A Vlasov equilibrium previously developed1 for steady state emission into a magnetized gap in coaxial geometry is equipped with electron, ion and neutral surface emission rules that accurately support the solution profiles. These algorithms are formulated in terms of novel drift kinetic fluid particle (DKFP) methods that conserve number, momentum, and enthalpy to machine precision. The cathode boundary conditions are those of a perfect conductor that emits a electron flux radially, azimuthally, and axially. The anode boundary conditions are those of a perfectly absorbing conductor. The cathode carries a fixed current and the radial gap is set to a fixed voltage. The angular momentum of emitted electrons around the cathode is found to materially change the orbit turning points. When energy conserving solutions are examined it is found that axial velocities must remain bounded above by a well defined function of radius, magnetic field, and voltage. A fully nonlinear and self consistent Vlasov-Poisson problem is formulated and solved for the space charge distribution implied by the Vlasov equilibrium. Moments of the Vlasov distribution then determine the shunt impedance of the gap and the criteria for "warm" magnetic insulation of the coaxial line. The DKFP emission scheme must then benchmark to these profiles in the gap if it is to resolve these steady state properties. The theory limits to Ottinger's critical current magnetization picture for cold electrons, but shows a properly non-singular behavior in the electron density profile at the radial turning points and so properly reduces the enhancement of ion flux across the gap.

Wire ablation rates are important features in any examination of precursors or transparent mode implosions of wire arrays. When ion temperatures in a Ti wire plasma corona exceed a few eV, the process of resonant charge exchange competes with elastic scattering. Ions pushed into the corona from an anode bias wire array can be expected to drive a fast neutral wind into the surrounding volume, while a cathode bias wire array would not show the strong neutral wind.

In this paper, a theoretical model is described and demonstrated that serves as a useful tool for understanding K-shell radiating Z-pinch plasma behavior. Such understanding requires a self-consistent solution to the complete nonlocal thermodynamic equilibrium kinetics and radiation transport in order to realistically model opacity effects and the high-temperature state of the plasma. For this purpose, we have incorporated into the MACH2 two-dimensional magnetohydrodynamic (MHD) code [R. E. Peterkin et al., J. Comput. Phys. 140, 148 (1998)] an equation of state, called the tabular collisional radiative equilibrium (TCRE) model [J. W. Thornhill et al., Phys. Plasmas 8, 3480 (2001)], that provides reasonable approximations to the plasma’s opacity state. MACH2 with TCRE is applied toward analyzing the multidimensional implosion behavior that occurred in Decade Quad (DQ) [D. Price et al., Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] argon gas puff experiments that employed a 12cm diameter nozzle with and without a central gas jet on axis. Typical peak drive currents and implosion times in these experiments were ∼6MA and ∼230ns. By using Planar Laser Induced Fluorescence measured initial density profiles as input to the calculations, the effect these profiles have on the ability of the pinch to efficiently produce K-shell emission can be analyzed with this combined radiation-MHD model. The calculated results are in agreement with the experimental result that the DQ central-jet configuration is superior to the no-central-jet experiment in terms of producing more K-shell emission. These theoretical results support the contention that the improved operation of the central-jet nozzle is due to the better suppression of instabilities and the higher-density K-shell radiating conditions that the central-jet configuration promotes. When we applied the model toward projecting argon K-shell yield behavior for Sandia National Laboratories’ ZR machine (∼25MA peak drive currents, ∼100ns implosion times) [D. McDaniel et al., Proceedings of the 5th International Conference on Dense Z-Pinches, Albuquerque, NM, 2002, edited by J. Davis, C. Deeney, and N. R. Pereira (American Institute of Physics, New York, 2002), Vol. 651, p. 23] for experiments that utilize the 12cm diameter central-jet nozzle configuration, it predicts over 1MJ of K-shell emission is attainable.

The prospects for achieving net energy production with pB11 fuel have recently considerably brightened. Studies have shown that the multi-GG field potentially obtainable with modest dense plasma focus devices have the effect of reducing the flow of energy from the ions to the electrons and thus suppressing bremsstrahlung radiation that cools the plasma. We report here on new simulations that indicate that net energy production may be achievable in high-magnetic-field devices at peak currents as low as 2.3 MA. While these simulations only model the dense plasmoid formed in the focus, new simulation techniques can allow a full particle-in-cell simulation of DPF functioning over the wide range of time and space scales needed. Such simulations will be of great value in the next round of experiments that will use pB11 fuel.

: We propose a novel use of laser induced breakdown channels to establish a transmission line through air, which terminates at a distant load object.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Energetic implosions, using two or three load wires to create a focused axial stagnation of dense wire cores amidst the assembled precursor plasma, are examined with respect to the trade between the implosion mass lost to precursor ablation and the mass or kinetic energy available at stagnation. The calculated kinetic energy at stagnation serves as the primary source for the output X-radiation which is estimated with a tabulated collisional radiative model.

Summary form only given. We focus on the radiative characteristics and cooling rate as a function of the initial gas puff mass profile distribution. A benchmark test of the code will be made by comparisons with experimental results obtained on the DQ pulsed power generator. The experiments employed 8 cm and 12 cm diameter nozzles. One of the goals of this effort is to identify the gas puff load that minimize the development of RT instabilities during its implosion phase and optimize the corresponding emission characteristics and spectrum.

