A necessary and sufficient condition on scattering for the regularly hyperbolic systems

The present paper is devoted to finding a necessary and sufficient condition on the occurence of scattering for the regularly hyperbolic systems with time-dependent coefficients whose time-derivatives are integrable over the real line. More precisely, it will be shown that the solutions are asymptotically free if the coefficients are stable in the sense of the Riemann integrability as time goes to infinity, while each nontrivial solution is never asymptotically free provided that the coefficients are not R-stable as times goes to infinity. As a by-product, the scattering operator can be constructed. It is expected that the results obtained in the present paper would be brought into the study of the asymptotic behaviour of Kirchhoff systems.Comment: 16 page

Progress in Elastic Recoil Detection Analysis

Elastic recoil detection analysis (ERDA) with heavy ion beams has evolved into a universal ion beam analysis (IBA) method for simultaneous analysis of almost all elements, with an essentially constant detection sensitivity. The method is based on the detection and identification of recoiling atoms that have been elastically scattered from a sample by an incident heavy ion beam. The principal characteristics of heavy-ion ERDA are outlined and illustrated using examples of data obtained with time of flight (TOF) and dE-E detector systems. The potential and limitations of the quantitative analysis were explored. For this purpose, a number of thin layer samples were measured using different projectiles and energies. Desorption of the surface materials during ERDA measurements was determined as a function of the probing ion fluence. As the differential cross-sections for scattering were enhanced for heavy projectiles, the beam dose to which the sample was exposed to during measurements was reduced by using heavy ion beams. However the higher cross-sections caused an increase of the desorption. An essential part of this study was dedicated to study those topics that limit the accuracy of the analysis in heavy ion TOF-ERDA, namely: uncertain stopping forces, quantification accuracy, irradiation induced damage, depth resolution, and the role of multiple and plural scattering. Possible approaches to improve the sample characterisation efficiency and accuracy were studied by using a gas ionisation detector. This study concentrates on the noise reduction, detection characterisation, and analysis procedures. The focus was upon the effect of the large solid angle and position sensitivity on the irradiation induced damage, depth resolution, mass resolution, and elemental sensitivity. The reliability of the concentration distributions obtained with heavy ion ERDA was strongly affected by the surface structure, surface roughness and multiple scattering. These effects were studied by comparing Monte Carlo simulations with the experimental results. The analysis procedure was developed to enable the characterisation of novel materials such as atomic layer deposited thin films and nanoparticles. Data handling and storage was improved to facilitate and speed up the analysis procedures.Nykyteknologian kannalta materiaalien tärkeimmät ominaisuudet sijoittuvat aineen pintakerroksiin. Lisäksi materiaalitutkimuksessa keskitytään enenevässä määrin nanorakenteisiin, kuten nanokiteisiin ja nanoputkiin. Eräs keskeinen materiaalitutkimuksen ongelma on tämän muutamista nanometreistä muutamiin satoihin nanometreihin paksun kerroksen ominaisuuksien analysointi. Ionisuihkuihin perustuvia analysointimenetelmiä (IBA, ion beam analysis) käytetään yleisesti alkuainekoostumuksen analysointiin. Tässä tutkimuksessa keskitytään rekyylispektroskopiaan (ERDA, elastic recoil detection analysis), joka perustuu energeettisten hiukkasten törmäyksessä syntyvän rekyyliatomin havainnointiin. ERDA menetelmässä näytteen analysointiin käytetään usein raskaita ammusioneja, jotka kiihdytetään sähköstaattisella kiihdyttimellä useiden kymmenien megaelektronivolttien energioihin. Kiihdytettyjen hiukkasten ja tutkittavan materiaalin törmäyksessä ammushiukkaset siroavat ja näytteen atomit saavat rekyylin, joka irrottaa atomin näytteestä. ERDA menetelmässä nämä rekyyliatomit ja sironneet ammushiukkaset havainnoidaan sopivalla ilmaisimella. Menetelmässä on mahdollista analysoida näytteen kaikki alkuaineet, aina vedystä raskaimpiin yhdellä mittauksella. Erilaisten havaittavien hiukkasten takia ilmaisinlaitteistolta vaaditaan kykyä tunnistaa hiukkaset ja mitata näiden energia. Tässä tutkimuksessa selvitetään lentoajan mittaukseen perustuvan ERDA ilmaisimen (TOF-ERDA, time-of-flight ERDA) rajoituksiin ja mahdollisiin parannuksiin, jotta menetelmä sopisi nykyisen materiaalitutkimuksen kannalta kiinnostaviin näytteisiin. Keskeisimmät ongelmat TOF-ERDA menetelmässä ovat lentoajan mittauksen tarkkuus (aikaresoluutio) ja ilmaisimen äärelliseen havainnointikulman aiheuttama energian hajonta. Yleisesti IBA menetelmät, joissa määritetään näytteen alkuaineiden syvyysjakaumia, pohjautuvat materiaalin kykyyn jarruttaa varattuja hiukkasia. Aineen jarrutuskyvylle on olemassa erilaisia teoreettisia ja puolikokeellisiin malleja. IBA menetelmissä käytetyimmät mallit pohjautuvat kokeelliseen dataan ja näiden mallien tarkkuus riippuu saatavilla olevan datan määrästä ja tarkkuudesta. Osa tästä tutkimuksesta keskittyy menetelmiin, joilla hiukkasten energian menetys aineessa voidaan mitata ja tästä edelleen materiaalin jarrutuskyky määrittää. Saatuja tuloksia ja parannuksia on käytetty useiden erityyppisten materiaalien alkuaineanalyyseissä

