Search

Выполнены расчеты излучения бальмеровской серии водорода и линии гелия HeI 5876. Рассматриваются условия атмосфер холодных звезд. Задавались температура, концентрация и колонковая плотность газа. Рассмотрена возможная роль надтепловых частиц, которые представлены электронным газом с температурой 200 эВ. Лучистый перенос учитывался в рамках модели Соболева – Бибермана – Холстейна. Вероятность выхода в частотах линий вычислялась для свертки профилей Доплера и Хольцмарка в случае водорода и для фойгтовского профиля в случае гелия. Решена система кинетических уравнений, описывающих стационарную населенность дискретных уровней и континуума водорода и гелия. Учтены связанно-связанные, связанно-свободные радиационные и ударные переходы. Без учета быстрых частиц в холодном газе (6000 K) бальмеровский декремент является очень крутым, а с учетом быстрых частиц – пологим. В горячем газе (12000 K) декремент может смениться инкрементом. Поток в линии гелия достигает нескольких процентов от потока в Hα при наличии потока быстрых электронов ∼ 106 эрг/см2/с или в горячем газе (T ≳ 15000 K)., The authors calculated the intensities of hydrogen Balmer lines and the HeI Lambda 5876 line. The input gas parameters such as temperature, concentration, and column density correspond to solar and solar-type star atmospheres. The influence of fast particles (electrons) was also considered. The radiative transfer in spectral lines frequencies is treated in the frame of the Sobolev-Biberman-Holstein approximation in such a way that hydrogen lines have the Doppler and the Holtzmark convolution profile, and helium lines have the Voight profile. In equations describing the hydrogen and the helium energetic level occupation, the terms encompass the rates of bound-bound, bound-free radiative and collisional processes. The Balmer decrement in cold gas (6,000 K) is quite steep without fast particles, being sloping with fast particles. In warm gas (12,000 K), decrement can change into increment. The HeI Lambda 5876 flux becomes as large as several percent of the H_alpha flux only in the hot atmosphere (>15,000 K) or the atmosphere affected by a strong fast particle flux., Известия Крымской астрофизической обсерватории, Выпуск 118 (3) 2022, Pages 33-38

In most present-day tokamaks, the majority of the heating power comes from sources such as neutral-beam injection (NBI) and other types of auxiliary heating which allow for the transfer of energy to the plasma by a small population of externally introduced fast particles. The behavior of the fast ions is important for the overall plasma dynamics, and understanding their influence is vital for the success of any future magnetic confinement devices. In the TUMAN-3M tokamak, it has been noted that the loss of fast particles during NBI can lead to dramatic changes in the rotation velocity profiles, as they are responsible for the negative radial electric field on the periphery.

Alfvén waves are electromagnetic waves that occur in magnetised plasmas. Alfvén waves are routinely observed in tokamaks — toroidal devices that confine plasma using magnets. Energetic ions that are used to heat the plasma within tokamaks can drive the Alfvén waves unstable. Additionally, alpha particles produced in fusion reactions may destabilise the wave. Alfvén waves with sufficiently high amplitudes can eject energetic particles from the plasma, damaging the reactor and decreasing fusion efficiency. When these waves are not strong enough to eject particles from the plasma, their benign behaviour can be used to diagnose the plasma. This technique is known as magnetohydrodynamic (MHD) spectroscopy. In this thesis, we outline three new techniques of MHD spectroscopy that we have developed. The first new method of MHD spectroscopy was developed in plasmas composed of hydrogen and deuterium in the Mega Ampere Spherical Tokamak (MAST). Compressional Alfvén eigenmodes (CAEs) and global Alfvén eigenmodes (GAEs) were suppressed in plasmas with high hydrogen concentrations. At the highest hydrogen concentrations investigated, high frequency ion-ion hybrid waves appeared. We used a 1D model of the refractive index and wave-particle resonances to explain these observations and estimate the relative ion concentration at which the spectrum of excited waves changed. These estimates agreed with experimental observations, suggesting the spectrum of excited waves can be used to diagnose the relative ion concentrations for plasmas with two ion species. The second new form of MHD spectroscopy was developed using observations of axisymmetric modes in experiments on the Joint European Torus (JET). Axisymmetric modes do not change in the toroidal direction and are driven unstable by energy gradients in the fast particle distribution function. Therefore, we can use observations of the axisymmetric mode to infer information about the gradient of the fast particle energy distribution function. We explained how these axisymmetric modes can exist without heavy damping. We also examined how the elongation of the plasma column modifies the mode using numerical and analytical tools. The final MHD spectroscopic technique was developed for JET plasmas injected with pellets of frozen deuterium, which are used to refuel the plasma core. We demonstrated how key pellet parameters can be inferred from dramatic changes to the Alfvén eigenfrequencies that we observed in JET. MHD spectroscopy of pellet injected plasmas was enabled by generalising two 3D MHD codes to incorporate 3D density profiles. 3D density profiles were generated using a model for the expansion of the pellet wake along a magnetic field line derived from the fluid equations. From the change in mode frequency, we estimate the density of the pellet wake and the time-scale for poloidal homogenisation of the wake. Before presenting these studies, we introduce the basics of fusion, tokamaks, and the models used to describe tokamak plasmas. We then discuss the MHD waves that we will use for MHD spectroscopy of tokamak plasmas, and how these waves are excited by fast particles. The three new methods of MHD spectroscopy are then discussed.

