Outer Baffle Research Articles

First SOLEDGE3X-EIRENE simulations of the ITER Neon seeded burning plasma boundary up to the first wall

Boundary plasma simulations are essential to estimate expected divertor and first wall (FW) heat and particle loads on ITER during burning plasma operation. A key missing feature of existing SOLPS simulations (Pitts et al., 2019) is the absence of a plasma solution out to the main chamber walls, essential to self-consistently estimate the gross sputtering of wall material. Here, SOLEDGE3X is applied for the first time to obtain up-to-the wall burning plasma solutions of the ITER boundary plasma at the nominal PSOL = 100 MW of the main SOLPS database simulations, including He ash, Ne seeding but without fluid drifts. Compared with the most recent SOLPS-ITER simulations, our simulations show differences in the exact impurity distribution, but the key results for divertor and wall heat flux remain consistent. In the context of the ITER re-baselining exercise (Pitts, 2024), in which the Be FW armour is proposed to be exchanged for tungsten (W), estimates of W wall sources are key to the assessment of likely core contamination and hence impact on fusion gain. We compare the W gross erosion rates due to the different species excluding W self-sputtering. For the cases simulated spanning 0.27%–0.47% separatrix-averaged Ne concentration and 7.5×1022s−1−1.95×1023s−1 D fuelling, Ne8+ remains the largest contributor to the sputtering flux with the largest source being the outer divertor and baffle. The species-wise contribution to W sputtering changes with fuelling with sputtering due to lower Ne charge states being significant at low D fuelling. In general, the gross W sputtering source is found to decrease with increase in D fuelling and increase with increased Ne seeding.

Numerical study of divertor detachment in TCV H-mode scenarios

The effect of divertor closure and nitrogen seeding on the detachment process has been studied by performing 2D numerical simulations of tokamak à configuration variable (TCV) H-mode divertor scenarios with the SOLEDGE3X-EIRENE edge plasma transport code. The simulations reveal that, in the cases with only deuterium gas fuelling, detachment occurs at a similar level of divertor neutral pressure (0.76 Pa), despite the difference in divertor closure achieved by changing the length of the outer baffle. Nitrogen reduces the target temperature with little effect on the upstream density and momentum loss but drops the upstream pressure, leading to a decrease in the target particle flux and divertor neutral pressure. Furthermore, when the radiation front starts to move up from the outer target, the peak parallel heat flux level at the outer target remains approximately the same ( MW m−2), regardless of whether it is a deuterium fuelling scan, a nitrogen seeding scan at a fixed fuelling rate, or a change in the length of the outer baffle. An empirical partial detachment qualifier calibrated on AUG experimental data was compared with the TCV simulations. The results show good agreement in detachment state prediction, indicating the potential of this detachment qualifier to be applied in devices of different sizes, emphasizing the combined influence of input power entering the divertor, neutral pressure, and the concentration and species of impurity in achieving divertor detachment.

Parameter dependencies of the separatrix density in low triangularity L-mode and H-mode JET-ILW plasmas

The midplane electron separatrix density, n e,sep, in JET-ILW L-mode and H-mode low triangularity deuterium fuelled plasmas exhibits a strong explicit dependence on the averaged outer divertor target electron temperature, n e,sep ∼ T e,ot −1/2. This dependence is reproduced by analytic reversed two point model (rev-2PM), and arises from parallel pressure balance, as well as the ratio of the power and momentum volumetric loss factors, (1 − f cooling)/(1 − f mom-loss). Quantifying the influence of the (1 − f cooling) and (1 − f mom-loss) loss factors on n e,sep has been enabled by measurement estimates of these quantities from L-mode density (fueling) ramps in the outer horizontal, VH(C), and vertical target, VV, divertor configurations. Rev-2PM n e,sep estimates from the extended H-mode and more limited L-mode datasets are recovered to within ±25% of the measurements, with a scaling factor applied to account for use of , an averaged quantity, rather than flux tube resolved target values. Both the (1 − f cooling) and (1 − f mom-loss) trends and recovery of n e,sep using the rev-2PM formatting are reproduced in EDGE2D-EIRENE L-mode-like and H-mode-like density scan simulations. The general lack of a divertor configuration effect in the JET-ILW n e,sep trends can be attributed to a significant influence of main chamber recycling, which has been shown in the EDGE2D-EIRENE results to moderate n e,sep with respect to changes in divertor neutral leakage imposed by changes in the divertor configuration. The unified n e,sep vs trends can, however, be broken if large modifications to the divertor geometry (e.g. complete removal of the outer divertor baffle structure) are introduced in the model. The more pronounced high-field side high density region formation in the VH(C) configuration with reduced clearance to the separatrix does not appear to have a significant influence on the outer midplane separatrix and pedestal parameters when mapped to , although conditions at the inner midplane could not be assessed.

