Publications de Stephan Brunner

Modelling of ETG turbulent transport in the TCV pedestal

Stephan Brunner, Stefano Coda, Benoît Labit, Oleg Krutkin

Results of the first gyrokinetic simulations of the TCV pedestal are presented. Two discharges at varying levels of gas puffing are considered as input parameters for the local GENE simulations. Linear and nonlinear simulations are carried out for electron ...

2025

Particle-in-cell methods in edge plasma physics: the PICLS code

Stephan Brunner, Laurent Villard, Giovanni Di Giannatale

Over the past decades, multiple gyrokinetic codes have shown to be able to simulate turbulence and associated transport in the core of Tokamak devices. However, their application to the edge and scrape-off layer (SOL) region presents significant challenges ...

2025

A Quasilinear Model for Momentum Transport Including Rotation and Electron-scale Turbulence

Stephan Brunner, Justin Richard Ball, Haomin Sun

In a previous paper, a new gyrokinetic quasilinear model was proposed to study turbulent momentum transport in tokamaks with up-down asymmetric plasma shaping and toroidal flow shear (Sun et al 2024 Nuclear Fusion 64 036026). In this work, we start by appl ...

IOP Publishing Ltd2025

Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part I: Linear simulations

Stephan Brunner, Justin Richard Ball, Arnas Volcokas

This study examines the impact of low and zero magnetic shear, along with rational values ofsafety factor, on linear mode behavior in tokamak plasmas. We focus on how magnetic field linetopology and parallel domain length influence linear mode structures a ...

IOP Publishing Ltd2025

Collisional effects on positive and negative triangularity through local and global temperature gradient-driven and flux-driven gyrokinetic simulations

Stephan Brunner, Laurent Villard, Moahan Murugappan, Giovanni Di Giannatale

In this work, we explore the effects of collisions on turbulent transport, focusing on two different TCV magnetic equilibria featuring positive and negative triangularity. The investigation is conducted using gyrokinetic modeling. Both gradient-driven and ...

2025

Global electromagnetic gyrokinetic simulations of internal transport barriers in reversed-shear tokamaks

Stephan Brunner, Laurent Villard, Moahan Murugappan, Justin Richard Ball, Arnas Volcokas, Giovanni Di Giannatale

Internal transport barriers (ITB) form through turbulence suppression, often observed when the safety factor profile exhibits an off-axis minimum. This work aims at improving our understanding of the conditions enabling the development of an ITB, using a m ...

2025

Reducing Turbulent Transport in Tokamaks by Combining Intrinsic Rotation and the Low Momentum Diffusivity Regime

Stephan Brunner, Justin Richard Ball, Haomin Sun

Based on the analysis of a large number of high-fidelity nonlinear gyrokinetic simulations, we propose a novel strategy to improve confinement in spherical tokamak plasmas by combining up-down asymmetric flux surface shaping with the Low Momentum Diffusivi ...

IOP Publishing Ltd2025

Effects of Kinetic Ballooning Modes on the electron distribution function in the core of high-performance tokamak plasmas

Stephan Brunner

This article is dedicated to study the physical causes of a long-standing issue experienced in different tokamak devices throughout the last decades: the observed discrepancies between electron cyclotron emission (ECE) and Thomson Scattering (TS) diagnosti ...

IOP Publishing Ltd2025

Nonlinear Effects in Fluctuation Short Pulse Reflectometry

Stephan Brunner, Stefano Coda, Oleg Krutkin

The fluctuation short pulse reflectometry diagnostic is simulated with the full-wave CUWA code for ad-hoc turbulence and simplified geometry. The nonlinear effects on the measurements are investigated while accounting for the plasma curvature, probing angl ...

IOP Publishing Ltd2025

Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part II: Nonlinear simulations

Stephan Brunner, Justin Richard Ball, Arnas Volcokas

Using local nonlinear gyrokinetic simulations and building up on linear results from acompanion paper (Volcokas 2024 Submitted for publication), we demonstrate that turbulenteddies can extend along magnetic field lines for hundreds of poloidal turns in tok ...

