F. Yilmaz

Ablation dominated implosion dynamics of aluminum and stainless steel nested cylindrical wire arrays

The results of experiments with combined aluminum (Al) and stainless steel (SS) alloy 304, nested wire arrays from the 1 MA COBRA generator at Cornell University are presented. The loads studied consisted of a 6 mm diameter inner array and a 13 mm diameter outer array with a different material in each array: SS or aluminum. Al implodes before SS in all loads studied, even when Al was on the inner array. The new wire ablation dynamic model and spectroscopic modeling are used to interpret these data. The observed implosion dynamics are likely a result of the higher ablation rate of Al. These initial results suggest that combining wire materials with different ablation rates in wire array loads could be developed into a useful technique for x-ray pulse shaping and radiation yield optimization.

Radiation Yield and Dynamics of Planar Wire‐Array Plasma

In our experiments, 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 sub‐keV and keV 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 to and radiation performance of wire‐array Z‐pinches.

Implosion dynamics and Spectroscopy of X-pinches and Wire arrays with doped Al wires on the UNR 1MA Z-pinch generator

The study of implosion dynamics and spectroscopy of X‐pinches and wire arrays with Al wires alloyed or coated with other near‐Z or higher‐Z materials is discussed. In particular, X‐pinches from two combined Al 5056 and Mo wires and composed from four identical Al 5056 (5%Mg) wires and Cu clad Al (90% Al and 10%Cu) are studied. In addition, wire arrays with Alumel wires (95% Ni and 5% Al) and with Al 5056 wires (uncoated) and coated with 5% NaF are investigated. Spatially‐resolved and integrated x‐ray spectral data and time integrated and time‐gated pinhole x‐ray images accumulated in these X‐pinch and wire array experiments on the UNR 1MA Zebra generator are analyzed. Modeling of K‐shell radiation from Mg provides K‐shell plasma parameters for all Al 5056 wire experiments, whereas modeling of L‐shell radiation from Ni, Cu, and Mo provide parameters for L‐shell plasmas. The importance of using different materials or dopants for understanding of implosion dynamics of different wire materials is illustrated.

Implosion Dynamics in Conical Wire Array Z-pinches

We present initial results from imploding conical wire array experiments performed on both the MAGPIE generator (1MA, 240ns) at Imperial College London and the Nevada Terawatt Facility’s Zebra generator (1MA, 100ns) at University of Nevada, Reno. This paper will discuss the implosion dynamics of conical wire arrays, including initial implosion of the cathode end of the array and the formation of a magnetic bubble.

X‐ray Spectroscopy and Imaging of Combined X‐pinches with Mo and W wires at Cornell and UNR 1MA Pulsed Power Devices

X‐pinch experiments using combined Mo and W wires were implemented on the 1MA Cornell University (CU) COBRA and University of Nevada, Reno (UNR) ZEBRA facilities. Spatially‐resolved and integrated x‐ray spectral data and time integrated and time‐gated pinhole x‐ray images accumulated in these X‐pinch experiments are analyzed. In particular, x‐ray L‐shell spectra of Mo ions and M‐shell spectra of W ions have been studied. A non‐LTE collisional‐radiative (CR) atomic kinetic model of Mo, successfully applied before to interpret UNR and CU x‐ray spectra from Mo X‐pinches, was used here to provide plasma parameters from L‐shell Mo radiation from the combined (W/Mo) X‐pinches. The recently developed non‐LTE CR model of W based on FAC atomic structure code data has been applied to identify and diagnose the spectral features of W ions and to provide parameters of the plasma from M‐shell W radiation from W/Mo X‐pinches. As a result, the radiative properties of W/Mo X‐pinches produced on two 1 MA university‐scale p...

Seeded Perturbations in Wire Array Z‐Pinches

Controlled seeding of perturbations is employed to study the evolution of wire array z‐pinch implosion instabilities which strongly impact x‐ray production when the 3D plasma stagnates on axis. Wires modulated in radius exhibit locally enhanced magnetic field and imploding bubble formation at discontinuities in wire radius due to the perturbed current path. Wires coated with localized spectroscopic dopants are used to track turbulent material flow. Experiments and MHD modeling offer insight into the behavior of z‐pinch instabilities.