Experimental and computational investigation of solid suspension and gas dispersion in a stirred vessel

Hydrodynamics and residence time distribution (RTD) of fluid elements are key parameters to characterize the performance of stirred vessel. They are governed by geometric and operating parameters of the stirred vessel (SV). In the present work, the performance of the stirred vessel is studied using computational fluid dynamics (CFD) with realizable k−ε turbulence model. The multiple reference frame and sliding mesh approach are used for impeller motion. The solid–liquid flow and associated solid suspension characteristics are predicted using the two-fluid model (Euler–Granular). The performance of the stirred vessel is characterized by analyzing predicted velocity magnitude, solid concentration (suspension quality), and solid sedimentation. This is compared with the stirred vessel with draft tube baffle configuration (three inner baffles and six outer baffles). The recirculatory flow in draft tube SV helps to achieve uniform suspension and less sedimentation. Further, CFD simulations are carried out in Lagrangian way to analyze chaotic mixing among fluid elements. This is qualitatively analyzed using Poincaré map and quantitatively evaluated using Shannon entropy. The extent of chaotic mixing in draft tube SV is found to be high. The performance of the stirred vessel is further investigated through stimulus–response tracer techniques (RTD) to detect design flaws such as bypass and dead zones. This is analyzed for a wide range of operating parameters and identified optimum conditions (flow rate, impeller speed) for the operation of SV. The four different outlet pipe locations are chosen in SV. The bypass and dead volume are analyzed accordingly, and an optimum outlet pipe location is found. To reduce the extent of non-ideal parameters, three different gas source locations are considered and gases are dispersed in the form of bubbles. The gas dispersion at optimum gas injection point is found to reduce non-ideal parameters and improve the design of stirred vessel.

Numerical modelling of the impact of leakage under divertor baffle in WEST

In WEST experimental campaign C5, the divertor pumping capability has been improved by sealing the space between the divertor outer baffle and the vacuum vessel. It is expected that the degree of baffle leakage influences the transport of neutral particles inside the main chamber, which affects the detachment onset. Knowing the exact impacts of leakage and understanding the physical processes behind it are helpful for the study and control of plasma detachment. We investigate the impact of leakage by performing transport simulations through SOLEDGE-EIRENE code considering several cases with different leakage levels. Starting from the basic simulation case, non-constant radial transport coefficients obtained by the feedback control method are applied to achieve a better match with the experimental one (#54903) in L-mode. Based on the basic case, the evolution of plasma regimes from sheath limited regime to detached one in different wall geometries has been studied by ramping the upstream density. The numerical results show that the cases with closed or reduced leakage under the baffle have better performance in trapping the neutral particles and higher neutral pressure near the baffle. The neutral compression ratio is increased by a factor up to 4, leading to more significant momentum and power dissipation in the divertor, thus lowering the detachment threshold in n e,sep by up to 16%. At the same time, a much higher gas puff rate by a factor up to 22 is needed to maintain an equivalent n e,sep level in the case without or reduced leakage. For all the cases here, there exist characteristic parameters on which the baffle closure has no obvious influence on their value when plasma starts to detach. The evolution of radiator height as a function of target temperature shows no sensitivity to the leakage, which gives some insight into the stable detachment control strategy in the future. Finally, simulation results are compared with available neutral pressure measurements from WEST campaigns to verify the predictions from the simulation. • The impact of wall geometry (characterized by different sizes of leakage under the divertor baffle) on detachment properties in WEST is investigated using SOLEDGE-EIRENE transport code. • Radial non-constant transport coefficients obtained by the feedback control method are applied in the simulation, allowing a better match with experimental results in L-mode. • The case with less leakage has better performance in trapping the neutral particles and has higher neutral pressure near the target, leading to greater power dissipation in the divertor, thus decreasing the detachment threshold in upstream separatrix density. • The evolution of the radiation front and the sensitivity of the detachment process to multiple parameters under the influence of leakage have been investigated. • Simulation results are compared with available neutral pressure measurements from WEST campaigns to verify the predictions from the simulation with respect to the impact of leakage.

