Progress in beam focusing and compression for warm-dense matter experiments

Abstract

The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm-dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30-mA K + ion beam with initial kinetic energy 0.3 MeV, axial compression leading to ∼50-fold current amplification and simultaneous radial focusing to beam radii of a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to our Neutralized Drift Compression Experiment and associated beam diagnostics that are under development to reach the necessary higher beam intensities, including (1) greater axial compression via a longer velocity ramp using a new bunching module with approximately twice the available volt seconds (Vs); (2) improved centroid control via beam steering dipoles to mitigate aberrations in the bunching module; (3) time-dependent focusing elements to correct considerable chromatic aberrations; and (4) plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >10 13 cm −3.