Publications de Stephan Brunner

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Two-dimensional Vlasov simulations of nonlinear electron plasma waves are presented, in which the interplay of linear and nonlinear kinetic effects is evident. The plasma wave is created with an external traveling wave potential with a transverse envelope ...

This contribution will present a feasibility study and conceptual design of a tangential phase-contrast imaging (PCI) diagnostic for the new JT60SA tokamak. PCI is a well-known technique for measuring density fluctuations. Tangential launching, combined with an appropriate spatial filtering technique, affords the measurement highly improved spatial localization, as demonstrated in particular on the TCV tokamak. Tangential ports of 20cm diameter are envisioned to be used on JT60SA, obviating the need to moun

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 ...

A widespread method for gyrokinetic simulations relies on the discretization of distribution functions with numerical markers. The electromagnetic field is typically represented on a grid by finite differences or finite elements (Particle-In-Cell, PIC). When simulating large-sized systems, this method encounters performance losses, both locally (intra-CPU) and globally (inter-CPU) because the amount of communicated data increases. Another approach, Particle-In-Fourier (PIF), takes advantage of the anisotrop

Global gradient driven gyrokinetic simulations performed with the Gyrokinetic Electromagnetic Numerical Experiment (GENE) code are used to investigate Tokamak a configuration variable (TCV) plasmas with negative triangularity. Considering limited L-mode pl ...

Modern supercomputer architectures are evolving towards embedding more and more cores per compute node, often making use of accelerators such as GPUs, in which thousands of threads can be executed concurrently. To make legacy codes profit efficiently from such resources usually requires a major refactoring effort. I will present the strategy that we adopted for the production code ORB5, a global gyrokinetic Particle-In-Cell (PIC) code for studying turbulence in tokamak plasmas, developed by many physicists

Using the local (flux-tube) version of the Eulerian code GENE (Jenko et al 2000 Phys. Plasmas 7 1904), gyrokinetic simulations of microturbulence were carried out considering parameters relevant to electron-internal transport barriers (e-ITBs) in the TCV t ...

Following recent observations of unstable Toroidal Alfven Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried o ...

An electron density gradient driven instability identified as the toroidal branch of the universal drift instability is studied using a global gyrokinetic model treating both electrons and ions fully nonadiabatically and valid at all orders in the ratio of ...

In this work, a Fourier solver [B.F. McMillan, S. Jolliet, A. Bottino, P. Angelino, T.M. Tran, L Villard, Comp. Phys. Commun. 181 (2010) 7151 is implemented in the global Eulerian gyrokinetic code GT5D [Y. Idomura, H. Urano, N. Aiba, S. Tokuda, Nucl. Fusio ...

It is believed that low frequency microinstabilities such as ion temperature gradient (ITG) driven modes and trapped electron modes (TEMs) are largely responsible for the experimentally observed anomalous transport via the ion and electron channels in a to ...

In this work, we highlight an issue that may reduce the accuracy of many local nonlinear gyrokinetic simulations – turbulent self-interaction through the parallel boundary condition. Given a sufficiently long parallel correlation length, individual turbule ...

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 ...

Plasma Turbulence studied by means of Correlation-ECE in the TEM domain in TCV Electron temperature fluctuations in the TEM domain have been measured in TCV using the correlation-ECE diagnostics [1]. Significant broadband electron temperature fluctuations are found radially extending between 0.3

In this work, role of nonadiabatic untrapped electrons in the context of a global ion temperature gradient driven mode has been investigated. In past studies, untrapped electrons have been assumed to be able to respond "instantaneously" to a disturbance. I ...

Strong E × B plasma flow shear is beneficial for reducing turbulent transport. However, traditional methods of driving flow shear do not scale well to large devices such as future fusion power plants. In this paper, we use a large number of nonlinear gyrokinetic simulations to study a novel approach to increase flow shear: decreasing the momentum diffusivity to make the plasma "easier to push". We first use an idealized circular geometry and find that one can obtain low momentum diffusivity at tight aspect

A solution to the full two-dimensional eigenvalue problem of electrostatic microinstabilities in a tokamak plasma is presented in the framework of gyrokinetic theory. The approach is the generalization of methods previously developed for a cylindrical system [S. Brunner and J. Vaclavik, Phys. Plasmas 5, 365 (1998)]. By solving the spectral problem in a special Fourier space adapted to the curved geometry, orbit width as well as Larmor radius can be kept to all orders. For a first numerical implementation, a

The frequency dependence (13.56-70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinan

Transport analyses using first principle turbulence codes as well as 1½-D transport codes often study transport properties between the plasma axis and a normalized radius around 0.8. In this region, heat transport shows significant stiffness properties leading to R/LTe values that are relatively independent of auxiliary input power. In this work, we study experimentally in the TCV tokamak, the transport properties of the edge region, close to the last closed flux surface, namely between ρV=0.8 and 1 (ρψ≥0.9

Electron-scale micro-turbulence driven by the electron temperature gradient (ETG) instability has recently been shown to impact the electron heat transport in tokamaks. Given the relevance of these mechanisms for ITER scenarios, a new study has been carrie ...

Stephan Brunner

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Two-dimensional Vlasov simulation of electron plasma wave trapping, wavefront bowing, self-focusing, and sideloss

Tangential phase-contrast imaging for fluctuation measurements in JT–60SA: a conceptual study

Sheath constraints on turbulent magnetised plasmas

The Particle-In-Fourier (PIF) Approach Applied to Gyrokinetic Simulations

Nonlocal effects in negative triangularity TCV plasmas

Porting a Legacy Global Lagrangian PIC Code on Many-Core and GPU-Accelerated Architectures

Non-Linear Gyrokinetic Simulations of Microturbulence in TCV Electron Internal Transport Barriers

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Toroidal Universal Drift Instability: A Global Gyrokinetic Study

Parallel filtering in global gyrokinetic simulations

A comprehensive gyrokinetic description of global electrostatic microinstabilities in a tokamak

Eliminating turbulent self-interaction through the parallel boundary condition in local gyrokinetic simulations

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

Plasma Turbulence studied by means of Correlation-ECE in the TEM domain in TCV

Role of nonadiabatic untrapped electrons in global electrostatic ion temperature gradient driven modes in a tokamak

Physics of the low momentum diffusivity regime in tokamaks and its experimental applicability

Global approach to the spectral problem of microinstabilities in tokamak plasmas using a gyrokinetic model

Sheath impedance effects in very high frequency plasma experiments

On the non-stiffness of edge transport in L-modes

Investigation of the role of electron temperature gradient modes in electron heat transport in TCV plasmas