Design of a Novel Variable Geometry Divertor for Tokamaks

The divertor is a key component of fusion reactors, allowing exhaust of gas, impurities, and helium ash to preserve plasma purity. The divertor geometry strongly affects plasma performance, and it is designed to be compatible with different plasma shapes in present-day fusion experiments. We present a novel concept for a variable geometry divertor, in which the divertor baffle tiles are reorientable by external actuation. Implementation of this concept in a medium-sized research tokamak would uniquely provide the flexibility to tailor divertor geometry to the plasma configuration and also enable study of the effect of divertor closure on plasma performance. To ensure compatibility with typical tokamak operations, the adjustable divertor must withstand the effects of significant mechanical and thermal stresses such as MW/m2-scale heat fluxes and large electromagnetic fields, e.g., disruption forces. The technological solutions for actuation mechanisms, cooling system, gas baffling and plasma-facing components are assessed. A functional reduced-scale model with movable outer divertor target baffle tiles is developed and the actuation mechanism is tested.

Manufacturing of lower divertor cassette of JT-60SA

First divertor cassette covering a 10° sector in the toroidal direction has been manufactured for JT-60SA. Modularized plasma facing components such as inner and outer targets, baffles, and domes are assembled into the divertor cassette. All plasma facing components are actively cooled. Carbon armor tiles bolted to water-cooled copper alloy heat sinks are used to remove heat loads of 0.3–1MW/m2 for 100 s and 10 MW/m2 for less than 5 s. The divertor cassette has two pipe joints between it and the inlet and outlet pipes on the vacuum vessel side. After removing the divertor cassette, the inner target can be replaced by cutting and welding the other two pipe joints with the divertor cassette. A remote pipe welding tool has been developed both to install the divertor cassette into the vacuum vessel and to connect the inner target with the divertor cassette. The space around the cooling pipes is so limited that they are cut and welded remotely from the inside for replacement. The laser welding method was used, and the focusing mirror inside the pipe was rotated to perform circumferential welding. As a countermeasure for welding groove misalignment, the aiming accuracy of the laser was improved by simultaneously controlling the rotation and lifting of the tool. Thereby, reliable welding is achieved even with large gaps of up to 0.5 mm and grooves with a maximum angular deviation of 0.5 ° between connecting pipes. The outer diameter of the cooling pipe is 59.8 mm, the wall thickness is 2.8 mm, and the material is SUS316L. After connecting the inner target, the other plasma facing components have been assembled into the first lower divertor cassette. When installing the divertor cassette towards the vacuum vessel, the laser welding tool described above is used to connect the cooling pipes between divertor cassette and vacuum vessel in JT-60SA, because the outer diameter and wall thickness of the cooling pipe are the same as the inner target.

Design optimization of a shell and tube heat exchanger with staggered baffles using neural network and genetic algorithm

A shell and tube heat exchanger with staggered baffles (STHX-ST) is designed by integrating the features of both segmental and helical baffles, which produces a helical flow in the shell side. This work studies the effect of different parameters on the performance of the STHX-ST through numerical analysis. Shell inner diameter, tube outer diameter, baffle cut, baffle spacing, and baffle orientation angle are the design parameters. Multi-objective optimization using genetic algorithm (GA) is carried out to maximize the heat transfer rate while minimizing the pressure drop. The objective functions for optimization are approximated using artificial neural networks (ANNs). The training data for ANNs are simulated from CFD analysis as per the Taguchi orthogonal test table. The optimal solution obtained from the Pareto front has a maximum heat transfer of 154555 W for a minimum pressure drop of 88083.86 Pa.