Evaluation of tritium retention in plasma facing components during JET tritium operations

An assessment of the tritium (T) inventory in plasma facing components (PFC) during JET T and deuterium-tritium (DT) operations is presented based on the most comprehensive ex situ fuel retention data set on JET PFCs from the 2015-2016 ILW3 operating period is presented. The global fuel retention is 4.19 x 10(23) D atoms, 0.19% of injected fuel. The inner divertor remains the region of highest fuel retention (46.5%). The T inventory in PFCs at the end of JET operations is calculated as 7.48 x 10(22) atoms and is informative for accountancy, clean-up efficacy and waste liability assessments. The T accumulation rate at the upper inner divertor during JET DT operations has been used to assess the requirements and frequency of operation of a new laser induced desorption diagnostic to be installed on JET for the final DT experiments in 2023.Peer reviewe

Thermal diffusivity degradation and point defect density in self-ion implanted tungsten

Using transient grating spectroscopy (TGS) we measure the thermal diffusivity of tungsten exposed to different levels of 20 MeV self-ion irradiation. Damage as low as 3.2 × 10−4 displacements per atom (dpa) causes a measurable reduction in thermal diffusivity. Doses of 0.1 dpa and above, up to 10 dpa, give a degradation of ̴55% from the pristine value at room temperature. Using a kinetic theory model, the density of irradiation-induced point defects is estimated based on the measured changes in thermal diffusivity as a function of dose. These predictions are compared with point defect and dislocation loop densities observed in transmission electron microscopy (TEM). Molecular dynamics (MD) predictions are combined with the TEM observations to estimate the density of point defects associated with defect clusters too small to be probed by TEM. When these “invisible” defects are accounted for, the total point defect density agrees well with that estimated from TGS for a range of doses spanning 3 orders of magnitude. Kinetic theory modelling is also used to estimate the thermal diffusivity degradation expected due to TEM-visible and invisible defects. Finely distributed invisible defects appear to play a much more important role in the thermal diffusivity reduction than larger TEM-visible dislocation loops. This work demonstrates the capability of TGS, in conjunction with kinetic theory models, to provide rapid, quantitative insight into defect densities and property evolution in irradiated materials.Peer reviewe

The effect of high-pressure torsion on irradiation hardening of Eurofer-97

We investigate the effect of nano-structuring by high-pressure torsion (HPT) on the irradiation performance of Eurofer-97. Material was deformed to shear strains from 0 to ∼230, and then exposed to Fe3+ irradiation doses of 0.01 and 0.1 displacements-per-atom (dpa). Nanoindentation hardness increases monotonically with deformation, and with irradiation for the undeformed material. For both damage levels, less irradiation hardening is observed in severely deformed material. This effect is most prominent in the strain range ∼60 to ∼160, suggesting that nano-structuring may provide an approach for reducing irradiation hardening