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Electron acceleration due to the interaction between a neutralized ion beam and background plasma

Long-time evolution of the two-stream instability of an ion beam pulse propagating through a background plasma is investigated using a large-scale, one-dimensional kinetic simulation. After initial saturation of the two-stream instability due to particle trapping in the plasma wave, significant portion of the initially trapped in the wave field electrons become detrapped and move ahead of the ion beam. It is found that particles can be accelerated in front of the ion beam at a potential amplitude lower than predicted because the cold background electrons are moderately heated as they travel through the plasma wave generated due to the initial two-stream instability. The potential wells in the plasma wave is non-sinusoidal because of the modulations in both ion and electron densities. The detrapped electron population forms an electron beam that propagates faster than the ion beam and starts to interact with the background plasma ahead of the beam pulse. Secondary two-stream instability between the streaming electrons and background plasma electrons develops ahead of the ion beam pulse leading to heating of the background electrons. The heating of plasma electrons and beam ions eventually extinguish the instability.