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  1. Conservative velocity mappings for discontinuous Galerkin kinetics

    Francisquez, Manaure ; Cagas, Petr ; Shukla, Akash ; ... - Journal of Computational Physics
    Continuum computational kinetic plasma models evolve the distribution function of a plasma species fs on a phase-space grid over time. In many problems of interest the distribution function has limited extent in velocity space; hence, using a uniform, highly refined mesh would be costly and slow. Nonuniform velocity grids can reduce the computational cost by placing more degrees of freedom where fs is appreciable and fewer where it is not. In this work we introduce a first-of-its kind discontinuous Galerkin approach to nonuniform velocity-space discretization using mapped velocity coordinates. This new method is presented in the context of a gyrokineticmore » model used to study magnetized plasmas. We create discretizations of collisionless and collisional terms using mappings in a way that exactly conserves particles and energy. Numerical tests of such properties are presented, and we show that this new discretization can reproduce earlier gyrokinetic simulations using grids with up to 6–60 times fewer cells and 22X-60X speed-ups depending on dimensionality, geometry and plasma parameters.« less

  2. Unraveling In-Situ Formation of Surface Nickel Nitride Structures in Plasma-Assisted Catalytic Ammonia Synthesis

    Kondratowicz, Christopher ; Zheng, Yiteng ; Liu, Ning ; ... - Journal of Physical Chemistry Letters
    We report the in situ formation of Ni nitride for plasma-assisted ammonia synthesis. Both the surface nitrogen concentration and the ammonia formation rate exhibit dependence on the N2:H2 feed ratio. The maximum surface nitrogen concentration occurs at a N2:H2 ratio of 4:1, and the maximum catalytic activity occurs at 2:1. In contrast, the formation of gas phase radicals is less sensitive to feed composition, indicating that Ni nitride is more kinetically relevant to ammonia production than gas-phase radicals. The plasma-induced formation of Ni nitride is therefore proposed to be a critical contributor to the synergistic effects in plasma-assisted catalytic ammoniamore » synthesis. Additionally, Ni nitride alters the surface reaction mechanism of plasma-assisted ammonia synthesis, with the rate-determining-step (RDS) shifting to surface-bound NH3 formation rather than N2 activation at temperatures below 373 K. These findings provide mechanistic insight that opens opportunities for optimizing the performance of plasma-assisted catalytic ammonia synthesis« less

  3. Mantaray: A Rust Package for Ray Tracing Ocean Surface Gravity Waves

    Irving, Bryce ; Castelao, Guilherme P. ; Beyers, Colin ; ... - Journal of Open Source Software
    Ocean surface gravity waves are an important component of air-sea interaction, influencing energy, momentum, and gas exchanges across the ocean-atmosphere interface. In specific applications such as refraction by ocean currents or bathymetry, ray tracing provides a computationally efficient way to gain insight into wave propagation. In this paper, we introduce Mantaray, an open-source software package implemented in Rust, with a Python interface, that solves the ray equations for ocean surface gravity waves. Mantaray is designed for performance, robustness, and ease of use. The package is modular to facilitate further development and can currently be applied to both idealized and realisticmore » wave propagation problems (Fig. 1).« less

  4. Modeling of convective cells, turbulence, and transport induced by a radio-frequency antenna in the tokamak boundary plasma

    Umansky, Maxim V. ; Dudson, Ben D. ; Jenkins, Thomas G. ; ... - Plasma Physics and Controlled Fusion
    The edge turbulence model Hermes (Dudson et al 2017 Plasma Phys. Control. Fusion 59 05401) is set up for plasma boundary simulations with an radiofrequency (RF) antenna, using parameters characteristic of a tokamak edge. Cartesian slab geometry is used with thin plate limiters representing the ion cyclotron range of frequency (ICRF) antenna side-wall limiters. Ad-hoc DC electric biasing of the limiters, motivated by calculations with VSim (Nieter et al 2004 J. Comput. Phys. 196 448), represents an induced RF sheath rectified potential in the plasma turbulence model. Flux-driven turbulence simulations demonstrate a realistic distribution of plasma profiles and fluctuations. Theremore » is a clear effect of the antenna sheath voltage leading to formation of convective cells; bias-induced convective transport flattens the scrape-off layer density profile and fluctuations penetrate into the shadow region of the limiters as the bias voltage increases. Turbulent transport for impurity ions is inferred by following ion trajectories in the simulated plasma turbulence fields, showing Bohm-like effective diffusion rates. All in all, the model elucidates the key physical phenomena governing the effects of ICRF-induced antenna biasing on the tokamak boundary plasma.« less

