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Pulsed-power hydrodynamics (PPH) is an evolving application of low-impedance pulsed-power technology. PPH is particularly useful for the study of problems in advanced hydrodynamics, instabilities, turbulence, and material properties. PPH techniques provide a precisely characterized controllable environment at the currently achievable extremes of pressure and material velocity. The Atlas facility, which is designed and built by Los Alamos National Laboratory, is the world's first, and only, laboratory pulsed-power system designed specifically for this relatively new family of pulsed-power applications. Atlas joins a family of low-impedance high-current drivers around the world, which is advancing the field of PPH. The high-precision cylindrical magnetically imploded liner is the tool most frequently used to convert electromagnetic energy into the hydrodynamic (particle kinetic) energy needed to drive strong shocks, quasi-isentropic compression, or large-volume adiabatic compression for the experiments. At typical parameters, a 30-g 1-mm-thick liner with an initial radius of 5 cm and a moderate current of 20 MA can be accelerated to 7.5 km/s, producing megabar shocks in medium density targets. Velocities of up to 20 km/s and pressures of > 20 Mbar in high-density targets are possible. The first Arias liner implosion experiments were conducted in Los Alamos in September 2001. Sixteen experiments were conducted in the first year of operation before Arias was disassembled, moved to the Nevada Test Site (NTS), and recommissioned in 2005. The experimental program resumed at the NTS in July 2005. The first Atlas experiments at the NTS included two implosion dynamics experiments, two experiments exploring damage and material failure, a new advanced hydrodynamics series aimed at studying the behavior of particles of damaged material ejected from a free surface into a gas, and a series exploring friction at sliding interfaces under conditions of high normal pressure and high relative velocities. Longer term applications of PPH and the Atlas system include the study of material interfaces subjected to multimegagauss magnetic fields, material strength at high strain rate, the properties of strongly coupled plasmas, and the equation of state of materials at pressures approaching 10 Mbar. Index Terms--Capacitor banks, circuit model, damage, friction, high current, hydrodynamics, hydrodynamic simulation, liner implosion, material properties, pulsed-power, radiography, spall.

Several plasma targets have been proposed for compression by imploding liners, ranging from magnetically-confined to wall-supported concepts. In all cases, a critical issue remains one of preventing the high atomic-number material of the finer from penetrating the plasma and countering the gain in plasma temperature sought by compression. Two factors foster development of such deleterious penetration: the creation of a liquid/vapor layer at the liner surface at high magnetic fields, and disruption of this layer by Rayleigh-Taylor instability in the final stages of plasma compression. Within a general consideration of issues of liner compression of plasma, we discuss reactor cost optimization by use of plasma at pressures intermediate between the values of conventional magnetically- or inertially-confined fusion concepts. We also describe the development of an equilibrium layer of vapor adjacent to the liner surface at high magnetic fields, the instability of such a thin layer, and the consequences of liner deceleration and rebound for reactor concepts and research progress. Index Terms--Controlled thermonuclear fusion, imploding liners, magnetized-target fusion, Rayleigh-Taylor instability.

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 2 112 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 AI 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 21/2-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. Index Terms--Field-reversed configuration, liner implosion, magnetized plasma compression, magnetized target fusion.

Preparation of the target plasma represents a critical issue in liner compression techniques to achieve fusion conditions. We consider the use of an ultrahigh speed plasma flow from a special coaxial-gun arrangement known as the plasma flow switch. Experiments have demonstrated that this arrangement can provide plasma flows with speeds in excess of 2000 km/s. Stagnation of such a plasma flow results in fully stripped aluminum plasma with electron temperatures of 30 keV. Substitution of deuterium or a deuterium-tritium mixture could provide target plasma at kilovolt temperatures within an imploding liner. Such temperatures suggest that, even if substantial heat loss occurred during liner compression, fusion-level temperatures would be possible. The concatenation of events to generate the ultrahigh speed flow, to direct it into the implosion chamber, and to arrange liner dynamics for effective compression demands numerical simulation, which is based on initial analytical estimates. Both types of calculation for exploring this concept are discussed. Index Terms--Controlled fusion, imploding liners, plasma dynamics, pulsed-power.

Pulsed power hydrodynamics experiments typically involve multi-megajoule capacitor banks or magnetic-flux compression generators imploding thin-walled cylinders of solid-density metal by the electromagnetic force associated with axial currents in excess of 10 MA. Much of this activity operates with technology developed for other applications (e.g., soft X-ray generation), which can be significantly larger than actually required for the scientific objectives of such experiments. This is particularly true if imaging diagnostics (e.g., proton radiography) with greater spatial and temporal resolution become available, permitting implosion experiments of smaller scale size. This paper develops scaling relationships for liner implosions driven capacitively (direct or transformer coupled) or by magnetic-flux compression generators and indicates a substantial reduction in system energy with reduced scale size. A set of five dimensionless parameters describes all three circuit arrangements in a unified framework. Index Terms--Hydrodynamics, imploding liners, pulsed power, scaling laws.

