Beam instability induced by space charge oscillation during final beam bunching for heavy ion inertial fusion

Beam instability excited by space charge effect is investigated by particle simulations during final beam bunching in heavy ion inertial fusion. The beam current is continuously increased along the beam transport line with longitudinal bunch compression. A transverse particle-in-cell simulation is carried out with a simple model of beam current increase. The multiparticle simulation shows emittance growth accompanied by the restructuring of charge distribution in the interior of the beam. An analytical stability criterion for the high-current beam transport predicts the growth of density fluctuation by the space charge effect. Although results indicate that an abrupt emittance growth is induced by the space charge oscillation at critical tune depression in the final buncher, the increase of emittance can be estimated as high as 23% at the worst case during the bunching process.