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Ischebeck, R.

Paper Title Page
TPAE049 The UCLA/SLAC Ultra-High Gradient Cerenkov Wakefield Accelerator Experiment 3067
 
  • M.C. Thompson, H. Badakov, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • M.J. Hogan, R. Ischebeck, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • P. Muggli
    USC, Los Angeles, California
  • A. Scott
    UCSB, Santa Barbara, California
  • R.B. Yoder
    ,
 
  Funding: Work Supported by U.S. Dept. of Energy grant DE-FG03-92ER40693.

An experiment is planned to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range. This new UCLA/SLAC collaboration will take advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., sz = 20 μm at Q = 3 nC). The electron beam will be focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 μm / OD = 325 μm and ID = 100 μm / OD = 325 μm. The pulse length of the electron beam will be varied in order to alter the accelerating gradient and probe the breakdown threshold of the dielectric structures. In addition to breakdown studies, we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain information about the strength of the accelerating fields. Status and progress on the experiment are reported.

 
RPAT082 Coherent Transition Radiation To Measure the SLAC Electron Bunch Length 4102
 
  • P. Muggli
    USC, Los Angeles, California
  • C.D. Barnes, M.J. Hogan, P. Krejcik, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • R. Ischebeck, H. Schlarb
    DESY, Hamburg
 
  Funding: Work supported by U.S. DOE.

Ultrashort electron bunches are now available at Stanford Linear Accelerator Center and are use mainly to produce short bursts of x-rays in a magnetic undulator and for plasma wakefield acceleration experiments. The shortest bunches have an rms longitudinal width of ˜10 microns, and a peak current of about 30 kA. Methods to measure such short bunch lengths include electro-optic modulation of a short laser pulse in a nonlinear crystal and coherent transition (CTR) autocorrelation. The transition radiation spectrum emitted by the bunches when traversing a 1 micron thin titanium foil is coherent for wavelengths longer that the bunch length and extends into the millimeter wavelength range. A CTR far-infrared autocorrelator was used to measure the bunch length as a function of the accelerator. The results obtained with this autocorrelator are the only measurements of the SLAC ultra-short bunches to date. Experimental results, as well as the limitations of the measurements and the future improvements to the autocorrelator will be presented.

 
RPAT078 Bunch Length Measurements Using Coherent Radiation 4027
 
  • R. Ischebeck, C.D. Barnes, I. Blumenfeld, F.-J. Decker, M.J. Hogan, R.H. Iverson, P. Krejcik, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • C.E. Clayton, C. Huang, D.K. Johnson, W. Lu, K.A. Marsh
    UCLA, Los Angeles, California
  • S. Deng, E. Oz
    USC, Los Angeles, California
  • N.A. Kirby
    Stanford University, Stanford, Califormia
 
  Funding: Work supported by Department of Energy contracts DE-AC02-76SF00515 (SLAC), DE-FG03-92ER40745, DE-FG03-98DP00211, DE-FG03-92ER40727, DE-AC-0376SF0098, and National Science Foundation grants No. ECS-9632735, DMS-9722121 and PHY-0078715.

The accelerating field that can be obtained in a beam-driven plasma wakefield accelerator depends on the current of the electron beam that excites the wake. In the E-167 experiment, a peak current above 10kA will be delivered at a particle energy of 28GeV. The bunch has a length of a few ten micrometers and several methods are used to measure its longitudinal profile. Among these, autocorrelation of coherent transition radiation (CTR) is employed. The beam passes a thin metallic foil, where it emits transition radiation. For wavelengths greater than the bunch length, this transition radiation is emitted coherently. This amplifies the long-wavelength part of the spectrum. A scanning Michelson interferometer is used to autocorrelate the CTR. However, this method requires the contribution of many bunches to build an autocorrelation trace. The measurement is influenced by the transmission characteristics of the vacuum window and beam splitter. We present here an analysis of materials, as well as possible layouts for a single shot CTR autocorrelator.

 
RPAT079 Resolution of Transverse Electron Beam Measurements Using Optical Transition Radiation 4042
 
  • R. Ischebeck, F.-J. Decker, M.J. Hogan, R.H. Iverson, P. Krejcik, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • C.E. Clayton, C. Huang, W. Lu
    UCLA, Los Angeles, California
  • S. Deng, E. Oz
    USC, Los Angeles, California
  • M. Lincoln
    Stanford University, Stanford, Califormia
 
  Funding: Work supported by Department of Energy contracts DE-AC02-76SF00515 (SLAC), DE-FG03-92ER40745, DE-FG03-98DP00211, DE-FG03-92ER40727, DE-AC-0376SF0098, and National Science Foundation grants No. ECS-9632735, DMS-9722121 and PHY-0078715.

In the plasma wakefield acceleration experiment E-167, optical transition radiation is used to measure the transverse profile of the electron bunches before and after the plasma acceleration. The distribution of the electric field from a single electron does not give a point-like distribution on the detector, but has a certain extension. Additionally, the resolution of the imaging system is affected by aberrations. The transverse profile of the bunch is thus convolved with a point spread function (PSF). Algorithms that deconvolve the image can help to improve the resolution. Imaged test patterns are used to determine the modulation transfer function of the lens. From this, the PSF can be reconstructed. The Lucy-Richardson algorithm is used to deconvolute this PSF from test images.