Space — Time Focused Light Plasma Beams for ICF Fusion

Abstract

Experiments on the propagation and space focusing in vacuum of 200ns pulses of 100–500 kV and 0.1–1A/cm² alkali plasma beams are reported. A 100cm² area hot zeolite ion source uniformly emits a periodic array of 16 slab beamlets on 6mm centers. A 2-stage ion accelerator electrostatically focuses this array through grids to an observed ~0.1° mean angular divergence just after the exit grid. Each 3mm by 10cm beamlet is nearly 100% neutralized by secondary electrons during transmission through a backbiased 80% transparent thin honeycomb plate. This neutralized plasma beamlet is injected into an evacuated drift tube, transported with effectively 100% efficiency and space focused onto a 6cm wide strip 4 meters away. A plasma beam equilibrium and stability theory is presented which accounts for initial, thermal, and space-charge contributions to beam focusing. For the measured mean angular divergence of ~.4 degrees, the theory deduces an effective 11eV transverse temperature, relates this temperature to various sources of electron and ion emittance, and predicts that plasma beams accelerated to practical super power generator potentials of 5–15MeV would realize the sub milli-radian angular divergence profiles observed in computer simulation experiments. Experiments on plasma beam time focusing in vacuum are also reported. Measured time compression ratios of ≲20:1, and corresponding current amplification ratios of ≲10:1 are presented. This is well bevond the prior state of the art for 100keV beams with >100mA/cm² current density. A theory is presented which demonstrates that the observed time focusing could only be accomplished for less than 1% deviations from the appropriate voltage ramp — thereby establishing experimentally the accuracy of the ORCA-I precision tapered pulseline.