Radiative characteristics of pulsed power driven Z-pinch aluminumplasmas

In this paper, we study the dynamics of a massive aluminum Z-pinch plasma load and evaluate its performance as a soft X-ray radiator. A radiation hydrodynamic model self-consistently driven by a circuit describes the dynamics. Comparisons are made for the K- and L-shell soft X-ray emission as a function of the ionization dynamic model. The ionization dynamic models are represented by: 1) a time-dependent nonequilibrium (NEQ) model, 2) a collisional radiative equilibrium (CRE) model, and 3) a local thermodynamic equilibrium (LTE) model. For all three scenarios the radiation is treated 1) in the free streaming optically thin approximation where the plasma is treated as a volume emitter and 2) in the optically thick regime where the opacity for the lines and continuum is self-consistently calculated online and the radiation is transported through the plasma. Each simulation is carried out independently to determine the sensitivity of the implosion dynamics to the ionization and radiation model, i.e., how the ionization dynamic model affects the radiative yield and emission spectra. Results are presented for the L- and K-shell radiation yields and emission spectra as a function of photon energy from 10 eV to 10 keV. Also, departure coefficients from LTE are presented for selected levels and ionization stages     

Spectroscopic diagnosis of nested-wire-array dynamics and interpenetration at 7 MA

Nested-wire array experiments have been conducted at the 7 MA level with 150 ns implosion times from an outer diameter of 40 mm. Analysis of spectral data indicates that material from the outer array preferentially occupies the high temperature core of the stagnated pinch independent of the interwire gap in the range of 1.1 to 4.5 mm.     

Buoyant magnetic flux tubes enhance radiation in Z pinches

In numerous experiments, magnetic energy coupled to strongly radiating Z-pinch plasmas exceeds the thermalized kinetic energy, sometimes by a factor of 2-3. We demonstrate that the enhanced energy coupling may be due to the buoyancy rise of toroidal magnetic flux tubes converging to the axis through the unstable pinch plasma. We derive an explicit formula for the enhanced dissipation rate and apply this formula to reconsider an old problem of power balance in a steady-state Z pinch, and then to analyze a new challenge of producing K-shell 3 to 10 keV radiation in long-pulse Z-pinch implosions.     

Ion viscous heating in a magnetohydrodynamically unstable Z pinch at over 2 x 10(9) Kelvin

Pulsed power driven metallic wire-array Z pinches are the most powerful and efficient laboratory x-ray sources. Furthermore, under certain conditions the soft x-ray energy radiated in a 5 ns pulse at stagnation can exceed the estimated kinetic energy of the radial implosion phase by a factor of 3 to 4. A theoretical model is developed here to explain this, allowing the rapid conversion of magnetic energy to a very high ion temperature plasma through the generation of fine scale, fast-growing m = 0 interchange MHD instabilities at stagnation. These saturate nonlinearly and provide associated ion viscous heating. Next the ion energy is transferred by equipartition to the electrons and thus to soft x-ray radiation. Recent time-resolved iron spectra at Sandia confirm an ion temperature Ti of over 200 keV (2 x 10(9) degrees), as predicted by theory. These are believed to be record temperatures for a magnetically confined plasma.     

Measurement of temperature, density, and particle transport with localized dopants in wire-array Z pinches

Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.     

Wire number doubling in high-wire-number regime increasesZ-accelerator X-ray power

Doubling the number of tungsten wires from 120 to 240, keeping the mass fixed, increased the radiated X-ray power relative to the electrical power at the insulator stack of the Z accelerator by (35±15)% for 8.75- and 20-mm radii Z-pinch wire arrays. One-dimensional radiation magneto hydrodynamic calculations suggest that the arrays were operating in a quasi “plasma-shed” regime, where the plasma generated by the individual wires partially merge prior to the inward implosion of the entire array     

Mass-profile and instability-growth measurements for 300-wire Z-pinch implosions driven by 14-18 MA

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.     

Optimal wire-number range for high x-ray power in long-implosion-time aluminum Z pinches

Experiments performed on the 8-MA Saturn accelerator to investigate the effects of interwire gap spacing on long-implosion-time Z pinches have resulted in the observation of a regime of optimal wire number. The experiments varied the wire number of 40 and 32 mm diam arrays, resulting in interwire gaps from 3.9 to 0.36 mm, with fixed mass and length. aluminum K-shell powers up to 3.4 TW were measured, with long, slow rising, lower power x-ray pulses for interwire gaps greater than 2.2 mm and less than 0.7 mm, and short, fast rising, higher power pulses for interwire gaps in the range 0.7-2.2 mm.     

Use of phosphine gold acetylides [(R3P)AuCCR] to form phosphine gold derivatives of tetra-iron and penta-iron clusters

Five new gold acetylides, [AuCCR], with hydroxyl or amino functions in the organic radical R have been prepared. From these, nine phosphine complexes [(R₃P)AuCCR] with R = Ph or Cy were synthesised. Reactions between the phosphine gold acetylides [(Ph₃P)AuCCC(Me)(OH)Et] or [(Cy₃P)AuCCC(Me)(OH)Et] and the iron carbonyl cluster [Et₄N][Fe₄N(CO)₁₂] gave both neutral [(R₃P)AuFe₄N(CO)₁₂] and ionic compounds [(R₃P)₂Au][Fe₄N(CO)₁₂]. Reaction with the penta-iron cluster [Et₄N][Fe₅N(CO)₁₄] afforded [(R₃P)₂Au][Fe₅N(CO)₁₄], [(R₃P)₂Au][Fe₄N(CO)₁₂] and [(R₃P)AuFe₄N(CO)₁₂]. The gold-iron clusters were characterised with spectroscopic methods (IR, NMR and Mössbauer) and in the case of [(Cy₃P)AuFe₄N(CO)₁₂] a single-crystal X-ray analysis.