arXiv subjects

E. Lanti

Publications and source records attributed to E. Lanti.

8 recordsLinked to original sources

arXiv2026

SPECTRE: A robust solver for 3D equilibria with arbitrary topology

We present SPECTRE, a new equilibrium code based on the Multi-Region relaxed MHD model for robustly calculating 3D equilibria with general magnetic topology, allowing for flux surfaces, magnetic islands, and chaos. The code builds on a previous MRxMHD solver, SPEC, but performs significantly better thanks to a new formulation of force, the use of a stable trust-region-based least squares minimization scheme, as well as several additional features. SPECTRE is verified through application to configurations with known equilibrium solutions, in vacuum and with finite beta, both in the fixed boundary and the free boundary mode. Notably, these include vacuum equilibria of a quasi-axisymmetric (QA) device in fixed-boundary mode, and of W7-X in the free-boundary mode, along with a classical stellarator finite-beta free-boundary case. Finally, the solver is applied to a modern optimized finite-beta quasi-isodynamic (QI) configuration, where we demonstrate calculation of a strongly-shaped equilibrium with a core island which is in agreement with a HINT calculation.

physics.plasm-ph↗

arXiv2026

Energetic particles, Shafranov shift and finite $\beta$ effects on TAE, KBM and ITG instabilities in global electromagnetic gyrokinetic simulations

Burning plasma is computationally challenging to simulate due to the multi-scale interactions between energetic particles (EPs), Alfven eigenmodes, and microinstabilities that drive turbulence. Many studies circumvent this difficulty by focusing on a single instability and making the corresponding simplifying assumptions. However, these approximations do not necessarily preserve the global instability spectrum, leading to conflicting results and inconsistencies. In this work, we identify the minimal set of assumptions needed to model a burning plasma self-consistently with the modes and species in the system. Using the global gyrokinetic code ORB5, to systematically evaluate the impact of commonly adopted assumptions on the plasma response. We find it is essential to include Shafranov shift and finite $\beta$ effects from all magnetically confined species. Otherwise, unphysical electromagnetic modes like internal kinks and kinetic ballooning modes (KBMs) appear to dominate the instability spectrum. The EP contribution to the Shafranov shift is particularly important, stabilizing both the toroidal ion temperature gradient (ITG) and toroidal Alfven eigenmode (TAE) at the longer wavelengths (low toroidal mode numbers). For TAEs, these effects significantly reduce the linear growth rate, which saturates instead of proportionally increasing with EP fraction. In the nonlinear regime ITG-driven heat and particle fluxes are unaffected by the Shafranov shift in self-consistent magnetic equilibria. While the the nonlinear saturation level of the TAE remains unchanged across all cases, unlike for the ITG case Shafranov shift does reduce the TAE-driven EP fluxes.

physics.plasm-ph↗

arXiv2026

Role of Shafranov shift, zonal structures on the behavior of TAEs, AAEs and microinstabilities in the presence of energetic particles

In future nuclear fusion reactors, even a small fraction of fusion-born energetic particles (EP) about 100 times hotter than the thermal bulk species, contributes substantially to the kinetic pressure and therefore affect the MHD equilibrium, mainly via the Shafranov shift. In this work, we perform first-principles numerical simulations using the gyrokinetic, electromagnetic, global code ORB5 to study the effect of a self-consistent finite $\beta$ equilibrium on the arising Alfv\'en Eigenmodes (destabilized by EPs), Ion Temperature Gradient (ITG), and Kinetic Ballooning Modes (KBM) microturbulence (destabilized by thermal species). Linearly, we explore the complex interplay between EP fraction, bulk gradients and a self-consistent Shafranov shift on the plasma stability. We choose single toroidal mode numbers to represent the system's instabilities and study the characteristic nonlinear evolutions of TAEs, KBMs and ITGs separately and including the axisymmetric field response to each mode separately. This study focuses on the impact of Shafranov shift equilibrium consistency, as well as the self-generated zonal ${E \times B}$ flows, the saturation levels and resulting heat and particle fluxes. In the ITG cases including the $n=0$ perturbations reduces turbulent fluxes, as expected, however, for the TAE cases including the $n=0$ perturbations is shown to enhance the fluxes. We show for the first time that Axisymmetric Alfv\'en Eigenmodes (AAEs) play a role in this mechanism.

physics.plasm-ph↗

arXiv2022

Gyrokinetic particle-in-cell simulations of electromagnetic turbulence in the presence of fast particles and global modes

Global simulations of electromagnetic turbulence, collisionless tearing modes, and Alfven Eigenmodes in the presence of fast particles are carried out using the gyrokinetic particle-in-cell codes ORB5 (E. Lanti et al, Comp. Phys. Comm., ${\bf 251}$, 107072 (2020)) and EUTERPE (V. Kornilov et al, Phys. Plasmas, ${\bf 11}$, 3196 (2004)) in tokamak and stellarator geometries. Computational feasibility of simulating such complex coupled systems is demonstrated.

