Suprathermal Electron Generation Transport and Deposition in CO₂ Laser Irradiated Targets

Abstract

In CO₂ laser interaction with matter most of the absorbed energy is initially channeled into a hot electron distribution. In many cases, resonance absorption is thought to be the dominant mechanism producing this distribution. Stimulated scattering may also play an important role.

In the coronal region of the laser plasma, hot electrons suffer losses that fall into two basic categories. First, hot electron energy is used in the sheath to accelerate fast ions. In some cases this can be a very efficient process. This is an important interaction, since some ICF concepts use energetic ions as the drive mechanism. The other coronal loss mechanism is the loss of energy to cold electrons through the drawing of a return current. Some aspects of the absorption and coronal loss processes will be illustrated by experiments on laser irradiated shells.

Experiments on both axial and lateral energy transport and deposition in spherical targets are described. A variety of diagnostics have been used to measure hot electron transport and deposition including bremsstrahlung and inner shell radiation and soft x-ray temperature measurements. Self-generated electric and magnetic fields play an important role in the transport and deposition of the hot electrons. In some cases distinct patterns of surface deposition consistent with magnetic field configurations have been observed.