Planar Wire Arrays Research Articles

Magnetostatic and magnetohydrodynamic modeling of planar wire arrays

For the past 2 years the planar wire array loads have proven their ability to create powerful x-ray radiation sources at the pulsed power facilities with the current level ranging from 1to3MA. Several key features of the implosion and ablation dynamics of the planar wire arrays distinguish them from the wire arrays of the conventional cylindrical design. The uneven current partition through the array wires in planar geometry results in a significant difference between the ablation rates of the outermost and the innermost array wires. This difference is even higher in a double row planar array geometry. According to the three-dimensional magnetohydrodynamic simulations the effect of the delayed ablation of the inner array wires can result in effective mitigation of the Rayleigh–Taylor instability modes. The high number (200–300) of wires in a cylindrical array is preferable to ensure fine azimuthal symmetry of an array implosion. However this requirement is not a great concern for the planar wire array loads, which implode along the plane of wires. Hence, the low-wire-number planar array loads are naturally optimized for the Z-pinch experiments at short pulse (100ns) 1MA facilities. The application of planar wire array loads at high current accelerators is attractive for the purposes of the inertial confinement fusion because of the relative compactness of these loads and their potential for radiation pulse shaping.

Double planar wire array as a compact plasma radiation source

Magnetically compressed plasmas initiated by a double planar wire array (DPWA) are efficient radiation sources. The two rows in a DPWA implode independently and then merge together at stagnation producing soft x-ray yields and powers of up to 11.5kJ∕cm and more than 0.4TW∕cm, higher than other planar arrays or low wire-number cylindrical arrays on the 1MA Zebra generator. DPWA, where precursors form in two stages, produce a shaped radiation pulse and radiate more energy in the main burst than estimates of implosion kinetic energy. High radiation efficiency, compact size (as small as 3–5mm wide), and pulse shaping show that the DPWA is a potential candidate for ICF and radiation physics research.

Radiative properties of implosions of combined X-pinches and planar wire arrays composed from different wire materials on the UNR 1 MA Z-pinch generator

The radiation from implosions of X-pinches and planar wire arrays, which consist of alloyed Al and Mo wires, on the UNR 1MA ZEBRA generator was studied. Combined, planar-loop X-pinches are good surrogate sources for studying radiative properties of Z-pinch plasmas that can be of small size, high density and high temperature as are standard X-pinches. Further, the X-pinches consist of the wires from different materials and can also exhibit distinct radiation properties. In particular, combined X-pinches studied in this work used an Al 5056 (5% Mg) wire in the anode (cathode) loop and a Mo wire in the cathode (anode) loop. Combined planar wire arrays had from 10 to 15 wires arranged in one plane and consisted of the same two wire materials as used in the X-pinches. We find that planar wire arrays radiate significant peak power. Spatially-resolved and spatially integrated X-ray spectral data as well as time integrated pinhole X-ray images were analyzed. Non-LTE kinetic models were applied to study the axial gradients of electron temperatures and densities in these X-pinch and Z-pinch plasmas. Specifically, X-ray spectra of K-shell Al and Mg, and L-shell Mo were modeled. As a result, we discuss the dependence of the plasma spatial structure, temperature, density, and opacity. The importance of using different materials or alloys for Z-pinch plasma diagnostics is illustrated.

Properties of a planar wire arrays Z-pinch source and comparisons with cylindrical arrays

Planar wire array plasmas created by a 1 MA current discharge provide a novel method to investigate dense plasma dynamics, heating mechanism and radiation properties. This is a strongly inhomogeneous on small scale plasma, which has high resistivity with density and magnetic field dependence. The planar array dynamics leads to generation of a plasma with a chain of hot spots in a dense, high-opacity column. The single planar array consists of a number of wires with inter-wire separation of ≤1 mm in a linear row. It has been shown that a strongly inhomogeneous on small scale planar wire array plasma can radiate much more energy than the kinetic energy of imploding plasma. The results of recent experiments on scaling of radiation yields and powers with array masses, materials, inter-wire gaps and array width at 1 MA, 1.5 TW power Z-pinch Zebra generator at University of Nevada at Reno are presented. Radiation properties of planar arrays were compared with low-number cylindrical arrays and compact cylindrical array loads. Data on the generation of the hot spots during implosion of planar array plasma and its impact on the radiation pulse are reported.

Wire dynamics model of the implosion of nested and planar wire arrays

This paper presents the wire dynamics model (WDM), which can effectively replace the generic 0D (zero-dimensional) model in simulation of the implosions of arbitrary shaped wire arrays, including high-wire-number nested and planar array loads at multi-MA generators. Fast and inexpensive WDM modeling can predict the array implosion time and the rate of thermalization of the kinetic energy, and can estimate the timing of the x-ray pulse. Besides serving the purposes of the design and optimization of the wire array loads of complex configurations, the WDM reproduces the specific features of the wire array implosion dynamics due to the inductive current transfer, which makes the WDM a valuable amplification of the magnetohydrodynamic models.

Planar Wire Array as Powerful Radiation Source

The radiative performance of Al, Ni, and W planar wire arrays, to which little energy could be coupled via the conventional magnetic-to-kinetic conversion mechanism, is investigated. However, the planar wire arrays were shown to radiate much more energy in a short intense peak than possible due to dissipation of the kinetic energy. The planar array gives the unique possibility of seeing the evolution of the small-scale inhomogeneity of wire-array plasmas during wire ablation and implosion phases and highlights the importance of the Hall plasma phenomena and their impact on the dynamics, energy coupling, and radiation performance of wire-array Z-pinches

Radiation properties and implosion dynamics of planar and cylindrical wire arrays, asymmetric and symmetric, uniform and combined X-pinches on the UNR 1-MA zebra generator

In the following experiments, we studied implosions of different wire arrays and X-pinches produced on the 1-MA Zebra generator at the University of Nevada, Reno. Diagnostics included both spatially-resolved and time-gated X-ray imaging and spectroscopy, and laser probing. In particular, we compared planar wire arrays, to which little energy could be coupled via the conventional magnetic-to-kinetic conversion mechanism, to cylindrical wire arrays of comparable dimensions and mass. The planar wire arrays were shown to radiate much higher peak power and more energy in subkiloelectronvolt and kiloelectronvolt spectral ranges than cylindrical wire arrays. We tested the theoretical conjecture that enhanced resistivity due to the small-scale inhomogeneity of wire-array plasmas has a major effect on dynamics, energy coupling and radiation performance of wire-array Z-pinches. The study of Al, Alumel, and W cylindrical wire arrays shows a wide variety of characteristic behaviors in plasma implosions discussed hereinafter. Additional experimental results for symmetric and asymmetric, uniform stainless steel, Cu, Mo, combined Al/Mo, Mo/Al, Al/W, W/Al, and Mo/W X-pinches are also presented. New data for the total radiation yield are obtained. The planar structures of X-pinch plasma and the corresponding electron beam was observed for most of X-pinches. The generation of hot spots along original wires positions-cooler than those from the cross-wire region-and arc structures with hot spots between wires were found for X-pinches composed from Al, Cu, and W wires.

Ultrahigh-density nanowire lattices and circuits.

We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.

Advanced self-organized epitaxy for GaAs quantum wire arrays

Advanced nanostructure fabrication methods based on GaAs self-organized epitaxy are developed. Using these methods, free-standing quantum wires and bridge-type planar quantum wire arrays are realized. These new technologies will provide a powerful tool for fabricating future quantum wave devices.