  5. Dehydrogenation vs Apparent Hydrogenation: Unraveling the Mechanisms of He and O2 Plasma Etching on Colloidal Nanocrystal Films

    Shaw, Santosh ; Silva, Tiago ; Bobbitt, Jonathan M. ; ... - ACS Applied Materials and Interfaces
    Removing organic ligands from colloidal nanoparticles is critical for fabricating solid-state devices, yet accurately quantifying this removal remains a significant analytical challenge. Here, we establish a robust and accessible method for this quantification by calibrating Raman spectroscopy against precise ion beam analysis (IBA) for nanoparticle assemblies (CNAs) processed by helium (He) and oxygen (O2) plasmas. We demonstrate that the calibration curves are remarkably independent of plasma power and pressure, depending critically only on the choice of feed gas. He plasma induces rapid dehydrogenation and cross-linking, evidenced by a much faster decrease in the C–H Raman signal relative to the actualmore » carbon loss. Conversely, O2 plasma leads to a surprising “apparent hydrogenation”, where the carbon backbone is removed significantly faster than the C–H signal diminishes. This counterintuitive effect is explained by a serial mechanism of oxidative fragmentation; β-scission cleaves the alkyl chains, and subsequent stabilization steps enrich the remaining film with hydrogen-rich methyl-terminated fragments, while carbon is efficiently removed as volatile CO. This work provides calibrated functions that enable the rapid determination of absolute carbon content in processed CNAs using simple Raman spectroscopy with uncertainties of ∼8% for O2 and ∼12% for He plasma, offering a vital tool for both process diagnostics and fundamental studies of plasma–matter interactions in colloidal nanocrystal films.« less

  6. STORM: Scrape-off layer turbulence in tokamak fusion reactors

    Omotani, John T. ; Dickinson, D. ; Dudson, Ben D. ; ... - Computer Physics Communications
    The scrape-off layer of a tokamak fusion reactor carries the plasma exhaust from the hot core plasma to the material surfaces of the reactor vessel. The heat loads imposed by the exhaust are a critical limit on the performance of fusion power plants. Turbulent transport of the plasma regulates the width of the scrape-off layer plasma and must be modelled to understand the intensity of these heat loads. STORM is a plasma turbulence code capable of simulating three dimensional turbulence across the full scrape-off layer of a tokamak fusion reactor, using a drift reduced, collisional fluid model. STORM uses mostlymore » finite difference schemes, with a staggered grid in the direction parallel to the magnetic field. We describe the model, geometry and initialisation options used by STORM, as well as the numerical methods, which are implemented using the BOUT++ plasma simulation framework. BOUT++ has been enhanced alongside the development of STORM, providing better support for staggered grid methods. We summarise these enhancements, including a detailed explanation of the parallel derivative methods, which underwent a major update for version 4 of BOUT++.« less

  7. Spectrally accelerated edge and scrape-off layer gyrokinetic turbulence simulations

    Frei, B. J. ; Ulbl, P. ; Trilaksono, J. ; ... - Computer Physics Communications
    This paper presents the first gyrokinetic (GK) simulations of edge and scrape-off layer (SOL) turbulence accelerated by a velocity-space spectral approach in the full-f GK code GENE-X. Building upon the original grid velocity-space discretization, we derive and implement a new spectral formulation and verify the numerical implementation using the method of manufactured solution. We conduct a series of spectral turbulence simulations focusing on the TCV-X21 reference case (Oliveira et al., 2022 [26]) and compare these results with previously validated grid simulations (Ulbl et al., 2023 [25]). The spectral approach reproduces the outboard midplane (OMP) profiles (density, temperature, and radial electricmore » field), dominated by trapped electron mode (TEM) turbulence, with excellent agreement and significantly lower velocity-space resolution. As a consequence, the spectral approach reduces the computational cost (CPUh) by at least an order of magnitude, of approximately 50 for the TCV-X21 case. This enables high-fidelity GK simulations to be performed within a few days on modern CPU-based supercomputers for medium-sized devices and establishes GENE-X as a powerful tool for studying edge and SOL turbulence, moving towards reactor-relevant devices like ITER.« less

