Heat Load Problem Research Articles

Calculation and prediction of divertor detachment via impurity seeding by using one-dimensional model

Abstract Achieving the divertor detachment helps to alleviate excessive heat load and sputtering problems on the target plates, thereby prolonging the lifetime of divertor components for fusion devices. In order to provide a rapid but relatively reliable prediction of plasma parameters along the flux tube for future devices design, a one-dimensional (1D) modeling code for the impurity seeded detached divertor operational point has been developed based on the Python language, which is a fluid model based on the previous work.[1] The experimental observation of the onset of divertor detachment by neon (Ne) and argon (Ar) seeding in EAST is well reproduced by using the 1D modeling code. The comparison of the 1D modeling and 2D simulation by SOLPS-ITER code for CFETR detachment operation with Ne and Ar seeding also shows good consistency. The predictions of the radiative power loss and requirement of the corresponding impurity concentration for achieving divertor detachment via different impurity seeding for the high heating power scenarios on EAST and CFETR Phase II by the 1D model are also presented. Based on the predictions, the optimized parameter space for divertor detachment operation on EAST and CFETR has also been determined. Such a simple but reliable 1D model can provide a reasonable parameter inputs for a detailed and accurate analysis by 2D or 3D modeling tools through rapid parameter scanning.

Performance of the merged APPLE-Knot undulator for soft x-ray beamline in medium energy ring

APPLE-Knot undulator can effectively solve the on-axis heat load problem and is proven to perform well in VUV beamline and soft x-ray beamline in high energy storage ring. However, for soft x-ray beamline in a medium energy ring, whether the APPLE-Knot undulator excels the APPLE undulator is still a question. Here, a merged APPLE-Knot undulator is studied to generate soft x-ray in a medium energy ring. Its advantages and problems are discussed. Though the on-axis heat load of the APPLE-Knot undulator is lower in linear polarization modes compared to the APPLE undulator, its flux is lower. The APPLE-Knot undulator shows no advantage when only fundamental harmonic is needed. However, in circular polarization mode, the APPLE-Knot undulator shows the ability to cover a broader energy range which can remedy the notable shortcoming of the APPLE undulator.

Semi-analytic approximation of the temperature field resulting from moving heat loads

Moving heat load problems appear in many manufacturing processes, such as lithography, welding, grinding, and additive manufacturing. The simulation of moving heat load problems by the finite-element method poses several numerical challenges, which may lead to time consuming computations. In this paper, we propose a 2D semi-analytic model in which the problem in two spatial dimensions is decoupled into three problems in one spatial dimension. This decoupling significantly reduces the computational time, but also introduces an additional error. The method is applied to a wafer heating example, in which the computational time is reduced by a factor 10 at the cost of a 4% error in the temperature field.

First EMC3-Eirene simulations of the TCV snowflake divertor

One of the approaches to solve the heat load problem in a divertor tokamak is the so called ‘snowflake’ (SF) configuration, a magnetic equilibrium with two nearby x-points and two additional divertor legs. Here we report on the first EMC3-Eirene simulations of plasma- and neutral particle transport in the scrape-off layer of a series of TCV SF equilibria with different values of σ, the distance between the x-points normalized to the minor radius of the plasma. The constant cross-field transport coefficients were chosen such that the power- and particle deposition profiles at the primary inner strike point (SP) match the Langmuir probe measurements for the σ = 0.1 case. At the secondary SP on the floor, however, a significantly larger power flux than that predicted by the simulation was measured by the probes, indicating an enhanced transport across the primary separatrix. As the ideal SF configuration (σ = 0) is approached, the density as well as the radiation maximum are predicted to move from the target plates upward to the x-point by the simulation.

Super-X Divertor Simulation for HCSB-DEMO Conception Design

HCSB-DEMO concept design is carried out at SWIP. In order to handle power from a core plasma region, a super-X divertor is preliminarily designed and investigated for HCSB-DEMO. It increases the target surface area by expanding the magnetic flux surface with another X-point generated near the targets and increases the parallel connection length by moving the outer divertor target to larger R and Z. The heat load at the targets is investigated by B2.5-Eirene. With heating power flowing into SOL/divertor regions being P = 600 MW, when the density at the separatrix is ne = 3.5 × 1019 m−3, the peak heat load at the inner and outer divertor is 9.2 MW/m2 and 3.7 MW/m2, respectively, which is much less than those of the standard divertor without impurity seeding, and also below the design targets (10 MW/m2). Thus the super-X divertor may work well for HCSB-DEMO to solve the high heat load problem at the divertor target without impurity seeding from this preliminary concept design and simulation.

