Behaviors of impurity in ITER plasma with standard type I ELMy H-mode and steady-state scenarios

Self-consistent simulations of impurity behaviors in ITER plasmas in standard Type I ELMy H-mode and steady-state scenarios are investigated using 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transports, including electron and ion thermal, hydrogenic and impurity transports, are predicted using a linear combination of anomalous and neoclassical transports. An anomalous transport is calculated using a theory-based Multimode (MMM95) model; while the neoclassical transport is calculated using NCLASS model. The temperature and density boundary conditions are described at the top of the pedestal. Two different models for hydrogenic and impurity boundary density conditions are considered. The first model is called a “static boundary density model,” in which the hydrogenic and impurity densities at the boundary are fixed. For the second model, called a “dynamic boundary density model,” the hydrogenic and impurity densities at the boundary are assumed to be a large fraction of its line-averaged density. For simplicity, the pedestal temperature is assumed to be a constant in all simulations. The combination of a core transport model together with the boundary density models is used to simulate the time evolution of plasma current, temperature, and density profiles for ITER plasmas in standard type I ELMy H-mode and steady-state scenarios. As a result, the behaviors of impurity in ITER plasmas can be investigated. It is found in both ITER scenarios that the total amount of impurity, including beryllium and helium, in plasma core increases rapidly in early state and reaches a steady-state value. The level of impurity content in the steady state depends sensitively on the impurity boundary conditions. The effective charge at the edge is found to be about 1.4 and 1.1 using a static boundary density model and a dynamic boundary density model, respectively. It is also found that the hydrogenic and impurity transports in ITER plasmas for both scenarios is dominated by the kinetic ballooning modes, while the ITG and TEM modes provide the largest contributions for both thermal transports in most of region. In addition, a sensitivity study is carried out to investigate the impacts of pedestal temperature, pedestal density and line-averaged density on the impurity behaviors. It is found that increasing the pedestal temperature results in a reduction of the impurity content. On the other hand, increasing the pedestal density, line-averaged density or impurity influx result in an increase of the impurity content.     

Influence of plasma pedestal profiles on access to ELM-free regimes in ITER

The influence of current density and pressure gradient profiles in the pedestal on the access to the regimes free from edge localized modes (ELMs) like quiescent H-mode in ITER is investigated. Using the simulator of MHD modes localized near plasma boundary based on the KINX code, calculations of the ELM stability were performed for the ITER plasma in scenarios 2 and 4 under variations of density and temperature profiles with the self-consistent bootstrap current in the pedestal. Low pressure gradient values at the separatrix, the same position of the density and temperature pedestals and high poloidal beta values facilitate reaching high current density in the pedestal and a potential transition into the regime with saturated large scale kink modes. New version of the localized MHD mode simulator allows one to compute the growth rates of ideal peeling-ballooning modes with different toroidal mode numbers and to determine the stability region taking into account diamagnetic stabilization. The edge stability diagrams computations and sensitivity studies of the stability limits to the value of diamagnetic frequency show that diamagnetic stabilization of the modes with high toroidal mode numbers can help to access the quiescent H-mode even with high plasma density but only with low pressure gradient values at the separatrix. The limiting pressure at the top of the pedestal increases for higher plasma density. With flat density profile the access to the quiescent H-mode is closed even with diamagnetic stabilization taken into account, while toroidal mode numbers of the most unstable peeling-ballooning mode decrease from n = 10?40 to n = 3?20.     

Stiffness and rigidity of the temperature profile in a tokamak

The notions of “stiffness” and “rigidity” of the temperature profile in a tokamak are introduced and formalized. By stiffness is meant the consistency of the profile when the plasma density, boundary temperature, and heating power change. By rigidity is meant the strong dependence of the central temperature on the boundary temperature. Analytical and numerical estimates carried out in a transport model with critical temperature gradients show that, at a low boundary temperature (the L-mode), the profiles are, as a rule, stiff but are not rigid. For a sufficiently high temperature pedestal in the H-mode, there exists a parameter range in which the profiles are stiff and at the same time rigid. However, when the pedestal temperature is too high and the deposited power profile is flat, the temperature profile may be neither stiff nor rigid. This behavior of the electron temperature profile was observed in a number of H-mode discharges with high plasma densities in the DIII-D and JET tokamaks. An analysis is also made of the stiffness and rigidity of the temperature profiles in the MAST and T-10 tokamaks.     

