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PROGENITOR-EXPLOSION CONNECTION AND REMNANT BIRTH MASSES FOR NEUTRINO-DRIVEN SUPERNOVAE OF IRON-CORE PROGENITORS
We perform hydrodynamic supernova (SN) simulations in spherical symmetry for over 100 single stars of solar metallicity to explore the progenitor-explosion and progenitor-remnant connections established by the neutrino-driven mechanism. We use an approximative treatment of neutrino transport and replace the high-density interior of the neutron star (NS) by an inner boundary condition based on an analytic proto-NS core-cooling model, whose free parameters are chosen such that explosion energy, nickel production, and energy release by the compact remnant of progenitors around 20 M{sub Sun} are compatible with SN 1987A. Thus, we are able to simulate the accretion phase, initiation of the explosion, subsequent neutrino-driven wind phase for 15-20 s, and the further evolution of the blast wave for hours to days until fallback is completed. Our results challenge long-standing paradigms. We find that remnant mass, launch time, and properties of the explosion depend strongly on the stellar structure and exhibit large variability even in narrow intervals of the progenitors' zero-age main-sequence mass. While all progenitors with masses below {approx}15 M{sub Sun} yield NSs, black hole (BH) as well as NS formation is possible for more massive stars, where partial loss of the hydrogen envelope leads to weak reverse shocks and weak fallback. Our NS baryonic masses of {approx}1.2-2.0 M{sub Sun} and BH masses >6 M{sub Sun} are compatible with a possible lack of low-mass BHs in the empirical distribution. Neutrino heating accounts for SN energies between some 10{sup 50} erg and {approx}2 Multiplication-Sign 10{sup 51} erg but can hardly explain more energetic explosions and nickel masses higher than 0.1-0.2 M{sub Sun }. These seem to require an alternative SN mechanism.
Coupled Decay Heat and Thermal Hydraulic Capability for Loss-of-Coolant Accident Simulations
As the nuclear energy industry considers ways to achieve improved economics in the current fleet of light-water reactors (LWRs), one possible approach is to operate each cycle for longer durations. This causes a greater portion of the fuel to be burned and reduces the frequency of outages, which ultimately reduces the cost to operate the reactor. However, this also leads to higher burnup fuels than has traditionally been allowed in these reactors. Thus, there are concerns about integrity of high-burnup (HBu) fuel, especially during accident conditions such as loss-of-coolant accidents (LOCAs), as shown by Capps et al.. To investigate these concerns, advanced modeling and simulation capabilities are being leveraged to determine the susceptibility of HBu fuel to fuel fragmentation, relocation, and dispersion (FFRD). Improvements have previously been made to fuel performance capabilities to more accurately model these phenomena; multiphysics simulations have also been conducted to determine the power and burnup histories of the HBu fuel, which are needed as inputs for the fuel performance calculations. Most recently, new statistical approaches have been developed to identify a subset of fuel rods that have greater FFRD susceptibility, reducing the total number of fuel performance simulations required. Prior LOCA simulations have relied on the TRACE systems code, which can model the core and primary loop during accident conditions. TRACE includes many models for various aspects of the primary loop, but two sets of models are important for this report. First, TRACE uses a lumped-fuel approach for modeling the core. This approximates the ~50,000 fuel rods in the core with a much smaller number of rods. The rods can be lumped in various ways as determined by the user. For example, one lumped rod may be used to represent all rods in an assembly, sometimes with an additional rod representing the hottest fuel rod. However, due to runtime constraints and complexity of modeling, a more common approach is to group several assemblies or larger regions of the core into single lumped rods. These lumping schemes apply not only to fuel rods but to flow channels as well. Second, TRACE has several different models for treating decay heat, ranging from pregenerated decay heat curves based on an ANSI/ANS-5.1 standard (hereinafter abbreviated simply as ANSI) to explicit time-dependent heat inputs from the user. None of these models account for differences in isotopics between different rods, which is an approximation the work in this report seeks to eliminate. This report focuses on the implementation of coupled decay heat capabilities in the Virtual Environment for Reactor Applications (VERA) code suite to address a gap identified in previous LOCA simulations. This constitutes an improvement for both the lumped-fuel and decay heat models in TRACE. VERA has been developed to perform high-fidelity, whole-core multiphysics simulations for LWRs. Previously, during the Consortium for Advanced Simulation of LWRs (CASL) program, the emphasis was on providing accurate steady-state analysis—with a secondary focus on reactivity insertion accident (RIA) analysis—to address operational challenges in the nuclear energy industry. Under the Department of Energy (DOE) Nuclear Energy Advanced Modeling and Simulation (NEAMS) program, these capabilities are being extended to a broader range of transient analyses with the goal of quantifying the risk of fuel failures such as FFRD. To properly model such conditions with VERA, decay heat calculations have been integrated with the multiphysics to enable rod-by-rod thermal hydraulic (TH) conditions to be driven by the decay heat in long-running accidents such as LOCAs.
