Pellet injection into H-mode ITER plasma with the presence of internal transport barriers

The impacts of pellet injection into ITER type-1 ELMy H-mode plasma with the presence of internal transport barriers (ITBs) are investigated using self-consistent core-edge simulations of 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transport is predicted using a combination of a semi-empirical Mixed B/gB anomalous transport model, which can self-consistently predict the formation of ITBs, and the NCLASS neoclassical model. For simplicity, it is assumed that toroidal velocity for ω _E×B calculation is proportional to local ion temperature. In addition, the boundary conditions are predicted using the pedestal temperature model based on magnetic and flow shear stabilization width scaling; while the density of each plasma species, including both hydrogenic and impurity species, at the boundary are assumed to be a large fraction of its line averaged density. For the pellet’s behaviors in the hot plasma, the Neutral Gas Shielding (NGS) model by Milora-Foster is used. It was found that the injection of pellet could result in further improvement of fusion performance from that of the formation of ITB. However, the impact of pellet injection is quite complicated. It is also found that the pellets cannot penetrate into a deep core of the plasma. The injection of the pellet results in a formation of density peak in the region close to the plasma edge. The injection of pellet can result in an improved nuclear fusion performance depending on the properties of pellet (i.e., increase up to 5% with a speed of 1 km/s and radius of 2 mm). A sensitivity analysis is carried out to determine the impact of pellet parameters, which are: the pellet radius, the pellet velocity, and the frequency of injection. The increase in the pellet radius and frequency were found to greatly improve the performance and effectiveness of fuelling. However, changing the velocity is observed to exert small impact.     

Time evolution of the ion temperature in the T-10 tokamak during simultaneous pellet injection and electron-cyclotron resonance heating

Results are presented from studies of the time evolution of the ion temperature in the T-10 tokamak in the course of injection of several (up to five) deuterium pellets into a deuterium plasma the electron component of which is heated at the second harmonic of the electron gyrofrequency. It is shown that, at an electron cyclotron heating power of 900 kW, the injection of five pellets is accompanied by an increase in the ion temperature to 1200 keV, which is a record value for T-10. It is noted that energy exchange between the electron and ion components in these experiments is a purely classical, Coulomb process.     

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.     

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.     

Mechanical behavior of human embryonic stem cell pellet under unconfined compression

As a prelude to the understanding of mechanotransduction in human embryonic stem cell (hESC) differentiation, the mechanical behavior of hESCs in the form of cell pellet is studied. The pellets were tested after 3 or 5 weeks of cell culture in order to demonstrate the effect of the duration of cell culture on the mechanical properties of the pellets. A micromechanical tester was used to conduct unconfined compression on hESC pellet, and experimental, numerical, and analytical methods were combined to determine the mechanical properties of hESC pellet. It is assumed that the mechanical behavior of hESC pellets can be described by an isotropic, linear viscoelastic model consisting of a spring and two Maxwell units in parallel, and the Poisson’s ratio of the hESC pellet is constant based on pellet deformation in the direction perpendicular to the compression direction. Finite element method (FEM) simulation was adopted to determine the values of Poisson’s ratio and the five parameters contained in the viscoelastic model. The variations of Poisson’s ratio and the initial elastic modulus are found to be larger compared with those of the four other parameters. Results show that longer duration of cell culture leads to higher modulus of hESC pellet. The effect of pellet size error on the values of mechanical parameters determined is studied using FEM simulation, and it is found that the effect of size error on Poisson’s ratio and initial elastic modulus is much larger than that on the other parameters.     

