Storage Ring FELs

Paper	Title	Page
TUPPH007	Spatial Coherence Measurement of UVSOR-II Free Electron Laser
	O. V. Chubar, M.-E. Couprie SOLEIL, Gif-sur-Yvette K. Fukui University of Fukui, Fukui M. Hosaka Nagoya University, Nagoya M. Katoh, A. Mochihashi, M. Shimada UVSOR, Okazaki G. Lambert RIKEN Spring-8, Hyogo M. Labat CEA, Gif-sur-Yvette
	The well defined phase relationship of coherent radiation is wished for a large number of experiments. The advent of very small emittance electron beams allowed improvement of the transverse coherence of the undulators radiation and lead to extensive use of modern synchrotron facilities in the visible to x-ray domain. Nevertheless, Free Electron Lasers (in particular in the seeded Coherent Harmonic Generation (CHG) scheme) may offer additional capabilities such as shorter pulse duration, smaller spectral bandwidth, higher peak power and improved transverse coherence. Transverse coherence of the third Coherent Harmonic has been studied on the UVSOR-II storage ring (Japan) at 600 MeV, using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength with the double slit method. The improvement of the transverse coherence of the FEL radiation compared to spontaneous emission is shown via the visibility of the interference pattern resulting from double slits. The experimental results are compared to analytical calculations as well as to 3D FEL and wavefront propagation simulations performed with SRW.
TUPPH008	Beam Dynamics Studies on the UVSOR-II Free Electron Laser	236
	M.-E. Couprie SOLEIL, Gif-sur-Yvette M. Hosaka Nagoya University, Nagoya M. Katoh, A. Mochihashi, M. Shimada UVSOR, Okazaki G. Lambert RIKEN Spring-8, Hyogo M. Labat CEA, Gif-sur-Yvette
	In the Coherent Harmonic Generation Free Electron Laser configuration, an external laser source is seeded inside a first undulator. The interaction between the electron beam and this seed induces energy modulation of the bunch, further converted into a density modulation, producing coherent radiation in a second undulator. The energy modulation enhances the energy spread of the electron bunch, converted by the machine optics into a modification of its longitudinal distribution. In the case of a storage ring FEL, the electrons are re-circulating: the same bunch keeps interacting with the seeded laser, and relaxation of the distribution is only allowed in between two laser injections. Such specific dynamics has been studied on the CHG FEL of UVSOR-II storage ring (Japan). The electron beam stored at 600 MeV is seeded using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm wavelength, allowing radiation at 266 nm (third harmonic). A Streak Camera is used to record the evolution of the longitudinal profiles as a function of the repetition rate and average power of the seeding laser, leading to bunch lengthening and distortion dynamical analysis. It appeared that because the heating induced by the interaction remains local, the refreshment process of the electronic distribution is modified. The experimental results are compared to simulations using SYNC.
