Helyssen

Description

Helyssen, spin-off du Swiss Plasma Center de l'EPFL, se spécialise dans le développement de sources de plasma inductifs avancées. Leur concept innovant de réseau résonant a révolutionné les plasmas industriels en offrant des performances exceptionnelles par rapport aux sources traditionnelles. En mettant l'accent sur les sources de plasma RF à haute efficacité couplées inductivement et chauffées par les vagues, Helyssen a franchi des étapes importantes dans le domaine de la technologie du plasma. Leurs technologies exclusives permettent la production de plasmas à haute densité dans de grandes zones, ce qui entraîne des percées dans diverses industries telles que la fabrication de circuits intégrés, la production de cellules solaires, les applications d'emballages alimentaires et la stérilisation environnementale.

Source officielle

https://www.helyssen.com

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Catégories associées (14)

Concepts associés (30)

Cours associés (56)

Séances de cours associées (428)

MOOCs associés (11)

Personnes associées (80)

Publications associées (3)

Unités associées (23)

Turbulent transport regimes in the tokamak boundary

Maurizio Giacomin

The overall performance of a tokamak strongly depends on phenomena that take place in a thin region between the main plasma and the vessel wall, which is denoted as tokamak boundary. In fact, the formation of transport barriers in this region can significantly improve plasma confinement and, therefore, the tokamak fusion performance. In addition, the tokamak boundary determines the peak heat flux to the wall, an essential quantity for the design and the operation of fusion power plants, as well as the level of impurities in the core, the removal of fusion ash and the dynamics of neutral particles.The dynamics in the plasma boundary is strongly nonlinear and characterized by a wide range of length and time scales as well as by a complex magnetic field geometry that mayfeature one or more nulls of the poloidal magnetic field. Large-scale, three-dimensional turbulence simulations are therefore often required to disentangle the complex physicalmechanisms that govern this region.The thesis is focused on the analysis of the different turbulent transport regimes present in the plasma boundary as they appear from three-dimensional, flux-driven, global, two-fluid turbulence simulations carried out by using the GBS code, which is significantly extended here to allow the self-consistent simulation of the plasma dynamics coupled to a kinetic single-species neutral model in arbitrarily complex magnetic geometries. Considering single-null magnetic configurations, three turbulent transport regimes are identified: (i) a regime of suppressed turbulent transport at low values of collisionality and large values of heat source, (ii) a regime of developed turbulent transport at intermediate values of collisionality and heat source, and (iii) a regime of very large turbulent transport at high value of collisionality and density, which can be associated to the crossing of the density limit. By leveraging the results of GBS simulations, theory-based scaling laws of the pressure and density decay lengths in the near and far scrape-off layer are derived in the developed transport regime from a balance among heat source, turbulent transport across the separatrix and parallel losses at the vessel wall. The theoretical scaling of the pressure decay length in the near scrape-off layer is successfully validated against a multi-machine database of SOL width measurements at the outer target.By carefully analysing the transition to the regime of large turbulent transport, we show that the density limit can be explained by an enhancement of turbulent transport at thetokamak boundary when the density increases. This analysis leads to a theory-based scaling law of the maximum edge density achievable in tokamaks, which is in better agreement with a multi-machine database than the widely used Greenwald empirical scaling, thus significantly improving our understanding and predictive capability of thedensity limit, with important implications for the design and the operation of future fusion power plants.The thesis concludes by presenting the first turbulent simulations carried out in various snowflake magnetic configurations, which are used to investigate the effect of turbulenceand equilibrium flow on the heat flux distribution among the different strike points.

