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@PHDTHESIS{Loisch:426401,
      author       = {Loisch, Gregor},
      othercontributors = {Gruener, Florian and Oppelt, Anne and Ferrario, Massimo},
      title        = {{D}emonstrating {H}igh {T}ransformer {R}atio
                      {B}eam-{D}riven {P}lasma {W}akefield {A}cceleration},
      school       = {Universität Hamburg},
      type         = {Dissertation},
      address      = {Hamburg},
      publisher    = {Verlag Deutsches Elektronen-Synchrotron},
      reportid     = {PUBDB-2019-03713, DESY-THESIS-2019-024},
      series       = {DESY THESIS},
      pages        = {197},
      year         = {2019},
      note         = {Dissertation, Universität Hamburg, 2019},
      abstract     = {In this work, plasma wakefield acceleration with high
                      transformer ratios, i.e. highratios between acceleration of
                      witness particles to deceleration of driver particles, is
                      investigated experimentally.Particle-beam-driven plasma
                      wakefield acceleration (PWFA) is one of the primecandidates
                      for future compact accelerator technologies. In this scheme,
                      a highbrightness driver particle bunch enters a plasma and
                      initiates oscillations of plasma electrons by expelling them
                      from their equilibrium positions. Particles trailing the
                      driver bunch can be accelerated in the electric field
                      between regions of negative and positive charge excess
                      formed in this oscillation. Acceleration gradients of up to
                      several tens of GV/m have been demonstrated in experiment,
                      exceeding the gradients of conventional technology by orders
                      of magnitude. PWFA could thus allow to accordingly shrink
                      the size of an accelerator, possibly reducing size and cost
                      of an accelerator facility significantly.One key aspect of a
                      PWFA is the ratio between acceleration gradient behind the
                      driver and deceleration gradient inside the driver bunch.
                      This so-called transformer ratio defines the maximum
                      acceleration achievable for a given driver energy and is
                      closely connected to the achievable efficiency. In linear
                      wakefield theory the transformer ratio is limited to 2 for
                      longitudinally symmetric driver bunches, which typically
                      emerge from conventional accelerators. One proposed method
                      to achieve high transformer ratios (HTR) exceeding this
                      limit is to employ driver bunches with lengths of multiple
                      plasma skin depths and sawtooth-like, “triangular”
                      current profiles. Due to the complexity of shaping such
                      bunches and beam-plasma instabilities that can inhibit
                      stable acceleration, HTRs had thus far not been achieved in
                      PWFA.In the course of the present work, the driving of HTR
                      PWFA has been accomplished at the Photo-Injector Test
                      facility at DESY in Zeuthen (PITZ). Existing bunch shaping
                      capabilities at PITZ, based on photocathode laser pulse
                      shaping,were extended to the production of HTR-capable
                      driver bunches. An argon gasdischarge plasma cell was built
                      and optimised for providing the plasma acceleration medium
                      for the PITZ electron beam parameters. A novel plasma
                      density measurement method based on the self-modulation of
                      long electron bunches was developed and validated, which
                      enabled determination of plasma densities not accessible
                      with established methods. Following these preparations, a
                      transformer ratio of 4.6+2.2−0.7was observed
                      experimentally and reproduced in numerical simulations.},
      cin          = {ZEU-PITZ},
      cid          = {I:(DE-H253)ZEU-PITZ-20120731},
      pnm          = {631 - Accelerator R $\&$ D (POF3-631)},
      pid          = {G:(DE-HGF)POF3-631},
      experiment   = {EXP:(DE-H253)PITZ-20150101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29 / PUB:(DE-HGF)11},
      doi          = {10.3204/PUBDB-2019-03713},
      url          = {https://bib-pubdb1.desy.de/record/426401},
}