PLASMA PINCH FOR FINAL FOCUS AND TRANSPORT

Adiabatic plasma lens and Z-pinch channel transport represent attracti ve alternatives for the final transport of Heavy-Ion Fusion (HIF) beam s to target. Production of stable, reliable, precisely timed Z-pinches is a first step to establish this method of channel transport for HIF . Stable Z-pinches at currents greater than 30 kA over a distance of 4 00 mm were routinely produced at 3-10 Torr. The technique uses four di stinct steps: (1) laser ionization; (2) laser initiated resistor; (3) prepulse Z-pinch; and (4) high-current Z-pinch. The time interval betw een laser trigger and main-bank spark-gap trigger is controllable to l ess than 10 ns, limited by the firing characteristics of the spark gap . Optical channel diameters measured with a gated TV camera and correl ated with a current probe are approximately those needed for transport in fusion chamber. No large or small scale instabilities were observe d before the first current peak. A symmetric two-sided return path had a stable target interaction, even with inductively unbalanced current s. As expected, a single return path, 90 degrees to a single-pinch cha nnel had unstable alignment on the target, due to higher magnetic pres sure on the inside of the 90 degrees bend. (C) 1998 Elsevier Science B .V. All rights reserved.