| Paper | Title | Page |
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| MOPPH022 | Control of the Intensity of a Wave Interacting with Charged Particles | 83 |
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The interaction between a wave and a bunch of charged particles is encountered in many branches of applied physics ranging from particle accelerators to laser physics (Free Electron Laser). Generically, this self-consistent interaction leads to an exponential increase of the intensity of the wave, followed by an oscillating saturation. It is an interesting problem to regularize the saturated dynamics and thus improve the performance of the device. The aim of this paper is to show that it is possible to influence by external perturbation the dynamics of the particles in order to enhance the stability of the system resulting in a reduction of the oscillations of the waves. We apply a Hamiltonian control technique based on a small and apt modification of the potential to recreate or break up invariant (KAM) tori in phase space. We show that an appropriate tuning of the control parameters is able to reduce by an order of magnitude the amplitude of the oscillations without affecting the total power of the wave. This technique has been successfully implemented on a Travelling Wave Tube in the test-particle regime*.
* C. Chandre et al., Phys. Rev. Lett. 94, 074101 (2005) |
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| MOPPH025 | Free Electron Laser as Paradigmatic Example of Systems with Long-Range Interactions | 87 |
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| Long range interactions are such that the two-body interaction potential decreases at large distance with a power which is smaller or equal to the space dimension. Examples include gravitational forces, unshielded Coulombic interaction. In presence of long-range interactions, physics is very peculiar and a wide range of striking phenomena appears. In particular energy is non additive, hence the system under scrutiny cannot be divided into independent macroscopic parts, as it is usually the case for short-range interactions. These unexpected features are systematically detected, independently of the specific nature of the long-range interactions involved. FEL are one of the most interesting examples of systems with long-range interactions, where the interplay between collective (wave) and individual (particles) degrees of freedom is well known to be central and, in this respect, provides a unique experimental ground to investigate such universal pecularities. In this presentation I will review the main characteristics of such systems and dicuss the statistical theory of the Vlasov equation, a wide general approach that enables to analytically investigate the laser saturated regime. | ||
| MOPPH031 | The Saturated Regime of a Seeded Single-Pass Free Electron Laser: a Theoretical Investigation through the Statistical Mechanics of the Vlasov Equation | 103 |
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| The quasi-stationary state characterizing the saturation of a single-pass free-electron laser is governed by the Vlasov equation obtained by performing the continuum limit of the Colson-Bonifacio model. By means of a statistical treatment, this approach allows to predict analytically the saturated laser intensity as well as the final electron-beam energy distribution. In this paper we consider the case of coherent harmonic generation obtained from a seeded free-electron laser and present predictions for the first stage of the project FERMI at Elettra project at Sincrotrone Trieste. | ||
| TUPPH020 | Dynamics Control of the Elettra Storage Ring Free-Electron Laser with Digital Feedbacks | 356 |
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| The laser dynamics of a storage-ring free-electron laser (FEL) has two main sources of instabilities. First of all, as it is known, dynamical instabilities are developed as the FEL is moved away from the exact tuning between the period of the electron bunch(es) circulating into the ring and that of the photon pulse stored in the optical cavity. In addition, external (low-frequency) noise sources have a strong influence on the dynamical behaviour of the system and can perturb its dynamic. Different feedback techniques have been proposed in order to control dynamical instabilities and stabilize the FEL output. We present here a numerical and experimental investigation on the control of the Elettra SRFEL dynamics using the simultaneous combination of different feedbacks techniques that have been experimentally implemented by means of a Field ProgrammableGate Aarray (FPGA). |