Timothée NICOLAS

"Chargé de recherche" at CNRS

Research Interests :

Magnetohydrodynamic instabilities, simulation, magnetic reconnection, collisions in plasmas

I am specialized in the simulation of magnetohydrodynamic (MHD) instabilities in fusion plasmas. During my thesis, I used nonlinear MHD simulations to exhibit the particle redistribution mechanisms during the « sawtooth » instability. This mechanisms are qualitatively different from the ones associated with temperature redistribution, although the final result is the same: a significant flattening of core profiles occurs. During my first postdoc at the National Institute for Fusion Science, Japan, I showed that thermal dissipation effects significantly modify the way that interchange instabilities in stellarators react to diamagnetic effects. These dissipation effects are usually neglected, which makes comparison of mode rotation with the experimental observations difficult. During this period, I also learnt a lot about preconditioning MHD’s hyperbolic equations, in particular using multigrid methods. Since my second postdoc at the Swiss Plasma Center, EPFL, I have been working on the implementation of particle-particle collisions in Particle-In-Cell (PIC) codes for plasma simulation. I developed a novel algorithm to treat the collisions, both elegant and robust. I also work on binary collisions and its application to PIC codes.

Thesis

"Transport de particules induit par les dents-de-scie dans les plasmas de tokamak", Soutenue le 9 décembre 2013 au CEA Cadarache
Directeur de thèse : Xavier Garbet

Publications (selection)

T. Nicolas, J.-F. Luciani, H. Lütjens, X. Garbet and J. Graves, A novel approach to ion-ion Langevin self-collisions in particle-in-cell modules applied to hybrid MHDcodes. Plasma Physics and Controlled Fusion 59 (5), 054005 (2017) 

T. Nicolas and K. Ichiguchi. Dissipation and diamagnetic effects on the interchange mode growth rate and rotation in reduced magnetohydrodynamics applied to stellarators, Nuclear Fusion 56, 026008, 2016. 

S. Nishimura, T. Nicolas, X. Du. Effects of trapped energetic ions on the interchange mode. Fusion Engineering and Design 1188–1192 (2016).

K. Toi, S. Ohdachi, R. Ueda, K. Y. Watanabe, T. Nicolas, Y. Suzuki, K. Ogawa, K. Tanaka, Y. Takemura & LHD Experiment Group. Magnetohydrodynamic stability at the edge region in H-mode plasmas with long edge-localized-mode-free phases in the large helical device. Plasma Physics and Controlled Fusion, 58 (9), 094002 (2016).

J.-H. Ahn, X. Garbet, H. Lütjens, A. Marx, T. Nicolas, R. Sabot, J.-F. Luciani, R. Guirlet, O. Février, P. Maget. Non-linear dynamics of compound sawteeth in tokamaks. Physics of Plasmas (1994-present), 23(5), 052509 (2016). 

T. Nicolas, K. Ichiguchi, M. Sato, Y. Todo, Y. Suzuki, A. Ishizawa, S. Sakakibara, Three- Dimensional Numerical Analysis of Ion Diamagnetic E ects on Interchange Mode in Heliotron Plasmas. Plasma and Fusion Research, 10, 3403018, (2015)

K Ichiguchi, Y Suzuki, M Sato, Y Todo, T Nicolas, S Sakakibara, S Ohdachi, Y Narushima and BA Carreras. Three-dimensional MHD analysis of heliotron plasma with RMP. Nucl. Fusion, 55, 7 (2015).

J.P. Graves, M. Lennholm, I.T. Chapman, E. Lerche, M. Reich, B. Alper, V. Bobkov, R. Dumont, J.M. Faustin, P. Jacquet, F. Jaulmes, T. Johnson, D.L. Keeling, L. Yueqiang, T. Nicolas, et al. Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall. Plasma Physics and Controlled Fusion, 57, 1, page 014033 (2015).

T. Nicolas, H. Lütjens, J.-F. Luciani, X. Garbet, R. Sabot, Impurity behaviour during sawtooth activity in tokamak plasmas, Physics of plasmas, 21 (1), 012507 (2014).

T. Nicolas, R. Sabot, X. Garbet, H. Lütjens, J.-F. Luciani, A. Sirinelli, J. Decker, A. Merle and JET-EFDA Contributors, Particle ow during sawtooth reconnection: numerical simulations of experimental observations, Plasma Fusion Res. 8, 2402131 (2013)

T. Nicolas, R. Sabot, X. Garbet, H. Lütjens, J.-F. Luciani, Z. Guimaraes-Filho J. Decker, and A. Merle, Non-linear magnetohydrodynamic simulations of density evolution in Tore Supra sawtoothing plasmas, Physics of Plasmas, 19 (11), 112305 (2012)