TUCAU01	FELs and High-energy Electron Cooling	268
	Y. S. Derbenev Jefferson Lab, Newport News, Virginia V. Litvinenko BNL, Upton, Long Island, New York
	Electron cooling is extremely successful in cooling low and medium energy ions, including protons. ERLs are promising to extend the reach of traditional electron cooling to about 100 GeV/nucleon for heavy ions. Nevertheless, cooling of protons with energies from about 100 GeV (RHIC) to few TeV (LHC) becoming very complicated or even possible. Optical stochastic cooling [1] has potential to be an instrument of choice, but it has two main shortcomings: a) it requires significant modifications of the lattices of hadron machine and b) in the case of the protons it suffers from very inefficient interaction (radiation) of protons with TEM wave. It was suggested [2] to combine advantages of electrostatic interaction with broad-band FEL-amplifier in what is now called stochastic electron cooling. Such system will naturally fit into a straight section of modern high energy hadron colliders. In this paper we present description of the cooling process and give examples of FEL-based electron cooler for protons in RHIC and LHC. [1] A. Mikhalichenko and M. Zolotorev, Phys. Rev. Lett., 71, p.4146 (1993). [2] Ya. S. Derbenev, NIM A441 (2000) 223
	Slides
TUCAU02	Even Harmonic Generation on UVSOR-II Storage Ring
	M.-E. Couprie SOLEIL, Gif-sur-Yvette M. Hosaka Nagoya University, Nagoya M. Katoh, A. Mochihashi, M. Shimada UVSOR, Okazaki G. Lambert RIKEN Spring-8, Hyogo M. Labat CEA, Gif-sur-Yvette
	In the Coherent Harmonic Generation Free Electron Laser configuration, the electrons act as a non-linear medium radiating harmonics of a seed source (e.g., a laser). In the two-step seeding scheme, the seed field forces an energy modulation on the electron bunch in a modulator, converted into a density modulation as the electron beam travels through a dispersive section. Finally, in the radiator, the microbunched electron beam can emit coherently at the fundamental and the harmonics of the seed source. In this paper, successful even harmonic generation is reported on the CHG UV-FEL of UVSOR-II storage ring (Japan) at 600 MeV, using a 2.5 mJ, 1 kHz, 1.2 ps Ti:Sa laser at 800 nm. Second and fourth harmonics were generated using planar configuration of the undulators, and second harmonic was generated in helical configuration, in addition to already observed and studied third coherent harmonic. Such preliminary results allow attractive perspectives to understand further even harmonic generation process, still discussed among the FEL community: in single pass non-guided FELs, with planar undulators even harmonics are expected to vanish on-axis, a spectral selection that could be avoided with helical undulators.
	Slides
TUCAU03	Seeded Harmonic Generation with the Elettra Storage-Ring Free Electron Laser
	E. Allaria, M. B. Danailov, G. De Ninno, B. Diviacco, E. Karantzoulis, C. Spezzani, S. Tileva, M. Trovo, F. Curbis ELETTRA, Basovizza, Trieste M. Coreno CNR - IMIP, Trieste
	We have recently demonstrated that the Elettra storage-ring free-electron laser is well suited for producing intense VUV harmonic radiation in seeded "single-pass" configuration. After reviewing the experimental setup, we present here the temporal and spectral characterization of the harmonic pulse with respect to several adjustable parameters, such as the seed power, repetition rate (10 Hz ± 1 kHz) and pulse duration, the seed pulse-electron bunch temporal detuning and the strength of the dispersive section between undulators. Measured peak power in the working wavelength range (i.e., 260-130 nm for the reported experiments) is several orders of magnitude above spontaneous synchrotron radiation. We also show that measurements are in very good agreement with 3D numerical simulations. The obtained results make the Elettra storage-ring free-electron laser in seeded "single-pass" configuration an ideal test facility for next generation linac-based FELs and, at the same time, a ready-to-use light source for user experiments.
TUCAU04	A Versatile High Gain Storage Ring FEL Powered by a Distributed Optical Klystron
	J. Li, S. F. Mikhailov, V. Popov, Y. K. Wu FEL/Duke University, Durham, North Carolina N. Vinokurov BINP SB RAS, Novosibirsk
	In this work, we report the recent research results of a distributed optical klystron based storage ring FEL at Duke University, the DOK-1 FEL. The DOK-1 FEL is a hybrid system, comprised of four wigglers: two horizontal and two helical. This new FEL has demonstrated the highest FEL gain among storage ring based FEL oscillators using the distributed optical klystron configuration. The enhanced FEL gain of the DOK-1 FEL opens the door for storage ring based FELs to operate in the VUV region toward 150 nm. We have also realized controlled polarization switches of the FEL beam by a non-optical means through the manipulation of a buncher magnet. The DOK-1 FEL is a promising light source capable of rapid polarization switch in UV and VUV. The versatility of the DOK-1 FEL extends to many areas, including the ability of being operated as a multi-color light source for generation of coherent harmonic radiation.
	Slides