Spallation Ultracold Neutron Source of Superfluid Helium below 1 K

For the production of high-density ultracold neutrons (UCNs), we placed 0.8 K superfluid helium in a cold neutron moderator. We resolved previous heat-load problems in the spallation neutron source that were particularly serious below 1 K. With a proton-beam power of 400 MeV×1 μA, a UCN production rate of 4 UCN cm(-3) s(-1) at the maximum UCN energy of E(c)=210 neV and a storage lifetime of 81 s were obtained. A cryogenic test showed that the production rate can be increased by a factor of 10 with the same storage lifetime by increasing the proton-beam power as well as (3)He pumping speed.

Self-filtering extremely inclined X-ray crystal monochromator

It is shown that an extremely inclined X-ray double-crystal monochromator can diffract a beam with the required wavelength and at the same time may reflect a great deal of unwanted radiation in a broad range of Bragg angles. This is a generalization of the idea of Cowan & Brennan [Rev. Sci. Instrum.(1989),60, 1987–1990], which partially solves the radiation heat load problem. The properties of such a device are discussed. It is shown that in some cases the diffracted beam may be significantly broadened as a result of refraction effects. In these cases a four-crystal arrangement or an additional mirror is necessary.

Behavioural evidence for heat-load problems in Great Knots in tropical Australia fuelling for long-distance flight

Migratory shorebirds that live in the tropics prior to embarking on long (>5000 km) flights may face heat-load problems. The behaviour of a large sandpiper, the Great Knot (Calidris tenuirostris), was studied in Roebuck Bay, north-west Australia, from February to April 2000. We determined the incidence of heat-reduction behaviour in foraging and roosting birds in relation to breeding-plumage score (an index of migratory preparation) and microclimate variables. Heat-reduction behaviour (primarily raising the back feathers) was significantly related to breeding-plumage score and solar radiation. Raising back feathers may reduce the external heat load for a bird, or increase convective or cutaneous evaporative cooling. The results suggest that managing heat loads in tropical-wintering waders may become more difficult close to departure on migration.

Energetic Bottlenecks and Other Design Constraints in Avian Annual Cycles

The flexible phenotypes of birds and mammals often appear to represent adjustments to alleviate some energetic bottleneck or another. By increasing the size of the organs involved in digestion and assimilation of nutrients (gut and liver), an individual bird can increase its ability to process nutrients, for example to quickly store fuel for onward flight. Similarly, an increase in the exercise organs (pectoral muscles and heart) enables a bird to increase its metabolic power for sustained flight or for thermoregulation. Reflecting the stationary cost of organ maintenance, changes in the size of any part of the "metabolic machinery" will be reflected in Basal Metabolic Rate (BMR) unless changes in metabolic intensity also occur. Energetic bottlenecks appear to be set by the marginal value of organ size increases relative to particular peak requirements (including safety factors). These points are elaborated using the studies on long-distance migrating shorebirds, especially red knots Calidris canutus. Red knots encounter energy expenditure levels similar to experimentally determined ceiling levels of ca. 5 times BMR in other birds and mammals, both during the breeding season on High Arctic tundra (probably mainly a function of costs of thermoregulation) and during winter in temperate coastal wetlands (a function of the high costs of processing mollusks, prey poor in nutrients but rich in shell material and salt water). During migration, red knots phenotypically alternate between a "fueling [life-cycle] stage" and a "flight stage." Fueling red knots in tropical areas may encounter heat load problems whilst still on the ground, but high flight altitudes during migratory flights seem to take care of overheating and unacceptably high rates of evaporative water loss. The allocation principles for the flexible phenotypes of red knots and other birds, the costs of their organ flexibility and the ways in which they "organize" all the fast phenotypic changes, are yet to be discovered.

