Space charge and current neutralized ion beam transport in laser initiated transport channels

Abstract

Summary form only given, as follows. The transport of space charge dominated particle beams is of interest to many applications. The most challenging demands are found in the field of ion beam driven inertial confinement fusion. One of the possible solutions for final ion beam focusing and transport through the reactor chamber is discharge channel transport. This technique has the advantage of providing complete space charge and current neutralization of the ion beam. To be applicable to an ion beam driven fusion reactor, the final transport system has to avoid destructible structures in the reactor chamber. This is the primary reason to study laser initiated discharge channels. One important feature of final focusing and transport based on a plasma discharge is the large acceptance in the transverse phase space, which allows the transmission of beams with different initial angles to the channel axis. This provides the possibility to merge several individual beams in a neutralizing environment, reducing the number of beam entrances into the reactor chamber. A further advantage of a plasma based system is the large acceptance in the longitudinal phase space. This will allow to use simultaneously beams with different energy to drive the target, as assumed in different target designs for heavy ion beam fusion. Therefore plasma based focusing and transport relaxes the requirements for the accelerator significantly. Motivated by these advantages, neutralized beam transport and focusing in gas discharge plasmas is under investigation for heavy ion beam fusion at the Lawrence Berkeley National Laboratory (LBNL) and at GSI Darmstadt. The program is outlined and some experimental results of plasma diagnostics on the laser initiated discharge channel and of heavy ion beam transport experiments in these channels are discussed.