Defocusing of an ion beam propagating in background 
plasma due to two-stream instability

Authors:   Erinc Tokluoglu and Igor Kaganovich

Abstract:  The current and charge neutralization of charged particle beams by background plasma enables ballistic beam propagation and has a wide range of applications in inertial fusion and high energy density physics. However, the beam-plasma interaction can result in the development of collective instabilities that may have deleterious effects on ballistic propagation of an ion beam. In the case of fast, light-ion beams non-linear fields created by instabilities can lead to significant defocusing of the beam. We study an ion beam pulse propagating in a background plasma, which is subject to two-stream instability between the beam ions and plasma electrons, using PIC code LSP. The defocusing effects of the instability on the beam can be much more pronounced in small radius beams. We show through simulations that a beamlet produced from an ion beam passed through an aperture can be used as a diagnostic tool to identify the presence of the two-stream instability and quantify its defocusing effects. The effect can be observed on the National Drift Compression Experiment-II (NDCX-II) facility by measuring the spot size of the extracted beamlet propagating through several meters of plasma.
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Submitted to: Physics of Plasmas
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Download PPPL-5134 (pdf 4.5 MB 13pp)
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