Emittance growth induced by space charge effect during final beam bunching in heavy ion inertial fusion is investigated by particle simulations and theoretical considerations. Beam current is continuously increased along the beam transport with longitudinal bunch compression. Stability criterion of the high-current beam transport is also changed with the growth of space charge effect. Transverse particle simulation is carried out with a simple model of beam current increase. Multiparticle simulations with different initial distributions indicate emittance growth and the restructuring of charge distribution in the interior of the beam. Theoretical analysis for the instability due to strong space charge effect predicts unstable beam transport, and ensures the situation observed by particle simulation.
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