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Cowan, B. M.

Paper Title Page
THPMS050 Designing Photonic Bandgap Fibers for Particle Acceleration 3103
 
  • R. J. Noble, E. R. Colby, B. M. Cowan, C. M.S. Sears, R. Siemann, J. E. Spencer
    SLAC, Menlo Park, California
  
  Funding: Supported by U. S. Dept. of Energy contract DE-AC02-76SF00515

Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a periodic PBG fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the central defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity near the speed of light (SOL). We explore the design of the defect geometry to support well-confined accelerating modes in such PBG fibers. The details of the surface boundary separating the defect from the surrounding matrix are found to be the critical ingredients for optimizing the accelerating mode properties. We give examples of improved accelerating modes in fiber geometries with modified defect surfaces.

 
THPMS052 Optical Wakefield from a Photonic Bandgap Fiber Accelerator 3106
 
  • C. M.S. Sears, E. R. Colby, B. M. Cowan, R. Ischebeck, C. Mcguinness, R. J. Noble, R. Siemann, J. E. Spencer, D. R. Walz
    SLAC, Menlo Park, California
  • R. L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
  
  Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for there high coupling impedance and high damage threshold (>2 GV/m). As a first step in preparing a PBG accelerator, we propose to first observe the optical wakefield induced incoherently by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are coupled into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light phase velocities. By observing the wakefield using a spectrometer, the accelerating mode frequencies are determined.