The solenoidal transport option for IFE drivers and a near-term research facility

Abstract

Solenoidal magnets have been used as the beam transport system in all high current electron induction accelerators that have been built in the past several decades. They have also been considered for the front end transport system for heavy ion accelerators for Inertial Fusion Energy drivers, but this option has received very little attention in recent years. The analysis reported here was stimulated mainly by the recent effort to define an affordable “Integrated Research Experiment” (IRE) that can meet the near-term needs of the IFE program. Solenoidal transport has a very favorable scaling as the particle mass and kinetic energy are decreased (the main reason why it is preferred for electrons in the region below 50 MeV). A central contention of this paper is that a “front end” design based on solenoidal transport can form the basis of a significantly different overall driver architecture. With a solenoidal front end, we can consider drivers with a much smaller number of beam channels at low energy, and without beam combining. A fast-running code (named SALT) has been developed at LBNL to study the axisymmetric dynamics of a particle beam transported through a sequence of solenoids. The beam is modelled as a set of ringlets, with radius and momentum traced in the axial coordinate. Emittance growth, envelope matching, and phase space evolution are treated. Initial applications to IRE scale parameters are described.