Numerical investigation of optimal divertor gas baffle closure on TCV

A first set of divertor gas baffles has recently been installed in the TCV tokamak. In order to explore the physics determining the benefits and limitations of divertor baffling and to guide the design of a possible second generation of baffles, the effect of baffle closure is investigated using the 2D transport code SolEdge2D-EIRENE with realistic wall geometries. The baffle extension is scanned, first imposing the same upstream conditions as in previous SOLPS-ITER studies, then extending the parameter space to access detached plasma conditions. In attached plasma cases, divertor neutral compression is maximised by a Low-Field Side baffle length with an opening between the separatrix and the baffle tip of approximately 5 λ q , resulting in an increase in neutral compression by a factor 4 with respect to the unbaffled case. In detached cases this ratio can be improved by up to a factor 25 using higher baffle closures. This difference in behaviour between attached and detached conditions is explained by a model based on the ionisation mean free path of neutral particles recycled from the target. In some conditions, the optimal baffle extension in terms of neutral compression is found to be subject to high levels of intercepted upstream heat flux, which results in a peak heat flux on the baffles comparable to the one impinging on the outer target. The individual roles of the High-Field Side and Low-Field Side baffles are disentangled by means of dedicated simulations, which show a lower global impact of the inner baffle. This study suggests that an outer baffle with a gap of approximately 3 λ q , slightly more closed than the one presently installed, could further enhance the neutral compression ratio in cases where the ionisation front is detached. The biggest unknown in these simulations is related to far SOL particle transport, which could result in higher levels of baffle recycling and thus limit baffle performance.

Design of a built-in baffle for a Ritchey–Chretien optical system

A baffle effectively prevents direct rays of stray light from entering an optical system. Existing design methods can result in very long outer baffle lengths, increasing the weight and volume of the optical system, or large secondary mirror baffle sizes, increasing the central obscuration and resulting in the reduction of the illumination beam on the image. To overcome these challenges, a design method for a built-in baffle is presented. The designed built-in baffle for a typical Ritchey-Chretien optical system is compared with a conventionally designed baffle. The results show that when the length of outer baffle is shortened from 3456 to 2349.9mm, the modulation transfer function (MTF) increases from 0.361 to 0.421 in case 1, and when the length is shortened from 3456 to 1924.2mm, the MTF increases from 0.361 to 0.408 in case 2. Meanwhile, the stray light suppression capability is close to that of the traditional method.

The DEMO wall load challenge

For several reasons the challenge to keep the loads to the first wall within engineering limits is substantially higher in DEMO compared to ITER. Therefore the pre-conceptual design development for DEMO that is currently ongoing in Europe needs to be based on load estimates that are derived employing the most recent plasma edge physics knowledge.An initial assessment of the static wall heat load limit in DEMO infers that the steady state peak heat flux limit on the majority of the DEMO first wall should not be assumed to be higher than 1.0 MW m−2. This compares to an average wall heat load of 0.29 MW m−2 for the design assuming a perfect homogeneous distribution. The main part of this publication concentrates on the development of first DEMO estimates for charged particle, radiation, fast particle (all static) and disruption heat loads. Employing an initial engineering wall design with clear optimization potential in combination with parameters for the flat-top phase (x-point configuration), loads up to 7 MW m−2 (penalty factor for tolerances etc not applied) have been calculated. Assuming a fraction of power radiated from the x-point region between 1/5 and 1/3, peaks of the total power flux density due to radiation of 0.6–0.8 MW m−2 are found in the outer baffle region.This first review of wall loads, and the associated limits in DEMO clearly underlines a significant challenge that necessitates substantial engineering efforts as well as a considerable consolidation of the associated physics basis.

