A seminar led by
Dr. Laurent Lamy, Assistant astronomer at LESIA at the Paris Observatory
entitled :
Studying the magnetospheres of the solar system and beyond using radio observations:
From in situ space exploration to the Square Kilometer Array (SKA).
will be held Tuesday, May 31 at 10:30 a.m. in the Board Room – Department 322 of the PIIM laboratory (St. Jerome Campus)
Abstract: The magnetospheres of the planets of the solar system are the seat of intense electromagnetic auroral radiation, observed in various spectral ranges, and in particular in low frequency radio (long wavelengths). Several decades of in situ (from Viking/Voyager to Cassini/Juno) and ground-based (such as the Nançay Decametric Network) radio observations of these objects have allowed us to understand the diagnosis that these observations bring for the study and characterization of planetary magnetospheres. They also revealed a common non-thermal emission mechanism, the electron Maser Cyclotron instability, which allows to amplify very efficiently circularly polarized radio waves from electrons accelerated to kinetic energies of a few keV in plasma sparse and strongly magnetized regions. The advent of giant radio telescopes (such as LOFAR, NenuFAR and soon SKA) promises to considerably enlarge the number of detected magnetospheres, with already a few tens of cases of radio emissions from stars, brown dwarfs and possible exoplanets identified.
Bio : Laurent Lamy is an assistant astronomer at the Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA) of Paris Observatory, seconded to the Laboratoire d’Astrophysique de Marseille (LAM). He is a specialist in the comparative study of space plasmas, planetary magnetospheres and auroral processes. He is scientifically involved in various space radio instruments (Cassini, Juno, JUICE) and ground-based instruments (Nançay telescopes, NenuFAR, Réseau décamétrique, LOFAR, SKA).
The seminar will be preceded by a welcome breakfast at 10:00 am.
Abstract: Spatial diffusion of particles in periodic potential models has provided a good framework for studying the role of chaos in global properties of classical systems. A bidimensional “soft” billiard, which is a classical dynamics derived from an optical lattice hamiltonian system, is used to study diffusion transitions under variation of the control parameters. Sudden transitions between normal and ballistic regimes are found and characterized by inspection of topological changes in phase-space. Transitions correlated with increases in global stability area are shown to occur for energy levels where local maxima points become accessible, deviating trajectories approaching them. These instabilities promote a slowing down of the dynamics and an island myriad bifurcation phenomenon (fig 1-B), along with the suppression of long flights within the lattice. Other diffusion regime variations occurring within small intervals of control parameters are shown to be related to the emergence of a set of orbits with long flights, thus altering the total average displacement for long integration times but without global changes in phase-space.
Short bio:
Matheus Lazarotto is
a PhD student at University of S
ão Paulo (Brazil). He is currently visiting PIIM laboratory (Turbulence Plasma team) for 6 months in the framework of the
CAPES/COFECUB program. With a bachelor background in physics and a master’s in molecular dynamics, he currently works with dynamical hamiltonian systems and chaos, particularly with low-dimensional chaotic models in lattice potentials and wave-particle interaction.
Health conditions permitting, the talk will be preceded by a welcome breakfast at 10:15.
Abstract: The transport of energetic particles (EP) in tokamaks constitutes a fundamental problem for burning plasmas, as it can adversely impact the plasma energy balance and threaten the integrity of the fusion device. First-principles simulations of EP transport are therefore critical to elaborate burning plasmas scenarii that can mitigate these effects. However to be realistic, first-principles simulations need to incorporate a wide range of physical scales, as EP transport can arise from microturbulence, Alfvén eigenmodes, global MHD instabilities, and from the nonlinear interactions between each of these transport channels.
The global gyrokinetic code (GTC) has been previously used for the study of EP transport induced by microturbulence and Alfvén eigenmodes. GTC is now applied for the simulations of macroscopic MHD modes in DIII-D and ITER plasmas. The code capability at simulating current-driven MHD modes is first demonstrated by performing averification and linear validation of the internal kink instability in DIII-D plasmas with gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1/K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from a DIII-D discharge, these codes exhibit excellent agreements for the growth rate and mode structure of the n=1 internal kink mode in the ideal MHD limit by suppressing all kinetic effects. The simulated radial mode structures, obtained from linear simulations, are in reasonable agreement with the normalised electron cyclotron emission measurement after adjusting, within the experimental uncertainty, the safety factor q=1 flux-surface location in the equilibrium reconstruction. Furthermore, kinetic effects of thermal ions are found to decrease the kink growth rate in kinetic-MHD simulations, but increase the kink growth rate in gyrokinetic simulations, due to the additional drive of the ion temperature gradient and parallel electric field.
The validated MHD capability of GTC is then applied to study the fishbone instability in ITER plasmas. A prefusion ITER baseline scenario is considered in this analysis as part of the ITPA-EP activities. An associated DIII-D discharge is selected for experimental comparison of the simulations results, the selection being made in terms of similar q profile, normalized beta and plasmas profiles. The selected discharge exhibits clear n=1 fishbone bursts driven by fast ions from neutral beam injection (NBI). Fishbone modes are found to be triggered by energetic particles for both the DIII-D and ITER configurations, with similar mode structures. Preliminary nonlinear GTC results recover mode frequency down-chirping associated with resonant EP transport, that are key signatures of the fishbone instability.
Short bio: Dr. Guillaume Brochard is a post-doctoral fellow at the University of California, Irvine, in the team of Prof. Zhihong Lin. His research interests include energetic particle transport and instabilities in tokamak plasmas. He completed his PhD at CEA Cadarache / CPHT Ecole Polytechnique under the supervision of Dr. Hinrich Lütjens and Dr. Rémi Dumont.
Health conditions permitting, the talk will be preceded by a welcome breakfast at 10:00.
A seminar given by
Dr. Alan Durif
IRFM (CEA-Cadarache)
titled
Tungsten damage assessment tools for thermonuclear fusion reactor
will take place on
Wednesday, December 1st at 10:30
in the salle du Conseil – service 322 of the PIIM laboratory (Campus St. Jerome)
Abstract: One of the R&D focus in the European fusion energy program is to establish a physical and technological basis for reliable power exhaust during entire operational situations of a DEMOstrational power plant [1]. The tungsten divertor targets are the most thermally loaded in-vessel components in fusion reactor. Following the design adopted for ITER, the baseline PFC (Plasma Facing Component) for DEMO divertor is made of tungsten as armor material [1]. The PFCs lifetime is affected by material degradations under the different loadings including HHF (High Heat Flux) and neutron irradiation [2]. It has been reported a loss of mechanical properties due to recrystallization and embrittlement due to neutron irradiation. Latest finite elements modeling developments allow to predict component lifetime under HHF loading taking into account the influence of neutron irradiation and the progressive mechanical properties change due to recrystallization [3].
References
[1] G. Federici et al., Fusion Eng. Des., vol. 109–111, no. 2016
[2] S. Nogami, et al, Journal of Nuclear Material 543 (2021) 152506
[3] A.Durif et al, International Journal of Fracture, 2021.
The talk will be preceded by a welcome breakfast at 10:00.