Gravothermal evolution of dark matter halos with differential elastic scattering
Here, we study gravothermal evolution of dark matter halos in the presence of differential self-scattering that has strong velocity and angular dependencies. We design controlled N-body simulations to model Rutherford and Møller scatterings in the halo, and follow its evolution in both core-expansion and -collapse phases. The simulations show the commonly-used transfer cross section underestimates the effects of dark matter self-interactions, but the viscosity cross section provides an accurate approximation for modeling angular-dependent dark matter scattering. We investigate thermodynamic properties of the halo, and find that the three moments of the Boltzmann equation under the fluid approximation are satisfied. We further propose a constant effective cross section, which integrates over the halo's characteristic velocity dispersion with weighting kernels motivated by kinetic theory of heat conduction. The effective cross section provides a good approximation to differential self-scattering for most of the halo evolution. It indicates that we can map astrophysical constraints on a constant self-interacting cross section to an SIDM model with velocity- and angular-dependent scatterings.
Feasibility Studies on a Hexagonal-Lattice Core for a World-Class Cold Neutron Source
Cold neutrons have kinetic energies less than 5 meV and wavelengths greater than 4 Α. They can be transported over tens of meters through super-reflecting neutron guides with minimal losses. Cold neutrons are used to investigate the structure of larger molecular systems such as biological materials, polymers and aggregates, due to their preferential interaction with light elements and general ignorance towards heavy ones. Intense beams of cold neutrons are obtained from slowing down a source of thermal energy neutrons - which may be from either a research reactor or spallation neutron source - through some cryogenic moderator such as liquid hydrogen or deuterium. The present reactor at the NIST Center for Neutron Research (NCNR) - NBSR - is such a cold neutron source (CNS) facility which provides cold neutron beams for over 2,000 scientists performing various experiments annually. Feasibility studies on a replacement reactor for the NBSR are underway at NCNR with the primary purpose of optimized cold neutron production. Low enriched uranium (LEU) fuel is required for the new reactor to conform to nuclear non-proliferation agreements. The low thermal power rate of 20 MW is taken as a priority with a fuel cycle length designated as 30 days. A horizontal split compact core with a large D{sub 2}O reflector tank is currently proposed and studied, with the expectation of achieving much better cold neutron performance than the present NIST reactor (NBSR). A preliminary core design has been completed using MCNP6 modeling and simulation. The physics performance characteristics of the proposed new core indicate that the new design is competitive with the most notable existing advanced cold neutron sources. In previous studies, only rectangular shaped fuel elements were considered because they have similar external dimensions as the NBSR fuel elements. However, from a compact core standpoint, a square lattice is not the most effective geometry for a tight configuration. Moreover, the previous studies also showed that the square lattice of the fuel elements left little room to accommodate vertical insertion blade-type control elements. As a result, all control blades had to reside in the D{sub 2}O reflector, which made the design cumbersome (in that case the control blades must penetrate the reflector tank) and neutronically uneconomical. In this summary, a preliminary feasibility study on a hexagonal core lattice is performed to render an alternative geometry for the new reactor (HEX core) to provide sufficient space for the control elements. The identical LEU fuel (U{sub 3}Si{sub 2}/Al) with U-235 enrichment 19.75% is used in the new design. The maximum thermal power and fuel management scheme remain the same as the previous investigations (three 30-day cycled batches for each batch of three fuel elements). The horizontal split compact core concept is also applied in the hexagonal lattice core design, with the objective of creating maximum thermal flux traps between the split core halves. A detailed description of the model for the hexagonal lattice core is presented in the following section. The HEX core design achieves a number of successes over the previous split-core design. Given that much of the motivation of this work was based on implementation of control