Effect of Joule Heating and Thermal Radiation in Flow of Third Grade Fluid over Radiative Surface

This article addresses the boundary layer flow and heat transfer in third grade fluid over an unsteady permeable stretching sheet. The transverse magnetic and electric fields in the momentum equations are considered. Thermal boundary layer equation includes both viscous and Ohmic dissipations. The related nonlinear partial differential system is reduced first into ordinary differential system and then solved for the series solutions. The dependence of velocity and temperature profiles on the various parameters are shown and discussed by sketching graphs. Expressions of skin friction coefficient and local Nusselt number are calculated and analyzed. Numerical values of skin friction coefficient and Nusselt number are tabulated and examined. It is observed that both velocity and temperature increases in presence of electric field. Further the temperature is increased due to the radiation parameter. Thermal boundary layer thickness increases by increasing Eckert number.     

Impacts of pellets injected from the low-field side on plasma in ITER

Impacts of pellets injected from the low-field side (LFS) on plasma in ITER are investigated using the 1.5D BALDUR integrated predictive modeling code. In these simulations, the pellet ablation is described using the neutral gas shielding (NGS) model. The pellet ablation model is coupled with the plasma core transport model, which is a combination of the MMM95 anomalous transport model and NCLASS neoclassical transport model. The boundary conditions are assumed to be at the top of the pedestal, in which the pedestal parameters are predicted using a pedestal model based on the theoretical-based pedestal width scaling (either magnetic and flow shear stabilization width scaling, or flow shear stabilization width scaling, or normalized poloidal pressure width scaling) and the infinite-n ballooning mode pressure gradient limit. These pedestal models depend sensitively on the density at the top of the pedestal, which can be strongly influenced by the injection of pellets. The combination of the MMM95 and NCLASS models, together with the pedestal and NGS models, is used to simulate the time evolution of the plasma current, ion and electron temperatures, and density profiles for ITER standard type-I ELMy H-mode discharges during the injection of LFS pellets. It is found that the injection of pellets results in a complicated plasma scenario, especially in the outer region of the plasma and the plasma conditions at the boundary in which the pellet has an impact on increasing the plasma edge density, but reducing the plasma edge temperature. The LFS pellet has a stronger impact on the edge as compared to the center. For fusion performance, the pellet can result in either enhancement or degradation, depending sensitively on the pellet parameters; such as the pellet size, pellet velocity, and pellet frequency. For example, when a series of deuterium pellets with a size of 0.5 cm, velocity of 1 km/s, and frequency of 2 Hz are injected into the ITER plasma from the LFS, the plasma performance, evaluated in terms of Q _fusion, can increase to 72% of that before the use of pellets. It is also found that the injection of pellets results in an increase in the ion and electron densities, but does not enhance the central plasma density. On the other hand, it results in the formation of another peak of the plasma density in the outer region near the plasma edge. The formation of the density peak results in the reduction of plasma transports near the edge by decreasing the contributions of ion-temperature-gradient and trapped electron modes, as well as kinetic ballooning modes.     

Nonlinear theory of ion-acoustic waves in an electron-positron-ion plasma

An analytical nonlinear gasdynamic theory of ion-acoustic waves in an e-p-i plasma is developed for the case in which all the plasma components in the wave undergo polytropic compression and rarefaction. An exact solution to the basic equations is found and analyzed by the Bernoulli pseudopotential method. The parameter range in which periodic waves can propagate and the range in which solitary waves (solitons) exist are determined. It is shown that the propagation velocity of a solitary is always higher than the linear ion sound velocity. The profiles of all the physical quantities in both subsonic and supersonic waves are calculated. The results obtained agree well with both the data from other papers and particular limiting cases.     

Comparison of the measured and calculated time profiles of the leakage current in the magnetically insulated transmission line of the angara-5-1 facility

One of the factors limiting the transmission of the electromagnetic pulse to the load in high-power electrophysical facilities is the current leakage in magnetically insulated transmission lines (MITLs). In this paper, the Angara-5-1 eight-module facility with an output power up to 6 TW is considered. The experimental and calculated time profiles of the leakage current for eight-module shots with a dynamic load (cylindrical arrays made of 40 tungsten wires) and single-module shots with a solid cylindrical metal load are compared. When interpreting the results, the contribution of vacuum electrons to the leakage current at the transition from the cylindrical to the conical section of the MITL is taken into account.     

Modeling of the parametric dependence of the edge toroidal rotation

Modeling of the edge toroidal rotation and its dependence on the edge plasma parameters is performed by means of the B2SOPS5.0 transport code for ohmic shots both for MAST and ASDEX Upgrade configurations. The impact of plasma current, toroidal magnetic field, plasma density, and temperature is investigated. The connection between the toroidal rotation and edge radial electric field is also studied. The results of the simulation are consistent with the parametric dependence predicted analytically. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 9, pp. 791–797. The text was submitted by the authors in English.     