Heat load problems in deep X-ray lithography

A 3D mathematical model of a complete Deep X-Ray Lithography scanning unit based on the Finite Element Method (FEM) was developed to analyse the replication errors induced by the thermoelastic deformations occurring under irradiation. Different thermal and mechanical constraint conditions were considered in order to evaluate the maximum displacements of the irradiated mask area. The obtained results show that, to evaluate the replication errors, the support ring and its mechanical fittings have to be carefully considered in the model. It is observed that the absolute position error and the blur error and the error induced by the thermal expansion of the mask are both position dependent.

Extent and economic effect of heat loads on dairy cattle production in Australia.

To investigate the extent of heat load problems, caused by the combination of excessive temperature and humidity, in Holstein-Friesian cows in Australia. Also, to outline how milk production losses and consequent costs from this can be estimated and minimised. Long-term meteorological data for Australia were analysed to determine the distribution of hot conditions over space and time. Fifteen dairy production regions were identified for higher-resolution data analysis. Both the raw meteorological data and their integration into a temperature-humidity thermal index were compiled onto a computer program. This mapping software displays the distribution of climatic patterns, both Australia-wide and within the selected dairying regions. Graphical displays of the variation in historical records for 200 locations in the 15 dairying regions are also available. As a separate study, production data from research stations, on-farm trials and milk factory records were statistically analysed and correlated with the climatic indices, to estimate production losses due to hot conditions. Both milk yields and milk constituents declined with increases in the temperature-humidity index. The onset and rate of this decline are dependent on a number of factors, including location, level of production, adaptation, and management regime. These results have been integrated into a farm-level economic analysis for managers of dairy properties. By considering the historical patterns of hot conditions over time and space, along with expected production losses, managers of dairy farms can now conduct an economic evaluation of investment strategies to alleviate heat loads. These strategies include the provision of sprinklers, shade structures, or combinations of these.

An insertion device for the soft X-ray photochemistry beamline at SPring-8.

A figure-8 undulator is an insertion device (ID) proposed at SPring-8 to reduce the heat-load problems encountered with ordinary linear undulators. This device is useful when the K value is high in order to obtain low-energy photons as the fundamental of the undulator radiation. It has therefore been adopted as the ID for the soft X-ray photochemistry beamline (BL27SU) at SPring-8 because linearly polarized photons between 100 and 2000 eV are necessary for the experiments on this beamline. The figure-8 undulator for BL27SU is now under construction and, in the first phase of operation, is expected to cover the energy range down to 500 eV. In the second and third phases, the lowest energy may be reduced to 170 and 100 eV, respectively.

Metallic and nonmetallic X-ray monochromators for synchrotron sources

Individual monochromators using different materials have been developed to achieve maximum exploitation of the beam qualities of modern synchrotron facilities. Low absorbing materials have superior properties of reflectivity. These materials can also solve the enormous heat load problem of the high power X-ray beams of third generation storage rings. Use of mosaic crystals and tailored defect structures offer novel possibilities of reflectivity as well as energy resolution control.

Performance of x-ray optics at the European Synchrotron Radiation Facility

This paper gives an overview of the challenges, the strategies, and the solutions in x-ray optics research and development at the European Synchrotron Radiation Facility (ESRF), followed by an account of the practical experience gathered on the beamlines. The performances of state-of-the-art mirrors, single-crystal monochromators, and multilayer structures are given. Amongst the topics are: adaptive optics and cryogenic cooling to cope with the heat load problem, Bragg-Fresnel optics for microfocusing, x-ray phase plates for polarization production and analysis, and the use of diamond crystals. It is shown that today’s optical elements at the ESRF are capable of preserving the high quality of the present x-ray beams to a large extent.

Optics for high energy x-ray scattering applications (invited)

High energy photons in the range from 80 to 500 keV are a relatively new tool, which is provided with sufficient fluxes only by the latest generation of synchrotron sources. Due to the high energies and, respectively, very short wavelengths, new arrangements for monochromators or mirrors have to be investigated in addition to standard monochromator concepts. An overview of possible monochromator setups is given and the need for experiments to be performed at these energies is evaluated. Low absorption enables the use of rather thick absorbers in order to reduce the heat load problem, which is due to the high power synchrotron beam. Even monochromator crystals become semitransparent, thus giving the possibility of operating more than one experimental station using the same synchrotron beam. Focusing techniques may be applied, and monochromators with an increased bandwidth are of interest for providing sufficient monochromatic flux. The optical concept of the High Energy beamline ID15 at the ESRF is presented, where two different insertion devices can be used alternatingly. Monochromatic beam in the range from 30 to 80 keV is provided by the use of bent cooled Si monochromators and the results of the performance tests are shown.