EPFL2022

Particle transport in tokamak plasmas

Alexey Zabolotskiy

The transport of particles in magnetically confined plasmas is of great importance for the development of fusion energy. It will determine techniques for fuelling, for controlling impurity concentrations and for the removal of the alpha particles produced by fusion reactions. The issues related to particle transport have received, until relatively recently, less attention than those regarding heat transport. Besides the greater experimental difficulty of measuring particle transport, this may explain why our understanding of this subject is still incomplete. The aim of this thesis is to document and tentatively interpret the experimental density profile behaviour in the TCV (Tokamak à Configuration Variable) and JET (Joint European Torus) tokamaks in the framework of different theoretical and semi-empirical models. The TCV tokamak is well suited to transport studies due to its extreme shaping capability, which allows the exploration of a wide range of different plasma conditions. This versatility is matched by the powerful and flexible electron cyclotron heating (ECH) system on TCV, which allows a control of the local power deposition profiles and current drive profiles. A study of particle transport on the JET tokamak has allowed us to compare the results of TCV to those of a much larger device and supplement the TCV study with the analysis in reactor relevant high confinement regime (H-mode). The experimental information was compiled into a database of density profiles in steady state, containing nearly 1000 samples for TCV and 600 samples for JET. The data analyzed covered a wide range of discharge conditions, including low confinement regime (L-mode) and H-mode discharges, ECH, ICH (ion cyclotron heating), LHCD (low hybrid), beam heated plasmas and include fully current drive discharges. The most relevant parameters which influence the density profiles were determined by regression. A detailed analysis of the particle sources showed that edge fuelling in TCV and JET cannot be responsible for density gradient in the plasma bulk, confirming the presence of particle convection or a 'pinch'. The existence of an anomalous pinch was unambiguously demonstrated both on JET and on TCV by the observation of peaked density profiles in stationary, fully relaxed, fully current driven discharges and hence in the absence of the neoclassical Ware pinch. An unexpected difference in the parameter dependencies was found in L-and H-modes. In TCV and JET, density gradient lengths (or profile peaking parameters) in L-mode were found to depend on magnetic shear with no dependence on collisionality. This lack of collisionality dependence in L- mode is inconsistent with current theoretical models. H-mode density profiles in JET, on the other hand, are clearly dependent on collisionality in agreement with theory and a prior observation on ASDEX-Upgrade, while exhibiting only a weak or no dependence on shear and temperature profiles. It was found that for TCV and JET, L mode density peaking can be interpreted as being due to turbulent equipartition, which assumes conservation of the magnetic moment and the longitudinal invariant during transport. The observation of a reduction of peaking in TCV with ECH supports drift wave turbulence theory, which predicts the appearance of outward particle convection, when trapped electron modes are destabilized. In JET H-mode, the weak secondary correlation of peaking with the electron-ion temperature ratio Te/Ti, may also be considered, at least quantitatively, as being supportive of drift wave turbulence theory.

EPFL2005

Solid state nanocrystalline titanium oxide photovoltaic cells

The dye solar cell, is a novel photoelectrochemical solar cell presenting unique advantages, as the use of low cost materials and the potential simplicity of manufacturing. However, a liquid electrolyte is actually required for the transport of the photogenerated positive charges. A major breakthrough is the replacing of the liquid electrolyte by a solid-state hole conducting material – the aim of this work. First, the metal/TiO2 junction was investigated, with either silver or gold as rectifying contact. Sensitization was demonstrated, as action spectra were measured using different dyes. The evaporated metal could not enter the pores of the nanocrystalline TiO2 to contact all the dye molecules, hence only low photovoltaic performances were obtained. Furthermore, these metal/TiO2 junctions showed a high sensitivity to humidity and to forward bias polarization. The use of an electrically conducting polymer, poly(bithiophene), was studied in a metal/polymer junction and in TiO2/polymer devices with flat and nanocrystalline TiO2 electrodes. The photoelectric characterizations indicated that electrochemically reduced poly(bithiophene) was able to inject electrons into TiO2, i.e. sensitizing TiO2, and it acted as a hole conducting layer. Short-circuit current densities of 2-3 mA/cm2 were measured at an irradiation of 1.2 W/cm2. The open-circuit voltages were in the 250-350 mV range, depending on the light intensity and temperature. The use of a transparent hole conducting material, CuI, which is a wide bandgap p-type semiconductor, was demonstrated in a nanocrystalline junction made of highly porous sensitized TiO2 and solution-cast CuI. A short-circuit current of 1 mA/cm2 was achieved under one sun simulated light; the open-circuit voltage was 600 mV and the light-to-power conversion efficiency was 0.3 %. The peak quantum efficiencies of 8 % in the UV, and 3 % in the visible, showed that the nanocrystalline junction was working inefficiently, probably due to the poor electrical contact between the TiO2 nanocrystallites and the CuI crystals. Furthermore, the sensitizer was not tuned to inject holes into the valence band of CuI. As conclusion, a controlled-capillary pore based sensitized device is suggested. In this concept, all the internal surface of the TiO2 electrode coated with sensitizer is contacted with the transparent hole conducting layer, hence improving the photovoltaic properties of the device.