Experimental analysis and WallDYN simulations of the global nitrogen migration in ASDEX Upgrade L-mode discharges

This work presents ASDEX Upgrade experiments, where the nitrogen deposition and re-erosion on divertor manipulator samples and the effect of its transport through the plasma were studied. These results are compared to WallDYN-DIVIMP simulations based on SOLPS plasma backgrounds and employing an improved WallDYN model, which includes the effusion of nitrogen from saturated surfaces. On one hand, this allows the WallDYN code and the new saturation model with a comprehensive data set to be benchmarked, on the other hand the simulations help in the interpretation of the experimental results. Both, experimental results and simulations, show that the N content in the region of the outer strike line reaches its steady-state value within one discharge. The simulations also reproduce the experimentally observed nitrogen content in samples exposed to N2-seeded discharges. With respect to the boron deposition, the nitrogen deposition in a non-seeded discharge and the re-erosion of nitrogen discrepancies to the WallDYN-DIVIMP simulations are observed. Based on SDTrimSP simulations, these are attributed to the missing depth resolution of the WallDYN surface model. A detailed comparison of spectroscopic measurements to WallDYN simulations, based on a novel synthetic spectroscopy diagnostic for WallDYN, shows that the nitrogen fluxes in the plasma are well described by the simulations. From a comparison of several WallDYN-DIVIMP simulations employing customized onion-skin model plasma backgrounds the physical processes controlling the nitrogen concentration in the core plasma and the applicability of onion-skin model plasma backgrounds are discussed. From these simulations the private flux zone with the gas valve, the outer baffle and the high field side main wall are identified as the main sources for the nitrogen content of the core plasma.

Seeing the world through a dynamic biomimetic sonar

The outer baffle surfaces surrounding the sonar pulse emission and reception apertures of the biosonar system of horseshoe bats (family Rhinolophidae) have been shown to dynamically deform while actively sensing the environment. It is hypothesized that this dynamic sensing strategy enables the animal, in part, to cope with dense unstructured sonar environments. In the present work, a biomimetic dynamic sonar system inspired by the biosonar system of horseshoe bats has been assembled and tested. The sonar head features dynamic deforming baffles for emission (mimicking the bats’ noseleaf) and reception (pinnae). The dynamic baffles were actuated to change their geometries concurrently with the diffraction of the emitted ultrasonic pulses and returning echoes. The time-variant signatures induced by the dynamic baffle motions were systematically characterized in a controlled anechoic setting and the interaction between emission and reception dynamic signatures was investigated. The sonar was further tested in the context of natural environments with a specific focus on the interaction of dynamic ultrasonic pulse packets with natural targets. For both experimental approaches, a sonar with static baffle shape configuration was used as a reference to establish the impact of dynamic features.

离轴反射式空间天文望远系统设计及其杂散光抑制研究

In order to aim at a telescope system with large F number, long focal length, miniaturized dimension, high image quality and high stray light suppression, a three mirror off-axis anastigmatic telescope is designed based on the Cook type, of which f' is 24 m, F number is 16, field of view is 1.61. The outer baffle and the structures inside are designed. The stray light of telescope system is analyzed with stray light program to calculate the point sources transmittance (PST). The forward and backward ray tracing is combined to find the key surface and modify the optical and mechanical structure with optimization and iteration. The result shows that the modulation transfer functions (MTF) approaches the diffraction limit at all fields. When the evadable angle out of the field is 40, the PST is less than 10-11 and the system can achieve the requirement of stray light suppression.

Design of CASSEGRAIN telescope baffles with honeycomb entrance

The stray radiation suppression in Cassegrain family optical system is presented. The design method for ultra-short outer baffle with honeycomb structure is proposed. Meanwhile the constraint formulas for designing the geometries of primary baffle and secondary baffle are deduced when basing the characteristic and taking vignette into account. According to the ray trace simulated data, the point source transmittance values of the baffle are less than 10-10 when incident angles are larger than the rejection angle. The honeycomb-look front baffle guarantees a comparable performance of stray light suppression with traditional tube baffle, while reducing the size greatly.