blades into a concept which lacked them, it is notable that neutron economy was well-preserved in the process of achieving conservatively effective reactivity control; start-up k{sub eff} was in fact increased by 0.23% and peak thermal flux increased by ∼25%. A useful metric in determining the efficacy of resources towards creating an environment for the production of cold neutrons - dubbed the 'quality factor' (QF) - is the ratio of peak thermal neutron flux in a system to the total thermal power produced. Because HEX core's objectives are very focused in comparison to existing research reactors, it is fitting to pursue a design which out-performs all others in terms of some specific performance metric, namely this QF term. While HFIR remains the greatest cold neutron source in the world, it does so through use of HEU fuel (which will be replaced with LEU in the near future), and suffers a greater level of fast neutron contamination that is expected from the HEX design. The new core design achieves these successes due to the hexagonal lattice fuel arrangement, a 13.5% reduction in cladding mass, and a 13.1% reduction in fuel element volume. In spite of a 5.5% reduction in fuel mass, no compromises in reactor performance were noted. Provided the favorable characteristics shown of the control blade design, refueling intervals longer than the prescribed 30 days may be considered. It can be speculated that with these quantitative benefits, the overall capital and continuous costs of the HEX core design will be less than the previously proposed split-core concept.
DOE NETL Gas Hydrate Project FWP 65213: Kinetic Parameters for the Exchange of Hydrate Formers (Final Report)
This report documents the research activities sponsored by the U.S. Department of Energy, National Energy Technology Laboratory (NETL), by the Pacific Northwest National Laboratory (PNNL) for the gas hydrate project entitled, “Kinetic Parameters for the Exchange of Hydrate Formers.” This project started June 1, 2013 and concluded December 31, 2018, and comprised five budget periods, under FWP-65213. The overarching goal of this project was to gain an improved understanding of the dynamic processes of gas hydrate accumulations in geologic media by combining laboratory studies, numerical simulation, and analysis of shipboard infrared imaging of hydrate core samples. This project comprised four principal components: 1) fundamental laboratory investigations, 2) numerical simulator development and verification, 3) hydrate core characterization and analysis, and 4) applied laboratory and numerical investigations. Laboratory and field experiments have demonstrated the four core methodologies for producing natural gas hydrates from geologic formations: 1) depressurization, 2) thermal stimulation, 3) inhibitor injection, and 4) guest molecule exchange. Converting these methodologies into viable commercial technologies remains challenging, either from an economic or technical perspective. This project was largely focused with the technical challenges associated with the guest molecule exchange method, which is often referred to as gas swapping. Previous research by PNNL had shown that gas swapping with pure CO 2 was not feasible, as first originally thought, principally due to the formation of secondary hydrates, which clogged or reduced the effective permeability of the hydrate-bearing formation. This research was directed at discovering the potential for using mixtures of gases to affect the gas swapping methodology at commercial scales. The Ignik Sikumi Gas Hydrate Field Trial demonstrated the injection of a N 2 -CO 2 gas mixture into a natural gas hydrate bearing layer, and exchange behavior with the CH 4 hydrate former or guest molecules. The original concept behind the use of a N 2 -CO 2 was to maintain gas conditions at the reservoir state. Pure CO 2 would have existed under supercritical conditions, with an associated density closer to a liquid than gas. One of the key outcomes from this research project has been the discovery, through laboratory experiments and numerical simulation, that gas mixtures, especially those with components having different gas hydrate equilibria conditions provide a control option for the guest molecule exchange methodology. For example, the dissociation or formation of hydrate could be controlled by adjusting the composition of the gas mixture. This research project was dynamic in that the discoveries during each budget period would set the course of research during successive budget periods. Therefore, this report is arranged in chronological order progressing through the five budget periods of the project.