An impurity seeded radiative mantle for ITER

Self-consistent, coupled transport/MHD/scrape-off layer (SOL) divertor calculations indicate that a stable, radiating mantle can be maintained just inside the separatrix by iron impurity injection into the SOL in an ITER EDA model. The power flux to the divertor plate is reduced thereby by an order of magnitude or more. This reduction of the power exhausted to the divertor is predicted to be achieved without significant deleterious effect on the core power balance, without producing significant changes in the current profile that might trigger a disruptive collapse of the current channel and without inducing an H to L mode transition. These results suggest that an impurity seeded radiative mantle should be considered as part of the solution to the divertor heat load problem in ITER and other future tokamaks

Heat load problem of an entrance slit on an undulator beamline

The heat load on the entrance slit of a spherical grating monochromator on a high-flux undulator beamline at BESSY has been studied. The effect of the concentrated power profile was analyzed for two different slit geometries by using a finite element method. In the worst case of a mis-steered beam a slit blade would have to withstand 50 W and a maximum power density of 780 W/mm2. The temperature in the focal spot rises by about 90 and 110 K above the water temperature in the cooling at the back side. As a result of this, the slit blade itself expands depending on the slit model, by 15.3–16.5 μm. Even though most of the expansion could be compensated for, a bump remains in the center of the slit blade.

Characteristics of a SiC microwave absorber for a damped cavity

Development of a SiC microwave absorber for a damped cavity is presented. The SiC studied has a resistivity of 101–102 Ω cm, which is the expected value to damp higher-order modes (HOMs) in the cavity and also has high thermal conductivity. The absorber is attached to the cavity as a part of the beam duct. Since the SiC duct receives a large amount of energy from the electron (or positron) stored beam, it is very important to estimate the dissipation power in the SiC duct and to design a cooling mechanism. The heat load problem of the SiC duct is discussed and the results of high power testing of the SiC duct are presented. The damping mechanism for HOMs is based on the power dissipation due to the resistivity of SiC. The fine control of the resistivity of SiC in fabrication is very important. The preliminary results on this problem are also presented.

Diamond single crystals: the ultimate monochromator material for high-power x-ray beams

A review of the performance of diamond single crystals as a high heat load optical component for synchrotron x rays is given. It has been proven experimentally that the bandpass and the angular divergence of the monochromatic beam provided by a relatively thin diamond crystal used in an undulator beam are not degraded by thermal effects for a total power up to 280 W (8.7 W absorbed) at a heat flux up to 3.5 kW/mm² (109 W/mm² absorbed). These high heat load tests and model calculations have shown that edge-cooled diamond crystals at room temperature provide an easy and widely satisfactory solution to the heat load problems generated by undulator beams that are currently foreseen at the third-generation storage rings of the European Synchrotron Radiation Facility, the Advanced Photon Source, and the SPring-8 facilities. For this cooling geometry, diamond single crystals offer the additional advantage that beam multiplexing can be used. Currently available synthetic diamond crystals are sufficiently big for undulator beams and their crystalline perfection is adequate. Most of the crystals actually in use were prepared with their big surfaces (about 30 mm² in size) oriented parallel to the (100) netplanes, but more recently bigger samples whose surfaces are parallel to the (111) lattice planes were obtained. Thus, diamond single crystals are superior to all other monochromator materials for undulators and for cases where a loss of a factor of 2 in flux combined with a similar gain in resolution (as compared to silicon) are compatible with the experiments.

Multiple station beamline at an undulator X-ray source

The undulator X-ray source is an ideal source for many applications: the beam is brilliant, highly collimated in all directions, quasi-monochromatic, pulsed and linearly polarized. Such a precious source can feed several independently operated instruments by utilizing a downstream series of X-ray transparent monochromator crystals. Diamond in particular is an attractive monochromator as it is rather X-ray transparent and can be fabricated to a high degree of crystal perfection. Moreover, it has a very high heat conductivity and a rather small thermal expansion so the beam X-ray heat load problem is easily overcome. We describe a possible setup with three successive monochromators. We present data and analysis for focusing the beam in both the horizontal and vertical direction and discuss the focusing properties in both the Laue and Bragg geometry.