Changes in plasma catecholamines and behavior of rats during the anticipation of footshock

A chronic catheter was inserted into the ventral caudal artery of male Sprague-Dawley rats to allow for sampling of blood and measurement of blood pressure and heart rate in conscious animals without handling. The day after surgery, one group of rats was transferred individually from the home cage to a shock chamber and after 5 min received 60 footshocks (2.5 mA, 0.4 sec in duration, at 5-sec intervals). This procedure was repeated two additional times during the same day. Control animals were handled in an identical manner but were not shocked. Previous experience with footshock had no effect on basal plasma levels of norepinephrine (NE) and epinephrine (EPI) or on resting blood pressure and heart rate as measured 2 days after surgery. When transferred to the shock chamber, previously shocked rats had greater increases in plasma NE and EPI and heart rate. In addition, previously shocked rats were less active and defecated more frequently than did control rats. However, there were no differences in the responses of previously shocked and control rats to 5 min of intermittent footshock. Results of this study demonstrate an activation of the sympatho-adrenal medullary system and attendant changes in the cardiovascular system and behavior of rats during the anticipation of footshocks. This suggests that the functioning of sympathetic nervous system and the adrenal medulla provides a sensitive measure of arousal and fear in rats.     

Neurohypophyseal peptide levels in CSF and plasma during passive avoidance behavior in rats

Levels of vasopressin (AVP), oxytocin (OXT), and neurophysin (NP) in CSF and plasma of rats were determined during acquisition and retention of passive avoidance behavior. None of the levels of neurohypophyseal peptides in CSF were changed either during the adaptation period, or during acquisition or the retention of this behavior. Moreover, no differences were found in hormone levels in CSF of the various groups of rats subjected to different shock intensities during the acquisition trial. The marked differences in individual latencies of nonavoiding rats, and the differences in latencies due to a different shock intensity applied during the learning trial were not reflected by changes in CSF hormone levels. Neither AVP nor NP levels in plasma were affected by the different shock intensities applied, when measured at 20 min after the learning trial. In contrast, a decrease in plasma OXT levels was observed after application of a shock intensity of 0.25 mA during the learning trial. During retention of the passive avoidance response plasma levels of AVP, OXT and NP were not different from the levels found in the nonshocked groups. It is suggested that under the conditions used in this study the CSF is apparently not involved in the distribution of neurohypophyseal peptides to their possible sites of behavioral action in the brain.     

Studies of the impurity pellet ablation in the high-temperature plasma of magnetic confinement devices

The ablation of impurity pellets in tokamak and stellarator plasmas is investigated. Different mechanisms for shielding the heat fluxes from the surrounding plasma to the pellet surface are discussed. A model for impurity pellet ablation is developed that can account for both neutral and electrostatic shielding. It is shown that the experimental values of the impurity pellet ablation rate are well described by the neutral gas shielding model over a wide range of plasma temperatures and densities. Taking into account the electrostatic shielding leads to worse agreement between the predictions of the model and the experimental data; this result still remains unclear. Scaling laws are obtained that allow one to estimate the local ablation rate of impurity pellets made of various materials over a wide range of plasma parameters in the neutral gas shielding model.     

Nature of sterols affects plasma membrane behavior and yeast survival during dehydration

The plasma membrane (PM) is a main site of injury during osmotic perturbation. Sterols, major lipids of the PM structure in eukaryotes, are thought to play a role in ensuring the stability of the lipid bilayer during physicochemical perturbations. Here, we investigated the relationship between the nature of PM sterols and resistance of the yeast Saccharomyces cerevisiae to hyperosmotic treatment. We compared the responses to osmotic dehydration (viability, sterol quantification, ultrastructure, cell volume, and membrane permeability) in the wild-type (WT) strain and the ergosterol mutant erg6Δ strain. Our main results suggest that the nature of membrane sterols governs the mechanical behavior of the PM during hyperosmotic perturbation. The mutant strain, which accumulates ergosterol precursors, was more sensitive to osmotic fluctuations than the WT, which accumulates ergosterol. The hypersensitivity of erg6Δ was linked to modifications of the membrane properties, such as stretching resistance and deformation, which led to PM permeabilization during the volume variation during the dehydration-rehydration cycles. Anaerobic growth of erg6Δ strain with ergosterol supplementation restored resistance to osmotic treatment. These results suggest a relationship between hydric stress resistance and the nature of PM sterols. We discuss this relationship in the context of the evolution of the ergosterol biosynthetic pathway.     

