• E. Saldin, E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

Recent theoretical and experimental studies have shown that SASE FEL with a planar undulator holds a potential for generation of relatively strong coherent radiation at the third harmonic of the fundamental frequency. Here we present detailed study of the nonlinear harmonic generation in SASE FEL obtained with time-dependent FEL simulation code FAST. Using similarity techniques we present universal dependencies for temporal, spectral, and statistical properties of the third harmonic radiation from SASE FEL.

• R. Bonifacio, R. Bonifacio
  Universidade Federal de Alagoas, Maceio
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• N. Piovella
  Universita' degli Studi di Milano, MILANO
• G.R.M. Robb
  Strathclyde University, Glasgow
• A. Schiavi
  Rome University La Sapienza, Roma
• L. Serafini
  INFN-Milano, Milano

Funding: Istituto Nazionale di Fisica Nucleare (INFN), Italy

Quantum effects in high-gain FELs become relevant when ρ'=ρ(mcγ/ ћ k)<1. The quantum FEL parameter ρ' rules the maximum number of photons emitted per electrons. It has been shown that when ρ'<1 a "quantum purification" of the SASE regime occurs: in fact, the spectrum of the emitted radiation (randomly spiky in the usual classical SASE regime) shrinks to a very narrow single line, leading to a high degree of temporal coherence. From the definition of ρ it appears that in order to achieve the quantum regime, small values of ρ, beam energy and radiation wavelength are necessary. These requirements can be met only using a laser wiggler. In this work we state the scaling laws necessary to operate a SASE FEL in the Angstrom region. All physical quantities are expressed in terms of the normalized emittance and of two parameters: the ratio between laser and electron beam spot sizes and the ratio between Rayleigh range and electron β-function. The feasibility study of a Quantum SASE FEL experiment using parameters as those foreseen in the SPARC/PLASMONX projects in construction at the INFN Frascati is explicitly discussed.

• G. Andonian, A.Y. Murokh, C. Pellegrini, S. Reiche, J.B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California
• M. Babzien, I. Ben-Zvi, V. Litvinenko, V. Yakimenko
  BNL, Upton, Long Island, New York
• I. Boscolo, S. Cialdi, A.F. Flacco
  INFN-Milano, Milano
• M. Ferrario, L. Palumbo, C. Vicario
  INFN/LNF, Frascati (Roma)
• J.Y. Huang
  POSTECH, Pohang, Kyungbuk

The VISA II experiment entails use of a chirped beam to drive a high gain SASE FEL. The output radiation is diagnosed with a modified frequency resolved optical gating (FROG) technique. Sextupoles are implemented to correct the lonigtudinal aberrations affecting the high energy spread chirped beam during transport to the undulator. The double differential energy spectrum is measured with a pair of slits and a set of gratings. In this paper, we report on start-to-end simulations, radiation diagnostics, as well as intial experimental results; experimental methods are described.

• S. Krinsky
  BNL, Upton, Long Island, New York

Funding: Work supported by DOE contract number DE-AC02-98CH10886.

We consider three definitions of the number of temporal modes in SASE output. These are defined in terms of: (1) the number of minimum area phase space cells occupied by the radiation; (2) the pulse energy fluctuation; and (3) the Wigner function. The conditions under which these definitions are equivalent is discussed.

• J.-S. Oh, S. D. Jang, I.S. Ko, S. J. Kwon, W. Namkung, Y. G. Son, J.-H. Suh
  PAL, Pohang, Kyungbuk

Funding: Supported by the POSCO and the MOST, Korea

The PAL (Pohang Accelerator Laboratory) is persuading to construct a SASE-XFEL facility (PAL XFEL) that supplies coherent X-rays. The bright and stable electron beam is essential for the PAL XEL. The electron beams has to have an emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.5 MeV. In order to provide reasonably stable SASE output, the RF stability of 0.02% rms is required for both RF phase and amplitude. This is a technologically challenging issue for PAL XFEL. An inverter technology is to be applied to charge the PFN of a new modulator. Therefore, a new inverter system should provide very stable charging performances. This paper presents the development of an ultra stable klystron-modulator with an inverter power supply.

• G. Lambert, M. Bougeard, W. Boutu, P. Breger, M.-E. Couprie, D. Garzella, H. Merdji, P. Monchicourt, P. Salieres
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• B. Carre
  CEA/Saclay, Gif-sur-Yvette
• T. Hara, H. Kitamura, T. Shintake
  RIKEN Spring-8 Harima, Hyogo

In order to reach very short wavelengths in FEL, and to have a more compact, fully coherent and tunable source, a particular seeding configuration is foreseen to be tested as a demonstration experiment in 2006 into the SCSS phase 1 facility (Spring-8 Compact Sase Source, Japan). The external source is the 13th harmonic (61.5 nm) of a Ti: Sa laser (25 mJ, 10 Hz, 100 fs) generated in 10 Hz pulsed Xe gas cell. The harmonic generation process provides us with a intense (1 μJ) and ultra-short (50 fs) VUV beam. The design of the experiment implantation is discussed, taken into account the performances of the generation process, the focusing of the selected harmonic into the modulator, and the resistance of the optical components. Besides one should consider the vacuum needs, the geometrical problems and the mechanics for the under UHV mirrors translation. One first chamber is dedicated to the harmonic generation. A second one is used for spectral selection and adaptation of the harmonic in the modulator. Finally theoretical estimates of the performances relying on 1D simulations using PERSEO code and 3D simulations using GENESIS code are also given.

