Author: Sheppard, J.
Paper Title Page
MOOAB03 FACET First Beam Commissioning 46
  • G. Yocky, C.I. Clarke, W.S. Colocho, F.-J. Decker, M.J. Hogan, N. Lipkowitz, J. Nelson, P.M. Schuh, J.T. Seeman, J. Sheppard, H. Smith, T.J. Smith, M. Stanek, Y. Sun, J.L. Turner, M.-H. Wang, S.P. Weathersby, G.R. White, U. Wienands, M. Woodley
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The FACET (Facility for Advanced aCcelerator Experimental Tests) facility at SLAC has been under Construction since summer 2010. Its goal is to produce ultrashort and transversely small bunches of very high intensity (20kA peak current) to facilitate advanced acceleration experiments like PWFA and DLA. In June of 2011 the first electron beam was brought into the newly constructed bunch-compression chicane. Commissioning work included restarting the linac and damping ring, verifying hardware, establishing a good beam trajectory, verifying the optics of the chicane, commissioning diagnostic devices for transverse and longitudinal bunch size, and tuning up the beam size and bunch compression. Running a high-intensity beam through the linac without BNS damping and with large energy spread is a significant challenge. Optical aberrations as well as wakefields conspire to increase beam emittance and the bunch compression is quite sensitive to details of the beam energy and orbit, not unlike what will be encountered in a linear-collider final-focusing system. In this paper we outline the steps we took while commissioning as well as the challenges encountered and how they were overcome.
slides icon Slides MOOAB03 [9.167 MB]  
TUPPC052 Longitudinal Beam Tuning at FACET 1287
  • N. Lipkowitz, F.-J. Decker, J. Sheppard, S.P. Weathersby, U. Wienands, M. Woodley, G. Yocky
    SLAC, Menlo Park, California, USA
  Commissioning of the Facility for Advanced acCelerator Experimental Tests (FACET) at SLAC began in July 2011. In order to achieve the high charge density required for users such as the plasma wakefield acceleration experiment, the electron bunch must be compressed longitudinally from ~6 mm down to 20 microns. This compression scheme is carried out in three stages and requires careful tuning, as the final achievable bunch length is highly sensitive to errors in each consecutive stage. In this paper, we give an overview of the longitudinal dynamics at FACET, including beam measurements taken during commissioning, tuning techniques developed to minimize the bunch length, optimization of the new “W” chicane at the end of the linac, and comparison with particle tracking simulations. In addition, we present additional diagnostics and improved tuning techniques, and their expected effect on performance for the upcoming 2012 user run.  
MOPPP046 RF Gun Photocathode Research at SLAC 664
  • E.N. Jongewaard, R. Akre, A. Brachmann, W.J. Corbett, S. Gilevich, K. Grouev, P. Hering, P. Krejcik, J.R. Lewandowski, H. Loos, T. M. Montagne, J. Sheppard, P. Stefan, A.E. Vlieks, S.P. Weathersby, F. Zhou
    SLAC, Menlo Park, California, USA
  Funding: DOE contract DE-AC02-76SF00515.
LCLS is presently operating with a third copper photocathode in the original rf gun, with a quantum efficiency (QE) of ~1x10-4 and projected emittance eNx,y=0.45 μm at 250 pC bunch charge. The spare LCLS gun is installed in the SLAC Accelerator Structure Test Area (ASTA), processed to the design rf gradient of >120 MV/m. As part of a wider photocathode R&D program, a UV laser system and additional gun diagnostics are being installed at ASTA to measure QE, QE lifetime, and electron beam emittance under a variety of operating conditions. The near-term goals are to test and verify the spare photocathode production/installation sequence, including transfer from the final holding chamber to the rf gun. Mid- and longer-term goals include development of a rigorous understanding of plasma and laser-assisted surface conditioning and investigation of new, high-QE photocathode materials. In parallel, an x-ray photoemission spectroscopy station is nearing completion, to analyze Cu photocathode surface chemistry. In this paper we review the status and anticipated operating parameters of ASTA and the spectroscopy test chamber.
WEPPP010 FACET: SLAC's New User Facility 2741
  • C.I. Clarke, F.-J. Decker, R.J. England, R.A. Erickson, C. Hast, M.J. Hogan, S.Z. Li, M.D. Litos, Y. Nosochkov, J.T. Seeman, J. Sheppard, U. Wienands, M. Woodley, G. Yocky
    SLAC, Menlo Park, California, USA
  Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
FACET (Facility for Advanced Accelerator Experimental Tests) is a new User Facility at SLAC National Accelerator Laboratory. The first User Run started in spring 2012 with 20 GeV, 3 nC electron beams. The facility is designed to provide short (20 um) bunches and small (20 um wide) spot sizes, producing uniquely high power beams. FACET supports studies from many fields but in particular those of Plasma Wakefield Acceleration and Dielectric Wakefield Acceleration. The creation of drive and witness bunches and shaped bunch profiles is possible with "Notch" Collimation. FACET is also a source of THz radiation for material studies. Positrons will be available at FACET in future user runs. We present the User Facility and the available tools and opportunities for future experiments.
WEPPR040 Intensity Effects of the FACET Beam in the SLAC Linac 3024
  • F.-J. Decker, N. Lipkowitz, J. Sheppard, G.R. White, U. Wienands, M. Woodley, G. Yocky
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.
The beam for FACET (Facility for Advanced aCcelerator Experimental Tests) at SLAC requires an energy-time correlation ("chirp") along the linac, so it can be compressed in two chicanes, one at the mid point in sector 10 and one W-shaped chicane just before the FACET experimental area. The induced correlation has the opposite sign to the typical used for BNS damping, and therefore any orbit variations away from the center kick the tail of the beam more than the head, causing a shear in the beam and emittance growth. Any dispersion created along the linac has similar effects due to the high (>1.2% rms) energy spread necessary for compression. The initial huge emittances could be reduced by a factor of 10, but were still bigger than expected by a factor of 2-3. Normalized emittance of 2 um-rad in Sector 2 blew up to 150 um-rad in Sector 11 but could be reduced to about 6-12 um-rad for the vertical plane although the results were not very stable. Investigating possible root causes for this, we found locations where up to 10 mm dispersion was created along the linac, which were finally verified with strong steering and up to 7 mm settling of the linac accelerator at these locations.