Two-compartment behavior during transport of folate compounds in L1210 cell plasma membrane vesicles

Summary The transport of [³H] 1,l 5-formyltetrahydrofolate, [³H] folic acid, and [³H]methotrexate by L1210 cell plasma membrane vesicles exhibited multicompartmental behavior. Two separate vesicular compartments (parallel relationship) of approximately equal volume were revealed during measurements of influx and efflux. Flux in one compartment was rapid, saturable, highly temperature-sensitive, and inhibited by pCMBS. Flux in the other compartment exhibited all of the characteristics of passive diffusion. These results imply that our plasma membrane vesicle preparations consist of a mixture of two functional species. Transport of folate into one of these species occurs by passive diffusion alone, whereas transport into the other kind of vesicle occurs by both passive diffusion and carrier-facilitated transport.     

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.     

Study of L-H transition triggered by pellet injection based on a power threshold model

Simulations of ITER plasma during an L-H transition triggered by pellet injection are carried out using the 1.5D BALDUR integrated predictive modeling code. In these simulations, plasma core transport is predicted using a combination of the Multimode (MMM95) turbulent transport model and neoclassical transport (NCLASS) model. The pellet ablation behavior is described using the neutral gas shielding pellet model with the grad-B drift effect also included. Because of the increase of the plasma density and the reduction of the temperature, the plasma self-heating powers (ohmic heating and alpha heating) increase, whereas the plasma energy loss (through radiation) decreases. As a result, the total power across the separatrix increases. On the other hand, the L-H power threshold decreases. With all the changes of heating, an L-H transition can be induced even though the auxiliary heating is not enough for the L-H transition before pellet injection. It is also found that the L-H transition triggered by pellet injection depends sensitively on the pellet radius, but only moderately on the pellet velocity.     

Elevated plasma testosterone concentrations during stallion-like sexual behavior in mares (Equus caballus)

Mounting interactions in mares isolated from stallions and the relationship to stage of the estrous cycle and level of circulating hormones were studied for 3 years in a herd averaging 105 mares. Mares were assigned to mounting, standing, and control groups. A control mare was selected by being within 1 day of the number of days after ovulation in a mounting mare. A total of 15 mounting interactions were detected by chance observation during the 3 years. A blood sample was collected immediately after the mounting interaction from each mare in the three groups, and a transrectal ultrasonographic examination of the reproductive tract was done. Two mounting interactions occurred during the early luteal phase and 13 during the follicular phase. The interactions that occurred during the follicular phase were used for comparisons among groups. The interval between mounting and the next ovulation, diameter of the two largest follicles, and the number of follicles larger and smaller than 20 mm were not different significantly among the mounting, standing, and control groups. Testosterone concentrations were higher (P<0.01) in the mounting group (17.7+/-2.3 pg/ml) than in standing group (10.9+/-0.5 pg/ml), and the difference between the mounting group and the control group (12.8+/-0.6 pg/ml) approached significance (P<0.08). Concentrations of androstenedione, estradiol, estrone, and progesterone did not differ significantly among groups. Results indicated that mounting behavior between mares is rare, usually occurs during the follicular phase, and is related to high circulating concentrations of testosterone.     

Bacterial colonization of pellet softening reactors used during drinking water treatment

Pellet softening reactors are used in centralized and decentralized drinking water treatment plants for the removal of calcium (hardness) through chemically induced precipitation of calcite. This is accomplished in fluidized pellet reactors, where a strong base is added to the influent to increase the pH and facilitate the process of precipitation on an added seeding material. Here we describe for the first time the opportunistic bacterial colonization of the calcite pellets in a full-scale pellet softening reactor and the functional contribution of these colonizing bacteria to the overall drinking water treatment process. ATP analysis, advanced microscopy, and community fingerprinting with denaturing gradient gel electrophoretic (DGGE) analysis were used to characterize the biomass on the pellets, while assimilable organic carbon (AOC), dissolved organic carbon, and flow cytometric analysis were used to characterize the impact of the biological processes on drinking water quality. The data revealed pellet colonization at concentrations in excess of 500 ng of ATP/g of pellet and reactor biomass concentrations as high as 220 mg of ATP/m(3) of reactor, comprising a wide variety of different microorganisms. These organisms removed as much as 60% of AOC from the water during treatment, thus contributing toward the biological stabilization of the drinking water. Notably, only a small fraction (about 60,000 cells/ml) of the bacteria in the reactors was released into the effluent under normal conditions, while the majority of the bacteria colonizing the pellets were captured in the calcite structures of the pellets and were removed as a reusable product.     