Fast-particle driven Alfvén Eigenmodes have been observed in low-collisionality discharges with off-axis neutral beam injection (NBI), electron cyclotron resonance heating (ECRH) and a reduced toroidal magnetic field. During NBI and ECRH, toroidicity induced Alfvén Eigenmodes (TAEs) appear in frequency bands close to 200 kHz and energetic-particle-induced geodesic acoustic modes (EGAMs) are observed at about 40 and 80 kHz. When turning off ECRH in the experiment, those beam-driven modes disappear which can be explained by a modification of the fast-ion slowing down distribution. In contrast, coherent fluctuations close to the frequency of the beam-driven TAEs are present throughout the experiment. The modes are even observed during ohmic plasma conditions, which clearly demonstrates that they are not caused by fast particles and suggests an alternative drive, such as turbulence. The mode-induced fast-ion transport has been found to be weak and marginal in terms of the fast-ion diagnostic sensitivities. Measurements of the plasma stored energy, neutron rates, neutral particle fluxes and fast-ion D-alpha spectroscopy show good agreement with neoclassical modelling results from TRANSP. This is further supported by a similarly good agreement between measurement and modelling in cases with and without ECRH and therefore with and without the modes. Instead, a significant level of charge exchange losses are predicted and observed which generate a bump-on-tail fast-ion distribution function that can provide the necessary free energy to EGAMs. European Commission 633053

Gamma-ray spectroscopy (GRS) has become an established technique to determine properties of the distribution function of the energetic particles in the MeV range, which are fast ions from heating and fusion reactions or runaway electrons born in disruptions. In this paper we present a selection of recent results where GRS is key to investigate the physics of MeV range particles. These range from radio-frequency heating experiments, where theoretical models can be tested with an unprecedented degree of accuracy, to disruption mitigation studies, where GRS sheds light on the effect of the actuators on the runaway electron velocity space. We further discuss the unique observational capabilities offered by the technique in deuterium-tritium plasmas, particularly with regard to the inference of the energy- and pitch-resolved distribution function of the α particles born from fusion reactions in the plasma core.

