• P. Michel, P. Evtushenko, U. Lehnert, Ch. Schneider, R. Schurig, W. Seidel, J. Teichert, D. Wohlfarth
  FZR, Dresden

A FEL in the mid infrared range is one of the applications of the ELBE cw-electron accelerator. The successful operation of the lasing process for the different wavelength is mainly determined by the alignment of the optical cavities, the bunch length and the energy spread of the electron beam so as the transversal adjustment of the beam through the FEL. The energy spread and the bunch length of the electron beam have their minima at different phase conditions of the accelerator. For various energy settings of the accelerator a special adjustment of both parameters has to be found for the lasing process. The presentation describes the diagnostic tools used at ELBE for the correct alignment of the optical cavity, the steering of the electron beam through the FEL and the adjustment of the electron beam parameters with respect to energy spread and bunch length.

• A. Gover, A. Faingersh, M. Kanter, B. Kapilevich, B. Litvak, S. Peleg, Y. Socol, M. Volshonok
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
• M. Einat, Yu. Lurie, Y. Pinhasi, A. Yahalom
  CJS, Ariel

The Israeli Electrostatic Accelerator FEL (EA-FEL) is now being upgraded towards long pulse (1005s) operation and ultra-high resolution (10(-6)) single pulse coherent spectroscopy. We present quantitative estimations regarding the applications of controlled radiation chirp for spectroscopic applications with pulse-time Fourier Transform limited spectral resolution. Additionally, we describe a novel extraction-efficiency-improving scheme based on increase of accelerating voltage (boosting) after saturation is achieved. The efficiency of the proposed scheme is confirmed by theoretical and numerical calculations. The latter are performed using software, based on 3D space-frequency domain model. The presentation provides an overview of the upgrade status: the high-voltage terminal is being reconfigured to accept the accelerating voltage boost system; a new broad band low-loss resonator is being manufactured; multi-stage depressed collector is assembled.

• E.J. Minehara, R. Hajima, H. Iijima, N. Kikuzawa, R. Nagai, N. Nishimori, T. Nishitani, M. Sawamura, T. Yamauchi
  JAEA/FEL, Ibaraki-ken

The JAERI high power ERL-FEL has been extended to the more powerful and efficient free-electron laser (FEL) than 10kW for nuclear energy industries, and other heavy industries like defense, shipbuilding, chemical industries, environmental sciences, space-debris, and power beaming and so on. In order to realize such a tunable, highly-efficient, high average power, high peak power and ultra-short pulse FEL, we need the efficient and powerful FEL driven by the JAERI compact, stand-alone and zero boil-off super-conducting RF linac with an energy-recovery geometry. Our discussions on the ERL-FEL will cover the current status of the 10kW upgrading and its applications of non-thermal peeling, cutting, and drilling to decommission the nuclear power plants, and to demonstrate successfully the proof of principle prevention of cold-worked stress-corrosion cracking failures in nuclear power reactors under routine operation using small cubic low-Carbon stainless steel samples.

• 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.

• B.W.J. McNeil, G.R.M. Robb
  Strathclyde University, Glasgow
• M.W. Poole, N. Thompson
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

Funding: We acknowledge the support of the European Framework Programme 6 EUROFEL Design Study, CCLRC, and the Scottish Universities Physics Alliance.

Recent proof-of-principle simulations have demonstrated a method that allows a planar undulator FEL to lase so that the interaction with an odd harmonic of the radiation field dominates that of the fundamental [1]. This harmonic lasing of the FEL is achieved by disrupting the interaction between the fundamental radiation field and electrons as they propagate through the undulator while allowing the n-th harmonic interaction to evolve unhindered. The disruption of the interaction at the fundamental is achieved by a series of relative phase changes between electrons and the fundamental ponderomotive potential of 2k pi/n (k = 1, 2, 3, . . . ; k not equal to n). The corresponding phase change with the ponderomotive potential of the n-th harmonic is then 2k pi which, at least in a simple steady-state FEL model, will have no deleterious effect upon the harmonic interaction. Such phase changes are relatively easy to implement and indeed some current FEL designs would not require any structural modification. We present a more detailed analysis of harmonic lasing and use this to discuss potential benefits and applications in extending the operational bandwidth of FELs to shorter wavelengths.

[1] B.W.J. McNeil, G.R.M. Robb and M.W. Poole, Proceedings of Particle Accelerator Conference, Knoxville, USA (2005)

• G. De Ninno, E. Allaria, F. Curbis, M.B. Danailov, B. Diviacco, M. Marsi, M. Trovo
  ELETTRA, Basovizza, Trieste
• M. Coreno
  CNR - IMIP, Trieste
• S. Günster, D. Ristau
  Laser Zentrum Hannover, Hannover

Thanks to an intensive technological effort in the framework of the EEC Contract HPRI CT-2001-50025 (EUFELE), the European FEL at ELETTRA was able to break the previous record for the shortest wavelength of an FEL oscillator. Novel solutions were adopted for multilayer mirrors to allow FEL operation in the wavelength region between 160 and 190 nm, which is one of the main targets of the project. The characteristics of the FEL pulses measured at 176 nm (spectral profiles, high intensity, meV bandpass, MHz repetition rate) make it a competitive light source for spectroscopy, in particular for fluorescence studies in the VUV spectral range. Proof of principle experiments have been performed on different types of silica glasses, yielding information on the mechanisms of light absorption in this material.