• E. Saldin, E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

Influence of a linear energy chirp, imposed on the electron beam, on SASE process is studied analytically and numerically.

• R. Tatchyn
  SLAC, Menlo Park, California

The unusually long insertion devices being prepared for Angstrom-wavelength Free Electron Lassers (FELs) will generate spectral-angular distributions in the proposed experimental areas substantially different from those conventionally calculated for the far field. In this paper we report on computational simulations of near vs. far field distributions for the SLAC linac Coherent Light Source (LCLS) undulator, an insertion device approximateely 140 meters long. The properties of the coherent radiation as a limiting case of the near-field emission, for the special condition of a microbunched beam radiating along the undulator axis, are reviewed.

• J. Pflueger
  DESY, Hamburg

The undulator systems for the European XFEL project will produce 0.1nm radiation. Their length will exceed 200m. they will be segmented into 40-50 segments. There will be very demanding requirements on the performance of the undulator segments. The concept for building these systems will be explained in detail. This includes drive systems, magnet structures, control systems, phase shifter and othe components in the intersections as well. An important role plays the photon diagnostic station which is foreseen for each SASE FEL beam line. It can be used for steering the beam through the undulator line, for precision gap tuning of individual undulator segments and for precise phase matching of neighbouring devices. An important role plays the interaction with the undulator control system.

• Y. Kim, K. Floettmann, S. Schreiber
  DESY, Hamburg
• D. Son
  CHEP, Daegu

Funding: for the TTF2 VUV-FEL Team

By the help of nonlinearity in the longitudinal phase space, the VUV-FEL at the TESLA Test Facility phase 2 (TTF2) is under operating in the femtosecond (fs) FEL mode which generates coherent and ultra-bright SASE source with photon pulse duration time of around 20 fs (FWHM) and wavelength of around 32 nm. For the fs FEL mode operation, bunch length of electron beams should be compressed by two bunch compressors to have a leading spike in the longitudinal beam density distribution or peak current. The required peak current at the spike is higher than about 1.0 kA, and the spike length is shorter than around 200 fs (FWHM). In this paper, we describe our commissioning experiences to optimize two TTF2 bunch compressors for the fs FEL mode operation.

• M. Huening, A. Bolzmann, H. Schlarb
  DESY, Hamburg
• J.C. Frisch, D.J. McCormick, M.C. Ross, T.J. Smith
  SLAC, Menlo Park, California
• J. Rossbach
  Uni HH, Hamburg

The design of the VUV-FEL at DESY demands bunch lengths in the order of 50 fs and below.For the diagnostic of such very short bunches a transverse deflecting RF structure (LOLA) has been installed which streaks the beam according to the longitudinal distribution. Tests in the VUV-FEL yielded a rich substructure of the bunches. The most pronounced peak in the has a rms length of approximately 50 fs during FEL operation and below 20 fs FWHM at maximum compression. Depending on the transverse focusing a resolution between 10^-50 fs was achieved.

• Z. Huang
  SLAC, Menlo Park, California

Funding: Work supported by US Department of Energy contract DE-AC02-76SF00515.

High-gain free electron lasers (FEL) are being developed as extremely bright x-ray sources of a next-generation radiation facility. In this paper, we review the basic theory and the recent progress in understanding the startup, the exponential growth and the saturation of the high-gain process, emphasizing the self-amplified spontaneous emission (SASE). We will also discuss how the FEL performance may be affected by various errors and wakefield effects in the undulator.

In memory of the late scientist Ming Xie.

• R. Bonifacio, R. Bonifacio
  Universidade Federal de Alagoas, Maceio
• N. Piovella
  Universita' degli Studi di Milano, MILANO
• G.R.M. Robb
  Strathclyde University, Glasgow

We present a proof of principle of the novel regime of quantum SASE with propagation effects. Using a self-consistent system of Schrodinger-Maxwell equations, we show that the dynamics of the system is determined by a properly defined "quantum FEL-parameter", ρ', which rules the number of photons emitted per electron, as well as the electron recoil in units of ћk. In the limit ρ'>>1 the quantum model reproduces the classical SASE regime with random spiking behavior and broad spectrum. In this limit we show that the equation for the Wigner function reduces to the classical Vlasov equation. In the opposite limit, ρ'<1, we demonstrate "quantum purification" of SASE: the classical spiking behavior disappears and the power spectrum becomes very narrow so that the temporal coherence of the SASE spectrum is dramatically improved. Photon statistics, electron-photon entangled states, minimum uncertainty states and quantum limitations on bunching and energy spread will be discussed.