Thermonuclear fusion is the great scientific challenge of our century to solve the energy transition from fossil fuelsto clean, carbon-free mass energy. Tokamak technology is the most advanced technology to date for the success ofthis challenge. The importance of the energy transition in this sense is such that a world-wide scientific cooperationwas launched in November 1985 under the ITER (International Thermonuclear Experimental Reactor) programmebased in the south of France near Cadarache, a major French nuclear research centre.Fusion reactions occur naturally in the heart of the sun and therefore require extreme temperature and densityconditions. In terms of scale, to ensure the ignition of fusion by magnetic confinement, the plasma must be at atemperature of about ten keV and a density of 10^20 particles/m3.The study of Tokamak's plasma heating systems is largely adequate to meet these extreme conditions. Forthis purpose three main heating classes exist. The ohmic heating produced by the plasma current generally used toinitiate the plasma in Tokamak. Neutral Beam Injection (NBI) heating, which consists in injecting fast neutrals thatincrease the plasma energy by colliding with each other. Electromagnetic wave heating, which consists of sendinga wave into the plasma that will couple with it and includes three categories of heating, an ion heater called ICRH(Ion Cyclotron Resonance Heating), an electronic heater called ECRH (Electron Cyclotron Resonance Heating) andan ion and electronic heater called LHCD (Lower Hybrid Current Drive).The work presented in this thesis consisted in improving the modeling of ionic heaters by taking into accountthe feedback of the ionic distribution of plasma on the propagation and absorption of the ICRF wave(from the English Ion Cyclotron Resonance Frequency), used in ICRH heating, by creating a code coupling(NEMO/EVE/SPOT/RFOF) forming a workflow available on a European integrated modelling platform calledEUITM. Indeed, when the ionic distribution of the plasma presents a significant proportion of fast ions, previousmodels did not find all the neutron levels, indirect diagnosis of fast ions, produced by fusion reactions.This new workflow was tested using data from JET (Tokamak European based in Culham) using the synergyof NBI and ICRH, a heating scenario producing a large proportion of fast ions in the plasma. The comparison ofneutron levels found experimentally and via self-coherent modeling has demonstrated the importance of taking intoaccount the feedback of ion distribution in the absorption of the ICRF wave in the modeling of the synergy of ionheating systems.In addition, our simulations have demonstrated the effectiveness of the synergy effects of NBI and ICRH (comparedto their purely additive application) when the deposition of ionic particles produced by NBI is located nearthe resonance layer of the ICRH.One of the perspectives of this work is the combination of self-coherent modelling of ion heating sources with aequilibrium transport code. This would allow better consideration of the rapid ion dynamics produced by ICRH instudies of central accumulation of heavy impurities., La fusion thermonucléaire est le grand défi scientifique de notre siècle pour résoudre la transition énergétiquedes énergies fossiles à une énergie de masse, propre et décarbonée. La technologie des Tokamaks est celle la plusavancée à ce jour pour la réussite de ce défi. L'importance de la transition énergétique dans ce sens est tellequ'une coopération scientifique mondiale à vue le jour en novembre 1985 sous le programme ITER (de l'anglais :International Thermonuclear Experimental Reactor) basé dans le sud de la France à coté de Cadarache grand centrede recherche nucléaire français.Les réactions de fusions se produisent naturellement au coeur du soleil et donc demande des conditions de température et de densité extrêmes. En terme d'ordre de grandeur, pour assurer l'ignition de la fusion par confinementmagnétique le plasma doit être à une température d'une dizaine de keV et à une densité de 10^20 particules/m3.L'étude des systèmes de chauffage des plasmas de Tokamak permet en grande partie de répondre à ces conditionsextrêmes. Pour cela trois grandes classes de chauffage existent. Le chauffage ohmique produit par le courant plasmagénéralement utilisé pour initier le plasma dans le Tokamak. Le chauffage par injection de neutres nommé NBI(de l'anglais Neutral Beam Injection) qui consiste à injecter des neutres rapides qui en se ionisant augmentent parcollisions l'énergie du plasma. Le chauffage par onde électromagnétique qui consiste à envoyer une onde dans leplasma qui va se coupler avec celui-ci et regroupe trois catégories de chauffage, un chauffage ionique nommé ICRH(de l'anglais Ion Cyclotron Resonance Heating), un chauffage électronique nommé ECRH (de l'anglais ElectronCyclotron Resonance Heating) et un chauffage ionique et électronique nommé LHCD (de l'anglais Lower HybridCurrent Drive).Le travail présenté dans cette thèse a consisté à améliorer la modélisation des chauffages ioniques en tenantcompte de la rétroaction de la distribution ionique de plasma sur la propagation et l'absorption de l'onde ICRF (del'anglais Ion Cyclotron Resonance Frequency), utilisée dans le chauffage ICRH, par la création d'un couplage decodes (NEMO/EVE/SPOT/RFOF) formant un workflow disponible sur une plateforme de modélisation intégréeeuropéenne nommé EUITM. En eet lorsque la distribution ionique du plasma présente une part significative d'ionsrapides les modélisations précédentes ne retrouvaient pas la totalité des taux de neutrons, diagnostic indirect d'ionsrapides, produits par les réactions de fusion.Ce nouveau workflow a été testé à partir des données d'une décharge de JET (Tokamak Européen basé àCulham) utilisant la synergie des chauages NBI et ICRH, scénario de chauffage produisant une grande part d'ionsrapides dans le plasma. La comparaison des taux de neutron trouvés expérimentalement et via la modélisationauto-cohérente a prouvé l'importance de tenir compte de la rétroaction de la distribution ionique dans l'absorptionde l'onde ICRF dans la modélisation de la synergie des chauages ioniques.Par ailleurs nos simulations ont permis de démontrer l'efficacité des effets de synergie des chauffages NBI etICRH (par rapport à leur application de façon purement additive) lorsque le dépôt de particules ionique produitpar NBI est localisé proche de la couche de résonance du chauffage ICRH.Une des perspectives de ce travail est la combinaison de la modélisation auto-cohérente des sources de chauffageionique à un code de transport de d'équilibre. Cela permettrait une meilleure prise en compte de la dynamique desions rapides produit par ICRH dans le cadre des études d'accumulation centrale d'impuretés lourdes

Experiments with the new neutral beam injection source of TCV have been performed with high fast-ion fractions (>20%) that exhibit a clear reduction of the loop voltage and a clear increase of the plasma pressure in on- and off-axis heating configurations. However, good quantitative agreement between the experimental data and TRANSP predictions is only found when including strong additional fast-ion losses. These losses could in part be caused by turbulence or MHD activity as, e.g. high frequency modes near the frequency of toroidicity induced Alfvén eignmodes are observed. In addition, a newly installed fast-ion D-alpha (FIDA) spectroscopy system measures strong passive radiation and, hence, indicates the presence of high background neutral densities such that charge-exchange losses are substantial. Also the active radiation measured with the FIDA diagnostic, as well as data from a neutral particle analyzer, suggest strong fast-ion losses and large neutral densities. The large neutral densities can be justified since high electron temperatures (3–4 keV), combined with low electron densities (about 2 X 1019 m−3) yield long mean free paths of the neutrals which are penetrating from the walls.

The planned upgrade of the RFX-mod device is a good opportunity to widen the operational space of the machine, in both RFP and tokamak configurations. Installation of a power neutral beam injector is also envisaged and a NB system compatible with RFX-mod, formerly installed in TPE-RX, is already available on site. In this work, the METIS simulator is used to study the feasibility of TPE-RX injector integration in RFX-mod circular tokamak plasmas. METIS code allows the simulation of a full tokamak discharge, with the addition of the neutral beam injection (NBI) which, in METIS, is described by a decay equation applied in a simplified geometry and an analytical solution of the Fokker-Planck equation. In this work, RFX-mod scenarios with NBI have been studied, with careful attention to the beam absorption and plasma response to the additional heating. (C) 2017 Elsevier B.V. All rights reserved.

