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The expansion of a resistive plasma into an external magnetic field has been treated in the limit in which the magnetic field does not perturb the plasma motion. The use of a class of exact solutions for the purely radial motion of the plasma in the absence of a field permits the reduction of the electromagnetic problem to consideration of a diffusion equation for the magnetic stream function. Explicit solutions are derived for a resistive spherical plasma expanding into a uniform applied magnetic field. Representative numerical results related to laser-produced plasma experiments of Haught and Polk are presented.

The motion of a plasma produced by Q-spoiled laser irradiation of a LiH particle has been analyzed as a spherical hydrodynamic expansion of a quasineutral ideal gas of ions and electrons in local thermal equilibrium. Using Dawson's form of the plasma optical absorption coefficient, digital computer calculations were made for laser pulse and particle parameters approximating those of the experiments of Haught and Polk. Calculated distributions of plasma pressure, density, temperature, and velocity are in agreement with solutions obtained for the system of equations by the method of separation of variables. For given laser pulse energy, the calculated plasma energy is maximized for rise times and pulse widths of the order of the time required for expansion of the plasma to the size of the laser focal spot. The calculated energy of the plasma divided by its total number of ions and electrons was found to be approximately independent of the degree of ionization assumed.

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 × 1013 cm−3 at temperatures of 100 eV are confined for lifetimes up to 150 μsec in a minimum-B field compared with the 0.3 μsec 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.