S. Pokala

Dynamics of Copper Wire Arrays at 1 MA and 20 MA Generators

Experiments to study the implosion dynamics and radiation characteristics of copper z-pinches have been fielded at the 1 MA Zebra facility and the 20 MA Z facility. The impact of initial load mass, initial load diameter, and nesting of wire arrays on the precursor and the stagnated plasma has been evaluated through spectroscopy, shadowgraphy, and fluence measurements. Plasma parameters extracted from modeling of the time-integrated L-shell spectra indicate the presence of more than one plasma source contributing to the radiation, likely due to non-uniform hot spot x-ray emission or temporal gradients.

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.

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.

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.

Analsysis of soliton interaction with local defects in fiber Bragg grating

The interaction of a fiber Bragg grating point like soliton with local defects has been thoroughly analyzed. The stability of trapped solitons has also been discussed. The main finding reveals the reversal of the sign of interaction from attraction to repulsion. It is also observed that the attraction depends on the accuracy of the numerical simulations.