Séminaire LJKModèles et Algorithmes Déterministes: MODANT

Le Mercredi 17 Mars 2010 à 10h30 en Salle 1  Tour IRMA

Séminaire de Mr Fabrice DOVEIL (Université de Provence)

Dynamique hamiltonienne d'électrons dans un tube à ondes progressives, 1/2

Résumé:

1. Observation and Control of Hamiltonian Chaos in WaveParticle Interaction
Waveparticle interactions are central in plasma physics. The paradigm beamplasma system can be advantageously replaced by a traveling wave tube (TWT) to allow their study in a much less noisy environment. This led to detailed analysis of the selfconsistent interaction between unstable waves and an either cold [1] or warm [2] electron beam. More recently a test cold beam has been used to observe its interaction with externally excited wave(s). This allowed observing the main features of Hamiltonian chaos and testing a new method to efficiently channel chaotic transport in phase space. The successive topics will be: presentation of the TWT and its connection to plasma physics, resonant interaction of a charged particle in electrostatic waves, observation of particle trapping and transition to chaos, test of control of chaos.
The velocity distribution function of the electron beam is recorded with a trochoidal energy analyzer at the output of the TWT. An arbitrary waveform generator is used to launch a prescribed spectrum of waves along the 4m long helix of the TWT. The nonlinear synchronization of particles by a single wave responsible for Landau damping is observed [3]. We explore the resonant velocity domain associated with a single wave as well as the transition to large scale chaos when the resonant domains of two waves and their secondary resonances overlap [4]. This transition exhibits a devils staircase behavior when increasing the excitation level in agreement with numerical simulation [5].
A new strategy for control of chaos by building barriers of transport in phase space as well as its robustness is successfully tested [6]. The underlying concepts extend far beyond the field of electron devices and plasma physics [7].
References :
[1] Destruction of trapping oscillations, G. Dimonte and J.H. Malmberg, Phys. Fluids, 21, p 11881206, (1978)
[2] Experimental test of quasilinear theory, S.I. Tsunoda, F. Doveil and J.H. Malmberg, Phys. Fluids, B3, p 27472757, (1991)
[3] Experimental observation of nonlinear synchronization due to a single wave, F. Doveil, D.F.Escande and A. Macor, Phys. Rev. Lett, 94, p 085003, (2005)
[4] Experimental observation of resonance overlap responsible for Hamiltonian chaos, F. Doveil, Kh. Auhmani, A. Macor, and D. Guyomarch, Phys. Plasmas, 12, p 010702, (2005)
[5] Direct observation of a devils staircase in waveparticle interaction, F. Doveil, A. Macor and Y.Elskens, Chaos, 16, p 033103, (2006)
[6] Channelling chaotic transport in a waveparticle experiment, A. Macor, F. Doveil, C. Chandre, G.Ciraolo, R. Lima and M. Vittot, Eur. Phys. J. D, 41, p 519530, 2007)
[7] Observation of Hamiltonian chaos in waveparticle interaction, F. Doveil, A. Macor and A. Aissi, Celest. Mech. Dyn. Astr., 102, p 255272, (2008)
