Transient radiative bursts have been observed in systematic time-correlation with dust influx across the separatrix in JET ILW campaigns, [1]. Dust influx from PFC materials can produce transient temperature and density perturbations in the SOL. Are such local perturbations detectable by existing diagnostics? Could they be used as an additional monitor for safe operation? Results from the model illustrated here indicate that local densities of dust can produce bursts of acoustic waves in the low-temperature, low-density SOL, that could be detected by existing diagnostics.

Fuel accumulation in plasma-facing and structural materials used in fusion devices is highly important both for radiation safety and for the assessment of the impact of gas recycling on plasma operation. Co-deposition, that is simultaneous deposition of previously eroded plasma facing materials and plasma particles, is considered one of the primary sources of hydrogen fuel accumulation in tokamaks [1]. Helium (He) quantity in future reactors will be about the same as that of fuel particles due to deuterium-tritium (D-T) fusion reactions. It is well known that radiation/exposure causes much more material damage than hydrogen atoms such as He bubbles and nano-structures, known as "fuzz" [2]. As laboratory experiments have demonstrated [3], He is trapped in tungsten (W) samples by ion and plasma implantation. Therefore, it is important to investigate how He is accumulated in co-deposited or re-deposited layers observed in fusion devices. As reported in the literature [4] W-He co-deposits, which simulate the re-deposited layers, can be produced in the laboratory by exploiting magnetron sputtering technology. In this contribution, the laboratory production of reference coatings mimicking tokamak W-He deposits and the characterization of their morphology and He content are presented. The effect of the different process parameters on the properties of the coatings is also addressed. W-He films were deposited by magnetron sputtering with variations of pressure ranging from 1-5 Pa. The morphology of the coatings was investigated by Scanning Electron Microscopy (SEM) whereas the He content within the layer was measured by Laser Induced Desorption Spectroscopy (LIDS), Laser-Induced Breakdown Spectroscopy (LIBS) and Thermal Desorption Spectroscopy (TDS). He TDS spectra exhibit a broad desorption peak in the 500-600 K range and another one, significantly increased, at ~960 K. To quantify He content in the samples, a calibration procedure that takes into account the conductance and pumping speed of the device has been performed allowing the determination of the sensitivities of the mass spectrometers used as detectors for TDS and LIDS.

Erosion of plasma-facing components affects their lifetime and other plasma-material interaction (PMI) issues important for ITER. Microscale morphology is shown to have a significant effect on surface sputtering properties [1], thus influencing the erosion-deposition pattern in tokamaks. Linear plasma devices (LPDs) are a perfect testbed for the investigation of this topic due to their cost-effectiveness and well-controlled exposure conditions. Modelling of the experiments with PMI codes, like ERO2.0 [1-2], is then highly recommended to gain insight into relevant processes. Present work reports on the investigation of the role of roughness in the sputtering process of tungsten (W) by helium (He) plasma of the linear device GyM (B?80 mT). Helium is of great interest when studying PMI since it will be present in a fusion plasma as an intrinsic impurity and it will also be the main plasma species during ITER pre-fusion power operation. W coatings deposited on: silicon (Si) substrates with pyramids on the surface and four different average roughnesses (Ra?3, 300, 600, 900 nm), and graphite substrates with irregular surface and three different Ra (?7, 90, 280 nm), as well as reference polished bulk W samples (Ra?10 nm), have been exposed in GyM changing the incident He+ energy (EHe+) between one experiment and the other in 30 - 350 eV range (i.e. by applying different bias voltage values to the samples), for a fluence of 4.0e24 He+m-2. Net erosion of the samples has been estimated from mass loss data. Morphology modifications have been investigated by scanning electron and atomic force microscopies. Experimental outcomes have been finally compared to ERO2.0 results. Considering W/Si samples, surface modifications were limited to the formation of ripples at the nanoscale for EHe+>=250 eV. This allowed to evaluate the quasi-static effective sputtering yield (YW|GyM) from mass loss data, on the one hand, and run single time step ERO2.0 simulations, on the other hand. For EHe+<=200 eV, YW|GyM is negligible. For higher energies, YW|GyM decreases by increasing the mean value of the surface inclination angle distribution (?m), in agreement with ERO2.0 results. ?m is thus the key-parameter determining the erosion of the samples rather than Ra, as also pointed out in [3]. Moreover, YW|GyM is about one order of magnitude lower than that from ion beam experiments and binary collision approximation (BCA) calculations, confirming what was observed in other LPDs [4]. Since the energy and angular distributions of sputtered particles in ERO2.0 were provided by the BCA SDTrimSP code, the effective YW from the code is also higher than YW|GyM. Calibration of ERO2.0 input, as the sputtering distributions and the incoming plasma flux, was necessary to improve the quantitative agreement with experimental data. The exposures of W coatings deposited on graphite substrates and polished bulk W samples are currently ongoing and the results will be presented during the Conference.

