Particle Recycling Research Articles

Measurement of hydrogen permeation due to atomic flux using permeation probe in the spherical tokamak QUEST

Particle retention and recycling in plasma fusion devices are generally associated with the diffusion of atomic hydrogen into the materials. The resulted permeation of atomic hydrogen is known as plasma driven permeation (PDP). This permeation may also be significant, even in the walls, which are not directly exposed to the plasma. Under similar conditions, the permeation flux ( Γ perm) of hydrogen through a 30 μm thick Ni membrane heated at 412–575 K has been measured in the spherical tokamak QUEST. Γ perm is being measured during the scans of different operating parameters like RF power ( P RF), chamber pressure ( P chamber), discharge widths ( τ dis) and vertical magnetic field ( B Z). Simultaneously edge plasma density and spectral intensities of atomic (Balmer) lines and molecular (Fulcher) bands have been compared with the permeation measurements. A linear relationship has been established between the time integrated Γ perm i.e. permeation fluence ( Q perm) and the time integrated H α intensity i.e. H α fluence ( Q α). Q perm also shows a strong relationship with the edge plasma density and various spectral fluences. The obtained results are discussed for exploring the applicability of the permeation probes in measuring the atomic flux near the first walls.

Local Island Divertor Experiment

To achieve an improvement of plasma confinement by an effective edge plasma control, the local island divertor (LID) was originally proposed in the National Institute for Fusion Science in the early 1980s. The LID is a kind of island divertor that utilizes the island separatrix as the channeling magnetic structure of the divertor, and it has the particular characteristic of localizing the particle recycling in very small areas. Thus, it is possible to construct a compact closed divertor configuration with efficient pumping capability, which results in the low-recycling condition in the edge region. In this paper the LID project is reviewed, from the physics design phase with numerical validation or estimation of the LID principle to a recent experimental result of the superdense core mode, which is a promising discharge for next-generation devices.

Accelerated desupersaturation of reverse osmosis concentrate by chemically-enhanced seeded precipitation

A two-step chemically-enhanced seeded precipitation (CESP) process was demonstrated for accelerated desupersaturation of antiscalant-containing, gypsum-supersaturated model solutions, which mimicked reverse osmosis (RO) concentrate from RO desalting of agricultural drainage water of high mineral scaling propensity. In the CESP process, CaCO 3 precipitation is first induced via lime dosing for antiscalant scavenging, followed by subsequent CaSO 4 precipitation via gypsum seeding for concentrate desupersaturation. It was demonstrated that lime-precipitated CaCO 3 particles were able to scavenge generic and commercial polycarboxylic-acid antiscalants, thereby facilitating subsequent CaSO 4 precipitation to progress with minimal retardation. The study demonstrated via a series of batch CESP cycles that gypsum particle recycling can sustain CaSO 4 precipitation, suggesting that a continuous CESP process could be feasible. Process analysis suggests that CESP can be significantly less chemical-intensive than conventional precipitation softening and, with its integration as an intermediate RO concentrate demineralization process, can enable desalination water recovery enhancement via secondary RO desalting. For the present case of gypsum-saturated RO feed water, enhancement of overall water recovery from 63% up to 87% or higher appears to be feasible. The study suggests that there is merit for developing a continuous CESP process for high recovery RO desalting of brackish water of high gypsum scaling propensity.

Energy and Particle Balance Studies Under Full Boron and Lithium‐Coated Walls in TJ‐II

AbstractThe Spanish stellarator TJ‐II has been operated under lithium wall conditions for two years so far. Important changes in plasma parameters and, in particular, on particle recycling have been recorded with respect to the normal, boronized wall conditions previously prevailing. The specific effects that the new recycling scenario could have on the improved plasma parameters, and in particular to the global energy balance of electrons and protons are addressed in the present work. In addition, the possible increase in ion energies impinging on the walls should be mirrored by the incoming flux of sputtered lithium atoms. However, a strong decrease of the corresponding sputtering yield is recorded. This effect is analyzed in terms of possible material mixing effects among others (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A weakly compressible MPS method for modeling of open‐boundary free‐surface flow

