Formation and sustainability of H-mode regime in tokamak plasma via sources perturbations based on two-field bifurcation concept

A set of coupled particle and thermal transport equations is used to study a formation and sustainability of an edge transport barrier (ETB) in tokamak plasmas based on two-field bifurcation. The two transport equations are numerically solved for spatio-temporal profiles of plasma pressure and density. The plasma core transport includes both neoclassical and turbulent effects, where the latter can be suppressed by flow shear mechanism. The flow shear, approximated from the force balance equation, is proportional to the product of pressure and density gradients, resulting in non-linearity behaviors in this calculation. The main thermal and particle sources are assumed to be localized near plasma center and edge, respectively. It is found that the fluxes versus gradients regime illustrates bifurcation nature of the plasma. This picture of the plasma implies hysteresis properties in fluxes versus gradients space. Hence, near marginal point, the perturbation in thermal or particle sources can trigger an L-H transition. Due to hysteresis, the triggered H-mode can be sustained and the central plasma pressure and density can be enhanced

ELM triggering conditions for the integrated modeling of H-mode plasmas

Recent advances in the integrated modeling of ELMy H-mode plasmas are presented. A model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. Formation of the pedestal and the L-H transition is the direct result of ExB flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by either the ballooning or peeling MHD instabilities. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Burning Plasma Projections Using Drift Wave Transport Models and Scalings for the H-Mode Pedestal

OAK-B135 The GLF23 and Multi-Mode (MM95) transport models are used along with a model for the H-mode pedestal to predict the fusion performance for the ITER, FIRE, and IGNITOR tokamak designs. The drift-wave predictive transport models reproduce the core profiles in a wide variety of tokamak discharges, yet they differ significantly in their response to temperature gradient (stiffness). Recent gyro-kinetic simulations of ITG/TEM and ETG modes motivate the renormalization of the GLF23 model. The normalizing coefficients for the ITG/TEM modes are reduced by a factor of 3.7 while the ETG mode coefficient is increased by a factor of 4.8 in comparison with the original model. A pedestal temperature model is developed for type I ELMy H-mode plasmas based on ballooning mode stability and a theory-motivated scaling for the pedestal width. In this pedestal model, the pedestal density is proportional to the line-averaged density and the pedestal temperature is inversely related to the pedestal density

Integrated predictive modelling of JET H-mode plasma with type-I ELMs

It is well known that edge plasma parameters influence performance in many different ways (profile stiffness is probably one of the best known examples). In ELMy H-mode a thin region with improved transport characteristics (Edge Transport Barrier) c

Dependence of ITER Per for mance on Pedestal Temper atur e, Aver age Electr on Density, Auxiliar y Heating Power , and Impur ity Content

Abstr act Self-consistent modeling of ITER has been carried out using the 1.5D BALDUR integrated predictive modeling code. In these simulations, a core transport model is described by a combination of an anomalous transport and a neoclassical transport. An anomalous transport is calculated using the Multimode (MMM95) core transport model, while a neoclassical transport is computed using the NCLASS model. At the reference design point, it is found that ITER fusion power production improves with the increase of pedestal temperature, average electron density, and auxiliary heating power. However, the power production reduces with the increase of impurity content. For the variation of the density and auxiliary heating power, the fusion Q increases linearly with both parameters. It is also found that the sawtooth mixing radius tends to decreases with increasing of pedestal temperature, average electron density and auxiliary heating power; however, it increases with impurity content. In addition, the sawtooth frequency tends to increase with the increase of heating power; but decrease with pedestal temperature. Intr oduction The concept of magnetic confinement fusion (MCF) has long been explored to address the feasibility of nuclear fusion energy. The ITER project [1] is an international collaboration to investigate the scientific and technological feasibility of MCF. Producing fusion reactions which satisfy such a condition inside a tokamak requires our ability to both heat and contain high-temperature plasmas. Comprehensive computer simulations are needed to optimize to plasma conditions before actual experiments are carried on. In this study, the BALDUR integrated predictive modelling code [2] is used to carry out simulations of plasmas with the standard H-mode (high confinement) scenario, as it is the 35th EPS Conference on Plasma Phys. Hersonissos, 9 -13 June 2008 ECA Vol.32D, P-4.040 (2008 < Results and Discussions The BALDUR integrated predictive transport modeling code is used to carry out the until the pedestal temperature of 8 keV. This trend of nuclear fusion performance can be explained by the behavior of central temperature and density, which tend to decrease when the pedestal temperature is more than 8 keV. It can be also seen than the performance increase linearly with average electron density. However, the performance decreases when the auxiliary heating power or impurity content increases. The effect of pedestal temperature, average electron density, auxiliary heating power, and impurity content (Z eff ) variations on sawtooth oscillation is also investigated. Note that in all simulations, the sawtooth oscillation is considered after 15 sec until 597 sec. The sawtooth frequency and sawtooth mixing radius are averaged during last 30 sec of each simulation. It is found that the sawtooth frequency ranges from 0.2 Hz to 0.5 Hz and the sawtooth mixing radius ranges from 0.8 m to 1.1 m. The sawtooth mixing radius tends to decreases with increasing of pedestal temperature, average electron density and auxiliary heating power; however, it increases with impurity content. In addition, the sawtooth frequency tends to increase with the increase of heating power; but decrease with pedestal temperature. Conclusions Self-consistent modeling of ITER has been carried out using BALDUR integrated code. At the reference design point, it is found that ITER fusion power production improves with the increase of pedestal temperature, average electron density, and auxiliary heating power. However, the power production reduces with the increase of impurity content. For the variation of the density and auxiliary heating power, the fusion Q increases linearly with both parameters. It is also found that the sawtooth mixing radius tends to decrease with increasing pedestal temperature, average electron density and auxiliary heating power; however, it increases with impurity content. In addition, the sawtooth frequency tends to increase with the increase of heating power; but decrease with pedestal temperature

Density Functional Theory Simulations of Aluminium Alkoxide and Fluoride

A series of density functional theory (DFT) simulations was carried out to investigate the geometry and reaction pathways of aluminium alkoxides using three different exchange-correlation functionals, including the local-density approximation, generalized gradient approximation, and a hybrid functionals. The simulations of fluoride atoms (F) sticking to the Al alkoxide, varying their distances from 6.0 Aring to their intermediate states along a straight line for the corresponding energy surfaces, were performed. It is found that the structural optimization obtained from different exchange-correlation functionals exhibits similar molecular configurations. The reaction pathways for the synthesis of Al fluoride was also simulated by utilizing the transition state searches method for investing the reaction pathways, including linear synchronous (LST) and quadratic synchronous (QST) maximization to investigate the reaction intermediate, and the converged results for all the distances were successfully obtained. It is found that the F atom replace one of bridging and terminal isopropoxide groups at the final state equivalently converted to the surrounded solvent molecules