R.E. Peterkin

Compact toroid formation, compression, and acceleration

Research on forming, compressing, and accelerating milligram‐range compact toroids using a meter diameter, two‐stage, puffed gas, magnetic field embedded coaxial plasma gun is described. The compact toroids that are studied are similar to spheromaks, but they are threaded by an inner conductor. This research effort, named marauder (Magnetically Accelerated Ring to Achieve Ultra‐high Directed Energy and Radiation), is not a magnetic confinement fusion program like most spheromak efforts. Rather, the ultimate goal of the present program is to compress toroids to high mass density and magnetic field intensity, and to accelerate the toroids to high speed. There are a variety of applications for compressed, accelerated toroids including fast opening switches, x‐radiation production, radio frequency (rf) compression, as well as charge‐neutral ion beam and inertial confinement fusion studies. Experiments performed to date to form and accelerate toroids have been diagnosed with magnetic probe arrays, laser interf...

A virtual prototyping environment for directed-energy concepts

Enhancements in computation hardware and the development of novel software have enabled virtual prototyping in several areas of science and engineering. In particular, the authors discuss directed energy devices that generate high-power microwave pulses.

Implosion of solid liner for compression of field reversed configuration

The design and first successful demonstration of an imploding solid liner with height to diameter ratio, radial convergence, and uniformity suitable for compressing a field reversed configuration is discussed. Radiographs indicated a very symmetric implosion with no instability growth, with /spl sim/13x radial compression of the inner liner surface prior to impacting a central measurement unit. The implosion kinetic energy was 1.5 megajoules, 34% of the capacitor stored energy of 4.4 megajoules.

Experimental and Computational Progress on Liner Implosions for Compression of FRCs

Magnetized target fusion (MTF) is a means to compress plasmas to fusion conditions that uses magnetic fields to greatly reduce electron thermal conduction, thereby greatly reducing compression power density requirements. The compression is achieved by imploding the boundary, a metal shell. This effort pursues formation of the field-reversed configuration (FRC) type of magnetized plasma, and implosion of the metal shell by means of magnetic pressure from a high current flowing through the shell. We reported previously on experiments demonstrating that we can use magnetic pressure from high current capacitor discharges to implode long cylindrical metal shells (liners) with size, symmetry, implosion velocity, and overall performance suitable for compression of FRCs. We also presented considerations of using deformable liner-electrode contacts of Z-pinch geometry liners or theta pinch-driven liners, in order to have axial access to inject FRCs and to have axial diagnostic access. Since then, we have experimentally implemented the Z-pinch discharge driven deformable liner-electrode contact, obtained full axial coverage radiography of such a liner implosion, and obtained 2frac12 dimensional MHD simulations for a variety of profiled thickness long cylindrical liners. The radiographic results indicate that at least 16 times radial compression of the inner surface of a 0.11-cm-thick Al liner was achieved, with a symmetric implosion, free of instability growth in the plane of the symmetry axis. We have also made progress in combining 2frac12-D MHD simulations of FRC formation with imploding liner compression of FRCs. These indicate that capture of the injected FRC by the imploding liner can be achieved with suitable relative timing of the FRC formation and liner implosion discharges.

Simulations of a Plasma Flow Switch

In a portion of the experimental program using the SHIVA Star capacitor bank at the Air Force Weapons Laboratory (AFWL), a cylindrical foil load is imploded using an inductive store and a plasma flow switch. We have performed a number of two-dimensional simulations of the switch and load using the MHD code MACH2. In addition to explaining the data from the first series of experiments, the simulations led to design modifications of the basic plasma flow switch that resulted in improved current delivery and in enhanced radiation yield. The experimental results are reported in a companion paper by Degnan et al. The key modification was closing portions of the vane structure. The switch must be sealed shut or else substantial current will flow in the diffuse gas that is ablated from the walls of the switch barrel.