This work reports on the investigation of Eurofer-97 erosion behaviour when exposed to the deuterium plasma of the linear device GyM. The erosion dependence of Eurofer-97 on the deuterium ion fluence, 1025 m-2, and temperature of the samples, T = 600 K and 990 K, was addressed. A bias voltage of -200 V was applied to GyM sample holder during the experiments. Samples were deeply characterised by: profilometry, scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, Rutherford backscattering spectroscopy and particle-induced X-ray emission. The behaviour of Eurofer-97 erosion rate with the ion fluence strictly depends upon temperature. At 600 K, it was 0.14 nm/s after 4.7 × 1024 m-2, then decreased, reaching a steady state value of 0.01 nm/s from 8.0 × 1024 m-2. At 990 K instead, the erosion rate was roughly constant around 0.019 nm/s for 1025 m-2. The value at 2.35 × 1025 m-2 was slightly lower. The erosion rate at 990 K was greater than that at 600 K for every ion fluence. Microscopy and surface analysis techniques showed that Eurofer-97 erosion rate dependence on at 600 K was primarily determined by the preferential sputtering of iron and other mid-Z elements of the alloy, leading to a surface rich in W and Ta difficult to be sputtered. The erosion behaviour at 990 K was dominated by the morphology dynamics, instead. The different properties of the morphology developed at the two temperatures can explain the higher erosion rate at 990 K for all the ion fluences.

GyM is a linear plasma device operating at Istituto per la Scienza e Tecnologia dei Plasmi, Consiglio Nazionale delle Ricerche, Milan, with the original aim of studying basic plasma physics, such as turbulent processes. Since 2014, GyM experimental program has been mainly focused on the issue of plasma-material interaction (PMI) for magnetic confinement nuclear fusion applications. GyM consists of a stainless steel vacuum chamber (radius and length of 0.125 m and 2.11 m), a pumping system, a gas injection system, 10 magnetic field coils and two magnetron sources at 2.45 GHz, capable of delivering a total microwave power up to 4.5 kW. Highly reproducible steady-state plasmas of different gas species, at a maximum working pressure of ~10-1 Pa, can be obtained by electron cyclotron resonance heating in the resonance layer at 87.5 mT. Plasmas of GyM have electron and ion temperature <=15 eV and ~0.1 eV, respectively. The electron density is in the range of 1015-1017 m-3 and the ion flux is <=5 × 1020 ions?m-2s-1. Main plasma diagnostics of GyM comprise Langmuir probes, an optical emission spectrometer, a mass spectrometer and a fast camera system equipped with an image intensifier unit. For the purpose of investigating the topic of PMI, GyM is provided with two sample exposure systems. Both are biasable at a negative bias voltage down to -400 V, to tune the energy of the impinging ions. One of them is also equipped with a heating lamp and can reach and sustain a temperature of 990 K for several hours, thus allowing to study the role of sample temperature during the plasma-material interaction. This contribution presents the layout of GyM, the diagnostics, the sample exposure systems and the typical plasma parameters. A brief overview of the main PMI activities carried out so far and a description of future machine upgrades are also given.

Validazione statistica che, nelle ipotesi considerate, il numero dei conteggi ISS ottenuti via MD segue una distribuzione di Poisson

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

Post-mortem and in situ evidence is presented in favor of the generation of high-velocity solid dust during the explosion-like interaction of runaway electrons with metallic plasma-facing components in FTU. The freshly-produced solid dust is the source of secondary de-localized wall damage through high-velocity impacts that lead to the formation of craters, which have been reproduced in dedicated light gas gun impact tests. This novel mechanism, of potential importance for ITER and DEMO, is further supported by surface analysis, multiple theoretical arguments and dust dynamics modeling.

A modelling analysis is performed on JET D and DT discharges, where W dust influx across the separatrix, in the pedestal edge region may affect L-H-L mode transition. The experimental basis of the proposed approach stems from the observation that transient impurity events (TIEs) are often associated with the presence of a shower of particles seen in the camera images and with strong optical emission. If the localised source of radiation is a number of heated or ablated large dust particles, then the questions addressed here are: how far will the ablated dust material penetrate and what effect will this have on the edge of the pedestal in relevant JET D and in a high fusion yield D-T discharges. The methodology is based on the use of an upgraded version of the ballistic code DUSTTRACK and a new code PELLYTIX for dust ablation modelling. Considering a reasonable amount of dust released from the tiles, the analysis shows that the ablation-penetration depth is visible in the density profiles modification, but not disastrous for tokamak operation in high regimes.