physics.plasm-ph↗

arXiv2021

The GBS code for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary

A new version of GBS (Ricci et al. Plasma Phys. Control. Fusion 54, 124047, 2012; Halpern et al. J. Comput. Phys. 315, 388-408, 2016; Paruta et al. Phys. Plasmas 25, 112301, 2018) is described. GBS is a three-dimensional, flux-driven, global, two-fluid turbulence code developed for the self-consistent simulation of plasma turbulence and kinetic neutral dynamics in the tokamak boundary. In the new version presented here, the simulation domain is extended to encompass the whole plasma volume, avoiding an artificial boundary with the core, hence retaining the core-edge-SOL interplay. A new toroidal coordinate system is introduced to increase the code flexibility, allowing for the simulation of arbitrary magnetic configurations (e.g. single-null, double-null and snowflake configurations), which can also be the result of the equilibrium reconstruction of an experimental discharge. The implementation of a new iterative solver for the Poisson and Ampère equations is presented, leading to a remarkable speed-up of the code with respect to the use of direct solvers, therefore allowing for efficient electromagnetic simulations that avoid the use of the Boussinesq approximation. The self-consistent kinetic neutral model, initially developed for limited configurations, is ported to the magnetic configurations considered by the present version of GBS and carefully optimized. A new MPI parallelisation is implemented to evolve the plasma and neutral models in parallel, thus improving the code scalability. The numerical implementation of the plasma and neutral models is verified by means of the method of manufactured solutions. As an example of the simulation capabilities of the new version of GBS, a simulation of a TCV tokamak discharge is presented.

physics.plasm-ph↗

arXiv2020

Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade

Turbulence in tokamaks generates radially sheared zonal flows. Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can be driven unstable by an anisotropic energetic particle (EP) population leading to the formation of global radial structures, called EGAMs. The EGAMs can redistribute EP energy to the bulk plasma through collisionless wave-particle interaction. In such a way, the EGAMs might contribute to the plasma heating. Thus, investigation of EGAM properties, especially in the velocity space, is necessary for precise understanding of the transport phenomena in tokamak plasmas. In this work, the nonlinear dynamics of EGAMs without considering the mode interaction with the turbulence is investigated with the help of a Mode-Particle-Resonance (MPR) diagnostic implemented in the global gyrokinetic particle-in-cell code ORB5. An ASDEX Upgrade discharge is chosen as a reference case for this investigation due to its rich EP nonlinear dynamics. An experimentally relevant magnetic field configuration, thermal species profiles and an EP density profile are taken for EGAM chirping modelling and its comparison with available empirical data. The same magnetic configuration is used to explore energy transfer by the mode from the energetic particles to the thermal plasma including kinetic electron effects. For a given EGAM level the plasma heating by the mode can be significantly enhanced by varying the EP parameters. Electron dynamics decreases the EGAM saturation amplitude and consequently reduces the plasma heating, even though the mode transfers its energy to thermal ions much more than to electrons.

physics.plasm-ph↗

arXiv2019

ORB5: a global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry

This paper presents the current state of the global gyrokinetic code ORB5 as an update of the previous reference [Jolliet et al., Comp. Phys. Commun. 177 409 (2007)]. The ORB5 code solves the electromagnetic Vlasov-Maxwell system of equations using a PIC scheme and also includes collisions and strong flows. The code assumes multiple gyrokinetic ion species at all wavelengths for the polarization density and drift-kinetic electrons. Variants of the physical model can be selected for electrons such as assuming an adiabatic response or a ``hybrid'' model in which passing electrons are assumed adiabatic and trapped electrons are drift-kinetic. A Fourier filter as well as various control variates and noise reduction techniques enable simulations with good signal-to-noise ratios at a limited numerical cost. They are completed with different momentum and zonal flow-conserving heat sources allowing for temperature-gradient and flux-driven simulations. The code, which runs on both CPUs and GPUs, is well benchmarked against other similar codes and analytical predictions, and shows good scalability up to thousands of nodes.

physics.plasm-ph↗

arXiv2016

A portable platform for accelerated PIC codes and its application to GPUs using OpenACC

We present a portable platform, called PIC_ENGINE, for accelerating Particle-In-Cell (PIC) codes on heterogeneous many-core architectures such as Graphic Processing Units (GPUs). The aim of this development is efficient simulations on future exascale systems by allowing different parallelization strategies depending on the application problem and the specific architecture. To this end, this platform contains the basic steps of the PIC algorithm and has been designed as a test bed for different algorithmic options and data structures. Among the architectures that this engine can explore, particular attention is given here to systems equipped with GPUs. The study demonstrates that our portable PIC implementation based on the OpenACC programming model can achieve performance closely matching theoretical predictions. Using the Cray XC30 system, Piz Daint, at the Swiss National Supercomputing Centre (CSCS), we show that PIC_ENGINE running on an NVIDIA Kepler K20X GPU can outperform the one on an Intel Sandybridge 8-core CPU by a factor of 3.4.

physics.comp-ph↗