Two energies are identified that define the x-ray emission characteristics of Z-pinch array implosions. One, the kinetic energy per ion, is intensive, and the other, the kinetic energy per centimeter, is extensive. From a series of one-dimensional axisymmetric hydrodynamic calculations, we have calculated the dependence of the x-ray emission from aluminum implosions above 1 keV on these energies. These calculations are carried out for a specially chosen theoretical case where the kinetic energy that is generated during implosion is converted to thermal energy and x rays during the plasma collision on axis in the absence of current. In this case, we determine the I4 to I2 transition of the scaling of emission with peak current, I, as a parametric function of the kinetic energy per ion. We also determine a functional dependence of the emission on this energy when the mass of the imploded aluminum array is held fixed. It is seen that the ability of the plasma to radiate large amounts of energy in either I4 or I2 regimes is strongly dependent on the mass loading. Finally, some arguments are presented on how the breakpoint between I4 and I2 scaling is expected to scale when the atomic number of the array load is varied.

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A model is presented for the radially inhomogeneous Hg-Ar positive column discharge with properties similar to the standard fluorescent lamp. The model combines the electron excitation reactions and radiation trapping to self-consistently solve the spatially dependent species rate equations. Collision rates are evaluated from the electron distribution function determined from the inhomogeneous Boltzmann equation with the gradient term. Radiation processes are evaluated through frequency dependent cell-to-cell coupling constants. This general radiation transport method accounts for non-local photo-pumping, line overlap within the isotopic structure of the Hg resonance lines, and an emission line profile subject to partial frequency redistribution. The coupling constants agree with a more computationally intensive Monte Carlo code. The emission line profile provides an effective decay rate for the 185 nm line, which follows trends in measurements. In contrast, the use of a uniform constant escape factor for radiation trapping leads to centrally constricted profiles for the Hg excited states. Model results for the mean electron energy, distribution function and density distribution of Hg triplet levels are found to agree with existing spatially resolved data. Predicted and measured broad profiles for the Hg triplet levels are attributed to photo-pumping of the outer plasma regions by inner ones.

To examine prospects for gain in a Lyman-a recombination laser driven by a high-intensity, shortpulse laser, we calculate the residual energy in both hydrogen and helium during recombination after the ionizing pulse. The expected gain as a function of residual energy and density is then separately evaluated. The residual energy calculation includes above-threshold ionization (ATI) in the presence of a background plasma, as well as inverse-bremsstrahlung heating. At electron densities over 10" cm ' but below critical density, the plasma reduces the ATI energy by approximately a factor of 2, but without a previously reported dependence on the pulse width. Inverse-bremsstrahlung heating can be significant, but is not dominant for the parameters considered. Detailed recombination-laser gain calculations were performed for the Ly-a transitions of both H and He, using Stark profiles to represent the laser line cross section. To obtain gain of near 2 cm lasting at least a few ps, the H plasma temperature must be less than 3.5 eV and electron density between 4X 10" and 4X10" cm; for He, the temperature must be less than 15 eV and the electron density between 2X 10'8 and 2X10' cm '. Our calculations indicate that these conditions can be satisfied for H, if the driving laser intensity is above 4X 10' Wcm, and for He, if the laser intensity is above 1.7 X 10' W cm and the wavelength is below 0.6 pm.PACS number(s): 42.55. Vc, 32.80.Rm, 52.40.Nk, 52.50.Jm

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