Laser Induced Desorption Spectroscopy (LIDS) has been used to investigate the helium desorption from coatings and bulk tungsten in laboratory experiments as a prerequisite for the later application in-situ in the GyM linear device. Tungsten coatings were deposited on a silicon substrate by magnetron sputtering process. After a preliminary surface characterization and before studying the gas desorption by LIDS, both types of tungsten samples were exposed to helium plasma in the GyM linear device. A Nd:YAG laser with constant output power leading to a smooth controllable increase of layer temperature was used, resulting in a complete desorption of gases in a point heated by the laser. The desorbed gases were detected up to 200 amu/e with a QMS (Quadrupole Mass Spectrometer). The results of the application of LIDS on tungsten targets exposed to a wide range of helium fluxes, fluences, and impact energies under different surface temperatures are presented and compared with Thermal Desorption Spectrometry (TDS) and Laser Induced Breakdown Spectroscopy (LIBS).

The process of deep texturization of the crystalline silicon surface is intimately related to its promising diverse applications, such as bactericidal surfaces for integrated lab-on-chip devices and absorptive optical layers (black silicon?BSi). Surface structuring by a maskless texturization appeals as a cost-effective approach, which is up-scalable for large-area production. In the case of silicon, it occurs by means of reactive plasma processes (RIE?reactive-ion etching) using fluorocarbon CF4 and H2 as reaction gases, leading to self-assembled cylindrical and pyramidal nanopillars. The mechanism of silicon erosion has been widely studied and described as it is for the masked RIE process. However, the onset of the erosion and the reaction kinetics leading to defined maskless patterning have not been unraveled to date. In this work, we specifically tackle this issue by analyzing the results of three different RIE recipes, specifically designed for the purpose. The mechanism of surface self-nanopatterning is revealed by deeply investigating the physical chemistry of the etching process at the nanoscale and the evolution of surface morphology. We monitored the progress in surface patterning and the composition of the etching plasma at different times during the RIE process. We confirm that nanopattering issues from a net erosion, as contributed by chemical etching, physical sputtering, and by the synergistic plasma effect. We propose a qualitative model to explain the onset, the evolution, and the stopping of the process. As the RIE process is started, a high density of surface defects is initially created at the free silicon surface by energetic ion sputtering. Contextually, a polymeric overlayer is synthesized on the Si surface, as thick as 5 nm on average, and self-aggregates into nanoclusters. The latter phenomenon can be explained by considering that the initial creation of surface defects increases the activation energy for surface diffusion of deposited CF and CF2 species and prevents them from aggregating into a continuous Volmer-Weber polymeric film. The clusterization of the polymer provides the self-masking effect since the beginning, which eventually triggers surface patterning. Once started, the maskless texturing proceeds in analogy with the masked case, that is, by combined chemical etching and ion sputtering, and ceases because of the loss of ion energy. In the case of CF4/H2 RIE processes at 10% of H2 and by supplying 200 W of RF power for 20 min, nanopillars of 200 nm in height and 100 nm in width were formed. We therefore propose that a precise assessment of surface defect formation and density in dependence on the initial RIE process parameters can be the key to open a full control of outcomes of maskless patterning.

The JET 2019-2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power in 2019-2020, and tested the technical and procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle (?) physics in the coming D-T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed shattered pellet injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILWplasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design and operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D-T benefited from the highest D-D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER.

The report presents several statistical methods to validate the hypothesis that the Leis spectra, obtained through an MD code (Ne + on W110), continue to have two maxima and a minimum even when the azimuth angle is random

Modelling and analysis of transport and PSI in JET-ILW edge and divertor: Be/W erosion, fuel isotopes, molecules and dust.