IOP Publishing Ltd2025

On the importance of slow ions in the kinetic Bohm criterion

Stephan Brunner, Alessandro Geraldini

Between a plasma and a solid target lies a positively charged sheath of several Debye lengths λD width, typically much smaller than the characteristic length scale L of the main plasma. This scale separation implies that the asymptotic limit ε = λD/L → 0 i ...

Cambridge University Press2024

Verification of the Fourier-enhanced 3D finite element Poisson solver of the gyrokinetic full-f code PICLS

Stephan Brunner, Laurent Villard, Alberto Bottino, Moahan Murugappan

We introduce and derive the Fourier -enhanced 3D electrostatic field solver of the gyrokinetic full -f PIC code PICLS. The solver makes use of a Fourier representation in one periodic direction of the domain to make the solving of the system easily paralle ...

Elsevier2024

A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping

Stephan Brunner, Justin Richard Ball, Arnas Volcokas, Haomin Sun

In tokamak experiments, sufficiently strong E x B flow shear reduces turbulent transport, thereby improving the prospects for fusion power plants. It is therefore of great importance to efficiently explore parameter space to find where strong plasma flow c ...

IOP Publishing Ltd2024

Sheath constraints on turbulent magnetised plasmas

Stephan Brunner, Alessandro Geraldini

A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath wi ...

2024

Gyrokinetic turbulence modeling of a high performance scenario in JT-60SA

Stephan Brunner, Stefano Coda, Aylwin Iantchenko

Local gyrokinetic simulations are used to model turbulent transport for the first time in a representative high-performance plasma discharge projected for the new JT-60SA tokamak. The discharge features a double-null separatrix, 41 MW of combined neutral b ...

IOP Publishing Ltd2024

Validation of short-pulse reflectometry turbulence measurements with a synthetic diagnostic

Stephan Brunner, Stefano Coda, Umesh Kumar, Oleg Krutkin, Mackenzie Peter-Fulford Van Rossem, Samuele Mazzi

Experimental measurements of the turbulence amplitude utilizing a short pulse reflectometry method are presented. Two discharges with shaped plasma possessing opposite signs of triangularity are considered and a higher turbulence amplitude is found in the ...

IOP Publishing Ltd2024

Gyrokinetic flux-driven simulations in mixed TEM/ITG regime using a delta-f PIC scheme with evolving background

Stephan Brunner, Laurent Villard, Moahan Murugappan, Giovanni Di Giannatale

In the context of global gyrokinetic simulations of turbulence using a particle-in-cell framework, verifying the delta-f assumption with a fixed background distribution becomes challenging when determining quasi-steady state profiles corresponding to given ...

American Institute of Physics (AIP)2024

System size scaling of triangularity effects on global temperature gradient-driven gyrokinetic simulations

Stephan Brunner, Laurent Villard, Moahan Murugappan, Giovanni Di Giannatale

In this work, we explore the triangularity effects on turbulent transport employing global gyrokinetic simulations performed with the ORB5 code. Numerous experiments on the Tokamak á Configuration Variable (TCV) and, more recently, on the DIII-D machine, h ...

2024

Linear scattering theory of short-pulse reflectometry

Stephan Brunner, Stefano Coda, Oleg Krutkin

The linear scattering theory of short pulse reflectometry is presented. An expression for the scattering signal is obtained by applying the perturbation theory approach for solving the Helmholtz equation. Based on these analytical results, a method for mea ...

2023

Ultra long turbulent eddies, magnetic topology, and the triggering of internal transport barriers in tokamaks

Stephan Brunner, Justin Richard Ball, Arnas Volcokas

Local nonlinear gyrokinetic simulations of tokamak plasmas demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of poloidal turns when the magnetic shear is very small. By accurately modeling different field line topologies ...

IOP Publishing Ltd2023