Fast ions in W7-X will be produced either by neutral beam injection (NBI) or by ion-cyclotron resonant heating (ICRH). The latter presents the advantage of depositing power locally and does not suffer from core accessibility issues (Drevlak et al 2014 Nucl. Fusion 54 073002). This work assesses the possibility of using ICRH as a fast ion source in W7-X relevant conditions. The SCENIC package is used to resolve the full wave propagation and absorption in a three-dimensional plasma equilibrium. The source of the ion-cyclotron range of frequency (ICRF) wave is modelled in this work by an antenna formulation allowing its localisation in both the poloidal and toroidal directions. The actual antenna dimension and localization is therefore approximated with good agreement. The local wave deposition breaks the five-fold periodicity of W7-X. It appears that generation of fast ions is hindered by high collisionality and significant particle losses. The particle trapping mechanism induced by ICRH is found to enhance drift induced losses caused by the finite orbit width of trapped particles. The inclusion of a neoclassically resolved radial electric field is also investigated and shows a significant reduction of particle losses.

This work presents the results of a multi mode ITER study on Toroidal Alfven Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main conclusions from earlier studies of ASDEX Upgrade discharges can be transferred to the ITER scenario: global, nonlinear effects are crucial for the evolution of the multi mode scenario. This work focuses on the ITER 15 MA baseline scenario with with a safety factor at the magnetic axis of $q_0 =$ 0.986. The least damped eigenmodes of the system are identified with the gyrokinetic, non-perturbative LIGKA solver, concerning mode structure, frequency and damping. Taking into account all weakly damped modes that can be identified linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior: while in some parameter range, quasi-linear estimates turn out to be reasonable approximations for the nonlinearly relaxed energetic particle profile, under certain conditions low-n TAE branches can be excited. As a consequence, not only grow amplitudes of all modes to (up to orders of magnitude) higher values compared to the single mode cases but also, strong redistribution is triggered in the outer radial area between $\rho_\mathrm{pol} =$ 0.6 and 0.85, far above quasi-linear estimates., Comment: 14 pages, 20 figures; To be published as special issue in PPCF 12/2015 for EPS Lisbon invited talk

Turbulence and MHD instabilities can cause particle and energy transport from core to edge plasma in tokamaks. A consequence is the degradation of plasma confinement. Understanding and controlling those phenomena is of tremendous importance in view of next step fusion experiments such as ITER and DEMO. Fast ions, such as alpha particles or those ions generated by heating sources, are known to have direct and/or indirect interactions with turbulence and MHD instabilities. They may be used to control those phenomena. In this thesis, we study the interaction of fast particles with two different modes: the sawtooth instability; and the Ion Temperature Gradient (ITG) turbulence via the excitation of Energetic particle driven Geodesic Acoustic Modes (EGAMs). First, we report on the strong stabilization of sawteeth by fast deuterium ions, accelerated to the 100 keV range by neutral beam injection and subsequently to the MeV range by 3rd harmonic ion cyclotron resonance heating, in the JET tokamak. This stabilization is analysed and understood in the framework of a theoretical model (Porcelli's model). Second, we perform an analytical study of the linear excitation by fast ions of the electrostatic branch of EGAMs. In particular, by scanning the parameter space, we shed light on the relation and differences between EGAMs and Geodesic Acoustic Modes (GAMs). The latter are known to efficiently interact with turbulence but are harder to control than EGAMs. A good knowledge of this relation is of interest to understand whether GAMs and EGAMs are capable of similar interactions with turbulence. Finally, we use a three wave parametric decay model to study the interaction between EGAMs and ITG modes. The possible control of ITG turbulence by EGAMs is discussed in this framework., La turbulence et les instabilités MHD peuvent être à l'origine de transport de particules et d'énergie du plasma de cœur vers le plasma de bord dans les tokamaks. Une conséquence en est la dégradation du confinement. Comprendre et contrôler ces phénomènes est d'une importance majeure dans l’optique des prochaines expériences de fusion, telles qu'ITER ou le réacteur DEMO. Il a été montré que les ions rapides, tels que les particules alpha ou les ions générés par des sources de chauffage, ont des interactions directes et/ou indirectes avec la turbulence et les instabilités MHD. Ils pourraient dès lors être utilisés pour contrôler ces phénomènes. Dans cette thèse, nous étudions l'interaction des particules rapides avec deux modes différents : les dents de scie ; et la turbulence ITG (due à la présence d'un Gradient de Température Ionique) via l'excitation d'EGAM (Modes Géodésiques Acoustiques excités par des particules Energétiques). Dans un premier temps, nous rendons compte d'une forte stabilisation des dents de scie par des ions deutérium rapides dans le tokamak JET. Dans les expériences considérées, ces ions deutérium ont été accélérés jusqu'à environ 100 keV par l'injection de neutres, puis jusqu'à quelques MeV par l'utilisation de chauffage cyclotronique ionique à la 3è harmonique. Cette stabilisation est analysée et comprise dans le cadre d'un modèle théorique, le modèle de Porcelli. Dans un deuxième temps, nous réalisons une étude analytique de l'excitation linéaire de la branche électrostatique des EGAM par des particules rapides. Notamment, en parcourant l’ensemble des paramètres de contrôle pertinents, nous mettons en évidence la relation et les différences entre EGAM et d’autres modes similaires, les GAM. Ces derniers sont connus pour interagir avec la turbulence, mais sont plus difficiles à contrôler que les EGAM. Une bonne compréhension de cette relation devrait permettre de comprendre si GAM et EGAM interagissent de la même manière avec la turbulence. Finalement, nous décrivons l'interaction entre EGAM et modes ITG au travers d'un modèle de décroissance paramétrique à trois ondes. La possibilité de contrôler la turbulence ITG par les EGAM est discutée dans ce cadre.