Biodegradable polymers are viewed asa promisingeco-friendly solutionto replace conventional plastic polymers as packaging materials, reducing the enormous environmental impact that the latter involve[1]. However, biodegradable plastics still occupy a rather restrictedsection of the plastic food packagingmarketduesome limitations includingtheirpoorgas barrier andUV protectionproperties[2].In fact, both oxygen and UV light lead to oxidation processeswhich alter food quality and produce toxic compounds [3,4].In this regard, low temperature plasma technique can be exploited to fabricate multifunctional polymeric surfaces with significant enhanced performances. This approach is completelyenvironmentally friendly avoiding the use of toxic solvents or high temperatures that coulddamage the polymer structure[5,6]and it is crucial to extendthe use of biodegradable packaging and preservethe food quality.In this work we report onsurfacesmodificationsof two commercial biodegradable polymers by low temperature plasma processes. In particular, tungsten oxide (WOx) thin films were deposited by plasma magnetron sputtering on poly(lactic acid) (PLA)in orderto enhanceitsperformances in terms of barrier to oxygen and UV light protection. Moreover, plasma etching was employedto tailor the surface morphology of poly(butylene succinate) (PBS)resulting in a packaging with antimicrobial effect due to the nature inspired contact-killing mechanism.

Poly(butylene succinate) (PBS) films were processed by a radio frequency (RF; 13.56 MHz) low-pressure plasma of oxygen and argon/oxygen, and an oxygen plasma with an argon post- crosslinking plasma to improve their wettability property. Specimens were treated at different times with fixed power processing of 100 W (0.3 W/cm2) and a fixed pressure of 10 Pa. A significant change in hydrophilicity evaluated by the water contact angle was observed. The contact angle of a water drop decreased from 80o for the untreated sample to values lower than 5o for plasma-treated samples. The effect of ageing on the wettability of PBS substrates was also examined, showing a more pronounced trend in the first 4 h and reaching a plateau in the following days. However, partial surface hydrophilicity was maintained for up to 15 days. A practical application of the surface functionalization produced by plasma was obtained via the deposition of SiOx onto PBS surfaces; the study of films' oxygen permeability demonstrated that the plasma pre-treatment increased the adhesion between PBS and SiOx, resulting in significantly improved oxygen barrier properties. In order to evaluate the morphology and roughness modification caused by plasma exposure, atomic force microscopy characterization was carried out. Chemical information about treated surfaces, such as an increase in oxygen functional groups during plasma exposure, was measured by Fourier- transform infrared spectroscopy and X-ray photoelectron spectroscopy. Finally, the effects of plasma on crystallinity were investigated by X-ray diffraction.

Current studies on ammonia formation during nitrogen seeding experiments in tokamak divertors meet the need to find out the percentage of nitrogen converted in ammonia and study the reaction mechanism [1]. Useful information on the latter can be obtained also from the study of the inverse reaction through ammonia decomposition experiments. In this context ammonia formation and dissociation have been studied in GyM linear device and the catalytic effect of the wall on these processes has been investigated. Exploiting the versatility of GyM machine, made up of a cylindrical stainless steel (SS) vacuum vessel in which an additional tungsten (W) liner can be inserted, a comparison between the two frameworks with SS and W walls has been made. In ammonia formation experiments a mixture of nitrogen and deuterium has been injected with different gas concentrations. The amount of ammonia produced, quantified by chromatography analysis of the exhaust, was maximized up to 20% of nitrogen conversion by properly adjusting the N2:D2 ratio, the operating Te and ne, the type of wall material and the residence time of gases. The analysis of the intermediate species in plasma phase performed through the use of optical emission spectroscopy (OES) shows the progressive formation of ND species as the machine power increases and its correlation with the detected ammonia molecules by mass spectrometer (MS). In decomposition experiments ammonia was injected in mixture with helium (0,5% mol). Data from the analysis of the chemical composition of the exhaust collected during the experiments show that, under plasma conditions of Te = 7eV and ne = 6E+16 m-3, more than 30% of the ammonia fed into the reactor has been dissociated. The absence in OES spectra of spectral features due to nitrogen species suggests that no N2 is formed through ammonia decomposition. OES and MS don't provide any direct experimental evidence about the involvement of the material surface in the reaction mechanisms. However, some inferences are reasonable based on the known reactivity of the different species involved in the process. In experiments of ammonia decomposition it is most likely that under our experimental conditions the initial rupture of the ammonia molecules mainly occurs by electron impact and, possibly, through dissociative surface adsorption. In experiments of ammonia formation excited species, such as fragments of ammonia (ND), detected by OES, might be adsorbed and react on the surface with surface-adsorbed atomic deuterium species and form ammonia molecules by the well-known Eley-Rideal mechanism [2]. These considerations about the involvement of the chemical reactions on the wall of the plasma device, complemented with the OES and MS data, indicate, under the considered GyM conditions, that ND radicals play a leading role in the synthesis of ammonia while electron impact dissociation of NH3 molecules has got a key role in ammonia dissociation processes.