Development of a collisional radiative model for interpreting the spectroscopic measurements of ArII line emission

A collisional radiative model for an ArII ion is constructed. The populations of the excited states of ArII ions in a plasma of a magnetic confinement system are calculated. It is shown that, in such a plasma, the populations of metastable states are independent of the electron density but, at the same time, are fairly sensitive to the electron temperature. These results allow one to estimate the electron temperature from the measurements of the Doppler profiles of the spectral lines by the laser fluorescence diagnostics. The populations of nonmetastable states calculated as functions of the plasma parameters also make it possible to estimate the electron temperature from passive spectroscopy measurements.     

Convectively stable pressure profile in magnetic confinement systems with internal rings

A convectively stable pressure profile in a long multiple-mirror (corrugated) magnetic confinement system with internal current-carrying rings is calculated. The plasma energy content in the axial region can be increased by using an internal ring that reverses the on-axis magnetic field direction and gives rise to an average magnetic well near the axis. The pressure profile in the outer region—outside the magnetic well—is considered in detail. It is shown that, in the radial pressure profile, a pedestal can be formed that leads to a higher pressure drop between the center and the plasma edge. The pressure profile is calculated from the Kruskal-Oberman criterion—a necessary and sufficient condition for the convective stability of a collisionless plasma. The revealed pedestal arises near the boundary of the average magnetic well in the region of the smallest but alternating-sign curvature of the magnetic field lines due to a break in the convectively stable pressure profile. Such a shape of the stable pressure profile can be attributed to the stabilizing effect of the alternating-sign curvature of the field lines in the multiple-mirror magnetic confinement systems under consideration.     

Equations for nonlinear MHD convection in shearless magnetic systems

A closed set of reduced dynamic equations is derived that describe nonlinear low-frequency flute MHD convection and resulting nondiffusive transport processes in weakly dissipative plasmas with closed or open magnetic field lines. The equations obtained make it possible to self-consistently simulate transport processes and the establishment of the self-consistent plasma temperature and density profiles for a large class of axisymmetric nonparaxial shearless magnetic devices: levitated dipole configurations, mirror systems, compact tori, etc. Reduced equations that are suitable for modeling the long-term evolution of the plasma on time scales comparable to the plasma lifetime are derived by the method of the adiabatic separation of fast and slow motions.     

Simulation of the Plasma Density Evolution during Electron Cyclotron Resonance Heating at the T-10 Tokamak

In ohmically heated (OH) plasma with low recycling, an improved particle confinement (IPC) mode is established during gas puffing. However, after gas puffing is switched off, this mode is retained only for about 100 ms, after which an abrupt phase transition into the low particle confinement (LPC) mode occurs in the entire plasma cross section. During such a transition, energy transport due to heat conduction does not change. The phase transition in OH plasma is similar to the effect of density pump-out from the plasma core, which occurs after electron cyclotron heating (ECH) is switched on. Analysis of the measured plasma pressure profiles in the T-10 tokamak shows that, after gas puffing in the OH mode is switched off, the plasma pressure profile in the IPC stage becomes more peaked and, after the peakedness exceeds a certain critical value, the IPC-LPC transition occurs. Similar processes are also observed during ECH. If the pressure profile is insufficiently peaked during ECH, then the density pump-out effect comes into play only after the critical peakedness of the pressure profile is reached. In the plasma core, the density and pressure profiles are close to the corresponding canonical profiles. This allows one to derive an expression for the particle flux within the canonical profile model and formulate a criterion for the IPC-LPC transition. The time evolution of the plasma density profile during phase transitions was simulated for a number of T-10 shots with ECH and high recycling. The particle transport coefficients in the IPC and LPC phases, as well as the dependences of these coefficients on the ECH power, are determined.     

Enterohaemorrhagic and enteropathogenic Escherichia coli use a different Tir-based mechanism for pedestal formation

