Measurements of the ion emission from targets irradiated with
neodymium glass and iodine lasers were analyzed and a very significant
anomaly observed. The fastest ions with high charge number Z,
which usually are of megaelectron volt energy following the
relativistic self-focusing and nonlinear-force acceleration theory,
were reduced to less than 50 times lower energies when 1.2 ps laser
pulses of about 1 J were incident. We clarify this discrepancy by the
model of skin depth plasma front interaction in contrast to the
relativistic self-focusing with filament generation. This was indicated
also from the unique fact that the ion number was independent of the
laser intensity. The skin layer theory prescribes prepulse control and
lower (near relativistic threshold) laser intensities for
nonlinear-force-driven plasma blocks for high-gain ignition similar to
light ion beam fusion.
Weibel Instability in a Bi-Maxwellian Laser Fusion Plasma