AbstractA mesh‐free particle method, based on the moving particle semi‐implicit (MPS) interaction model, has been developed for the simulation of two‐dimensional open‐boundary free‐surface flows. The incompressibility model in the original MPS has been replaced with a weakly incompressible model. The effect of this replacement on the efficiency and accuracy of the model has been investigated. The new inflow–outflow boundary conditions along with the particle recycling strategy proposed in this study extend the application of the model to open‐boundary problems. The final model is able to simulate open‐boundary free surface flow in cases of large deformation and fragmentation of free surface. The models and proposed algorithms have been validated and applied to sample problems. The results confirm the model's efficiency and accuracy. Copyright © 2009 John Wiley & Sons, Ltd.

A review of plasma–wall boundary effects on core confinement and lithium applications to boundary-controlled magnetic fusion experiments

Reduced particle recycling in the edge region is often considered to be a necessary condition to achieve high-performance confinement in magnetic fusion experiments. However, it is also true that whenever or however core confinement improves, as a result edge recycling is reduced. To provide a logical interpretation of this circular cause-and-consequence relation, reviewed in this paper are some of the important data demonstrating plasma–wall boundary effects on core confinement and also those evaluating innovative wall concepts with lithium applied to sustain optimized boundary conditions for the operation of steady-state fusion power reactors.

Analysis of neutral particle recycling and pedestal fueling in a H-mode DIII-D discharge

A detailed analysis of neutral atom recycling and pedestal fueling in a DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] high-confinement mode discharge is presented. Experimental data and two-dimensional (2D) edge plasma fluid code calculations are employed to provide ion wall recycling and recombination neutral sources and background edge plasma parameters for a 2D edge neutral code calculation of detailed neutral density, ionization, and charge-exchange distributions throughout the edge pedestal, scrape-off layer and surrounding halo region, divertor, and private flux regions. The effectiveness of the different neutral sources for fueling the confined plasma is evaluated.

Carrier-free immobilized enzymes for biocatalysis

Methods for the preparation of carrier-free insoluble enzymes are reviewed. The technology of cross-linked enzyme aggregates has now been applied to a range of synthetically useful activities. Fusion proteins are also gaining momentum because they allow a relatively selective aggregation or even a specific self-assembly of the desired enzyme activity into insoluble particles in the absence of potentially denaturing chemicals required for precipitation and cross-linking. Recycling of insoluble protein particles for multiple rounds of batchwise reaction has been demonstrated in selected biotransformations. However, for application in a fully continuous biocatalytic process, low resistance to mechanical stress and high compressibility are issues for consideration on carrier-free enzyme particles.

Kilovoltage beam Monte Carlo dose calculations in submillimeter voxels for small animal radiotherapy

Small animal conformal radiotherapy (RT) is essential for preclinical cancer research studies and therefore various microRT systems have been recently designed. The aim of this paper is to efficiently calculate the dose delivered using our microRT system based on a microCT scanner with the Monte Carlo (MC) method and to compare the MC calculations to film measurements. Doses from 2-30 mm diameter 120 kVp photon beams deposited in a solid water phantom with 0.2 x 0.2 x 0.2 mm3 voxels are calculated using the latest versions of the EGSnrc codes BEAMNRC and DOSXYZNRC. Two dose calculation approaches are studied: a two-step approach using phase-space files and direct dose calculation with BEAMNRC simulation sources. Due to the small beam size and submillimeter voxel size resulting in long calculation times, variance reduction techniques are studied. The optimum bremsstrahlung splitting number (NBRSPL in BEAMNRC) and the optimum DOSXYZNRC photon splitting (Nsplit) number are examined for both calculation approaches and various beam sizes. The dose calculation efficiencies and the required number of histories to achieve 1% statistical uncertainty--with no particle recycling--are evaluated for 2-30 mm beams. As a final step, film dose measurements are compared to MC calculated dose distributions. The optimum NBRSPL is approximately 1 x 10(6) for both dose calculation approaches. For the dose calculations with phase-space files, Nsplit varies only slightly for 2-30 mm beams and is established to be 300. Nsplit for the DOSXYZNRC calculation with the BEAMNRC source ranges from 300 for the 30 mm beam to 4000 for the 2 mm beam. The calculation time significantly increases for small beam sizes when the BEAMNRC simulation source is used compared to the simulations with phase-space files. For the 2 and 30 mm beams, the dose calculations with phase-space files are more efficient than the dose calculations with BEAMNRC sources by factors of 54 and 1.6, respectively. The dose calculation efficiencies converge for beams with diameters larger than 30 mm. A very good agreement of MC calculated dose distributions to film measurements is found. The mean difference of percentage depth dose curves between calculated and measured data for 2, 5, 10, and 20 mm beams is 1.8%.