MoSST DAS: The First Working Geomagnetic Data Assimilation System
The Earth possesses an internal magnetic field (geomagnetic field) generated by convection in the outer core (geodynamo). Previous efforts have been focused along two distinct paths: (1) numerical geodynamo modeling to understand the origin of the geomagnetic field, and the mechanisms of geomagnetic secular variations (SV); and (2) geomagnetic field modeling to map the spatial/temporal variations of the field from geomagnetic data, and to derive core properties, e.g. inversion of core flow near the core-mantle boundary (CMB). Geomagnetic data assimilation is a new approach emerged over the past 5 years: surface observations are assimilated with geodynamo models for better understanding of the core dynamical state, and accurately prediction of SV. In collaboration with several geomagnetic research groups, we have developed the first working geomagnetic data assimilation system, Modular, Scalable, Self-consistent, and Three-dimensional (MoSST) DAS, that includes the MoSST numerical dynamo model; 7000 years of geomagnetic field maps from several field models utilizing satellite and ground observatory data, historical magnetic records and archeo/paleo magnetic data; and an ensemble based optimal interpolation (01) assimilation algorithm. With this system, we have demonstrated clearly that the assimilated core dynamical state is substantially different from those of pure geodynamo simulations. Ensemble assimilation runs also show the convergence of the assimilated solutions inside the core, suggesting that the simulation state is pulled closer to the truth via data assimilation. The forecasts from this system are also very accurate: the 5-year forecast of the geomagnetic field agrees very well with the observations; and the 5-year secular variation forecast is more accurate than the IGRF SV forecast models in the past. Using geomagnetic records up to 2009, we have made an SV forecast for the period from 2010-2015, and is a candidate SV model for IGRF-11.
TURBULENT MAGNETIC FIELD AMPLIFICATION FROM SPIRAL SASI MODES: IMPLICATIONS FOR CORE-COLLAPSE SUPERNOVAE AND PROTO-NEUTRON STAR MAGNETIZATION
We extend our investigation of magnetic field evolution in three-dimensional flows driven by the stationary accretion shock instability (SASI) with a suite of higher-resolution idealized models of the post-bounce core-collapse supernova environment. Our magnetohydrodynamic simulations vary in initial magnetic field strength, rotation rate, and grid resolution. Vigorous SASI-driven turbulence inside the shock amplifies magnetic fields exponentially; but while the amplified fields reduce the kinetic energy of small-scale flows, they do not seem to affect the global shock dynamics. The growth rate and final magnitude of the magnetic energy are very sensitive to grid resolution, and both are underestimated by the simulations. Nevertheless, our simulations suggest that neutron star magnetic fields exceeding 10{sup 14} G can result from dynamics driven by the SASI, even for non-rotating progenitors.
