P. MUGGLI, T. KATSOULEAS, S. LEE (USC), M. J. HOGAN, R. ASSMANN**, F.-J. DECKER, R. IVERSON, P. RAIMONDI, R.H. SIEMANN, D. WALZ (SLAC), B. BLUE, C. E. CLAYTON, E. DODD, R. HEMKER, C. JOSHI, K. A. MARSH, W. B. MORI, S. WANG (UCLA)
The E-157 Plasma Wakefield Acceleration (PWFA) experiment is aiming at studying large gradient (several hundred MeV/m) acceleration of electrons in plasmas. The 30 GeV Final Focus Test Beam (FFTB) of the Stanford Linear Accelerator Center (SLAC) is sent in an approximately 1.4 m long lithium plasma with a density in the 1-4e14 /cm3 range. The electron bunch density is larger than the plasma density (underdense plasma). The electrons of the head of the bunch completely expel the plasma electrons ('blow-out' regime), and create a pure ion channel for the core of the bunch to propagate through. The ion channel radial electric field exerts a strong focusing force on the bunch core leading to multiple betatron oscillations of the electron bunch envelope within the plasma. The plasma electrons rush back into the ion channel and generate a large amplitude (several hundred MV/m) longitudinal electric field (wake). The plasma density is tuned so that the trailing electrons of the same bunch experience the maximum wake field and are accelerated. The electron bunch spot size is monitored immediately before and after the plasma using Optical Transition Radiation (OTR). After the plasma the beam propagates through a bending magnet, and generates Cerenkov light in a thin piece of aerogel. The Cerenkov light is imaged and split to produce single-shot time integrated images of the bunch, as well picosecond time resolved energy spectra (in the dispersive plane of the magnet), and time resolved spot size (in the perpendicular plane) using a streak camera. The emission of soft x-rays associated with the betatron motion of the bunch electrons is monitored using a Si crystal reflector and surface barrier detectors. The experimental set-up, as well as results regarding betatron oscillations, bunch tail flipping, beam deflection, x-ray emission, and energy gain will be presented.
*Work supported by DOE Contract #ms DE-AC03-76SF00515, DE-AC-03-76SF0098 and DE-FG03-98-DP-00211, NSF Contract#ms ECS9617089 and DMS-9722171.
** Present address CERN
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