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 [micro]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. Index Terms--Diagnostics, implosions, liners, megampere.

As part of ongoing hydrodynamic code verification and validation efforts, a series of near-term liner experiments (NTLX) was designed for the Shiva Star capacitor bank at the Air Force Research Laboratory [1]. An aluminum liner that is magnetically imploded onto a central target by self-induced Lorentz forces drove the experiments. Target design utilized the adaptive mesh refinement Eulerian hydrodynamics code radiative adaptive grid eulerian (RAGE) in two- and three-dimensional. One-dimensional simulations of the liner driver utilizing the lagrangian magnetohydrodynamics code RAVEN are used to set the initial temperature and density profiles as well as liner velocity at impact time. During liner/target impact, a convergent shock is generated in the target that drives subsequent hydrodynamics experiments. In concentric targets, a cylindrically symmetric shock will converge on axis. The degree of shock symmetry observed characterizes the liner symmetry at impact. By shifting the target center away from the liner driver axis, variations in shock propagation velocity generate off-center shock convergence. Results indicate that RAVEN and RAGE are in excellent agreement for the calculated shock trajectory. However, a small but significant discrepancy does occur during the last few millimeters of run-in when convergence effects are greatest. The codes predict shock arrival times that are approximately 100 ns faster than those observed experimentally. Index Terms--Code validation, convergent shocks, hydrodynamics, pulsed power.

Electron - beam diodes driven by fast-rising, high-voltage pulses often operate with cold cathodes for which the presence of a plasma adjacent to the cathode surface is essential to obtain adequate electron emission. A consequence of such surface plasma, however, is closure of the interelectrode gap by plasma motion. Resistive heating of the plasma competes with work performed in expanding the plasma and heat transfer to the cold-cathode boundary. The resulting closure speed is calculated, using an MHD code, and found to agree well with results of experiments using organic-cloth cathodes at 35 kV. Computed plasma speeds are typically 8-12 km/s, and are relatively insensitive to the applied voltage. Gap closure due to the plasma motion calculated numerically corresponds to estimates based on impedance collapse in the experiments. Index Terms - Cathode, electron-beam diode, MHD simulation.

Explosive formed fuses (EFF's) use conducting elements that are deformed by explosive pressure (typically, against dielectric dies). This causes the fuse geometry to change, so that the conducting element cross section decreases. This enables a higher ratio of current conduction to current interrupt time than for normal fuses, and it enables more control of when current interruption occurs. In combination with a suitable output closing switch, EFF's can be used to obtain several hundred kilovolt voltage pulses from inductive stores to drive several ohm loads. With proper choices of inductive store, EFF geometry and material, and output closing switch features, such a voltage pulse can be approximately flat topped for microsecond duration and have a small fraction of microsecond risetime. We present theoretical analysis and circuit simulations which illustrate this, using scaled empirical EFF parameters for inductive stores in the 1 weber flux, several hundred nanohenry range. The circuit simulations were done using MicroCap-IV, with user defined elements. These simulations were done with static inductive stores and with explosive magnetic flux compression generators driving inductive stores. Index Terms - Explosive formed fuses, explosive magnetic flux compression, high impedance loads, high voltage pulses, inductive stores.

Experiments to form and accelerate compact toroid (CT) plasmas have been performed on the 9.4 MJ Shiva Star fast capacitor bank at Phillips Laboratory since late 1990. In this paper, we report our theoretical investigations of employing a CT as a very fast opening switch. A particular axisymmetric, albeit geometrically complex, switch design is studied with the help of 2 1/2-dimensional magnetohydrodynamic computer simulations. This design, called a magnetically-confined plasma opening switch (McPOS), accumulates magnetic energy in an inductive store. Because of its intrinsic stability, the switch can conduct current for ten or more microseconds, and can open in less than 100 ns - substantially less than the rise time of the capacitively produced electric current.

The development of electrically-propelled spacecraft is a major evolution in propulsion technology. Although the energy generated from electric propulsion was considered only as an alternative to chemical energy some years back, the system has shown advantages that could improve present space propulsion capabilities. Governments, universities and industry groups in several countries, such as the US, Germany and Japan, are now vigorously pursuing electric propulsion technology.

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 ~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. Index Terms--Capacitor bank, field reversed configuration, FRC, implosion, magnetized target fusion, megamp, MTF, radiography, solid liner.

Systems, such as Shiva Star, Atlas, and magnetic-flux compression generators (MCGs), that can deliver several megajoules at currents above 10 MA offer the opportunity for many interesting experiments in controlled fusion technology and basic material dynamics. Typical current rise-times of a few microsec. onds result, even with low inductance ([is less than] 20 nH) circuitry, because several megajoules are delivered at less than 200 kV. This means that conductor surfaces can move significantly relative to the skin-layer thickness, and surface plasmas can interfere with power flow. Success with such multimegampere technology, therefore, requires considerable attention to the detailed design of joints and conductor surfaces. This paper discusses these and other design considerations. It also describes opportunities enabled by operation above 10 MA. Index Terms--Megampere, pulsed power.