New results on planar wire array implosions and their comparison with cylindrical wire arrays on the 1 MA zebra generator

Summary form only given. Planar wire arrays were shown to produce the strong power and yield in EUV/X-ray region. The new results of the total radiation yield Et, time-resolved sub-keV and keV outputs, X-ray spectra and images from ten wire planar arrays from low-to high-Za materials were collected recently on Zebra at UNR. Data were compared with the similar mass cylindrical wire arrays results. Planar arrays were characterized by a short rise-time of a single radiation peak: up to 8 ns for sub-keV radiation and near 2 ns in keV and harder X-ray regions, and much higher peak power compared to cylindrical arrays usually having precursor and main peak with a fastest rise-time >10-15 ns. The largest Et>18 kJ was found for Cu and Mo planar arrays (up to 25% from an energy delivered to a load) that is higher than a maximum Etap15-16 kJ for Cu or 10 kJ for Alumel (Ni) cylindrical arrays. The radiating imploding plasma is strongly inhomogeneous. The plasma (few-mm thick in the EUV/sub-keV region) has within itself hundred-mum scale structures on the axis (in several keV quanta). The electron temperatures up to 800-1000 eV were estimated for Mo planar arrays that are much higher than for cylindrical arrays and comparable with the values for X-pinches. The implosion dynamics of wire arrays were studied using spectral and imaging techniques. The results were compared with radiation and MHD modeling

Spectroscopic modeling of radiation from planar wire arrays produced on the 1 MA pulsed power generator at UNR

Summary form only given. Planar wire arrays were shown to produce the record-high peak radiation powers and yields in sub-keV and keV among all other tested loads on the 1 MA pulsed power Zebra generator at UNR. Spectroscopic modeling of radiation from such wire arrays is essential for understanding of the plasma parameters achieved in their implosions. X-ray spectra and images from 10 wire planar arrays from Alumel (alloy with 95% of Ni and 5% Al), Cu (alloy with 4% of Ni), and Al/Cu (2 Al and 8 Cu wires) were accumulated in recent experiments on Zebra. In particular, axially resolved time integrated X-ray K-shell spectra of Al and L-shell spectra of Cu and Ni were recorded by a KAP crystal (in a spectral region from 6 to 15 Aring) through different slits. The same spectra were recorded by a time-gated spectrometer in a spectral region from 6 to 10.5 Aring. In addition, spatially integrated harder X-ray spectra were monitored by a LiF crystal. Non-LTE kinetic models of Al, Ni, and Cu provided spatially and time resolved plasma parameters. The comparison with X-pinch and cylindrical wire array data is presented. Advantages of using wire array loads from alloys with small concentrations of tracer or composed from wires of a different material for spectroscopic plasma diagnostics will be highlighted. The distinct features of wire arrays plasma dynamics, magnetic energy dissipation and radiation from planar wire arrays will be discussed

Radiative Properties, Structure, and Dynamics of Asymmetric and Symmetric, Uniform and Combined X-Pinches on 1MA Zebra Generator

Experimental results of studies of the 1MA symmetric and asymmetric, uniform stainless steel, Cu, Mo, combined Al/Mo, Mo/Al, Al/W, W/Al, and Mo/W X‐pinches are presented. Implosions of X‐pinches are studied by spatially‐resolved and time‐gated x‐ray imaging, spectroscopy, and laser probing diagnostics. New data for the total radiation yield are obtained. The planar‐shape structures of X‐pinch plasma and the corresponding electron beam is observed for the most of X‐pinches. The effects of generation of hot spots along original wires positions that are cooler than that from the cross‐wire region and arc structures from hot spots between wires are found for X‐pinches composed from Al, Cu and W wires.

Study of M-Shell Radiation of Tungsten Ions from X-Pinches with Different Compositions of Loads

Summary form only given. X-pinch experiments using 188 alloy and combined Mo/W wires were implemented at the Cornell 450 kA XP facility. The spatially resolved, time-gated and integrated X-ray line spectra have been recorded using different crystal spectrometers (time-gated ADP and time-integrated mica crystal spectrometers). In particular, K-shell and L-shell X-ray line spectra from Cr, Co, and Ni ions as well as M-shell spectra from W ions have been recorded through different filters in the same shot from the 188 wire alloy X-pinch. In addition, L-shell spectra of Mo ions and M-shell spectra of W ions have been studied produced from X-pinches composed from two different wires of Mo and W. Non-LTE collisional-radiative (CR) atomic kinetic models of Ni and Co have been developed earlier to identify the useful K- and L-shell diagnostic features in X-pinch plasmas from nichrome and conichrome alloys produced at the same Cornell XP device. These models along with the Mo model were used in the present work to interpret X-ray spectra from 188 alloys and to isolate M-shell spectra of W ions. The newly developed non-LTE CR model of W has been applied to identify and diagnose the spectral features of W ions in both types of X-pinches. The distinct features, similarities, and differences of these M-shell spectra of W ions have been analyzed and compared for both types of X-pinches. The future development of this work is discussed.