Three-dimensional supernova explosion simulations of 9-, 10-, 11-, 12-, and 13-M⊙ stars
Abstract Using the new state-of-the-art core-collapse supernova (CCSN) code fornax, we have simulated the three-dimensional dynamical evolution of the cores of 9-, 10-, 11-, 12-, and 13-M⊙ stars from the onset of collapse. Stars from 8 to 13 M⊙ constitute roughly 50 per cent of all massive stars, so the explosive potential for this mass range is important to the overall theory of CCSNe. We find that the 9-, 10-, 11-, and 12-M⊙ models explode in 3D easily, but that the 13-M⊙ model does not. From these findings, and the fact that slightly more massive progenitors seem to explode, we suggest that there is a gap in explodability near 12 to 14 M⊙ for non-rotating progenitor stars. Factors conducive to explosion are turbulence behind the stalled shock, energy transfer due to neutrino–matter absorption and neutrino–matter scattering, many-body corrections to the neutrino–nucleon scattering rate, and the presence of a sharp silicon–oxygen interface in the progenitor. Our 3D exploding models frequently have a dipolar structure, with the two asymmetrical exploding lobes separated by a pinched waist where matter temporarily continues to accrete. This process maintains the driving neutrino luminosity, while partially shunting matter out of the way of the expanding lobes, thereby modestly facilitating explosion. The morphology of all 3D explosions is characterized by multiple bubble structures with a range of low-order harmonic modes. Though much remains to be done in CCSN theory, these and other results in the literature suggest that, at least for these lower mass progenitors, supernova theory is converging on a credible solution.
AB initio free energy calculations of the solubility of silica in metallic hydrogen and application to giant planet cores
By combining density functional molecular dynamics simulations with a thermodynamic integration technique, we determine the free energy of metallic hydrogen and silica, SiO{sub 2}, at megabar pressures and thousands of degrees Kelvin. Our ab initio solubility calculations show that silica dissolves into fluid hydrogen above 5000 K for pressures from 10 and 40 Mbars, which has implications for the evolution of rocky cores in giant gas planets like Jupiter, Saturn, and a substantial fraction of known extrasolar planets. Our findings underline the necessity of considering the erosion and redistribution of core materials in giant planet evolution models, but they also demonstrate that hot metallic hydrogen is a good solvent at megabar pressures, which has implications for high-pressure experiments.
ON THE INTERNAL DYNAMICS OF THE STARLESS CORE L694-2
In order to understand the internal dynamics of starless cores, we take L694-2 as an example of starless cores and investigate its internal dynamics by comparing observed data of L694-2 to our two hydrodynamical simulations, which involve the gravitational collapse of marginally unstable Bonnor-Ebert and uniform cores in a quiescent region. From the comparisons, we find that the density structures of the models agree well with the observed density distribution of L694-2, but the velocity fields and HCN line profiles of the models differ from the observed ones. From the differences in the velocity fields and the HCN line profiles, we have reached the following conclusions on the internal dynamics of L694-2. First, L694-2 has different internal dynamics from the gravitational collapse of the marginally unstable Bonnor-Ebert core. Second, L694-2 has an infall speed faster than any other core that undergoes the gravitational collapse with a Bonnor-Ebert-like density structure in a quiescent region. Third, L694-2 has almost no motion at its surface. From further simulations, in which cores are perturbed by supersonic shocks and affected by an expanding inter-core medium, the differences in the HCN line profiles could be reduced considerably.
Global Ten-Moment Multifluid Simulations of the Solar Wind Interaction with Mercury: From the Planetary Conducting Core to the Dynamic Magnetosphere
In this work, we explore for the first time the tightly coupled interior-magnetosphere system of Mercury by employing a three-dimensional ten-moment multifluid model. This novel fluid model incorporates the nonideal effects including the Hall effect, electron inertia, and tensorial pressures that are critical for collisionless magnetic reconnection; therefore, it is particularly well suited for investigating collisionless magnetic reconnection in Mercury's magnetotail and at the planet's magnetopause. Additionally, the model is able to reproduce the observed magnetic field vectors, field-aligned currents, and cross-tail current sheet asymmetry (beyond magnetohydrodynamic approach), and the simulation results are in good agreement with spacecraft observations. We also study the magnetospheric response of Mercury to a hypothetical extreme event with an enhanced solar wind dynamic pressure, which demonstrates the significance of induction effects resulting from the electromagnetically coupled interior. More interestingly, plasmoids (or flux ropes) are formed in Mercury's magnetotail during the event, indicating the highly dynamic nature of Mercury's magnetosphere.