Turbulence and MHD instabilities can cause particle and energy transport from core to edge plasma in tokamaks. A consequence is the degradation of plasma confinement. Understanding and controlling those phenomena is of tremendous importance in view of next step fusion experiments such as ITER and DEMO. Fast ions, such as alpha particles or those ions generated by heating sources, are known to have direct and/or indirect interactions with turbulence and MHD instabilities. They may be used to control those phenomena. In this thesis, we study the interaction of fast particles with two different modes: the sawtooth instability; and the Ion Temperature Gradient (ITG) turbulence via the excitation of Energetic particle driven Geodesic Acoustic Modes (EGAMs). First, we report on the strong stabilization of sawteeth by fast deuterium ions, accelerated to the 100 keV range by neutral beam injection and subsequently to the MeV range by 3rd harmonic ion cyclotron resonance heating, in the JET tokamak. This stabilization is analysed and understood in the framework of a theoretical model (Porcelli's model). Second, we perform an analytical study of the linear excitation by fast ions of the electrostatic branch of EGAMs. In particular, by scanning the parameter space, we shed light on the relation and differences between EGAMs and Geodesic Acoustic Modes (GAMs). The latter are known to efficiently interact with turbulence but are harder to control than EGAMs. A good knowledge of this relation is of interest to understand whether GAMs and EGAMs are capable of similar interactions with turbulence. Finally, we use a three wave parametric decay model to study the interaction between EGAMs and ITG modes. The possible control of ITG turbulence by EGAMs is discussed in this framework., La turbulence et les instabilités MHD peuvent être à l'origine de transport de particules et d'énergie du plasma de cœur vers le plasma de bord dans les tokamaks. Une conséquence en est la dégradation du confinement. Comprendre et contrôler ces phénomènes est d'une importance majeure dans l’optique des prochaines expériences de fusion, telles qu'ITER ou le réacteur DEMO. Il a été montré que les ions rapides, tels que les particules alpha ou les ions générés par des sources de chauffage, ont des interactions directes et/ou indirectes avec la turbulence et les instabilités MHD. Ils pourraient dès lors être utilisés pour contrôler ces phénomènes. Dans cette thèse, nous étudions l'interaction des particules rapides avec deux modes différents : les dents de scie ; et la turbulence ITG (due à la présence d'un Gradient de Température Ionique) via l'excitation d'EGAM (Modes Géodésiques Acoustiques excités par des particules Energétiques). Dans un premier temps, nous rendons compte d'une forte stabilisation des dents de scie par des ions deutérium rapides dans le tokamak JET. Dans les expériences considérées, ces ions deutérium ont été accélérés jusqu'à environ 100 keV par l'injection de neutres, puis jusqu'à quelques MeV par l'utilisation de chauffage cyclotronique ionique à la 3è harmonique. Cette stabilisation est analysée et comprise dans le cadre d'un modèle théorique, le modèle de Porcelli. Dans un deuxième temps, nous réalisons une étude analytique de l'excitation linéaire de la branche électrostatique des EGAM par des particules rapides. Notamment, en parcourant l’ensemble des paramètres de contrôle pertinents, nous mettons en évidence la relation et les différences entre EGAM et d’autres modes similaires, les GAM. Ces derniers sont connus pour interagir avec la turbulence, mais sont plus difficiles à contrôler que les EGAM. Une bonne compréhension de cette relation devrait permettre de comprendre si GAM et EGAM interagissent de la même manière avec la turbulence. Finalement, nous décrivons l'interaction entre EGAM et modes ITG au travers d'un modèle de décroissance paramétrique à trois ondes. La possibilité de contrôler la turbulence ITG par les EGAM est discutée dans ce cadre.

