• 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.

• A.H. Lumpkin, W. Berg, M. Borland, N. Sereno
  ANL, Argonne, Illinois

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

The interest in bunch compression to generate higher peak current electron beams with low emittance continues in the free-electron laser (FEL) community. At the Advanced Photon source (APS) we have both an rf thermionic gun and an rf photocathode (PC) gun on the S-band linac. At the 150-MeV point in the linac, we have a flexible chicane bunch compressor whose four dipoles bend the beam in the horizontal plane. There is also a vertical bend dipole after the chicane that allows measurement of energy and horizontal beam size at the imaging screen station to study possible effects on emittance due to coherent synchrotron radiation (CSR) in the chicane. A far-infrared (FIR) coherent radiation monitor is located downstream of the chicane as well. We have begun recommissioning of this device with coherent transition radiation (CTR), but we also have directly observed CSR from the bunch-compressed beam as it transits the vertical dipole and goes into the down leg. The unique geometry allows simultaneous tracking of bunch length, horizontal emittance, and energy distribution effects. Initial measurements of the CSR and CTR as a function of linac phase are described.