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Direct observation of a "devil's staircase'' in wave-particle interaction

Fabrice Doveil·Alessandro Macor·Yves Elskens
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Abstract

We report the experimental observation of a "devil's staircase'' in a time dependent system considered as a paradigm for the transition to large scale chaos in the universality class of hamiltonian systems. A test electron beam is used to observe its non-self-consistent interaction with externally excited wave(s) in a Travelling Wave Tube (TWT). A trochoidal energy analyzer records the beam energy distribution at the output of the interaction line. An arbitrary waveform generator is used to launch a prescribed spectrum of waves along the slow wave structure (a 4 m long helix) of the TWT. The resonant velocity domain associated to a single wave is observed, as well as the transition to large scale chaos when the resonant domains of two waves and their secondary resonances overlap. This transition exhibits a "devil's staircase'' behavior for increasing excitation amplitude, due to the nonlinear forcing by the second wave on the pendulum-like motion of a charged particle in one electrostatic wave.

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Fabrice Doveil, Alessandro Macor, Yves Elskens. 2006-04-20. Direct observation of a "devil's staircase'' in wave-particle interaction. https://doi.org/10.1063/1.2216850

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