  8. Plasma-Assisted Surface Nitridation of Proton Intercalatable WO3 for Efficient Electrocatalytic Ammonia Synthesis

    Zhang, Zhiyuan ; Kondratowicz, Christopher ; Smith, Jacob ; ... - ACS Energy Letters
    Electrocatalytic nitrogen reduction (eNRR) offers a green pathway for the production of NH3 from N2 and H2O under ambient conditions. Transition metal oxynitrides (TMOxNy) are among the most promising catalysts but face challenges in achieving a high yield and faradaic efficiency (FE). This work develops a hybrid WOxNy/WO3 catalyst with a unique heterogeneous interfacial complexion (HIC) structure. This design enables in situ generation and delivery of highly active hydrogen atoms (H*) in acidic electrolytes, promoting nitrogen hydrogenation and the formation of nitrogen vacancies (Nv) on the WOxNy surface. This significantly enhances the selectivity of eNRR for NH3 synthesis while suppressingmore » the hydrogen evolution reaction (HER). A simple two-step fabrication process─microwave hydrothermal growth followed by plasma-assisted surface nitridation─was developed to fabricate the designed catalyst electrode, achieving an NH3 yield of 3.2 × 10–10 mol·cm–2·s–1 with 40.1% FE, outperforming most TMN/TMOxNy electrocatalysts. Multiple control experiments confirm that the eNRR follows an HIC-enhanced Mars–van Krevelen (MvK) mechanism.« less

  9. Vacuum commissioning and operation result after the KSTAR PFC upgrade

    Kim, Kwangpyo ; Lee, Hyunmyung ; Lee, Hyung ho ; ... - Fusion Engineering and Design
    The first vacuum commissioning after the installation of new tungsten mono-block cassette divertor has been successfully conducted in KSTAR. The tungsten divertor has been installed in the lower divertor region to handle the high divertor heat loads up to 10 MW/m2. On the one hand, the plasma facing components except for the tungsten divertor in the KSTAR vacuum vessel still consists of graphite tiles. Thus, it was much more challenging to maintain high-quality vacuum condition mainly because of various possible impurity sources inside the vessel compared with previous experiment campaigns. In this paper, the detailed procedure for securing vacuum conditionmore » of the KSTAR tokamak after the installation of the new tungsten divertor is presented. The vacuum condition is also examined regarding the plasma start-up and the long-pulse high-performance quality.« less

  10. An explicit, energy-conserving particle-in-cell scheme

    Ricketson, Lee F. ; Hu, Jingwei - Journal of Computational Physics
    We present an explicit temporal discretization of particle-in-cell schemes for the non-relativistic Vlasov equation that results in exact energy conservation when combined with an appropriate spatial discretization. The scheme is inspired by a simple, second-order explicit scheme that conserves energy exactly in the Eulerian context. We show that direct translation to particle-in-cell does not result in strict conservation, but derive a simple correction based on an analytically solvable optimization problem that recovers conservation. While this optimization problem is not guaranteed to have a real solution for every particle, we provide a correction that makes imaginary values extremely rare and stillmore » admits $$\mathcal{O}$$(10–12) fractional errors in energy for practical simulation parameters. We present the scheme in both electrostatic – where we use the Ampère formulation – and electromagnetic contexts. With an electromagnetic field solve, the field update is most naturally linearly implicit, but the more computationally intensive particle update remains fully explicit. Here, we also show how the scheme can be extended to use the fully explicit leapfrog and pseudospectral analytic time-domain (PSATD) field solvers. The scheme is tested on standard kinetic plasma problems, confirming its conservation properties.« less
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