Enterohaemorrhagic Escherichia coli (EHEC) adheres to the host intestinal epithelium, resulting in the formation of actin pedestals beneath adhering bacteria. EHEC and a related pathogen, enteropathogenic E. coli (EPEC), insert a bacterial receptor, Tir, into the host plasma membrane, which is required for pedestal formation. An important difference between EPEC and EHEC Tir is that EPEC but not EHEC Tir is tyrosine phosphorylated once delivered into the host. In this study, we assessed the role of Tir tyrosine phosphorylation in pedestal formation by EPEC and EHEC. In EPEC, pedestal formation is absolutely dependent on Tir tyrosine phosphorylation and is not complemented by EHEC Tir. The protein sequence surrounding EPEC Tir tyrosine 474 is critical for Tir tyrosine phosphorylation and pedestal formation by EPEC. In contrast, Tir tyrosine phosphorylation is not required for pedestal formation by EHEC. EHEC forms pedestals with both wild-type EPEC Tir and the non-tyrosine-phosphorylatable EPEC Tir Y474F. Pedestal formation by EHEC requires the type III delivery of additional EHEC factors into the host cell. These findings highlight differences in the mechanisms of pedestal formation by these closely related pathogens and indicate that EPEC and EHEC modulate different signalling pathways to affect the host actin cytoskeleton.     

Effects of environmental salinity and temperature on osmoregulatory ability, organic osmolytes, and plasma hormone profiles in the Mozambique tilapia (Oreochromis mossambicus)

The Mozambique tilapia, Oreochromis mossambicus, is capable of surviving a wide range of salinities and temperatures. The present study was undertaken to investigate the influence of environmental salinity and temperature on osmoregulatory ability, organic osmolytes and plasma hormone profiles in the tilapia. Fish were acclimated to fresh water (FW), seawater (SW) or double-strength seawater (200% SW) at 20, 28 or 35 degrees C for 7 days. Plasma osmolality increased significantly as environmental salinity and temperature increased. Marked increases in gill Na(+), K(+)-ATPase activity were observed at all temperatures in the fish acclimated to 200% SW. By contrast, Na(+), K(+)-ATPase activity was not affected by temperature at any salinity. Plasma glucose levels increased significantly with the increase in salinity and temperature. Significant correlations were observed between plasma glucose and osmolality. In brain and kidney, content of myo-inositol increased in parallel with plasma osmolality. In muscle and liver, there were similar increases in glycine and taurine, respectively. Glucose content in liver decreased significantly in the fish in 200% SW. Plasma prolactin levels decreased significantly after acclimation to SW or 200% SW. Plasma levels of cortisol and growth hormone were highly variable, and no consistent effect of salinity or temperature was observed. Although there was no significant difference among fish acclimated to different salinity at 20 degrees C, plasma IGF-I levels at 28 degrees C increased significantly with the increase in salinity. Highest levels of IGF-I were observed in SW fish at 35 degrees C. These results indicate that alterations in gill Na(+), K(+)-ATPase activity and glucose metabolism, the accumulation of organic osmolytes in some organs as well as plasma profiles of osmoregulatory hormones are sensitive to salinity and temperature acclimation in tilapia.     

Enterohaemorrhagic Escherichia coli Tir requires a C-terminal 12-residue peptide to initiate EspF-mediated actin assembly and harbours N-terminal sequences that influence pedestal length

Enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) both utilize type III secretion systems that translocate the effector protein Tir into the plasma membrane of mammalian cells in order to stimulate localized actin assembly into 'pedestals'. The Tir molecule that EPEC delivers is phosphorylated within its C-terminus on tyrosine-474, and a clustered 12-residue phosphopeptide encompassing this residue initiates an efficient signalling cascade that triggers actin polymerization. In addition to Y474, tyrosine-454 of EPEC Tir is phosphorylated, although inefficiently, and promotes actin polymerization at low levels. In contrast to EPEC Tir, EHEC Tir lacks Y474 and triggers pedestal formation in a phosphotyrosine-independent manner by interacting with an additional effector protein, EspF(U). To identify EHEC Tir sequences that regulate localized actin assembly, we circumvented the strict requirements for type III translocation and directly expressed Tir derivatives in mammalian cells by transfection. Infection of Tir-expressing cells with a Tir-deficient EHEC strain demonstrated that ectopically expressed Tir localizes to the plasma membrane, is modified by mammalian serine-threonine kinases and is fully functional for actin pedestal formation. Removal of portions of the cytoplasmic N-terminus of Tir resulted in the generation of abnormally long pedestals, indicating that this region of EHEC Tir influences pedestal length. In the presence of the entire N-terminal domain, a 12-residue peptide from the C-terminus of EHEC Tir is both necessary and sufficient to recruit EspF(U) and initiate actin pedestal formation. This peptide encompasses the portion of EHEC Tir analogous to the EPEC Tir-Y454 region and is present within the Tir molecules of all pedestal-forming bacteria, suggesting that this sequence harbours a conserved signalling function.     

