WEOA :: FEL Oscillators and Storage Ring FELs

Date/Time: 24-Aug-05 :: 08:30—10:15
Chair: M.-E. Couprie, CEA/Saclay, Gif-sur-Yvette

Paper Title Page
WEOA001 Feedback Control Of Dynamical Instabilities In Classical Lasers And Fels 391
 
  • S. Bielawski, C. Bruni, C. Szwaj
    PhLAM/CERCLA, Villeneuve d'Ascq Cedex
  • M.-E. Couprie, D. Garzella
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
  • G. De Ninno, B. Diviacco, M. Trovo
    ELETTRA, Basovizza, Trieste
  • D. Fanelli
    Universita di Firenze, Florence
  • M. Hosaka, M. Katoh, A. Mochihashi
    UVSOR, Okazaki
  • G.L. Orlandi
    ENEA C.R. Frascati, Frascati (Roma)
  • Y. Takashima
    Nagoya University Graduate School of Engineering, Nagoya
 
 

Dynamical instabilities lead to unwanted full-scale power oscillations in many classical lasers and FEL oscillators. For a long time, applications requiring stable operation were typically performed by working outside the problematic parameter regions. A breakthrough occurred in the nineties [1], when emphasis was made on the practical importance of unstable states (stationary or periodic) that coexist with unwanted oscillatory states. Indeed, although not observable in usual experiments, unstable states can be stabilized, using a feedback control involving arbitrarily small perturbations of a parameter. This observation stimulated a set of works leading to successful suppression of dynamical instabilities (initially chaos) in lasers, sometimes with surprisingly simple feedback devices [2]. We will review a set of key results, including in particular the recent works on the stabilization of mode-locked lasers, and of the super-ACO, ELETTRA and UVSOR FELs [3].

[1] Ott et al. Phys. Rev. Lett., 64, 1196 (1990). [2] Bielawski et al. Phys. Rev. A 47, 327 (1993). [3] Bielawski et al. Phys. Rev. E. 69, 045502 (2004), De Ninno & Fanelli, Phys. Rev. Lett. 92, 094801 (2004), Bruni et al., proc. EPAC 2004.

 
   
WEOA002 Storage Ring Free-Electron Laser Saturation for Chromatic and Achromatic Optics 399
 
  • M. Hosaka, M. Katoh, A. Mochihashi
    UVSOR, Okazaki
  • M.-E. Couprie, M. Labat
    CEA/Saclay, Gif-sur-Yvette
  • Y. Takashima
    Nagoya University Graduate School of Engineering, Nagoya
 
 

In a Storage Ring Free Electron Laser (FEL), the saturation mechanism results from the so-called "bunch heating” phenomenon. The periodic interaction between the electron bunch and the laser pulse within the cavity is responsible of the enhancement of the energy spread of the bunch correlated with a bunch lengthening. Recently, new electron beam optics aiming at achieving low emittance with distributed dispersive function  revealed a particular interest for the FEL. In the undulator straight section, these optics lead also to an increase of the transverse sizes of the beam, and to a significant change of the Touschek lifetime. Experimental results obtained on the Super-ACO and UVSORII FELs illustrating the change of saturation process according to the chromatic or achromatic optics will be given. They will be compared with simulations performed with the LAS model, which has been modified to represent this new saturation process.

 
   
WEOA003 First Lasing and Initial Operation of a Circularly Polarized Optical Klystron OK-5 FEL and a Variably Polarized Distributed Optical Klystron DOK-1 FEL at Duke 407
 
  • Y.K. Wu, J. Li, S. Mikhailov, V. Popov
    DU/FEL, Durham, North Carolina
  • N. Gavrilov, G. Kulipanov, O.A. Shevchenko, N. Vinokurov, P. Vobly
    BINP SB RAS, Novosibirsk
 
 

Funding: This work is supported by the U.S. AFOSR MFEL grant F49620-001-0370 and by U.S. DOE grant DE-FG05-91ER40665.

To improve the capability and performance of its light sources, the Duke FEL lab (DFELL) is upgrading its storage ring based FEL by replacing the existing linearly polarized OK-4 FEL with the next generation OK-5 FEL which is capable of delivering both linearly and circularly polarized light. To reduce and manage the risk associated with this project, the FEL upgrade is carried out in three phases. In the second phase of upgrade in 2005, two OK-5 wigglers are installed in a specially designed lattice where OK-4 wigglers remain, forming a distributed optical klystron FEL with hybrid wiggler magnets. In this paper, we report our commissioning experience of this distributed optical klystron FEL, including its first lasing in visible wavelengths and measured lasing spectra and power. We will also present our first experimental results on the FEL polarization manipulation using OK-4 and OK-5 wigglers. In addition, we report the performance enhancement of the Compton gamma-ray source driven by this FEL and initial FEL operation experience for user applications.

 
   
WEOA004 Phase-Space Tomography of Giant Pulses in Storage Ring FEL: Theory and Experiment
 
  • K. Chalut, S. Roychowdhury
    Duke University, Durham, North Carolina
  • V. Litvinenko, I.P. Pinayev
    BNL, Upton, Long Island, New York
 
 

The use of giant pulses in storage ring FEL provides for high peak power at the fundamental wavelength and for effective generating of high VUV harmonics. This process is accompanied by a complex nonlinear dynamics of electron beam, which cannot be described by simple models. In this paper we compare the results of numerical simulations, performed by self-consistent #uvfel code, with experimental observations of electron beam evolution in the longitudinal phase space. The evolution of the electron beam distribution was obtained from the images recorded by dual-sweep streak-camera. The giant pulse process occurs on a short fast time scale compared with synchrotron oscillation period, which make standard methods of tomography inapplicable. We had developed a novel method of reconstruction, an SVD-Based Phase-Space Tomography, which allows to reconstruct phase space distribution from as few as two e-bunch profiles separated by about 3 degrees of rotation in the phase space. This technique played critical role in reconstructing the evolution of electron beam evolution during giant pulse.