• L. Giannessi, M.C. Carpanese, F. Ciocci, G. Dattoli, A. Dipace, A. Doria, G.P. Gallerano, E. Giovenale, G. Parisi, M. Quattromini, A. Renieri, C. Ronsivalle, E. Sabia, S. Spampinati, I.P. Spassovsky
  ENEA C.R. Frascati, Frascati (Roma)
• D. Alesini, M.E. Biagini, A. Drago, M. Ferrario, V. Fusco, A. Ghigo, B. Spataro, C. Vaccarezza, C. Vicario
  INFN/LNF, Frascati (Roma)
• M. Bougeard, B. Carre, M.-E. Couprie, D. Garzella, M. LABAT, G. Lambert, H. Merdji, P. Salieres
  CEA/Saclay, Gif-sur-Yvette
• M. Mattioli, P. Musumeci, M. Petrarca
  Universita di Roma I La Sapienza, Roma
• M.  Migliorati, L. Palumbo
  Rome University La Sapienza, Roma
• M. Nisoli, S. Stagira, S. de Silvestri
  Politecnico/Milano, Milano
• L. P. Poletto, G. T. Tondello
  Univ. degli Studi di Padova, Padova

Funding: Work supported by the EU Commission in the sixth framework programme, contract no. 011935 – EUROFEL.

Sources based on high order harmonics generated in gas with high power Ti:Sa lasers pulses represent promising candidates as seed for FEL amplifiers for several reasons, as spatial and temporal coherence, wavelength tunability and spectral range, which extends down to the 10(-9)m wavelength scale. This communication is devoted to the description of a research work plan that will be implemented at the SPARC FEL facility in the framework of the EUROFEL programme. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in crystal (400nm and 266 nm) and in gas (266nm, 160nm, 114nm) from a high intensity Ti:Sa laser pulse.

• H. Freund
  SAIC, McLean
• M. Abo-Bakr, K. Goldammer, D. Kraemer, B.C. Kuske, A. Meseck
  BESSY GmbH, Berlin
• S. Biedron
  ANL, Argonne, Illinois

The BESSY FEL is based on a seeded cascade of High Gain Harmonic Generation (HGHG) sections followed by an amplifier to produce coherent and stable short wavelength output. Here, we report on comparative design studies carried out using the MEDUSA [1], and GENESIS [2] simulation codes. These two codes have each been used to successfully predict a variety of FEL designs and have agreed well with a number of important experiments. In addition, they were included in a comparative study of FEL simulation [3] that reported substantial agreement between the codes for the specific configurations studied. However, these codes are based on different assumptions. GENESIS treats the particle dynamics using a wiggler-averaged orbit approximation, the transverse electromagnetic field is treated using a field solver, and harmonics are not included. MEDUSA does not use the wiggler-averaged orbit approximation to treat particle dynamics, the transverse fields are treated using a Gaussian modal superposition, and harmonics are included self-consistently. Hence, the comparative study for an HGHG cascade is important. We report the results where the parameters of each stage have been optimized.

[1] H.P. Freund et al., IEEE JQE 36, 275 (2000). [2] S. Reiche, NIMA 429, 243 (1999). [3] S.G. Biedron et al., NIMA 445, 110 (2000).

• S. Sasaki, I. Vasserman
  ANL, Argonne, Illinois

Funding: Supported by the U.S. Dept. of Energy, BES-Office of Science, under Contract W-31-109-ENG-38.

Trajectory straightness through the undulator is critical for the success of the LCLS project. Environmental fields, including the earth’s field, will affect the trajectory. The earth’s field works as an external dipole field and, unless it is shielded or corrected, causes a bend in the electron trajectory through an undulator. We investigated the effects of the earth’s field and an iron plate which might be used as part of a girder. Modeling and calculation were performed using the code RADIA. A model with a large solenoid surrounding a seven-period undulator was used for the simulation. According to the calculations, the vertical component of the earth’s field at the undulator axis is enhanced by the undulator poles by a factor of 2.5. The horizontal on-axis component, however, is well shielded by the undulator poles and falls to less than 3% of its original strength. The effect of an iron plate located 200 mm below the undulator axis is negligibly small, so final Hall probe measurements can be done without the girder in place. However, the magnetic tuning of the undulator field must take into account the amplification of the vertical component of the environmental field in the LCLS tunnel.

• A.H. Lumpkin, W. Berg, N. Sereno, B.X. Yang, C. Yao
  ANL, Argonne, Illinois
• D.W. Rule
  NSWC, West Bethesda, Maryland

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

The challenge of providing nonintercepting beam diagnostics that address transverse parameters such as beam size and divergence in a linear transport line has been met. We have successfully used near-field imaging of optical diffraction radiation (ODR) from a 7-GeV electron beam passing near a single edge of a conducting screen to obtain beam size for the first time [1]. In this case appreciable visible wavelength ODR is emitted for impact parameters of 1 to 2 mm, values that are close to gamma times the reduced observation wavelength. We have now upgraded our imaging system to include an intensified camera; selectable bandpass filters, neutral density filters, and polarizers; a steering mirror; and an optical lens setup that provides either near-field or far-field imaging. The ODR has been obtained in both the single-edge mode and aperture mode with a single pulse of 3.3 nC. Beam-size resolution in the 20-50 micron regime is projected while beam position resolution to 10 microns with a smaller beam and higher optical magnification should be feasible with near-field imaging. Applications to high-energy accelerators that drive x-ray FELs or energy recovering linacs for light sources should be possible.

[1] A.H. Lumpkin et al., "First Near-Field Imaging of Optical Diffraction Radiation Generated by a 7-GeV Electron Beam,” submitted to Phys. Rev. Lett., May 4, 2005.

• S. Zhang, S.V. Benson, D. Douglas, D. Hardy, C. Hernandez-Garcia, K. Jordan, G. Neil, M.D. Shinn
  Jefferson Lab, Newport News, Virginia

Funding: This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Army Night Vision Laboratory, the Air Force Research Laboratory, and by DOE Contract DE-AC05-84ER40150.

The design and construction of an optical transport that brings synchrotron radiation from electron bunches to a fast streak camera in a remote area has become a useful tool for online observation of bunch length and stability. This paper will report on the temporal measurements we have done, comparison with simulations, and the on-going work for another imaging optical transport system that will make possible the direct measurement of the longitudinal phase space by measuring the bunch length as a function of energy.