IPM, Tehran
AUT, Tehran
Università di Firenze, Florence
CNRS/CPT, Marseille
* C. Chandre et al., Phys. Rev. Lett. 94, 074101 (2005)
FZR, Dresden
*Submitted as a poster to the FEL 2006 conference.
LBNL, Berkeley, California
RRCAT, Indore (M. P.)
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| MOPPH016 | Mode Couplings in a Raman Free-Electron-Laser with Ion-Channel Guiding | electron, wiggler, space-charge, coupling | 75 | ||||||
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The free-electron laser (FEL) theory in the collective or Raman regime relies on the unstable coupling between the radiation and the negative-energy space-charge wave. Due to the high density and low energy of electron beam a focusing mechanism like an axial magnetic field is usually required to guide the beam. We have shown in our previous study that, in addition to the above coupling that constitutes the regular FEL resonance, there are other unstable coupled-mode structures in the group II orbits. In the present analysis we are studying the mode-couplings when the electron beam is guided by an ion-channel. Using fluid model, a general dispersion relation of a FEL with a one-dimensional helical wiggler and an ion-channel guiding is derived. A numerical analysis of the general dispersion relation will be used to study interactions among all possible waves. In group II orbits, with relatively large wiggler induced velocities, new couplings between the negative and positive-energy space-charge waves as well as between the right and left circularly polarized electromagnetic waves are expected to be found. These instabilities are distinct from the usual FEL resonance.
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| MOPPH022 | Control of the Intensity of a Wave Interacting with Charged Particles | controls, laser, electron, resonance | 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*.
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* C. Chandre et al., Phys. Rev. Lett. 94, 074101 (2005) |
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| TUPPH015 | Remote Controlled IR-Diagnostic Station for the FEL at Rossendorf | diagnostics, laser, radiation, electron | 341 | ||||||
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The remote controlled diagnostic station delivers a small amount of the IR radiation by means of a system of relocatable mirrors and beam splitters to the spectrometer and to various power detectors working in different power ranges. Furthermore, a long wavelength MCT detector is integrated in the diagnostic station for gain and loss measurement in the whole wavelength range of the U27-FEL. The average radiation power available for the users can be reduced by a remote controlled attenuator. To characterize the optical micropulse duration we have built a non-collinear background-free autocorrelator as a part of the diagnostic station. By using a CdTe single-crystal for second-harmonic generation a broad wavelength coverage is obtained. Certain experiments require high pulse energies but moderate or low average power. For such experiments the repetition rate of the Rossendorf FEL can be reduced from 13 MHz to 1 kHz, in the future also to 1 Hz, by a semiconductor plasma switch excited with a synchronized Nd:YAG amplifier. This system is under commissioning and we will report on first results*.
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*Submitted as a poster to the FEL 2006 conference. |
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| TUPPH055 | A Design for an XUV FEL Driven by the Laser-Plasma Accelerator at the LBNL LOASIS Facility | electron, undulator, laser, radiation | 455 | ||||||
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We present a design for a compact FEL source of ultra-fast, high-peak flux, soft x-ray pulses employing a high-current, GeV-energy electron beam from the existing laser-plasma accelerator at LBNL's LOASIS facility. The proposed ultra-fast source would be intrinsically temporally synchronized to the drive laser pulse, enabling pump-probe studies in ultra-fast science with pulse lengths of ~10–25 fs. Owing both to the high current (>10 kA) and reasonable charge/pulse (~0.1-0.5 nC) of the laser-plasma-accelerated electron beams, saturated output fluxes are potentially on the order of 1014 photons/pulse. We examine devices based both on SASE and high-harmonic generated input seeds to give improved coherence and reduced undulator length, presenting both analytic scalings and numerical simulation results for expected FEL performance. A successful source would result in a new class of compact laser-driven FELs in which a conventional RF accelerator is replaced by a GeV-class laser-plasma accelerator whose active acceleration region is only several cm in length.
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| TUCAU04 | FEL Activities in India | undulator, gun, electron, linac | 496 | ||||||
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We are building a Compact Ultrafast Terahertz Free-Electron Laser (CUTE- FEL), designed to lase between 50 - 100 microns. It will be driven by a 15 MeV electron beam from a Plane-Wave Transformer linac. The undulator is a 5 cm period, 2.5 m long, PPM planar undulator. We present details of the FEL design and the present status of activities. We also present very preliminary plans for a short-wavelength SASE FEL in India.
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