Paper  Title  Page 

MOOB01  Beam Echo Effect For Generation Of ShortWavelength Radiation  15 


The Echoenabled Harmonic Generation (EEHG) FEL uses two modulators in combination with two dispersion sections that allow one to generate in the beam a highharmonic density modulation starting with a relatively small initial energy modulation of the beam.[1] After presenting the concept of the EEHG, we address several practically important issues, such as the effect of coherent and incoherent synchrotron radiation in the dispersion sections, the beam transverse size effect in the modulator, etc. Using a representative realistic set of beam parameters, we show how the EEHG scheme enhances the FEL performance and allows one to generate a fully (both longitudinally and transversely) coherent radiation. [1] G. Stupakov, PRL, 102, 074801 (2009). 



Towards SubAngstrom Coherent Light Sources: The Quantum FEL  


Shortwavelength Free Electron Lasers (FELs), which have recently produced intense, hard Xrays, are currently based on the concept of classical SelfAmplified Spontaneous Emission (SASE). In order to extend the production of intense, coherent radiation to subÅ wavelengths then an alternative to the conventional SASEFEL concept will be necessary, as conventional SASEFELs require long wigglers (~100m), large accelerators (~ km) and produce radiation which has poor temporal coherence. Recently, we have introduced the concept of the Quantum Free Electron Laser (QFEL). The QFEL is characterised by quantised electron momentum recoil and the emission of monochromatic, coherent radiation from a compact apparatus. This makes it appealing for applications requiring a high degree of temporal coherence. We show that a SASEQFEL may offer the possibility to produce intense, coherent radiation at subÅ wavelengths via harmonic generation. 



MOOB03  Deep Saturation Dynamics in a Free Electron Laser  23 


The regime of intensity (and bunching) oscillation following the FEL saturation is investigated using the ColsonBonifacio model. This regime is understood as an outofequilibrium metastable state, which slowly relaxes toward thermodynamical (Boltzmann) equilibrium. This dynamics is also characterized by a strong regularity, unexpected for an interaction between waves and large number of particles, as well as by lowdimensional phasespace structures in the electronbeam phase space. In this context, the switch from regimes associated to high gain (for small electronbeam energy spread) or very low gain (for large energy spread) can be interpreted as outofequilibrium phase transitions, a phenomenon which was recently explained by a mechanism of entropy maximization. 



MOOB04  Impact on a Seeded Harmonic Generation FEL of an Initial Energy Chirp and Curvature in the Electron Bunch Energy Distribution  27 


In a harmonic generation free electron laser (HG FEL), the electron beam entering the undulator can have an initial energy curvature besides an initial energy chirp. Solving the VlasovMaxwell equations within the 1D model, we derive an expression for the Green function for the seeded HG FEL process for the case of the electron beam having both an energy chirp and an energy curvature. We give an asymptotic closed form which is a good approximation in the exponential growth regime, and a series expression that allows the evaluation of the field envelope along the undulator in both lethargy and exponential growth regime. The latter is useful to study the HG FEL behavior in the short modulator, like that of the FERMI@Elettra project. The FEL radiation properties such as central frequency shift and frequency chirp are studied considering Gaussian laser seeds of different temporal duration in respect to the Green functions temporal duration. The energy chirp and curvature of the electron bunch result in a time dependent bunching factor for the FEL startup process in the radiator of the HG FEL like the FERMI@Elettra. The coherence properties of the FEL are examined. 



MOOB05  Comparison of HGHG and SelfSeeding for the Production of NarrowBandwidth Radiation in a FreeElectron Laser  31 


Narrow bandwidth FEL operation is one of the main challenges for future FEL facilities. Several schemes have been proposed to obtain a narrower bandwidth than that achievable with self amplified spontaneous emission starting from shotnoise. In this work the properties of two such schemese (high gain harmonic generation and selfseeding) are investigated and compared taking into account several nonideal beam effects, with particular attention paid to the effect of bandwidth broadening associated to nonlinear longitudinal phasespace. The comparison between the two schemes has been carried out with numerical simulations performed with GENESIS 1.3 and PERSEO FEL codes using both an idealized beam and realistic beams obtained with start to end simulations. 

