Beam loading by distributed injection of electrons in a plasma wakefield accelerator.
We show through experiments and supporting simulations that propagation of a highly relativistic and dense electron bunch through a plasma can lead to distributed injection of electrons, which depletes the accelerating field, i.e., beam loads the wake. The source of the injected electrons is ionization of the second electron of rubidium (Rb II) within the wake. This injection of excess charge is large enough to severely beam load the wake, and thereby reduce the transformer ratio T. The reduction of the average T with increasing beam loading is quantified for the first time by measuring the ratio of peak energy gain and loss of electrons while changing the beam emittance. Simulations show that beam loading by Rb II electrons contributes to the reduction of the peak accelerating field from its weakly loaded value of 43  GV/m to a strongly loaded value of 26  GV/m.
Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA.
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Vafaei-Najafabadi
Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA.
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Marsh
Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA.
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Clayton
Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA.
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An
Department of Electrical Engineering, University of California Los Angeles, Los Angeles, California 90095, USA and Department of Physics and astronomy, University of California Los Angeles, Los Angeles, California 90095, USA.
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Mori
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Joshi
Department of Physics and astronomy, University of California Los Angeles, Los Angeles, California 90095, USA and Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
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Lu
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA and Department of Physics, University of Oslo, 0316 Oslo, Norway.
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Adli
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Corde
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Litos
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Li
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Gessner
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Frederico
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Fisher
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Wu
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Walz
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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England
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Delahaye
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Clarke
SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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Hogan
Max Planck Institute for Physics, 80805 Munich, Germany.
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Muggli