Simulation study for divertor design to handle huge exhaust power in the SlimCS DEMO reactor

By the SOLDOR/NEUT2D simulation for divertor design study on a compact DEMO reactor, SlimCS, we estimated the prospect of handling the huge exhaust power in the divertor. Assuming exhaust power of 500 MW and ion outflux of 0.5 × 1023 s−1 into the scrape-off-layer, the peak heat load is estimated to be 70 MW m−2 on the outer target on the initial divertor design (vertical target) with the introduction of moderate gas puff flux and Ar fraction. This value significantly exceeds the allowable level of 10 MW m−2 which is an initial design target. By installing the ‘V-shaped corner’ in the bottom of the outer divertor target, and using strong gas puffing or Ar impurity injection, the detached condition with high particle recycling and radiation loss conditions is formed, and the peak heat load is successfully reduced below 10 MW m−2. It can also be demonstrated properly for the dependence of the exhaust power on the divertor heat load. Peak heat load is reduced exponentially with a decrease in the exhaust power and reaches 7 MW m−2 at Qtotal = 300 MW for moderate gas puff flux and Ar fraction.

A Comprehensive Fluidized Bed Combustion Model Coupled with a Radiation Model

A freeboard model of an overall FBC system model where radiation between particle and gas is accounted for through Stefan-Boltzmann law was modified by incorporation of a radiation model based on method of lines solution of discrete ordinates method. The predictive accuracy of the coupled code was tested by comparing its predictions with measurements taken on a refractory-lined, hybrid, pilot scale FBC as well as with predictions of unmodified system model. Comparisons show good agreement particularly for the test with recycle of fine particles. Significance of using a rigorous radiation model was illustrated by validating its predictions against measurements available on an industrial scale fluidized bed boiler. It was concluded that coupling a rigorous radiation model with an overall FBC system model is essential for accurate prediction of the behaviour of industrial boilers characterized by low surface to volume ratio and relatively colder water walls.

Residence time distribution: a tool to improve spray-drying control

Dairy powders are mainly obtained by spray drying, which is an effective process as it makes possible long-term storage at an ambient temperature. However, the control and design of this operation is still based on empirical knowledge. Improvement in product quality, which is governed by time/temperature history, thus involves greater understanding of the process via physico-chemical, thermodynamic and kinetic approaches. With regard to the latter, the residence time distribution (RTD) of the product provides valuable information about the product flow pattern in the dryer according to the operating conditions. The aim of this study was to determine the RTD of skim milk in a drying plant with different configurations, according to fine particle recycling (top of the chamber or internal fluid bed) and internal fluid bed thickness (4 to 16 cm). The RTD signal of the atomisation device was established first; then the RTD signals of the different spraydryer configurations were obtained by deconvolution of the experimental curves obtained and the RTD signal of the atomisation device, and modelled according to a combination of four reactor sets. The mean residence time of the product was only slightly modified by the dryer configuration (range 9.5 to 12 min). However, the results showed that a thicker internal fluid bed tends to increase mean residence time due to higher product retention, whereas top recycling of fine particles tends to decrease the mean residence time because of better agglomeration. RTD modelling provides additional information concerning the product flow rate fraction and the residence time distribution of each part of the dryer (chamber, cyclones and fluid bed), indicating that 60 to 80% of the powder passes through the cyclones, depending on the configuration. This study provides greater understanding of dryer operation, and allows further correlation between process parameters and biochemical changes (protein denaturation, Maillard reaction, etc.).