LANL Activities: FY12-Q2 National Risk Assessment Partnership (NRAP): Industrial Carbon Capture Program (Quarterly Report)
This report summarizes progress of LANL activities related to the tasks performed under the LANL FWP FE102-002-FY10, National Risk Assessment Partnership (NRAP): Industrial Carbon Capture Program. This FWP is funded through the American Recovery and Reinvestment Act (ARRA). Overall, the NRAP activities are focused on understanding and evaluating risks associated with large-scale injection and long-term storage of CO 2 in deep geological formations. One of the primary risks during large-scale injection is due to changes in geomechanical stresses to the storage reservoir, to the caprock/seals and to the wellbores. These changes may have the potential to cause CO 2 and brine leakage and geochemical impacts to the groundwater systems. While the importance of these stresses is well recognized, there have been relatively few quantitative studies (laboratory, field or theoretical) of geomechanical processes in sequestration systems. In addition, there are no integrated studies that allow evaluation of risks to groundwater quality in the context of CO 2 injection-induced stresses. The work performed under this project is focused on better understanding these effects. LANL approach will develop laboratory and computational tools to understand the impact of CO 2 -induced mechanical stress by creating a geomechanical test bed using inputs from laboratory experiments, field data, and conceptual approaches. The Geomechanical Test Bed will be used for conducting sensitivity and scenario analyses of the impacts of CO 2 injection. The specific types of questions will relate to fault stimulation and fracture inducing stress on caprock, changes in wellbore leakage due to evolution of stress in the reservoir and caprock, and the potential for induced seismicity. In addition, the Geomechanical Test Bed will be used to investigate the coupling of stress-induced leakage pathways with impacts on groundwater quality. LANL activities are performed under two tasks: (1) develop laboratory and computational tools to understand CO 2 -induced mechanical impacts and (2) use natural analog sites to determine potential groundwater impacts. We are using the Springerville-St. John Dome as a field site for collecting field data on CO 2 migration through faults and groundwater impacts as well as developing and validating computational models. During the FY12 second quarter we have been working with New England Research Company to construct a tri-axial core-holder. We have built fluid control system for the coreflood system that can be ported to perform in-situ imaging of core. We have performed numerical simulations for groundwater impacts of CO 2 and brine leakage using the reservoir model for Springerville-St John's Dome site. We have analyzed groundwater samples collected from Springerville site for major ion chemistry and isotopic composition. We are currently analyzing subsurface core and chip samples acquired for mineralogical composition.
Runtime Performance and Virtual Network Control Alternatives in VM-Based High-Fidelity Network Simulations
In prior work (Yoginath and Perumalla, 2011; Yoginath, Perumalla and Henz, 2012), the motivation, challenges and issues were articulated in favor of virtual time ordering of Virtual Machines (VMs) in network simulations hosted on multi-core machines. Two major components in the overall virtualization challenge are (1) virtual timeline establishment and scheduling of VMs, and (2) virtualization of inter-VM communication. Here, we extend prior work by presenting scaling results for the first component, with experiment results on up to 128 VMs scheduled in virtual time order on a single 12-core host. We also explore the solution space of design alternatives for the second component, and present performance results from a multi-threaded, multi-queue implementation of inter-VM network control for synchronized execution with VM scheduling, incorporated in our NetWarp simulation system.
Simulation for the fault current limiting operation of REBCO CORC superconducting cables with different core materials
With high power density and low loss, CORC superconducting cables composed of RE- Ba 2 Cu 3 O 7–δ (REBCO) coated conductors are of great interest for power transmission applications. They can also effectively be designed to serve as fault current limiters, thanks to their sharp superconducting-to-normal transition. Coupled electromagnetic-thermal finite element (FE) simulations implemented in COMSOL Multiphysics were developed and validated against the published results for the fault current limiting performance of two CORC cables of REBCO coasted conductors wound on either copper or stainless steel cores. For improved accuracy, temperature dependencies of electrical and thermal properties of all component materials were considered in the simulations. The simulations were performed in the cross-sections of the cables for every individual layer of each REBCO tape to deliver comprehensive understanding of evolution of the current distribution and temperature rise in those layers. Furthermore, the studies can suggest approaches to optimize cable design for fault current limiting (FCL) applications by assessing the role of individual components. In the paper, possible computational errors, challenges and improvements are also discussed.
