J. P. Apruzese

Basic considerations for scaling Z-pinch x-ray emission with atomic number

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 o...

K-shell line ratios and powers for diagnosing cylindrical plasmas of neon, aluminum, argon, and titanium

Abstract Detailed collisional-radiative-equilibrium calculations of the ratios of the first two resonance lines of the hydrogen- and helium-like ionic stages are presented as isocontours in temperature and density space along with the total power emitted from those stages. Taken together, the contours provide a one-to-one correspondence between line ratios and power outputs and the electron temperatures and ion densities of uniform, cylindrically symmetric, optically thick plasmas. The results are given for different sized neon, aluminum, argon, and titanium plasmas, and for temperatures which favor ionization to the K shell. The underlying physics determining the dependencies of the various quantities and some of the limitations of their application are discussed. These results are intended for use in the diagnosis of Z -pinch plasmas, and can provide insight into how their properties depend on generator and load design.

Neutron production and implosion characteristics of a deuterium gas-puff Z pinch

Experiments on the Z accelerator with deuterium gas puff implosions have produced up to 3.9×1013(±20%) neutrons at 2.34 MeV (±0.10MeV). Experimentally, the mechanism for generating these neutrons has not been definitively identified through isotropy measurements, but activation diagnostics suggest multiple mechanisms may be responsible. One-, two-, and three-dimensional magnetohydrodynamic (MHD) calculations have indicated that thermonuclear outputs from Z could be expected to be in the (0.3–1.0)×1014 range. X-ray diagnostics of plasma conditions, fielded to look at dopant materials in the deuterium, have shown that the stagnated deuterium plasma achieved electron temperatures of 2.2keV and ion densities of 2×1020cm−3, in agreement with the MHD calculations.

Titanium K-shell x-ray production from high velocity wire array implosions on the 20-MA Z accelerator

The advent of the 20-MA Z accelerator [R.B. Spielman, C. Deeney, G.A. Chandler, et al., Phys. Plasmas 5, 2105, (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z-pinch K-shell scaling theories. The 2-cm long titanium arrays, which were mounted on a 40-mm diameter, produced between 75{+-}15 to 125{+-}20 kJ of K-shell x-rays. Mass scans indicate that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7{+-}0.1 to 3.2{+-}0.2 keV and obtained a K-shell emission mass participation of up to 12%.

An analytic Voigt profile escape probability approximation

Abstract An efficient analytic Voigt profile escape probability approximation is presented and compared to exact numerical calculations. Using this analytic approximation, the two-level-atom source function is also computed for optically thick media, which have been previously evaluated exactly by Avrett and Hummer. Comparison with a more realistic laboratory plasma case also validates the usefulness of the approximation for economical modeling of radiation transport in optically thick plasmas.

Efficient argon K-shell radiation from a Z pinch at currents >15 MA

The first observations of gaseous load implosions with over 15 MA in >110 ns on the Z generator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] are reported. Starting from a diameter of over 8 cm, an argon double-shell Z pinch imploded to under 0.5 cm K-shell emission diameter. With a load mass of 0.8 mg/cm, K-shell x-ray output reached 274±24 kJ in a 15 TW peak power, 12 ns pulse. This record-high yield is consistent with the current-squared scaling predicted for the “efficient” emission regime.

Direct solution of the equation of transfer using frequency- and angle-averaged photon escape probabilities, with application to a multistage, multilevel aluminum plasma

Abstract : A formalism is developed which permits direct steady-state solution of the transfer equation using escape probabilities probabilities averaged over angle and frequency. A matrix of probability-based coupling coefficients, which are related to the kernel K1 is used to obtain the source function for a doppler profile in plane-parallel geometry. Comparison is made with exact solutions, establishing the high accuracy of the technique. The method is extendable to different physical situations by simply modifying the coupling coefficients. (Author)

Dynamics of a high-power aluminum-wire array Z-pinch implosion

Annular Al-wire Z-pinch implosions on the Saturn accelerator [D. D. Bloomquist et al., Proceedings, 6th Pulsed Power Conference (Institute of Electrical and Electronics Engineers, New York, 1987), p. 310] that have high azimuthal symmetry exhibit both a strong first and weaker second x-ray burst that correlate with strong and weaker radial compressions, respectively. Measurements suggest that the observed magnetic Rayleigh–Taylor (RT) instability prior to the first compression seeds an m=0 instability observed later. Analyses of axially averaged spectral data imply that, during the first compression, the plasma is composed of a hot core surrounded by a cooler plasma halo. Two-dimensional (2-D) radiation magnetohydrodynamic computer simulations show that a RT instability grows to the classic bubble and spike structure during the course of the implosion. The main radiation pulse begins when the bubble reaches the axis and ends when the spike finishes stagnating on axis and the first compression ends. These ...

Plasma conditions required for attainment of maximum gain in resonantly photo-pumped aluminum XII and neon IX

We present a detailed analysis of the plasma conditions required to optimize gain in two proposed x‐ray lasing schemes using resonant photo‐pumping. In one proposed configuration, the Si XIII line 1s2‐1s2p1P at 6.650 A pumps Al XII 1s2−1s3p1P at 6.635 A, inverting the Al XII n = 3 and n = 2 levels which are separated by 44 A. A similar approach which utilizes the Na X 1s2‐1s2p1P line at 11.00 A would invert the n = 4, 3, and 2 levels of Ne IX. Conditions in the pumped neon and aluminum plasmas, and in the pumping silicon plasma, are calculated using a multistage, multilevel atomic model with multifrequency radiation transport. For modeling the pumping sodium line we have inferred the intensity from a spectrum of a neon filled, laser‐imploded glass microballoon containing sodium impurities obtained at Rochester. The pump line intensities calculated for Si and inferred for Na are equivalent to blackbodies of 252 and 227 eV, respectively. It is found that peak gain for the 3‐2 lines of about 100 cm−1 occurs ...

Effect of pulse sharpening on imploding neon Z‐pinch plasmas

The radial implosion of hollow, cylindrical neon gas columns, driven by currents of up to 1.45 MA, produces a linear Z pinch with over 70% of the radiation in neon K lines. A plasma erosion opening switch (PEOS) is used to eliminate prepulse and to reduce the current rise time from ∼60 to ∼20 ns. Incorporation of the PEOS improves the uniformity of the Z pinch and increases the radiation yield.