Benoît Labit

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Scientist

benoit.labit@epfl.ch +41 21 693 45 62

Citizenship : French

Birth date : 22.06.1975

EPFL SB SPC-TCV
PPB 118 (Bâtiment PPB)
Station 13
CH-1015 Lausanne

+41 21 693 45 62
Office: PPB 118
EPFL > SB > SPC > SPC-TCV

Web site: Web site: https://spc.epfl.ch/

+41 21 693 45 62
Office: PPB 118
EPFL > E > E-DOC > EDPY-ENS

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Administrative data

Fields of expertise

H-mode physics
Plasma turbulence
Experimental physics
Numerical simulations

Current work

Deputy Task Force Leader for the MST1 EUROfusion Workpackage

PhD Thesis

Tokamak electron heat transport by direct numerical simulation of small scale turbulence

In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure, β or the normalized Larmor radius, ρ*.

The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters β and ρ*. The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve.

From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values.

The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkawa's formula. On the other hand, the crucial role of the electron normalized Larmor has been emphasized: the confinement time is inverse proportional to this parameter. Finally, the low dependence of turbulent transport with the magnetic shear and the inverse aspect ratio is also reported.

Although the transport level observed in the simulations is low compared to the experiments, we have tried a direct confrontation with Tore Supra results. This tokamak is well designed to study the electron heat transport. Keeping most of the parameters from a well referenced Tore Supra shot, the nonlinear simulation gives a threshold quite close to the experimental one. The observed turbulent conductivity is a factor fifty lower than the experimental one. An important parameter can not be matched: the normalized Larmor radius, ρ*.

This limitation has to be overcome in order to confirm this results. Finally, a rigorous confrontation between this result and gyrokinetic simulations has to conclude that the ETG instability cannot describe electron heat losses in tokamaks.

Keywords: thermonuclear fusion, tokamak, plasma, ETG turbulence, numerical simulations

Education

Docteur es Sciences

mention Rayonnement et Plasmas

Universit� de Provence Aix-Marseille I

22.10.2002

Licence et Maitrise de Physique

Universit� Paul Sabatier Toulouse III

Publications

Infoscience publications

201311

* Nitrogen-seeded divertor detachment in TCV L-mode plasmas

O. Fevrier; C. Theiler; J. R. Harrison; C. K. Tsui; K. Verhaegh et al.

Plasma Physics And Controlled Fusion

2020-03-01

DOI : 10.1088/1361-6587/ab6b00

Benoît Labit

Scientist

Fields of expertise

Current work

PhD Thesis

Education

Publications

Infoscience publications

201311

* Nitrogen-seeded divertor detachment in TCV L-mode plasmas

* Pedestal structure, stability and scalings in JET-ILW: the EUROfusion JET-ILW pedestal database

* Scrape-off layer transport and filament characteristics in high-density tokamak regimes

* Overview of physics studies on ASDEX Upgrade

* Experimental implementation of a real-time power flux estimator for the ITER first wall on the TCV tokamak

* Status, scientific results and technical improvements of the NBH on TCV tokamak

* Langmuir probe electronics upgrade on the tokamak a configuration variable

* Role of the pedestal position on the pedestal performance in AUG, JET-ILW and TCV and implications for ITER

* Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments

* ELM-induced cold pulse propagation in ASDEX Upgrade

* Conduction-based model of the Scrape-Off Layer power sharing between inner and outer divertor in diverted low-density tokamak plasmas

* Real time magnetic control of the snowflake plasma configuration in the TCV tokamak

* An improved understanding of the roles of atomic processes and power balance in divertor target ion current loss during detachment

* Scrape Off Layer (SOL) transport and filamentary characteristics in high density tokamak regimes

* Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond

* A locked mode indicator for disruption prediction on JET and ASDEX upgrade

* A Variable Structure Control Scheme Proposal for the Tokamak a Configuration Variable

