Numerical study of tearing mode seeding in tokamak X-point plasma

A detailed understanding of island seeding is crucial to avoid (N)TMs and their negative consequences like confinement degradation and disruptions. In the present work, we investigate the growth of 2/1 islands in response to magnetic perturbations. Although we use externally applied perturbations produced by resonant magnetic perturbation (RMP) coils for this study, results are directly transferable to island seeding by other MHD instabilities creating a resonant magnetic field component at the rational surface. Experimental results for 2/1 island penetration from ASDEX Upgrade are presented extending previous studies. Simulations are based on an ASDEX Upgrade L-mode discharge with low collisionality and active RMP coils. Our numerical studies are performed with the 3D, two fluid, non-linear MHD code JOREK. All three phases of mode seeding observed in the experiment are also seen in the simulations: first a weak response phase characterized by large perpendicular electron flow velocities followed by a fast growth of the magnetic island size accompanied by a reduction of the perpendicular electron velocity, and finally the saturation to a fully formed island state with perpendicular electron velocity close to zero. Thresholds for mode penetration are observed in the plasma rotation as well as in the RMP coil current. A hysteresis of the island size and electron perpendicular velocity is observed between the ramping up and down of the RMP amplitude consistent with an analytically predicted bifurcation. The transition from dominant kink/bending to tearing parity during the penetration is investigated

Dynamique non linéaire des îlots magnétiques dans les plasmas de fusion

Les modes de déchirement sont connus pour détériorer le confinement et limiter les performances dans les machines de fusion. Plusieurs études sur les modes de déchirements ont été menées, en incluant un degré croissant de complexité dans le modèle physique afin de mieux comprendre les observations expérimentales. Une de ces extensions est l'introduction d'une description du plasma comme un fluide à deux espèces, ions et électrons, dont les dynamiques sont fortement différentes. Un autre mécanisme physique connu pour être important est la courbure du champ magnétique non perturbé. Dans cette thèse, nous étudions les questions de la stabilité linéaire et de l'évolution non linéaire des îlots magnétiques, en présence de la courbure des lignes de champ et de la rotation diamagnétique, avec le code MHD non linéaire XTOR-2F, qui inclut le transport anisotrope de chaleur et les effets géométriques. Cette analyse est appliquée à une décharge entièrement non-inductive de Tore Supra. Ce mode d'opération est crucial pour démontrer la possibilité d'un fonctionnement continu sur un réacteur de type tokamak. Dans cette thèse, la possibilité d'une stabilisation complète des modes de déchirement par la rotation diamagnétique, en présence de la courbure toroidale des lignes de champ magnétique, est démontrée. Dans le domaine linéairement stable, le mode est métastable: le niveau de saturation dépend de la taille de l'îlot initial. Dans le domaine non linéaire, la saturation de l'îlot est fortement réduite par la rotation diamagnétique et par le nombre de Lundquist. La question de l'extrapolation des résultats obtenus vers la future generation de machines de fusion est également abordéeTearing modes are known to deteriorate the confinement and limit plasma performance in fusion devices. Various studies of this mode have been performed lately including an increasing level of complexity in the physical description which is required for understanding of experimental observations. One of such extensions is the introduction of diamagnetic rotation into the system. Another physical mechanisms known to be important for tearing mode dynamics is the curvature of unperturbed magnetic field lines and neoclassical physics. In this thesis we investigate the issues of linear stability of the tearing modes in a presence of both curvature and diamagnetic rotation using the non linear full-MHD toroidal code XTOR-2F, which includes anisotropic heat transport, diamagnetic and geometrical effects. This analysis is applied to one of the fully non-inductive discharges on Tore-Supra. Such experiments are crucially important to demonstrate reactor scale steady state operation for the tokamak. In this thesis, the possibility of full linear stabilization of the tearing modes by diamagnetic rotation in the presence of toroidal curvature is shown. In the linearly stable domain, the mode is metastable: saturation level depends on the seed island size. In the non linear regime, the saturation of n=1, m=2 mode is found to be strongly reduced by diamagnetic rotation and by Lundquist number. The question of extrapolation of the obtained results towards future generation of fusion devices is also addressed. In particular, for ITER size machines, the toroidal curvature is expected to be more important due to higher performance factor β

Linear stability of the tearing mode with two-fluid and curvature effects in tokamaks

International audienc

Curvature effect on tearing modes in presence of neoclassical friction

International audienc

Nonlinear dynamics of the tearing mode with two-fluid and curvature effects in tokamaks

International audienc

Розробка технології отримання жирових композицій з підвищеною окислювальною стабільністю