Design, fabrication, and operation of a high-energy liner implosion experiment at 16 megamperes

We discuss the design, fabrication, and operation of a liner implosion system at peak currents of 16 MA. Liners of 1100 aluminum, with initial length, radius, and thickness of 4 cm, 5 cm, and 1 mm, respectively, implode under the action of an axial current, rising in 8 /spl mu/s. Fields on conductor surfaces exceed 0.6 MG. Design and fabrication issues that were successfully addressed include: Pulsed Power-especially current joints at high magnetic fields and the possibility of electrical breakdown at connection of liner cassette insulator to bank insulation; Liner Physics-including the angle needed to maintain current contact between liner and glide-plane/electrode without jetting or buckling; Diagnostics-X-radiography through cassette insulator and outer conductor without shrapnel damage to film.

Enhancement of the radiation yield, in plasma flow switch experiments

The Shiva Star fast capacitor bank, an inductive store, and a plasma flow switch were used to deliver multimegaampere currents with submicrosecond rise times to cylindrical foil loads. A series of numerical simulations of the plasma flow switch/imploding load system were performed with the goal of discovering a way to boost the total power radiated by the imploding plasma as it stagnates on the axis of symmetry. The changes to the experimental design that were investigated include variations of the shape of the electrodes, size and mass of the load foil, structure of the axial view vanes, shape and mass of the switching plasma, material from which the load is constructed, the degree to which the load is bowed, and the energy of the capacitor bank. Radiation yields in the range 6-9 TW are predicted for future experiments on Shiva Star. >

Three-dimensional magnetic field enhancement in a liner implosion system

The magnetic field enhancement is calculated for a magnetically imploded liner system that has flux excluding radial vanes. For the thinnest vane tested the field is found to concentrate at the vanes to a maximum value of almost three times its ambient value with a corresponding temperature increase well above the melting point. These values are calculated using the three-dimensional magnetohydrodgnamic code, MACH3. Calculations are performed for three vane thicknesses, and the vane movement is estimated. A bound is established on the design specification of the vanes based the disruption of current delivery to the liner due to the movement of the vanes. >

Full Axial Coverage Radiography of Deformable Contact Liner Implosion Performed with 8 cm Diameter Electrode Apertures

diameter ratio, radial convergence, uniformity, and implosion velocity suitable forcompressing anFRC[3]. We obtained full axial coverage radiography ofa Ourrecent progress hasbeentoreplace themorestandard deformable contact imploding liner. Thisradiographic data sliding liner-electrode contacts withdeformable linerindicates thefeasibility ofusing avarying thickness inalong electrode contacts, whichenables theuseoflarge cylindrical solid liner, driven asa 12megampZ-pinch, to electrode apertures, suitable forFRCinjection. SeeFig. 1 achieve factor - 16cylindrical convergence, while using 8cm foraillustration ofthis concept. diameter aperture electrodes. TheAlliner was30cmlong, with9.78cminner diameter forits full length, 10.0cmouter Research ontheuseofimploding liners to diameter forthecentral 18cm ofitslength, andouter compress plasmas hasbeenreported byanumberof diameter increased linearly to10.2cmat1cmfromeitherresearchers. Thisincludes suggesting thegeneral concept electrode, andto11cmatelectrode contacts. Theelectrode ofusing liners tocompress plasma, andresearch on apertures allow injection ofField Reversed Configurations in shorter orlowervelocity liner implosions [4-17], and proposed future experiments onmagnetized target fusion. implosion ofaCu-Wliner withexplosives tocompress Indexterms: capacitor bank, Field Reversed Configuration, flux to200T[18]. FRC,Magnetized Target Fusion, MTF,imploding liner, radiography, megamp Uniform-thickness liner Variable-thickness

Virtual prototyping of directed energy weapons

This paper gives an overview of how RF systems, from pulsed power to antennas, may be virtually prototyped with the improved concurrent electromagnetic particle-in-cell (ICEPIC) code. ICEPIC simulates from first principles (Maxwells equations and Lorenzs force law) the electrodynamics and charged particle dynamics of the RF-producing part of the system. Our simulations focus on gigawatt-class sources; the relativistic magnetron is shown as an example. Such simulations require enormous computational resources. These simulations successfully expose undesirable features of these sources and help us to suggest improvements