We present a numerical study of sawtooth in ohmic tokamak plasmas with the XTOR-2F code. This study is, to our knowledge, the first to explore the long-term dynamics of the internal kink. Resistive MHD gives two regimes : stable oscillations or a saturated helicoidal state. Stabilizing diamagnetic drifts enable us to find sawteeth for pertinent experimental parameters. We also present the contributions made for the transition of the code toward the hybrid MHD-kinetic code XTOR-K, to include both kinetic and fluid effects. We chose a full-f, full-orbit kinetic model, coupled to the fluid part through a Newton-Krylov/Picard algorithm which is stable for the fundamental MHD modes. Orbit integration is done by the Boris algorithm, adapted in toroidal geometry. Invariants of motion do not accumulate numerically. Several methods, including a numerical temporal filter, are considered to reduce the noise on the particular pressure tensor.; Nous présentons une étude numérique des dents de scie dans un plasma de tokamak ohmique avec le code XTOR-2F. Cette étude est à notre connaissance la première à explorer la dynamique au long terme du kink interne. La MHD résistive prévoit deux régimes distincts : oscillations stables ou régime saturé hélicoïdal. Les dérives diamagnétiques stabilisantes permettent de retrouver des dents de scie pour des paramètres expérimentaux pertinents. On détaille aussi les contributions faites à la transition du code vers le code hybride MHD-cinétique XTOR-K, pour coupler effets cinétiques et fluides. On a choisi un modèle cinétique full-f, full-orbit couplé à la partie fluide par un algorithme Newton-Krylov/Picard stable vis-à-vis des modes MHD fondamentaux. L'avancée des particules est faite par l'algorithme de Boris, adapté en géométrie torique. Les invariants du mouvement ne dérivent pas numériquement. Différentes méthodes, entre autres un filtrage temporel numérique, sont envisagées pour réduire le bruit sur le tenseur de pression particulaire.

We present a numerical study of sawtooth in ohmic tokamak plasmas with the XTOR-2F code. This study is, to our knowledge, the first to explore the long-term dynamics of the internal kink. Resistive MHD gives two regimes : stable oscillations or a saturated helicoidal state. Stabilizing diamagnetic drifts enable us to find sawteeth for pertinent experimental parameters. We also present the contributions made for the transition of the code toward the hybrid MHD-kinetic code XTOR-K, to include both kinetic and fluid effects. We chose a full-f, full-orbit kinetic model, coupled to the fluid part through a Newton-Krylov/Picard algorithm which is stable for the fundamental MHD modes. Orbit integration is done by the Boris algorithm, adapted in toroidal geometry. Invariants of motion do not accumulate numerically. Several methods, including a numerical temporal filter, are considered to reduce the noise on the particular pressure tensor., Nous présentons une étude numérique des dents de scie dans un plasma de tokamak ohmique avec le code XTOR-2F. Cette étude est à notre connaissance la première à explorer la dynamique au long terme du kink interne. La MHD résistive prévoit deux régimes distincts : oscillations stables ou régime saturé hélicoïdal. Les dérives diamagnétiques stabilisantes permettent de retrouver des dents de scie pour des paramètres expérimentaux pertinents. On détaille aussi les contributions faites à la transition du code vers le code hybride MHD-cinétique XTOR-K, pour coupler effets cinétiques et fluides. On a choisi un modèle cinétique full-f, full-orbit couplé à la partie fluide par un algorithme Newton-Krylov/Picard stable vis-à-vis des modes MHD fondamentaux. L'avancée des particules est faite par l'algorithme de Boris, adapté en géométrie torique. Les invariants du mouvement ne dérivent pas numériquement. Différentes méthodes, entre autres un filtrage temporel numérique, sont envisagées pour réduire le bruit sur le tenseur de pression particulaire.

This paper considers various channels of gammaquantum generation via an ultra-short high-power laser pulse interaction with different targets.We analyse the possibilities to create a pulsed gamma-radiation source using laser triggering of some nuclear reactions and isomer targets. It is shown that sub-MeV monochromatic short pulse of gamma-radiation can be obtained with pulse energy of sub-mJ level from isomer target irradiated by intense laser pulse. For nuclear reaction channel in light- atom materials, it is shown that sub-PW laser pulse gives rise to formation about million gamma-photons of multi-MeV energy., {"references":["G.C.Baldwin and J.C.Solem \"Recoilless gamma-ray lasers\" Reviews of\nModern Physics, v.69, No.4,1085 (1997).","C.B.Collins, F.W.Lee, D.M.Shemell, B.D.DePaola, S.Olariu, and I.\nIovitzu Popescu \"The coherent and incoherent pumping of a gamma ray\nlaser with intense optical radiation\" J. Appl. Phys., 53, 4645 (1982).","ðÉ.ðÉ.ðÉndreev, ðÜ.Yu. Platonov, Yu.V. Rozhdestvenskii. \"Determination\nof the Radiation Cross Sections of Low-Energy Transitions of Isomeric\nNuclei from Observation of Laser-Induced g-Fluorescence\" JETP, 94,\n862, (2002).","V.B. Berestetskii, E.M. Lifshits, and L.P. Pitaevskii, Quantum\nElectrodynamics (Moscow, Nauka,1980).","S. Olariu, A. Olariu \"Induced emission of ╬│ radiation from isomeric\nnuclei\" Phys. Rev.C 58, 333 (1998).","H.Nakano, A.A.Andreev, J.Limpouch \"Femtosecond x-ray line emission\nfrom multiplayer targets irradiated by short laser pulses\", Applied\nPhysics B, 79, 469, 2004.","http://www.gel.usherbrooke.ca/casino/index.html","http://www-cxro.lbl.gov","P. M. Nilson, W. Theobald, J. F. Myatt, C. Stoeckl, M. Storm, J. D.\nZuegel, R. Betti, D. D. Meyerhofer, and T. C. Sangster \"Bulk heating of\nsolid-density plasmas during high-intensity-laser plasma interactions\"\nPHYSICAL REVIEW E 79, 016406 2009.\n[10] M.H. Key, M.D. Cable, et. al., \"Hot electron production and heating by\nhot electrons in fast ignitor research\" Phys. Plasmas 5, 1966 (1998).\n[11] S.C.Wilks, \"Simulations of ultraintense laser-plasma interactions\"\nPhys.Fluids B 5 (7), 2603 (1993).\n[12] L.D.Landau and E.M. Lifshits Theory of Field (Moscow, Nauka,1974).\n[13] P. Mora \"Plasma Expansion into a Vacuum\" Phys. Rev. Lett. 90,\n185002 (2003).\n[14] J. Fuchs, P. Antici, E. d-Humières, E. Lefebvre, M. Borghesi, E.\nBrambrink, C. A. Cecchetti, M. Kaluza, V. Malka, M. Manclossi, et al.\n\"Laser-driven proton scaling laws and new paths towards energy\nincrease\" Nature Physics 2, 48 (2005) .\n[15] A.A.Andreev, V.M.Komarov, I.A.Litvinenko, K.Yu. Platonov,\nA.V.Charukchev\"Generation of a Fast-Ion Beam upon the Interaction of\na Multiterawatt Picosecond Laser Pulse with a Solid Target\" JETP,\n94,222, 2002.\n[16] A.A. Andreev, \"Generation and Application of Ultra-high Laser Fields\",\nNova Sci. Publish. Inc. NY, 2000.\n[17] V.Yu. Bychenkov, V. T. Tikhonchuk, S.V. Tolokonnikov \"Laser\ninitiation of nuclear reactions by high energy ions\" JETP,115, 2080,\n(1999).\n[18] Ya.B. Zeldovich, Yu.P. Raizer Physics of shock wave and high\ntemperature phenomena. M., Nauka, 1966."]}