A Simple Method of H/He Influx Ratio Measurement as a Monitor for Machine Operation in LHD

In order to observe edge neutral recycling for fusion machine operation, the absolute values of Hα and HeI emissions have been usually analyzed with measurement of edge density and temperature. On the other hand, it is known that the temperature and density dependences of each line can be negated by taking the ratio between the two lines. The intensity ratio of Hα (6563 A) to HeI (5876 A or 6678 A) visible spectral lines is adopted, and the results are presented here instead of the method usually used for monitoring the edge particle recycling and the effect of wall conditioning in LHD. The ionization events per photon were calculated for both emissions using a collisional-radiative model, and the ratio of H+ flux (≡ H0 influx) to He+ flux (≡ He0 influx) was obtained. The Hα and HeI (5876 A) emissions in LHD have been measured using a monitor assembly with an interference filter and optical fiber array. The H+ /He+ flux ratio has been thus evaluated by integrating the Hα and HeI emissions from a 10-channel toroidal array. As an example of the measurement, all discharges performed during the past 9 years in LHD have been analyzed. The present method shows that the aftereffects of the H2 and He glow discharge cleaning for vacuum wall conditioning on the LHD discharges become clearly visible. The replacement of deposited atoms on the carbon divertor plates was also analyzed. It is found that the replacement is completed by 40-50 shot repetition of discharges. These results indicate the effectiveness of the present method as a good monitor for fusion machine operation.

Overview of the FTU results

Steady internal transport barriers (ITBs) are obtained in FTU at ITER-relevant magnetic field and density (ne0 ≥ 1.3 × 1020 m−3) in almost full non-inductive discharges, sustained by lower hybrid (LH) and electron cyclotron (EC) RF waves sources. Similarly to ITER, only electrons are directly heated which in turn heat ions via collisions and no momentum is injected. Collisions do not affect the mechanisms of turbulence suppression and energy transport. At the highest densities the ion thermal conductivity remains ≤ the ohmic level, while the energy confinement time exceeds the ITER 97-L scaling by about 1.6 times. The ITB radius can be varied in the range 0.2 ≤ r/a ≤ 0.65 modifying the radial profile of the LH driven current, acting mainly on the safety factor q. A liquid lithium limiter (LLL) of innovative design, composed of a mesh of porous capillaries, has been tested successfully for the first time on a medium size tokamak. The LLL surface showed no damage up to the maximum thermal load of 5 MW m−2. With LLL cleaner plasmas are obtained and the particle recycling strongly drops; new interesting regimes of particle transport arise at high density, with highly peaked profiles. Significant progress in disruption mitigation by means of EC power has shown that they can be avoided when absorption occurs directly on the MHD islands driving the disruption. Feedback control/suppression of MHD tearing modes (TM, m = 2) with EC waves has been achieved relying on a real-time detection of the TM and of its radial location. Testing the collective Thomson scattering in ITER-relevant configuration has stressed that avoiding backscattered radiation to the source is very crucial. The theory of the evolution of fishbone-like instabilities driven by LH generated supra-thermal electrons in FTU is outlined, and its relation to the trapped α particles dynamics is stressed.

Investigational Drugs Targeting HDL-C Metabolism And Reverse Cholesterol Transport

Low high-density lipoprotein cholesterol (HDL-C) levels are associated with higher risk of cardiovascular disease, even in patients receiving statin therapy. HDL-C has a number of potential atheroprotective mechanisms, including reverse cholesterol transport. HDL-C also has antioxidant, anti-inflammatory, vasodilatory and antithrombotic effects. A number of targets with the potential to raise HDL-C levels and/or increase reverse cholesterol transport have been identified. Plasma concentrations of HDL-C are the net result of the de novo production, catabolism and recycling of HDL-C particles, as well as the contribution to HDL-C from components of other lipoproteins. HDL-C levels can be modified by increasing the production of apolipoprotein A-I or by delaying the clearance of HDL-C from the plasma. Whether manipulation of these drug targets to raise HDL-C will result in cardiovascular event reduction remains to be determined.

Effect of Magnetic Configuration on the Neutral Particle Recycling in Compact Helical System

In devices such as Stellarator/Heliotron, nested magnetic surfaces are surrounded by the so-called separatrix layer, which consists of open field lines with various connection length to the vacuum chamber wall and/or divertor plates. In this paper, we study the strike point distribution of field lines on Compact Helical System chamber wall, especially under divertor configuration. Then, by using these distribution as the measure of neutral recycling source, Monte Carlo simulation of 3-D neutral transport is done. The results are compared with those obtained for different magnetic configuration.