Cross-verification of the global gyrokinetic codes GENE and XGC
A detailed cross-verification between two global gyrokinetic codes, the core continuum code GENE and the edge particle-in-cell code XGC, for the linear and nonlinear simulations of ion-temperature-gradient modes is carried out. With the recent developments in the edge gyrokinetics, it may be feasible someday to describe the whole tokamak plasma on turbulence timescales using a coupled gyrokinetic simulation model. Before pursuing this, the core code (GENE) and the edge code (XGC) must be carefully benchmarked with each other. The present verification provides a solid basis for future code coupling research. Also included in the benchmarking is the global particle-in-cell code ORB5, to raise the confidence in the quality of the obtained results. An excellent agreement between all three codes is obtained. Lastly, in order to facilitate a benchmark framework for other codes, we make a specific effort to provide all the relevant input parameters and precise details for each code.
Direct comparison of gyrokinetic and fluid scrape-off layer simulations
Typically, fluid simulations are used for tokamak divertor design. However, fluid models are only valid if the scrape-off layer (SOL) is highly collisional. This assumption is valid in many present-day experiments but is questionable in the upstream SOL of some high-power scenarios envisioned for burning plasmas and fusion pilot plants. This paper reports on comparisons between fluid and kinetic simulations of the SOL for upstream parameters and geometry representative of the Spherical Tokamak for Energy Production fusion pilot plant. The SOLPS-ITER (fluid) and Gkeyll (gyrokinetic) codes are operated in a two-dimensional axisymmetric mode, which replaces turbulence with ad-hoc diffusivities. In kinetic simulations, we observe that the ions in the upstream SOL experience significant mirror trapping. This substantially increases the upstream temperature and has important implications for impurity dynamics. We show that the mirror force, which is excluded in SOLPS’s fluid equations, enhances the electrostatic potential drop along the field line in the SOL. We also show that the assumption of equal main ion and impurity temperatures, which is made in commonly used fluid codes, is invalid for the regimes explored here. The combination of these effects results in superior confinement of impurities to the divertor region in kinetic simulations, consistent with our earlier predictions [Kotschenreuther et al., in 29th IAEA 29 Fusion Energy Conference (IAEA, London, UK, 2023)]. This effect can be dramatic, reducing the midplane impurity density by orders of magnitude. These results indicate that in lower collisionality SOL’s the tolerable downstream impurity densities may be higher than would be predicted by fluid simulations, allowing for higher radiated power while avoiding unacceptable core contamination. Our results highlight the importance of kinetic simulations for divertor design and optimization for fusion pilot plants.
Raptor
Raptor is an efficient Python-based tool for predicting the formation and morphology of stochastic lack of fusion defects in metal AM processes. A major obstacle for the qualification and certification of additively manufactured parts in critical applications continues to be performance variability caused in part by porosity-related defects. High-fidelity process models that could predict these defect features are currently too computationally expensive for component-level analysis. To address this, Raptor employs a high-performance geometric method to model the dynamic melt pool rather than relying on computationally intensive thermal fluid dynamics. This allows Raptor to rapidly identify regions of unmelted material that correspond to lack of fusion pores. The efficiency of this approach significantly reduces the time and resources needed for generating 3D defect predictions, which enables users to conduct large-scale parameter studies and evaluate how process variations affect part quality. The framework offers operational flexibility; users can execute simulations through a simple command line interface or integrate core functions as a library within larger computational workflows. Simulation outputs include 3D porosity maps for visualization and tools for quantitative morphological analysis. These results are suitable for direct comparison with experimental characterization data from methods such as X-ray computed tomography and can be used for statistical process optimization.