Alexey Mishchenko | Max Planck Institute for plasma physics (original) (raw)

Papers by Alexey Mishchenko

Journal of Plasma Physics, Jul 31, 2023

In this paper, we summarize our recent work on gyrokinetic applications in electronpositron and n... more In this paper, we summarize our recent work on gyrokinetic applications in electronpositron and non-neutral plasma. The electrostatic stability of electron-positron plasmas was investigated in dipole and slab geometries, with and without ion admixture. The gyrokinetic dispersion relation was derived and, for the slab case, extended to non-neutral plasmas. Here, we further extend the gyrokinetic formulation to the relativistic regime. Electron-positron plasmas are found to be remarkably stable as long as perfect symmetry between the two species prevails, but instabilities appear if this symmetry is broken, for instance by the introduction of impurities or magnetic curvature.

Nuclear Fusion

Global electromagnetic gyrokinetic simulations are performed with the particle-in-cell code ORB5 ... more Global electromagnetic gyrokinetic simulations are performed with the particle-in-cell code ORB5 for an ITER pre-fusion-power-operation plasma scenario, with half-field (2.65 T) and half-current (7.5 MA). We report on a ‘multi-scale‘ analysis of the discharge, considering eigenmodes and instabilities across three scale-lengths (n < 35, 45 < n < 70, n > 100). Although the scenario will nominally have neutral beam heating with particles injected with 1 MeV, Alfvén eigenmodes are investigated in the absence of such source, and reversed shear, toroidal and elliptical Alfvén eigenmodes are found with weak damping for moderately low toroidal mode numbers (10 ⩽ n ⩽ 35). At higher toroidal mode numbers (40 ⩽ n ⩽ 70), unstable Alfvénic modes have been observed close to rational surfaces and are labelled as beta-induced Alfvén eigenmodes (BAEs)/Alfvénic ion temperature gradient modes, since their frequency is associated with the BAE gap and they are driven by the bulk plasma on th...

Simulation of Alfvén eigenmodes in tokamaks and stellarators

Electromagnetic simulations of tokamaks and stellarators

Nonlinear gyrokinetic investigation of the interaction of Alfvén instabilities and energetic-particle driven geodesic acoustic modes

47th EPS Conference on Plasma Physics, 2021

Global gyrokinetic PIC simulations for stellarators and heliotrons with emphasis on experimentally relevant scenarios

Verification of the delta-f kinetic electron physics in XGC

Pullback approach for gyrokinetic electromagnetic simulations

Implementation of the electromagnetic ``pullback transformation scheme'' in the gyrokinetic code XGC

Gyrokinetic investigation of the nonlinear interaction of Alfvénic modes and turbulence A. Bianca... more Gyrokinetic investigation of the nonlinear interaction of Alfvénic modes and turbulence A. Biancalani, A. Bottino, A. di Siena, Ö. Gürcan, T. Hayward-Schneider, F. Jenko, P. Lauber, A. Mishchenko, P. Morel, I. Novikau, F. Vannini, L. Villard, and A. Zocco 1 Max Planck Institute for Plasma Physics, Garching, Germany, 2 The University of Texas at Austin, USA, 3 Laboratoire de Physique des Plasmas / Ecole Polytechnique / CNRS, Palaiseau, France, 4 Max Planck Institute for Plasma Physics, Greifswald, Germany, EPFL-SPC, Lausanne, Switzerland e-mail (speaker): biancalani@ipp.mpg.de

Tokamak plasmas are examples of complex systems where multiple spatial and temporal scales are in... more Tokamak plasmas are examples of complex systems where multiple spatial and temporal scales are intrinsically linked. Microturbulence, meso-scale zonal structures (ZS, like zerofrequency zonal flows and geodesic acoustic modes) and macroscopic MHD instabilities like Alfvénic modes (AM), mutually interact either due to the modification of the equilibrium profiles, or by direct coupling via wave-wave nonlinear interaction. In particular, a strong interest recently raised in understanding the generation of ZS by AM, due to the strong implications in modifying the turbulent transport. The gyrokinetic global particle-in-cell code ORB5 [1, 2] was developed for turbulence studies, extended to its electromagnetic multi-species version, and verified and benchmarked for the linear dynamics of mictroturbulence modes, ZS and AM. The importance of the kinetic electron effects in the ZS dynamics has also been emphasized with ORB5 [3]. Recent simulations with ORB5, have investigated the nonlinear d...

Nuclear Fusion, 2019

The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radiu... more The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of a temperature of with was transiently accomplished, which corresponds to with a peak diamagnetic energy of and volume-averaged normalized plasma pressure . The routine access to high plasma densities was opened w...

Journal of Plasma Physics, 2018

Gyrokinetic stability of plasmas in different magnetic geometries is studied numerically using th... more Gyrokinetic stability of plasmas in different magnetic geometries is studied numerically using the GENE code. We examine the stability of plasmas, varying the mass ratio between the positive and negative charge carriers, from conventional hydrogen plasmas through to electron–positron plasmas. Stability is studied for prescribed temperature and density gradients in different magnetic geometries: (i) An axisymmetric, circular flux surface, low$\unicode[STIX]{x1D6FD}$(tokamak) configuration. (ii) A non-axisymmetric quasi-isodynamic (optimised stellarator) configuration using the geometry of the stellarator Wendelstein 7-X. We also present the analytic theory of trapped particle modes in electron–positron plasmas. We found similar behaviour of the growth rate and real frequency compared to previous studies on the tokamak case. We are able to identify two distinct regimes dominated by modes propagating in the electron diamagnetic direction and modes propagating in the ion/positron diamag...

