Dorothy : Waltz

https://digitalcommons.library.umaine.edu/mmb-ps/3451/thumbnail.jp

The Bohemians

https://digitalcommons.library.umaine.edu/mmb-ps/2375/thumbnail.jp

IR reflectivity measurements depending on carbon film thickness

Abstract: In thermonuclear controlled fusion machines using magnetic confinement, carbonisations are realised to prevent metal impurities to enter into the fusion plasma made with hydrogen elements; it consists in helium glows in which methane gas is injected . The methane molecule is broken and the carbon deposits on all inside vessel surfaces : inner walls as well as optic elements like windows and mirrors . We studied the dependence of the reflectivity of infrared thermography stainless steel mirrors with carbon films thickness in the 3-5 m bandwidth . The presented results show a decrease of less than 10% of the temperature announced by the camera . . Magnetic fusion : Thermonuclear controlled fusion Although plasma particles are trapped in non-material magnetic barriers, atomic collisions appear and diffusion, convection,conduction and radiation phenomena occur; this implies heating of contact surfaces . That is why an infrared thermographic system is developped to measure and survey these heatings which can lead to a failure of one of the plasma facing component inside the tokamak [2] . . IR thermographic diagnostic : The Tore Supra IR thermographic diagnostic consists, until now, in three endoscopes [fig 2] situated at 120° one from the other on the top of the tokamak; they are remotely controled so that every element inside the vessel can be observed . Images of objects inside the vessel are captured by a movable stainless steel mirror and returned to an optical system through a sapphire window . This window is necessary to keep http://dx.doi.org/10.21611/qirt.2000.049 ultra high vacuum inside the torus vessel . Inframetrics 3-5 m cameras recuperate images from the optical system which transported them . Plasma inside the tokamak encounters surfaces made of, or covered with graphite . This graphite is sputtered and redeposited during or after plasma is stopped . Furthermore carbonisations are made to cover metal inner walls of the vessel with carbon so that metal impurities rate inside the plasma is lower . Carbonisation, and its erosion, was extensively studied . Experimental apparatus : Our carbonisation system was installed in a special vessel Two 2 polished mirrors, set back to back, are supposed to be hidden from carbon deposition and centimeter by centimeter are exposed to the glow (see . Experimental results : Six carbon films 1 cm x 3 cm wide were obtained : 50 monolayers, 150, 250, 350, 450 and 550 monolayers thick [ The two mirrors present the same visual aspect . A correlation between film thickness and colour was established by J. Winter in his study of carbonisation in Textor tokamak Reflectivity results for both mirrors are presented below [ Reproducibility of our reflectivity measurements is in the order of +/-2 % . Our deposits need special care because of their poor adhesion : we lost part of the thickest deposits by rubbing with a plastic bag . Mirrors surfaces were made very smooth and then it is not so surprising that our films have little adhesion as thick they are . Furthermore, electrostatic interaction may increase this effect . Indeed carbonisation films have quite high electrical resistivity . For example, on Textor samples 1 -10 6 cm was typically measured Measurement of the 550 monolayers zone where the deposit is and where it peeled, was undertaken . Reflectivity of the undamaged part of the film is the lowest . Reflectivity of the peeled film is half between that latter and that of 0 -150 monolayers . If we consider the worst result which means 550 undamaged monolayers deposited, we find that the real temperature is underestimated by less than 10 per cent; this may be dangerous in our application especially at high temperatures : for example, the copper melting point is at 1083°C, with our results the temperature indicated by infrared cameras is around 975°C, but inside the copper 15 bar water circulate to refregirate the plasma facing components which means that with our measurement we wouldn't understand why there is a water leak in the machine; this leak implies no experiment for three months to mend damaged parts and to restart the machine . . Conclusion : We realised carbonisation with variable thicknessses on two polished stainless steel mirrors used in the infrared 3-5 m band . Their reflectivity before and after carbonisation was measured, on the different thicknesses of the films formed . Below 150 monolayers the reflectivity does not change . Beyond 150 monolayers, a decrease is observed . If deposit peels, reflectivity is only modified but does not come back to the value with few deposit . Over 450 monolayers the deposit shows waves which show poor film adhesion . The two mirrors have the same results even if they were set back to back for carbonisation, one looking at the anode, the other looking at the opposite . We deduced from these reflectivity measurements that in the case of the thickest deposit the real temperature of the tokamak element is under evaluated by less than 10 % . Acknowledgements : The authors want to thank A Grosman for fruitfull discussion and P. Maillet and his team for their advices and help for that work to be done

Ultra-Efficient PrPSc Amplification Highlights Potentialities and Pitfalls of PMCA Technology

In order to investigate the potential of voles to reproduce in vitro the efficiency of prion replication previously observed in vivo, we seeded protein misfolding cyclic amplification (PMCA) reactions with either rodent-adapted Transmissible Spongiform Encephalopathy (TSE) strains or natural TSE isolates. Vole brain homogenates were shown to be a powerful substrate for both homologous or heterologous PMCA, sustaining the efficient amplification of prions from all the prion sources tested. However, after a few serial automated PMCA (saPMCA) rounds, we also observed the appearance of PK-resistant PrPSc in samples containing exclusively unseeded substrate (negative controls), suggesting the possible spontaneous generation of infectious prions during PMCA reactions. As we could not definitively rule out cross-contamination through a posteriori biochemical and biological analyses of de novo generated prions, we decided to replicate the experiments in a different laboratory. Under rigorous prion-free conditions, we did not observe de novo appearance of PrPSc in unseeded samples of M109M and I109I vole substrates, even after many consecutive rounds of saPMCA and working in different PMCA settings. Furthermore, when positive and negative samples were processed together, the appearance of spurious PrPSc in unseeded negative controls suggested that the most likely explanation for the appearance of de novo PrPSc was the occurrence of cross-contamination during saPMCA. Careful analysis of the PMCA process allowed us to identify critical points which are potentially responsible for contamination events. Appropriate technical improvements made it possible to overcome PMCA pitfalls, allowing PrPSc to be reliably amplified up to extremely low dilutions of infected brain homogenate without any false positive results even after many consecutive rounds. Our findings underline the potential drawback of ultrasensitive in vitro prion replication and warn on cautious interpretation when assessing the spontaneous appearance of prions in vitro

Model for screening of resonant magnetic perturbations by plasma in a realistic tokamak geometry and its impact on divertor strike points

This work addresses the question of the relation between strike-point splitting and magnetic stochasticity at the edge of a poloidally diverted tokamak in the presence of externally imposed magnetic perturbations. More specifically, ad-hoc helical current sheets are introduced in order to mimic a hypothetical screening of the external resonant magnetic perturbations by the plasma. These current sheets, which suppress magnetic islands, are found to reduce the amount of splitting expected at the target, which suggests that screening effects should be observable experimentally. Multiple screening current sheets reinforce each other, i.e. less current relative to the case of only one current sheet is required to screen the perturbation.Comment: Accepted in the Proceedings of the 19th International Conference on Plasma Surface Interactions, to be published in Journal of Nuclear Materials. Version 2: minor formatting and text improvements, more results mentioned in the conclusion and abstrac

Plasma-wall interaction studies within the EUROfusion consortium: Progress on plasma-facing components development and qualification

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.European Commission; Consortium for Ocean Leadership 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART