Heating uniformity of a microwave discharge plasma to redistribute a solid fuel layer inside a cryogenic target for inertial confinement fusion

Abstract

In the plasma layering technique, a microwave discharge plasma is turned on in the void of a nonuniform solid fuel layer inside a cryogenic laser fusion target to redistribute the nonuniform layer into a uniform one. The heating uniformity of the plasma initiated by a one-dimensional electric field was examined experimentally and theoretically by making a glow discharge in a quartz shell located in a strong microwave field at room temperature. The heating uniformity on the inner surface of the shell was estimated by measuring the surface temperature of the shell. When the frequency of the external electric field was 2.45 GHz, the resultant measured heating uniformity at the gas density of <0.7 g/m3 should be sufficient to obtain a uniform solid fuel layer for laser implosion experiments. At higher gas densities, the heating uniformity was insufficient because of the nonuniform distribution of the plasma. Countermeasures to improve the uniformity are discussed.