CXSFIT Code Application to Process Charge-Exchange Recombination Spectroscopy Data at the T-10 Tokamak

The applicability of the CXSFIT code to process experimental data from Charge-eXchange Recombination Spectroscopy (CXRS) diagnostics at the T-10 tokamak is studied with a view to its further use for processing experimental data at the ITER facility. The design and operating principle of the CXRS diagnostics are described. The main methods for processing the CXRS spectra of the 5291-Å line of C⁵⁺ ions at the T-10 tokamak (with and without subtraction of parasitic emission from the edge plasma) are analyzed. The method of averaging the CXRS spectra over several shots, which is used at the T-10 tokamak to increase the signal-to-noise ratio, is described. The approximation of the spectrum by a set of Gaussian components is used to identify the active CXRS line in the measured spectrum. Using the CXSFIT code, the ion temperature in ohmic discharges and discharges with auxiliary electron cyclotron resonance heating (ECRH) at the T-10 tokamak is calculated from the CXRS spectra of the 5291-Å line. The time behavior of the ion temperature profile in different ohmic heating modes is studied. The temperature profile dependence on the ECRH power is measured, and the dynamics of ECR removal of carbon nuclei from the T-10 plasma is described. Experimental data from the CXRS diagnostics at T-10 substantially contribute to the implementation of physical programs of studies on heat and particle transport in tokamak plasmas and investigation of geodesic acoustic mode properties.     

Heat balance of the human body: influence of variations of locally distributed parameters

Human body temperature control is characterized by a local dependence of system variables and parameters. Essential properties regarding inhomogeneity of the passive system have been investigated using mathematical methods. The general diffusion-equation has been solved using implicit finite difference methods with nonlinear boundary conditions. In order to allow comparison with experimental results, a simple ideal controller has been defined. On the basis of an inhomogeneous cylinder model with four concentric layers, influences of variations due to differences between tissues and individuals or measurements of parameters such as basal metabolism and conductivity have been studied. Stationary temperature profiles calculated for homogeneous and inhomogeneous conditions have been compared. Finally, the influence of blood flow has been discussed, as well as the stationary behaviour of profiles due to blood flow and blood flow control. The change of sign of curvature of temperature profile is possible only if blood flow mechanisms and the local distribution of metabolism are taken into account.     

Effect of Escherichia coli lipopolysaccharide on the microviscosity of liver plasma membranes and hepatocyte suspensions and monolayers

The fluorescence probe 1,6-diphenylhexa-1,3,5-triene (DPH) was used for monitoring structural perturbations induced by lipopolysaccharide (LPS) of Escherichia coli (0111:B4) in plasma membranes of rat liver. Changes in microviscosity were observed in plasma membrane preparations from control rats after treatment with LPS and in plasma membrane preparations from liver perfused with LPS. In both systems fluorescence polarization was measured from which microviscosity was calculated. This parameter increases with LPS treatment. From temperature dependence studies was inferred that LPS interaction with plasma membrane preparations induces an increase of both the polarization term (r0/r-1)-1 and flow activation energy (delta E). Addition of LPS to hepatocyte suspensions also induces an increase on microviscosity and a delay in the fall of microviscosity induced by a temperature rise in hepatocyte monolayers grown on microcover slides. These data suggest that LPS interaction can be attributed to its binding to membrane hydrophobic regions in a non-specific manner.     

Enterohaemorrhagic and enteropathogenic Escherichia coli Tir proteins trigger a common Nck-independent actin assembly pathway

The Tir proteins of enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC respectively) are each translocated into the host plasma membrane where they promote F-actin pedestals in epithelial cells beneath adherent bacteria, but the two proteins act by different means. The canonical EPEC Tir becomes phosphorylated on tyrosine residue 474 (Y474) to recruit the host adaptor protein Nck, and also stimulates an inefficient, Nck-independent pathway utilizing tyrosine residue 454 (Y454). In contrast, the canonical EHEC Tir lacks Y474 and instead utilizes residues 452-463 to recruit EspF(U), an EHEC-specific effector that stimulates robust Nck-independent actin assembly. EHEC Tir Y458 and EPEC Tir Y454 are both part of an asparagine-proline-tyrosine (NPY) sequence. We report that each of the EHEC Tir NPY residues is required for EspF(U) recruitment and pedestal formation, and each of the EPEC Tir NPY residues is critical for inefficient, Nck-independent pedestal formation. Introduction of EspF(U) into EPEC dramatically enhanced Nck-independent actin assembly by EPEC Tir in a manner dependent on NPY(454). These results suggest that EPEC and EHEC Tir trigger a common Nck-independent actin assembly pathway and are both derived from an ancestral Tir molecule that utilized NPY to stimulate low-level pedestal formation.