non-universal features of glassy relaxation in propylene carbonate

It is demonstrated that the susceptibility spectra of supercooled propylene carbonate as measured by depolarized-light-scattering, dielectric-loss, and incoherent quasi-elastic neutron-scattering spectroscopy within the GHz window are simultaneously described by the solutions of a two-component schematic model of the mode-coupling theory (MCT) for the evolution of glassy dynamics. It is shown that the universal beta-relaxation-scaling laws, dealing with the asymptotic behavior of the MCT solutions, describe the qualitative features of the calculated spectra. But the non-universal corrections to the scaling laws render it impossible to achieve a complete quantitative description using only the leading-order-asymptotic results.Comment: 37 pages, 16 figures, to be published in Phys. Rev.

Anomalous diffusion and the first passage time problem

We study the distribution of first passage time (FPT) in Levy type of anomalous diffusion. Using recently formulated fractional Fokker-Planck equation we obtain three results. (1) We derive an explicit expression for the FPT distribution in terms of Fox or H-functions when the diffusion has zero drift. (2) For the nonzero drift case we obtain an analytical expression for the Laplace transform of the FPT distribution. (3) We express the FPT distribution in terms of a power series for the case of two absorbing barriers. The known results for ordinary diffusion (Brownian motion) are obtained as special cases of our more general results.Comment: 25 pages, 4 figure

Stable mode-locked pulses from mid-infrared semiconductor lasers

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.Comment: 26 pages, 4 figure

Low-lying quadrupole collective states of the light and medium Xenon isotopes

Collective low lying levels of light and medium Xenon isotopes are deduced from the Generalized Bohr Hamiltonian (GBH). The microscopic seven functions entering into the GBH are built from a deformed mean field of the Woods-Saxon type. Theoretical spectra are found to be close to the ones of the experimental data taking into account that the calculations are completely microscopic, that is to say, without any fitting of parameters.Comment: 8 pages, 4 figures, 1 tabl

Uncoupled continuous-time random walks: Solution and limiting behavior of the master equation

A detailed study is presented for a large class of uncoupled continuous-time random walks (CTRWs). The master equation is solved for the Mittag-Leffler survival probability. The properly scaled diffusive limit of the master equation is taken and its relation with the fractional diffusion equation is discussed. Finally, some common objections found in the literature are thoroughly reviewed.Comment: Preprint version of an already published paper. 8 page

On distributions of functionals of anomalous diffusion paths

Functionals of Brownian motion have diverse applications in physics, mathematics, and other fields. The probability density function (PDF) of Brownian functionals satisfies the Feynman-Kac formula, which is a Schrodinger equation in imaginary time. In recent years there is a growing interest in particular functionals of non-Brownian motion, or anomalous diffusion, but no equation existed for their PDF. Here, we derive a fractional generalization of the Feynman-Kac equation for functionals of anomalous paths based on sub-diffusive continuous-time random walk. We also derive a backward equation and a generalization to Levy flights. Solutions are presented for a wide number of applications including the occupation time in half space and in an interval, the first passage time, the maximal displacement, and the hitting probability. We briefly discuss other fractional Schrodinger equations that recently appeared in the literature.Comment: 25 pages, 4 figure

Neutrino Interferometry In Curved Spacetime

Gravitational lensing introduces the possibility of multiple (macroscopic) paths from an astrophysical neutrino source to a detector. Such a multiplicity of paths can allow for quantum mechanical interference to take place that is qualitatively different to neutrino oscillations in flat space. After an illustrative example clarifying some under-appreciated subtleties of the phase calculation, we derive the form of the quantum mechanical phase for a neutrino mass eigenstate propagating non-radially through a Schwarzschild metric. We subsequently determine the form of the interference pattern seen at a detector. We show that the neutrino signal from a supernova could exhibit the interference effects we discuss were it lensed by an object in a suitable mass range. We finally conclude, however, that -- given current neutrino detector technology -- the probability of such lensing occurring for a (neutrino-detectable) supernova is tiny in the immediate future.Comment: 25 pages, 1 .eps figure. Updated version -- with simplified notation -- accepted for publication in Phys.Rev.D. Extra author adde