FAST is a new machine proposed to support ITER experimental exploitation as well as to anticipate DEMO relevant physics and technology. FAST is aimed at studying, under burning plasma relevant conditions, fast particle (FP) physics, plasma operations and plasma wall interaction in an integrated way. FAST has the capability to approach all the ITER scenarios significantly closer than the present day experiments using deuterium plasmas. The necessity of achieving ITER relevant performance with a moderate cost has led to conceiving a compact tokamak (R = 1.82 m, a = 0.64 m) with high toroidal field (B(T) up to 8.5 T) and plasma current (I(p) up to 8 MA). In order to study FP behaviours under conditions similar to those of ITER, the project has been provided with a dominant ion cyclotron resonance heating system (ICRH; 30 MW on the plasma). Moreover, the experiment foresees the use of 6 MW of lower hybrid (LHCD), essentially for plasma control and for non-inductive current drive, and of electron cyclotron resonance heating (ECRH, 4 MW) for localized electron heating and plasma control. The ports have been designed to accommodate up to 10 MW of negative neutral beams (NNBI) in the energy range 0.5-1 MeV. The total power input will be in the 30-40 MW range under different plasma scenarios with a wall power load comparable to that of ITER (P/R similar to 22 MW m(-1)). All the ITER scenarios will be studied: from the reference H mode, with plasma edge and ELMs characteristics similar to the ITER ones (Q up to approximate to 1.5), to a full current drive scenario, lasting around 170s. The first wall (FW) as well as the divertor plates will be of tungsten in order to ensure reactor relevant operation regimes. The divertor itself is designed to be completely removable by remote handling. This will allow us to study (in view of DEMO) the behaviour of innovative divertor concepts, such as those based on liquid lithium. FAST is capable of operating with very long pulses, up to 170s, despite being a copper machine. The magnets initial operation temperature is 30 K, with cooling provided by helium gas. The in vessel components, namely FW and divertor, are actively cooled by pressurized water above 80 degrees C. The same water is also used to bake the vacuum vessel. FAST is equipped with ferromagnetic inserts to keep the toroidal field magnet ripple down to 0.3%.

A systematic study of high energetic alpha particle interaction with microinstability driven turbulence (ITG) is presented. The alpha particles are considered to be passive, thus not modifying the fine structure of the turbulence, and modelled as Maxwellian distributed. Both the turbulent fields and the evolution of the alpha distribution are computed by means of an Eulerian, flux tube code. It is shown how significant transport of high pressure distributions can occur, and how the direction and the intensity of the particle flux is sensitive to the choice of the temperature scale length of the alpha distribution, due to thermodiffusive phenomena. The diffusivity of an ITER-like case is studied, starting from an analytical treatment of the density and temperature profiles, which we show to be significant. New interpretative tools, by means of a single particle following code, are also presented. © 2008 American Institute of Physics.