Impact of arcing on carbon and tungsten: from the observations in JT-60U, LHD and NAGDIS-II

Arcing is a long-standing plasma–surface interaction issue, and the issue is currently being revived. This paper assesses the impact of arcing in fusion devices based on the observations in JT-60U, the Large Helical Device (LHD) and the linear divertor simulator NAGDIS-II. To investigate the first initiation process of arcing, field emission currents from several tungsten samples are measured. It is shown that the field emission current increases significantly after tungsten is exposed to helium plasmas. A postmortem analysis of JT-60U tiles reveals that arcing phenomena occurred on carbon baffle plates inside the vacuum vessel in JT-60U. From the observation of the arc trails recorded on the baffle plate, the amount of eroded materials is discussed. The arcing seems to occur frequently on the inner baffles rather than the outer baffles. From LHD, it is shown that the arcing can be initiated on nanostructured tungsten even without transient events. The erosion of tungsten by arcing will become an important issue in a fusion reactor, where helium fluence is significantly increased. From the experiments in NAGDIS-II, it is shown that arcing can be initiated even without transient heat load when the target voltage is low enough, e.g. −500 V. Frequent initiation of arcing annihilates the nanostructure growth due to helium plasma irradiation on the surface.

静止轨道对地观测光学系统外遮光罩设计

The affects of direct sunlights before and after midnights on the imaging quality and thermal stability of an earth observation optical system on geostationary satellite in space were investigated.According to the characteristics of solar heat flux on the geostationary orbit,the energy density of direct sunlight projecting to the optical system was analyzed and a dimensionless parameter named sunlight inhibitory ratio determined by outer baffle′s height,shape dimension and sun inclination was deduced.It was used to describe the inhibitory ability of outer baffle in the optical system for the direct sunlight and also used as a design principle for the height of outer baffle.The program based on Monte-Carlo method was compiled to solve the sunlight inhibitory ratio of different shape outer baffles in different sun inclination scenarios.In a real design,the sunlight inhibitory ratio was selected to be 0.5 at equinox and the final outer baffle height is about 1.8 times of the east-west axis length of the outer baffle's bottom side.This way,the incidence sunlight in the optical system from the baffle is three hours.The result satisfies the dimension requirements of satellite payloads.

基于散射模型设计外遮光罩

基于散射模型设计外遮光罩

A new design approach for shell-and-tube heat exchangers using imperialist competitive algorithm (ICA) from economic point of view

Cost minimization of shell-and-tube heat exchangers is a key objective. Traditional design approaches besides being time consuming, do not guarantee the reach of an economically optimal solution. So, in this research, a new shell and tube heat exchanger optimization design approach is developed based on imperialist competitive algorithm (ICA). The ICA algorithm has some good features in reaching to the global minimum in comparison to other evolutionary algorithms. In present study, ICA technique has been applied to minimize the total cost of the equipment including capital investment and the sum of discounted annual energy expenditures related to pumping of shell and tube heat exchanger by varying various design variables such as tube length, tube outer diameter, pitch size and baffle spacing. Based on proposed method, a full computer code was developed for optimal design of shell and tube heat exchangers and different test cases are solved by it to demonstrate the effectiveness and accuracy of the proposed algorithm. Finally the results are compared to those obtained by literature approaches. The obtained results indicate that the ICA algorithm can be successfully applied for optimal design of shell and tube heat exchangers with higher accuracy in less computational time.

Design of lower divertor for JT-60SA

Construction has just begun in the JT-60 Super Advanced (JT-60SA) tokamak project, which is part of the Japanese domestic program and the Japan – EU international program “ITER Broader Approach”. All plasma facing components (PFCs) will be actively cooled because they are exposed to high heat flux for long duration. A lower single-null closed divertor with a vertical target (VT) will be installed when experiments begin. A divertor cassette integrated with coolant pipe connections will be used for remote handling maintenance. Each cassette covers a 10° sector in the toroidal direction. Modularized PFCs such as VTs, baffles, and domes will be assembled on divertor cassettes. Static structural analysis shows that the displacement and stress in the divertor module are generally small for determining the dead weight, coolant pressure, and electromagnetic forces (EMFs). However, the support structure of the outer baffle requires improvement because eddy currents generate concentrated overturning EMFs.