EPFL1996

Une cellule photovoltaïque, ou cellule solaire, est un composant électronique qui, exposé à la lumière, produit de l’électricité grâce à l’effet photovoltaïque. La puissance électrique obtenue est proportionnelle à la puissance lumineuse incidente et elle dépend du rendement de la cellule. Celle-ci délivre une tension continue et un courant la traverse dès qu'elle est connectée à une charge électrique (en général un onduleur, parfois une simple batterie électrique).

Un film photovoltaïque ou cellule solaire en couche mince ou encore couche mince photovoltaïque est une technologie de cellules photovoltaïques de deuxième génération, consistant à l'incorporation d'une ou plusieurs couches minces (ou TF pour ) de matériau photovoltaïque sur un substrat, tel que du verre, du plastique ou du métal. Les couches minces photovoltaïques commercialisées actuellement utilisent plusieurs matières, notamment le tellurure de cadmium (de formule CdTe), le diséléniure de cuivre-indium-gallium (CIGS) et le silicium amorphe (a-Si, TF-Si).

vignette| Meilleurs rendements de différentes technologies de cellules photovoltaïques mesurés en laboratoire depuis 1976. Le rendement d'une cellule photovoltaïque, parfois noté η, est le rapport entre l'énergie électrique générée par effet photovoltaïque d'une part et l'énergie électromagnétique reçue par la cellule photovoltaïque sous forme de rayonnement solaire d'autre part. Avec la latitude et le climat du lieu d'installation, le rendement des cellules solaires d'un dispositif photovoltaïque détermine la production d'énergie électrique annuelle du système.

vignette|On peut apercevoir les cellules photovoltaïques organiques Les cellules photovoltaïques organiques sont des cellules photovoltaïques dont au moins la couche active est constituée de molécules organiques. Leur développement constitue une tentative de réduction du coût de l'électricité photovoltaïque, sans conteste la principale barrière pour cette technologie, mais on espère aussi qu'elles seront plus fines, flexibles, faciles et moins chères à produire, tout en étant résistantes.

Le circuit intégré (CI), aussi appelé puce électronique, est un composant électronique, basé sur un semi-conducteur, reproduisant une ou plusieurs fonctions électroniques plus ou moins complexes, intégrant souvent plusieurs types de composants électroniques de base dans un volume réduit (sur une petite plaque), rendant le circuit facile à mettre en œuvre. Il existe une très grande variété de ces composants divisés en deux grandes catégories : analogique et numérique.

Topics in solar power

Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic effect. Concentrated solar power systems use lenses or mirrors and solar tracking systems to focus a large area of sunlight to a hot spot, often to drive a steam turbine.

Microprocesseur

vignette|Un Intel 4004 dans son boîtier à seize broches, premier microprocesseur commercialisé. vignette|Architecture de l'Intel 4004. vignette|L'intérieur d'un Intel 80486DX2. Un microprocesseur est un processeur dont tous les composants ont été suffisamment miniaturisés pour être regroupés dans un unique boîtier. Fonctionnellement, le processeur est la partie d'un ordinateur qui exécute les instructions et traite les données des programmes.

Énergie de fusion nucléaire

vignette| L'expérience de fusion magnétique du Joint European Torus (JET) en 1991. L'énergie de fusion nucléaire est une forme de production d'électricité du futur qui utilise la chaleur produite par des réactions de fusion nucléaire. Dans un processus de fusion, deux noyaux atomiques légers se combinent pour former un noyau plus lourd, tout en libérant de l'énergie. De telles réactions se produisent en permanence au sein des étoiles. Les dispositifs conçus pour exploiter cette énergie sont connus sous le nom de réacteurs à fusion nucléaire.

Chimie alimentaire

vignette|Valentina Domenici, chimiste italienne, analysant de l'huile d'olive La chimie alimentaire est la branche de la chimie qui étudie la composition des aliments et leur évolution au cours de la fabrication, du stockage, de la préparation et de la digestion. Elle s'intéresse aux réactions chimiques impliquant les substances présentes dans les aliments. Les réactions améliorant la conservation et certaines propriétés (organoleptiques, nutritives) du produit sont recherchées.

Solar power