arXiv subjects

C. Evain

Publications and source records attributed to C. Evain.

5 recordsLinked to original sources

arXiv2026

Synchronization of Synchrotron Radiation Bursts during a spatio-temporal Instability in accelerator-Based source

Synchronization is a fundamental phenomenon in dynamical systems, occurring in a wide range of contexts such as mechanical, chemical, biological, and social systems. In this work, we explore a novel manifestation of synchronization in accelerator-based light sources, specifically in storage rings where relativistic electron bunches circulate and emit synchrotron radiation, used for user experiments. In such systems, a systematic spatio-temporal instability arises when the bunch contains a large number of electrons. This instability is characterized by the spontaneous formation of microstructures within the bunch, which appear with a bursting behavior. We demonstrate that these bursting events can be synchronized with an external sinusoidal signal by modulating the electric field in a radiofrequency (RF) cavity. This external modulation induces typical synchronization features such as Arnold tongues at fundamental, harmonic, and subharmonic frequencies of the natural bursting rate, as well as phase-slip phenomena near the synchronization threshold. The synchronization mechanism is analyzed using numerical simulations based on the Vlasov-Fokker-Planck equation, and a proof-of-principle experiment is conducted at the SOLEIL synchrotron facility.

nlin.AO↗

arXiv2020

Topological swing in Bloch oscillations

We report new oscillations of wavepackets in quantum walks subjected to electric fields, that decorate the usual Bloch-Zener oscillations of insulators. The number of turning points (or sub-oscillations) within one Bloch period of these oscillations is found to be governed by the winding of the quasienergy spectrum. Thus, this provides a new physical manifestation of a topological property of periodically driven systems that can be probed experimentally. Our model, based on an oriented scattering network, is readily implementable in photonic and cold atomic setups.

cond-mat.mes-hall↗

arXiv2018

Coherent Terahertz synchrotron radiation mastered by controlling the irregular dynamics of relativistic electron bunches

Spontaneous formation of spatial structures (patterns) occurs in various contexts, ranging from sand dunes and rogue wave formation, to traffic jams. These last decades, very practical reasons also led to studies of pattern formation in relativistic electron bunches used in synchrotron radiation light sources. As the main motivation, the patterns which spontaneously appear during an instability increase the terahertz radiation power by factors exceeding 10000. However the irregularity of these patterns largely prevented applications of this powerful source. Here we show how to make the spatio-temporal patterns regular (and thus the emitted THz power) using a point of view borrowed from chaos control theory. Mathematically, regular unstable solutions are expected to coexist with the undesired irregular solutions, and may thus be controllable using feedback control. We demonstrate the stabilization of such regular solutions in the Synchrotron SOLEIL storage ring. Operation of these "controlled unstable solutions" enables new designs of high charge and stable synchrotron radiation sources.

physics.acc-ph↗

arXiv2016

Direct observation of spatio-temporal dynamics of short electron bunches in storage rings

In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of Terahertz Coherent Synchrotron Radiation (THz CSR). Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses (a broadband Terahertz comb) stemming from the shortness of the electron bunches. Above this threshold, a large part of the emission is dominated by drifting structures, which appear through spontaneous self-organization. These challenging single-shot THz recordings are made possible by using a recently developed photonic time stretch detector with a high sensitivity. The experiment has been realized at the SOLEIL storage ring.

physics.acc-ph↗

arXiv2015

Observing microscopic structures of a relativistic object using a time -stretch strategy

Emission of light by a single electron moving on a curved trajectory (synchrotron radiation) is one of the most well-known fundamental radiation phenomena. However experimental situations are more complex as they involve many electrons, each being exposed to the radiation of its neighbors. This interaction has dramatic consequences, one of the most spectacular being the spontaneous formation of spatial structures inside electrons bunches. This fundamental effect is actively studied as it represents one of the most fundamental limitations in electron accelerators, and at the same time a source of intense terahertz radiation (Coherent Synchrotron Radiation, or CSR). Here we demonstrate the possibility to directly observe the electron bunch microstructures with subpicosecond resolution, in a storage ring accelerator. The principle is to monitor the terahertz pulses emitted by the structures, using a strategy from photonics, time-stretch, consisting in slowing-down the phenomena before recording. This opens the way to unpreceeded possibilities for analyzing and mastering new generation high power coherent synchrotron sources.

physics.acc-ph↗