Summary form only given. Argon gas puff Z-pinches are used as sources of pulses of K shell X radiation. The density and velocity distributions of these gas puffs determine the quality of their subsequent implosions. These distributions are controlled by carefully designed annular nozzles. The effect of changes in the nozzle design on the quality of the gas puff can be assessed by directly examining the measured density distributions. Computational fluid dynamic simulation can assist in this process by providing insight into the structures and improving the fabricate/test cycle convergence. Magnetohydrodynamic (MHD) simulation can provide a relatively quick evaluation of the density distribution a given nozzle shape produce, and of the quality of the pinch that result from a given density distribution. Thus it may be possible to design improvements in nozzle shape without subjective evaluation of the density distribution.

Summary form only given. Femtosecond laser produced plasmas from clustered gases are known to produce Larmor radiation even in the absence of an ambient magnetic field. If however a fixed magnetic field is introduced along with the primary laser pulse, the laser generated electron cloud from the cluster will experience some measure of confinement and enhancement or control of the radiation yield and spectrum may be possible. The detailed accounting of the radiation intensity requires a relativistic treatment of the electron orbits for only in that domain does the Larmor radiation appear. On the other hand the standard formulation for the radiation source is also subject to strong modification in that limit when the spatial scale of the acceleration competes with the "radiation formation length". An ambient magnetic field can be expected to allow some control of these length scales and also contain the cluster ions for the duration of the Larmor radiation pulse. The proposed model will examine the free electron and ion trajectories in the magnetized cluster plasma and assess the expected Larmor radiation source function and spectrum.

Summary form only given. Plasma radiation source (PRS) loads of a few larger diameter wires offer a relatively unexplored path to energetic implosions. Such loads with larger initial wire diameters and load radii will provide lower inductance at the expense of more precursor plasma involvement. In contrast to closed arrays with hundreds of fine wires, this relatively unexplored path to energetic implosions would use two or three load wires of appropriately heavier mass and aims to create a focused axial stagnation of dense wire cores amidst the assembled precursor plasma. Initial studies of low wire count loads show promising results with respect to initial inductance and available stagnation energy. Here we examine the trade space of stagnation energy, machine current, implosion time, and delivered mass for several drivers in common use. In contrast to earlier WDM formulations with inductance matrix elements good only in the thin wire limit, the present work makes full use of a new analytic result that accounts for proximity effects among the wire cores and a direct Lorentz gauge field solver to treat the TM mode set at the midplane in the pinch region. The current elements associated with the coronal plasma are then axial filaments constrained by the local conductivity, thermal gradients, and fluid velocity. A fluid particle representation enables the resolution of precursor plasma flows and wire core stagnation. Radiation yields are estimated with tabular CRE methods.

Z-PINCH PHYSICS RADIATION FROM WIRE ARRAYS. This report describes the theory support of DTRA's Plasma Radiation Source (PRS) program carried out by NRL's Radiation Hydrodynamics Branch (Code 6720) in FY 2002. Included is work called for in DTRA MIPR 02-2045M - ''Plasma Radiation Theory Support'' and in DOE's Interagency Agreement DE-AI03-02SF22562 - ''Spectroscopic and Plasma Theory Support for Sandia National Laboratories High Energy Density Physics Campaign''. Some of this year's work was presented at the Dense Z-Pinches 5th International Conference held June 23-28 in Albuquerque, New Mexico. A common theme of many of these presentations was a demonstration of the importance of correctly treating the radiation physics for simulating Plasma Radiation Source (PRS) load behavior and diagnosing load properties, e.g, stagnation temperatures and densities. These presentations are published in the AIP Conference Proceedings and, for reference, they are included in Section 1 of this report. Rather than describe each of these papers in the Executive Summary, they refer to the abstracts that accompany each paper. As a testament to the level of involvement and expertise that the Branch brings to DTRA as well as the general Z-Pinch community, eight first-authored presentations were contributed at this conference as well as a Plenary and an Invited Talk. The remaining four sections of this report discuss subjects either not presented at the conference or requiring more space than allotted in the Proceedings.

The use of a free surface boundary condition for radiation streaming into an optically thin exterior region of a plasma radiation source (PRS) is developed and tested within the Mach2 code. The matching problem for diffusive and free streaming radiation flux at an interface is solved in the presence of energy exchange between the diffusing radiation and the ambient electron fluid. It is found that the ratio of Planck to Rosseland opacity is a strong modifier of the radiation temperature profile required to meet the match condition. Moreover, as compared to an external radiation temperature boundary condition, a free surface boundary condition predicts a radiation fluence more compatible with a semithin emission regime assessed by the tabular CRE model. The free surface condition also removes the need to assess the radiation temperature at simulation boundaries far away from the PRS.

With restrictive Courant criteria, the time integration of a radiation diffusion equation is generally done by a fully or partially implicit method. Relaxation methods are often effective and cooperative relaxation refers to a technique that will diffuse each spectral radiation group as a separate operation and combine the changes to a full spectrum. Successive passes over the groups provide convergence, as well as conserving energy over time, space and spectrum. Linearized and fully nonlinear variations on the method are discussed.