The object of research is the process of fat oxidation at elevated and standard temperatures. Fats are used in chemical, pharmaceutical, food and other industries. Oxidative deterioration changes the composition of fats, reduces the efficiency of chemical reactions involving fats and the quality of final products. An urgent task is to increase the oxidative stability of fats. The oxidative stability of fat compositions based on rapeseed, high-oleic sunflower and palm oils by the induction period at a temperature of 110 °C was investigated. The induction periods of the initial oils were 408.48 min., 795.87 min. and 630.2 min., respectively. Rational ratios of oils in the compositions were found: high-oleic sunflower: palm (50:50) %; rapeseed: high-oleic sunflower: palm (16.67:66.67:16.67) %; rapeseed: high-oleic sunflower: palm (33.33:33.33:33.33) %. The induction periods of the mixtures are 650.57 min., 710.56 min. and 670.56 min., respectively. The increase in the oxidative stability of the developed compositions using the mixture of synthetic antioxidants (butylhydroxyanisole, butylhydroxytoluene and tert-butylhydroquinone) in an amount of 300 mg/kg of fat mixture was studied. The induction periods of the developed compositions were 910.80 min., 1279.01 min. and 1072.90 min., respectively. The physicochemical parameters of compositions with the addition of antioxidants after 5 months of storage at a temperature of (20±2) °C were determined. The peroxide values of the compositions were 5.65; 3.28; 4.50 ½ O mmol/kg, respectively. The research results make it possible to produce fats with increased oxidative stability and necessary properties, to predict induction periods of fat compositions depending on the concentrations of components. This will increase the profitability of production and the quality of fats obtainedОб’єктом дослідження є процес окислення жирів за підвищеної та стандартної температури. Жири застосовуються у хімічній, фармацевтичній, харчовій та інших галузях промисловості. Окислювальне псування змінює склад жирів, знижує ефективність хімічних реакцій за участю жирів та якість кінцевих продуктів. Актуальним завданням є підвищення окислювальної стабільності жирів. Досліджено окислювальну стабільність жирових композицій на основі ріпакової, соняшникової високоолеїнової та пальмової олій за періодом індукції за температури 110 °С. Періоди індукції початкових олій склали 408,48 хв., 795,87 хв. та 630,2 хв. відповідно. Встановлено раціональні співвідношення олій у складі композицій: соняшникова високоолеїнова: пальмова (50:50) %; ріпакова: соняшникова високоолеїнова: пальмова (16,67:66,67:16,67) %; ріпакова: соняшникова високоолеїнова: пальмова (33,33:33,33:33,33) %. Періоди індукції сумішей складають 650,57 хв., 710,56 хв. та 670,56 хв. відповідно. Досліджено підвищення окислювальної стабільності розроблених композицій з використанням суміші синтетичних антиоксидантів (бутилгідроксианізол, бутилглідрокситолуол та трет-бутилгідрохінон) у кількості 300 мг/кг жирової суміші. Періоди індукції розроблених композицій склали 910,80 хв., 1279,01 хв. та 1072,90 хв. відповідно. Визначено фізико-хімічні показники композицій з додаванням антиоксидантів після 5 місяців зберігання за температури (20±2) °С. Пероксидні числа композицій склали 5,65; 3,28; 4,50 ½ О ммоль/кг відповідно. Результати досліджень дають можливість виробляти жири з підвищеною окислювальною стабільністю з необхідними властивостями, прогнозувати періоди індукції жирових композицій в залежності від концентрацій компонентів. Це підвищить рентабельність виробництва та якість одержаних жирі

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

International audienceJOREK is a massively parallel fully implicit non-linear extended magneto-hydrodynamic(MHD) code for realistic tokamak X-point plasmas. It has become a widely used versatile simulation code for studying large-scale plasma instabilities and their control and is continuously developed in an international community with strong involvements in the European fusion research programme and ITER organization. This article gives a comprehensive overview of the physics models implemented, numerical methods applied for solving the equations and physics studies performed with the code. A dedicated section highlights some of the verification work done for the code. A hierarchy of different physics models is available including a free boundary and resistive wall extension and hybridkinetic-fluid models. The code allows for flux-surface aligned iso-parametric finite element grids in single and double X-point plasmas which can be extended to the true physical walls and uses a robust fully implicit time stepping. Particular focus is laid on plasma edge and scrape-off layer (SOL) physics as well as disruption related phenomena. Among the key results obtained with JOREK regarding plasma edge and SOL, are deep insights into the dynamics of edge localized modes (ELMs), ELM cycles, and ELM control by resonant magnetic perturbations, pellet injection, as well as by vertical magnetic kicks. Also ELM free regimes, detachment physics, the generation and transport of impurities during an ELM, and electrostatic turbulence in the pedestal region are investigated. Regarding disruptions, the focus is on the dynamics of the thermal quench (TQ) and current quench triggered by massive gas injection and shattered pellet injection, runaway electron (RE) dynamics as well as the RE interaction with MHD modes, and vertical displacement events. Also the seeding and suppression of tearing modes (TMs), the dynamics of naturally occurring TQs triggered by locked modes, and radiative collapses are being studied

Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade

\u3cp\u3eWithin the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (n\u3csub\u3ee,sep\u3c/sub\u3e/n\u3csub\u3eG\u3c/sub\u3e ∼ 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.\u3c/p\u3