Publications by Stephan Brunner

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We consider the communication costs of gyrokinetic plasma physics simulations running at large scale. For this we apply virtual decompositions of the toroidal domain in three dimensions and additional domain cloning to existing simulations done with the OR ...

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 ...

Research on the Tokamak à Configuration Variable (TCV) addresses a wide range of key questions relevant to ITER and future fusion power plants. Over the past two years, highly productive experimental campaigns have led to major advances across several areas: the ITER baseline scenario; pedestal properties in low-collisionality, peeling-limited conditions; and the development of high-

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, non-inductive regimes. Alternative high-confinement scenarios have likewise received significant attention, with re

Gyrokinetic simulations are computationally extremely demanding due to the high dimensionality of the physical phase space and the interplay between plasma particles and electromagnetic fields. It is thus essential to make full use of the available numerical resources to be able to simulate more complex physical problems. With the aim of optimizing the gyrokinetic Particle-In-Cell code ORB5 towards exascale computing, a particle sorting method is implemented to increase data locality. Furthermore, different

This work reports on the development and numerical implementation of the linear electromagnetic gyrokinetic (GK) model in a tokamak flux-tube geometry using a moment approach based on the expansion of the perturbed distribution function on a velocity-space ...

Microturbulence can produce stationary fine-scale radial corrugations on the plasma density and temperature gradients in magnetic confinement fusion devices. We study the effect of these corrugations, focusing on electron temperature gradient (ETG) transport in the tokamak pedestal, and report three main findings. 1) In the presence of a sinusoidal background temperature gradient corrugation, each ETG mode splits into three distinct eigenvalues, with one being the original, one being more unstable and one b

A Phase-contrast imaging (PCI) diagnostic provides measurements of line-integrated electron density fluctuations. Localisation along the laser beam path can be achieved with a spatial filter that selects the wave-vector directions of the fluctuations contr ...

The tokamak a configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019-20 campaign its c ...

Nonlinear, kinetic simulations of stimulated Raman scattering (SRS) under laser-fusion conditions present a bursting behavior. Different explanations for this regime have been given in previous studies: saturation of SRS by increased nonlinear Landau damping [K. Estabrook et al., Phys. Fluids B 1, 1282 (1989)], and detuning due to the nonlinear frequency shift of the plasma wave [H. X. Vu et al., Phys. Rev. Lett. 86, 4306 (2001)]. Another mechanism, also assigning a key role to the trapped electrons is prop

A new three-dimensional code, VENUS+delta f, for neoclassical transport calculations in nonaxisymmetric toroidal systems is presented. Numerical drift orbits from the original VENUS code and the delta f method developed for tokamak transport calculations a ...

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 ...

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 ...

For self-consistent ICRF heating simulations, four codes have been coupled: VMEC[1] provides a fully shaped, anisotropic 3D MHD equilibrium (bi- Maxwellian distribution function), transferred to Boozer coordinates by TERPSICHORE[2]. The full-wave code LEMan[3,4] provides the IC wave field, power deposition and wave numbers (new anisotropic dielectric tensor and upshifted k). Finally, VENUS[5,6] computes the evolution of the distribution function due to ICRF heating and Coulomb collisions on the background t

In this article an approximated version of the multi-species, non-linear Coulomb collision operator is derived via the use of a truncated moment expansion of the distribution function to compute the Rosenbluth potentials. The evolution of the distribution ...

In the scope of the study of low-frequency electrostatic microinstabilities in tokamak plasmas, attention has been focused on the effect of trapped ions. The ballooning transform has been applied to the gyrokinetic equation, for the case of a large aspect ratio plasma with circular magnetic surfaces. A new eigenvalue code has been developed to solve the resulting integral equation, for the case of adiabatic electrons and full ion dynamics, thus taking into account both circulating and trapped ions. The goal

We present a fully-global linear gyrokinetic simulation code (GYGLES) aimed at describing the unstable spectrum of the ion-temperature-gradient modes in toroidal geometry. We formulate the Particle-In-Cell method with finite elements defined in magnetic coordinates, which provides excellent numerical convergence properties. The poloidal mode structure corresponding to k(parallel to) = 0 is extracted without approximation from the equations, which reduces drastically the numerical resolution needed. The code

An analytical 1D model based on the WKB approximation is used to study the properties of a short pulse reflectometry diagnostic in a magnetic fusion device. Expressions linking the pulse delay with the parameters of the turbulence near the cut-off layer ar ...

The effect of plasma shape on confinement has been experimentally explored in the TCV tokamak revealing that the core electron heat transport is significantly reduced by a negative triangularity configuration, which could indicate a (partial) stabilization ...

In this work, we modify the standard flux tube simulation domain to include arbitrary ion gyroradius-scale variation in the radial profile of the safety factor. To determine how to appropriately include such a modification, we add a strong ion gyroradius-s ...

The global stability of toroidicity induced Alfven eigenmodes (TAEs) in the presence of fast ions in realistic tokamak fusion-grade plasmas is analysed with a global, perturbative approach. Volume averaged fast particle betas for marginal stability are obtained and analysed for a wide range of plasma parameters such as the fast ion radial density profile width, the ratio of birth velocity to the Alfven velocity on axis and the bulk plasma bets. There is evidence of different stability behaviour of two types

Stephan Brunner

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Prediction of the Inter-Node Communication Costs of a New Gyrokinetic Code with Toroidal Domain

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

Progress and innovations in the TCV tokamak research programme

Hybrid OpenMP/MPI parallelization of the charge deposition step in the global gyrokinetic Particle-In-Cell code ORB5

Moment-based approach to the flux-tube linear gyrokinetic model

Turbulence Saturation Via Fine-scale Profile Shearing in Fusion Plasmas

A synthetic phase-contrast imaging diagnostic with spatial filtering for gyrokinetic simulations

Overview of the TCV tokamak experimental programme

Trapped-particle instability leading to bursting in stimulated Raman scattering simulations

Venus plus delta f: A bootstrap current calculation module for 3-D configurations

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

Linear scattering theory of short-pulse reflectometry

Self-consistent ICRF simulations in fully shaped anisotropic plasmas

Moment approach of the multi-species non-linear Coulomb collision operator adapted to particle-in-cell codes

Applicability of the ballooning transform to trapped ion modes

Finite element approach to global gyrokinetic Particle-In-Cell simulations using magnetic coordinates

A method for density fluctuation measurements using pulse reflectometry

The effect of plasma triangularity on turbulent transport:modelling TCV experiments by linear and non linear gyrokinetic simulations

Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear

Global Marginal Stability of Taes in the Presence of Fast Ions