The effect of the magnetic topology on particle recycling in the ergodic divertor of TEXTOR

The influence of the divertor geometry of the dynamic ergodic divertor (DED) in TEXTOR on particle recycling is discussed. The geometry can be varied by the choice of the base mode, the edge safety factor and the divertor coil current. The divertor volume is split into the upstream and the downstream area. Strong plasma flows in the downstream area, essential for high screening efficiency, are predicted. The source strength of deuterium and carbon in the downstream area is estimated by using the two-dimensional distribution of Dα and CIII emission in front of the target. The results are compared to EMC3 and ERO-code calculations.

Poloidal Distribution Measurement of Inward Neutral Flux in LHD

Three emission lines of neutral helium, i.e., the λ 667.8 nm (21P-31D), λ 728.1 nm (21P-31S), and λ 706.5 nm (23P-33S) lines, are observed with an array of parallel lines-of-sight which covers an entire poloidal cross section of the plasma in the Large Helical Device (LHD). Their emission locations and intensities are determined from the Zeeman profiles. The electron temperature and density are evaluated from intensity ratios among the observed emission lines at each emission location and the poloidal distribution of ionization flux or its equivalent quantity, inward neutral particle flux, is derived with the help of collisional-radiative model calculations. A relatively strong neutral flux is observed at the inboard-side X-point and this result implies a high particle recycling in the inboardside divertor region. The result is consistent with the ion flux distribution onto the helically located divertor plates measured with Langmuir probes.

Influence of the Wall Characteristics on the Development of MARFE in Tokamaks

Multifaceted asymmetric radiation from the edge (MARFE) normally develops in fusion devices close to the density limit. MARFE is considered a result of thermal instabilities excited under critical conditions through different mechanisms: impurity radiation, recycling of neutral particles, anomalous transport of charged particles and energy. Recent experiments on tokamaks TEXTOR and JET show that plasma-wall interaction, leading to release of recycling neutrals and impurities, plays a very important role for the formation of MARFE. In the present contribution we develop further the MARFE models based on the instability of particle recycling on the tokamak wall by including a simple description for the release of recycling neutrals from the wall surface into the plasma. This development takes into account the time delay between the out flow of charged particles from the plasma and in flux of neutrals. The linear stability analysis shows that this does not change the critical plasma density for the MARFE formation but modifies significantly the growth rate of unstable perturbations developing when the density exceeds the threshold. These findings are confirmed in a non-linear consideration by solving the equations for the particle, momentum and energy transfer in the plasma coupled with the wall particle balance equations. This is done in a one-dimensional approximation by taking into account the variation of the main plasma parameters in the poloidal direction and making averaging in the radial direction over the plasma edge width of the penetration depth of neutrals. The intrinsic poloidal asymmetry of the system, defining the MARFE localization, is introduced by the Shafranov shift of magnetic flux surfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thematic review series: Patient-Oriented Research. What have we learned about HDL metabolism from kinetics studies in humans?

Plasma measurements of lipids, lipoproteins, and apolipoproteins provide information on the static levels of these fractions without providing key information on the dynamic fluxes of lipoproteins in the circulation. Kinetics studies, in contrast, provide additional information on the production and clearance rates of lipoproteins and the flow of lipids and apolipoproteins through lipoprotein fractions. This information is crucial in accurately delineating the metabolism of HDL in plasma, because plasma concentrations of HDL are the net result of the de novo production and catabolism of HDL as well as the recycling of HDL particles and the contribution to HDL from components of other lipoproteins. Studies aimed at measuring the metabolism of HDL particles have shown that HDL metabolism in vivo is complex and consists of multiple components. Kinetics studies provide a window into the metabolism of HDL, allowing us to better understand the mechanisms of HDL decrease in human conditions and the functionality of HDL particles. Here, we review the progress in our understanding of HDL metabolism derived from in vivo kinetics studies, focusing primarily on studies in humans but also reviewing key studies in animal models.