Physics of Plasmas

Plasma shaping may have a stronger effect on global turbulence in tight-aspect-ratio tokamaks tha... more Plasma shaping may have a stronger effect on global turbulence in tight-aspect-ratio tokamaks than in conventional-aspect-ratio tokamaks due to the higher toroidicity and more acute poloidal asymmetry in the magnetic field. In addition, previous local gyrokinetic studies have shown that it is necessary to include parallel magnetic field perturbations in order to accurately compute growth rates of electromagnetic modes in tight-aspect-ratio tokamaks. In this work, the effects of elongation and triangularity on global, ion-scale, linear electromagnetic modes are studied at National Spherical Torus Experiment (NSTX) aspect ratio and high plasma β using the global gyrokinetic particle-in-cell code XGC. The effects of compressional magnetic perturbations are approximated via a well-known modification to the particle drifts that was developed for flux-tube simulations [Joiner et al., Phys. Plasmas 17, 072104 (2010)], without proof of its validity in a global simulation, with the gyrokinet...

5th Asia Pacific Conference on Plasma Physics (AAPPS-DPP 2020), 2021

Journal of Plasma Physics, 2020

Linear gyrokinetic simulations of magnetically confined electron–positron plasmas are performed f... more Linear gyrokinetic simulations of magnetically confined electron–positron plasmas are performed for the first time in the geometry and parameter regimes likely to be relevant for upcoming laboratory experiments. In such plasmas, the density will be sufficiently small as to render the plasma effectively collisionless. The magnetic field will be very large, meaning that the Debye length will exceed the gyroradius by a few orders of magnitude. We show the results of linear simulations in flux tubes close to the current carrying ring and also in the bulk of the plasma, demonstrating the existence of entropy modes and interchange modes in pair plasmas. We study linear stability and show that in the relevant configurations, almost complete linear stability is attainable in large swathes of parameter space.

Global gyrokinetic multi-model simulations of ITG and Alfvénic modes for tokamaks and the first operational phase of Wendelstein 7-X

Several results from applying the global gyrokinetic particle-in-cell code EUTERPE to tokamak and... more Several results from applying the global gyrokinetic particle-in-cell code EUTERPE to tokamak and stellarator configurations are presented. Linear low-mode-number AITG modes were simulated for an LHD-like equilibrium. Using a Fourier solver approach, long-time fully kinetic runs of damped TAEs could be performed. Super-resolution methods allowed us to accurately resolve the continuous Alfvén spectrum. Results from a hybrid approach (CKA-EUTERPE code), which couples an MHD code with a gyrokinetic code are presented. Although perturbative, it offers a relatively fast way to investigate the destabilisation of Alfvén modes by fast particles. TAE saturation amplitudes and their scaling with collisionality were investigated in a tokamak as well as in Wendelstein 7-X. Also frequency chirping in the non-linear phase of the simulation could be observed. Linear electrostatic gyrokinetic simulations for Wendelstein 7-X and an LHD-like configuration show the influence of a radial neoclassical e...

Plasma Physics and Controlled Fusion, 2021

The nonlinear dynamics of beta-induced Alfvén eigenmodes (BAEs) driven by energetic particles (EP... more The nonlinear dynamics of beta-induced Alfvén eigenmodes (BAEs) driven by energetic particles (EPs) in the presence of ion-temperature-gradient turbulence is investigated, by means of selfconsistent global gyrokinetic simulations and analytical theory. A tokamak magnetic equilibrium with large aspect ratio and reversed shear is considered. A previous study of this configuration has shown that the electron species plays an important role in determining the nonlinear saturation level of a BAE in the absence of turbulence (Biancalani et al 2020 J. Plasma Phys.). Here, we extend the study to a turbulent plasma. The EPs are found modify the heat fluxes by introducing energy at the large spatial scales, mainly at the toroidal mode number of the dominant BAE and its harmonics. In this regime, BAEs are found to carry a strong electron heat flux. The feed-back of the global relaxation of the temperature profiles induced by the BAE, and on the turbulence dynamics, is also discussed.

Physics of Plasmas, 2016

The linear dynamics of Alfvén modes in tokamaks is investigated here by means of the global gyrok... more The linear dynamics of Alfvén modes in tokamaks is investigated here by means of the global gyrokinetic particle-in-cell code NEMORB. The model equations are shown and the local shear Alfvén wave dispersion relation is derived, recovering the continuous spectrum in the incompressible ideal MHD limit. A verification and benchmark analysis is performed for continuum modes in a cylinder and for toroidicity-induced Alfvén Eigenmodes. Modes in a reversed-shear equilibrium are also investigated, and the dependence of the spatial structure in the poloidal plane on the equilibrium parameters is described. In particular, a phase-shift in the poloidal angle is found to be present for modes whose frequency touches the continuum, whereas a radial symmetry is found to be characteristic of modes in the continuum gap.