Magnetic Field Confinement of Laser Irradiated Solid Particle Plasmas

Laser irradiation of a small solid particle of lithium hydride in vacuum results in the generation of a spherically symmetric, isolated, highly ionized plasma. Experimental studies with such plasmas formed within mirror and minimum‐ B magnetic field up to 8 kG show that the expanding plasma can be captured by the magnetic field and the expansion kinetic energy thermalized, in agreement with a simple magnetohydrodynamic model of the plasma‐magnetic field interaction. In the experiments, the major plasma loss occurs through the mirror loss cones, and mass spectrometer measurements show rapid escape of the highly ionized lithium followed by a more gradual decay of hydrogen indicating a scattering mechanism for the plasma decay. Plasmas with densities of 3 × 10 13 cm −3 at temperatures of 100 eV are confined for lifetimes up to 150 μ sec in a minimum‐ B field compared with the 0.3 μ sec lifetime associated with the free plasma expansion. Both the magnitude and the temperature dependence of the plasma decay from a minimum‐ B containment field are consistent with plasma loss by Coulomb collisional scattering into the magnetic field loss cones.