Differential rotation of plasma in the GOL-3 multiple-mirror trap during injection of a relativistic electron beam

Results of spectral and magnetic diagnostics of plasma differential rotation in the GOL-3 multiplemirror trap are presented. It is shown that the maximum frequency of plasma rotation about the longitudinal axis reaches 0.5 MHz during the injection of a relativistic electron beam into the plasma. The data of two diagnostics agree if there is a region with a higher rotation frequency near the boundary of the electron beam. Plasma differential rotation can be an additional factor stabilizing interchange modes in the GOL-3 facility.     

Experimental studies of the behavior of the ion plasma component during disruptive instability in a tokamak

Results are presented from experimental studies of the behavior of the plasma ion component during disruptive instability in the TVD and DAMAVAND tokamaks. It is shown that the ion temperature increases during a major disruption by a factor of 1.5–2. The ions are accelerated predominantly across the magnetic field near the rational magnetic surfaces. Results on the ion acceleration along the magnetic field indicate that disruptions are accompanied by the generation of longitudinal electric fields that are aligned in opposite directions at the plasma periphery and near the plasma axis.     

Development of beam-plasma instability during the injection a low-energy electron beam into the ionospheric plasma

Results are presented from an active experiment on the injection of charged particle beams into the ionospheric plasma. The experiment was carried out in 1992 onboard the Intercosmos-25 satellite and the Magion-3 daughter satellite (APEX). A specific feature of this experiment was that both the ion and electron beams were injected upward, in the same direction along the magnetic field. The most interesting results are the excitation of HF and VLF-LF waves and the generation of fast charged particle flows, which were recorded on both satellites.     

Repetition-Related Reductions in Neural Activity during Emotional Simulations of Future Events

Simulations of future experiences are often emotionally arousing, and the tendency to repeatedly simulate negative future outcomes has been identified as a predictor of the onset of symptoms of anxiety. Nonetheless, next to nothing is known about how the healthy human brain processes repeated simulations of emotional future events. In this study, we present a paradigm that can be used to study repeated simulations of the emotional future in a manner that overcomes phenomenological confounds between positive and negative events. The results show that pulvinar nucleus and orbitofrontal cortex respectively demonstrate selective reductions in neural activity in response to frequently as compared to infrequently repeated simulations of negative and positive future events. Implications for research on repeated simulations of the emotional future in both non-clinical and clinical populations are discussed.     

Alterations in plasma catecholamines and behavior during acute stress in spontaneously hypertensive and Wistar-Kyoto normotensive rats

The responsiveness of the sympathoadrenal system to stress was assessed in spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats at 6, 18, and 48 weeks of age. Two days after insertion of a tail arterial catheter, each rat was transferred from its home cage to a shock chamber, and after 5 min received 60 footshocks over a 5 min interval. Blood samples were taken from undisturbed rats when in the home cage, 3–5 min after transfer to the shock chamber, and at the end of shock. An additional group of naive SHR and WKY rats was exposed to footshock and behavioral responses were recorded. There were no strain differences in levels of norepinephrine (NE) or epinephrine (EPI) while rats were undisturbed in their home cages. Transfer to the shock chamber resulted in a greater increase in plasma levels of both catecholamines in SHRs of each age. A similar pattern was evident after footshock; SHR rats had significantly higher post-shock levels of plasma NE and EPI than age-matched WKY rats. During shock, SHR rats were more active and jumped and reared more frequently than WKYs. These results demonstrate that the sympathoadrenal system of SHR rats is more responsive than normotensive rats to stressful stimuli and that this hyper-responsitivity is independent of increases in blood pressure. The excessive discharge of NE and EPI into plasma during stress may contribute to the development and maintenance of high blood pressure in SHR rats.