Superthermische Teilchen, die durch Zusatzheizung oder Fusionsprozesse erzeugt werden, können vorhandene MHD-Instabilitäten in einem Fusionsplasma zusätzlich destabilisieren oder sogar zu neuen 'Energetischen-Teilchen-Moden' führen. Um solche Moden untersuchen zu können, wurde ein neuer linearer gyrokinetischer MHD-Code entwickelt und getestet, LIGKA (Linear Gyrokinetic Shear Alfvén Physics), dem das 'gyrokinetische MHD-Modell' zugrunde liegt [H.Qin et al, Phys. Plasmas 5, 1035 (1998)]. Dieses Modell besteht aus drei linearen Gleichungen, die aus der allgemeinen, nichtlinearen gyrokinetischen Lagrangefunktion abgeleitet werden: der Quasi-Neutralitätsgleichung, der gyrokinetischen Momentengleichung und der gyrokinetischen Gleichung selbst, die die gestörte Verteilungsfunktion beschreibt. Entwickeln nach dem Larmorradius, Bilden einiger Fluidmomente und Beschränken auf Scher-Alfvén-Moden resultiert in einer selbstkonsistenten, nicht-perturbativen, elektromagnetischen Formulierung, die es möglich macht, nicht nur Anwachs- und Dämpfungsraten, sondern auch durch die energetischen Teilchen modifizierte Eigenfunktionen zu berechnen. Im Vergleich zu früheren numerischen Implementierungen, wurden einige wesentliche Verbesserungen und Erweiterungen vorgenommen: es können sowohl analytische als auch numerische Gleichgewichte verwendet werden, und die Integration über die ungestörten Teilchenbahnen wird mit dem driftkinetischen Code HAGIS (S.D.Pinches, CPC 111, 131 (1998)) exakt ausgeführt. Darüber hinaus werden endliche Bananenbreiten berücksichtigt indem ausnützt wird, dass in einer linearen Formulierung die Diskretisierung der gestörten Potentiale in radialer Richtung mit der Integration über die Teilchenorbits vertauscht werden kann. Es wurden erfolgreich Vergleichsrechnungen mit anderen idealen MHD Codes für (1,1) interne Kink-Moden und TAE-Gap-Moden ausgeführt. Für diese beiden Arten von Moden wurde untersucht, welche Änderungen sich durch kinetische Effekte (Hintergrundteilchen, superthermische Teilchen) ergeben, und die Ergebnisse wurden mit anderen kinetischen Codes verglichen. In a plasma with a population of superthermal particles generated by heating or fusion processes, kinetic effects can lead to the additional destabilisation of MHD modes or even to additional (energetic particle) modes. In order to describe these modes, a new linear gyrokinetic MHD code has been developed and tested, LIGKA (Linear Gyrokinetic Shear Alfvén Physics), based on the theoretical gyrokinetic MHD model [H.Qin et al, Phys. Plasmas 5, 1035 (1998)]. This framework provides a set of linear equations derived from the general nonlinear gyrokinetic Lagrangian: the quasi neutrality equation, the gyrokinetic moment equation and the equation for the perturbed distribution function itself. A finite Larmor radius expansion together with the construction of some fluid moments and specification to the shear Alfvén regime results in a self-consistent, electromagnetic, non-perturbative model, that allows not only for growing or damped eigenvalues but also for a change in mode-structure of the magnetic perturbation due to the energetic particles. Compared to previous implementations, this model is coded in a more general and comprehensive way. LIGKA uses a fourier decomposition in the poloidal coordinate and a finite element discretisation in the radial direction. Both analytical and numerical equilibria can be treated. Integration over the unperturbed particle orbits is performed with the drift-kinetic code HAGIS [S.D.Pinches, CPC 111, 131 (1998)] which accurately describes the particles' trajectories. Furthermore, finite-banana-width effects are implemented in a rigorous way since the linear formulation of the model allows to exchange the unperturbed orbit integration and the discretisation of the perturbed potentials in the radial direction. The resulting model is formulated as an eigenvalue problem and solved iteratively. The code has been successfully benchmarked with other ideal MHD codes for the (1,1) internal kink and for TAE gap modes. For these two types of modes also kinetic modifications due to the background and due to superthermal particles have been investigated and benchmarks with other kinetic codes have been carried out.

International audience; in the European fusion roadmap, ITER is followed by a demonstration fusion power reactor (DEMO), for which a conceptual design is under development. This paper reports the first results of a coherent effort to develop the relevant physics knowledge for that (DEMO Physics Basis), carried out by European experts. The program currently includes investigations in the areas of scenario modeling, transport, MHD, heating & current drive, fast particles, plasma wall interaction and disruptions.

Experiments with the new neutral beam injection source of TCV have been performed with high fast-ion fractions (>20%) that exhibit a clear reduction of the loop voltage and a clear increase of the plasma pressure in on- and off-axis heating configurations. However, good quantitative agreement between the experimental data and TRANSP predictions is only found when including strong additional fast-ion losses. These losses could in part be caused by turbulence or MHD activity as, e.g. high frequency modes near the frequency of toroidicity induced Alfven eignmodes are observed. In addition, a newly installed fast-ion D-alpha (FIDA) spectroscopy system measures strong passive radiation and, hence, indicates the presence of high background neutral densities such that charge-exchange losses are substantial. Also the active radiation measured with the FIDA diagnostic, as well as data from a neutral particle analyzer, suggest strong fast-ion losses and large neutral densities. The large neutral densities can be justified since high electron temperatures (3-4 keV), combined with low electron densities (about 2 x 10(19) m(-3)) yield long mean free paths of the neutrals which are penetrating from the walls.