* Progress toward divertor detachment on TCV within H-mode operating parameters

* Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade

* Application of a two-fluid two-point model to SolEdge2D-EIRENE simulations of TCV H-mode plasma

* The effect of the secondary x-point on the scrape-off layer transport in the TCV snowflake minus divertor

* Millimeter-wave beam scattering by edge-plasma density fluctuations in TCV

* Pedestal structure and energy confinement studies on TCV

* The effect of the secondary x-point on the scrape-off layer transport in the TCV snowflake minus divertor

* Disruption avoidance through the prevention of NTM destabilization in TCV

* Parameter dependences of small edge localized modes (ELMs)

* Fluctuation characteristics of the TCV snowflake divertor measured with high speed visible imaging

* Filamentary velocity scaling validation in the TCV tokamak

* Impurity seeding for suppression of the near scrape-off layer heat flux feature in tokamak limited plasmas

* Analysis of wall-embedded Langmuir probe signals in different conditions on the Tokamak à Configuration Variable

* Dependence of the L-Mode scrape-off layer power fall-off length on the upper triangularity in TCV

* Experimental observations of modes with geodesic acoustic character from the core to the edge in the TCV tokamak

* Divertor power load studies for attached L-mode single-null plasmas in TCV

* Detachment evolution on the TCV tokamak

* TCV experiments towards the development of a plasma exhaust solution

* TCV divertor upgrade for alternative magnetic configurations

* Effect of plasma geometry on divertor heat flux spreading: MONALISA simulations and experimental results from TCV

* Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution

* Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV

* Exploring drift effects in TCV single-null plasmas with the UEDGE code

* Understanding and suppressing the near Scrape-Oﬀ Layer heat flux feature in inboard-limited plasmas in TCV

* Spectroscopic investigations of divertor detachment in TCV

* Poloidal asymmetry in the narrow heat flux feature in the TCV scrape-off layer

* Overview of the TCV tokamak program: scientific progress and facility upgrades

* Blob properties in full-turbulence simulations of the TCV scrape-off layer

* Non-linear simulations of the TCV Scrape-Off Layer

* Results from recent detachment experiments in alternative divertor configurations on TCV

* Numerical study of potential heat flux mitigation effects in the TCV snowflake divertor

* Enhanced (E)over-right-arrow x (B)over-right-arrow drift effects in the TCV snowflake divertor

* Experimental investigation of neon seeding in the snowflake configuration in TCV

* X-Point-Position-Dependent Intrinsic Toroidal Rotation in the Edge of TCV

* X-point Position Dependence of Edge Intrinsic Toroidal Rotation on TCV

* Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

* Heat loads in inboard limited L-mode plasmas in TCV

* Impact of a narrow limiter SOL heat flux channel on the ITER first wall panel shaping

* High density experiments in TCV ohmically heated and L-mode plasmas

* Threshold power for the transition into H-mode for H, D, and He plasmas in TCV

* Power exhaust in the snowflake divertor for L- and H-mode TCV tokamak plasmas

* First EMC3-Eirene simulations of the TCV snowflake divertor

* Theory-based scaling of the SOL width in circular limited tokamak plasmas

* Plasma radiation dynamics with the upgraded Absolute Extreme Ultraviolet tomographical system in the Tokamak a Configuration Variable

* Bifurcated Helical Core Equilibrium States in Tokamaks

* Recent TCV results – innovative plasma shaping to improve plasma properties and insight

* Dependence of L-mode confinement on the electron cyclotron power deposition profile in the TCV tokamak

* Three-Dimensional Imaging of a Radially Propagating Plasma Blob Using Conditional Sampling Techniques

* Blob motion and control in simple magnetized plasmas

* Blob-induced toroidal momentum transport in simple magnetized plasmas

* Electrostatic instabilities, turbulence and fast ion interactions in the TORPEX device

* "Snowflake" H Mode in a Tokamak Plasma

* Observation of a critical pressure gradient for the stabilization of interchange modes in simple magnetized toroidal plasmas

* Cross-field plasma blob motion in an open magnetic field line configuration