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This paper considers plane wave coupling to a transmission line consisting of an aerial wire above a conducting ground. Simple circuit models are constructed for the terminating impedances at the ends of the line including radiation effects. We consider the following load topologies: open circuit, short circuit, and grounded rods. Results from the transmission line model with these loads show good agreement with full-wave simulations.

We investigate the electric penetration case of the first principles multipole-based cable braid electromagnetic penetration model reported in the Progress in Electromagnetics Research B 66, 63–89 (2016). We first analyze the case of a 1-D array of wires: this is a problem which is interesting on its own, and we report its modeling based on a multipole-conformal mapping expansion and extension by means of Laplace solutions in bipolar coordinates. We then compare the elastance (inverse of capacitance) results from our first principles cable braid electromagnetic penetration model to that obtained using the multipole-conformal mapping bipolar solution. These results are found in a good agreement up to a radius to half spacing ratio of 0.6, demonstrating a robustness needed for many commercial cables. We then analyze realistic cable implementations without dielectrics and compare the results from our first principles braid electromagnetic penetration model to the semiempirical results reported by Kley in the IEEE Transactions on Electromagnetic Compatibility 35, 1–9 (1993). Although we find results on the same order of magnitude of Kley's results, the full dependence on the actual cable geometry is accounted for only in our proposed multipole model which, in addition, enables us to treat perturbations from those commercial cables measured.

It is well-known that a slotted resonant cavity with high-quality factor exhibits interior electromagnetic (EM) fields that may be even larger than the external field. The authors aim to reduce the cavity's EM fields and quality factor over a frequency band analytically, numerically, and experimentally by introducing microwave absorbing materials in the cavity. A perturbation model approach was developed to estimate the quality factor of loaded cavities, which is validated against full-wave simulations and experiments. Results with 78.7 mils (2 mm) thick ECCOSORB-MCS absorber placed on the inside cavity wall above and below the aperture slot (with only 0.026% cavity volume) result in a reduction of shielding effectiveness >19 dB and reductions in quality factor >91%, providing confirmation of the efficacy of this approach.

This paper provides an overview of the electromagnetic frequency domain simulation capabilities of the Electromagnetic Theory department at Sandia National Laboratories via a description of two of its codes. EIGER is a Method of Moments code for electromagnetic simulations, but it only runs on traditional CPUs, not on new architectures. Gemma is in development to replace EIGER and will run on many architectures, including CPUs, GPUs, and MICs, by leveraging the Kokkos library.

The ITER blanket system provides shielding of the plasma controlling field coils and vacuum vessel from the plasma heat flux as well as nuclear heating from the plasma. In addition to the thermal r...

We propose a cable braid electromagnetic penetration model that is based on first-principles and is derived strictly from the geometrical parameters of the cable in question. We apply this formulation to the case of a one-dimensional array of wires, which can also be modeled analytically via a multipole-conformal mapping expansion for the wire charges and is extended by means of Laplace solutions in bipolar coordinates. Both electric and magnetic penetrations are analyzed, and comparisons are performed between results from the first principles cable braid electromagnetic penetration model and those obtained using the multipole-conformal mapping expansion method. We find results in very good agreement when using up to the octopole moment (for the first principles model), covering a dynamic range of radius-to-half-spacing ratio up to 0.6. These results give us the confidence that our first principles model is applicable to the geometric characteristics of many commercial cables.

We report in this paper a first principles, multipole-based cable braid electromagnetic penetration model. We apply this formulation to the case of a one-dimensional array of wires, which can be modeled analytically via a multipole-conformal mapping expansion for the wire charges and extension by means of Laplace solutions in bipolar coordinates. We analyze both electric and magnetic penetrations and compare results from the first principles cable braid electromagnetic penetration model to those obtained using the multipole-conformal mapping expansion method. We find results in very good agreement when using up to the octopole moment (for the first principles model), covering a dynamic range of radius-to-half-spacing ratio up to 0.6. These results give us the confidence that our first principles model works within the geometric characteristics of many commercial cables.

High-voltage arc formation near a dielectric material is a complex process by which surface charging, secondary electron emission, and photoelectron emission modify the local electric field to determine the arc path and breakdown threshold. Strong electric field enhancement at the triple-point junction of dielectric, metal, and atmosphere may act to generate initiating electrons to seed prompt formation of streamers. This study investigates the fundamental role of dielectrics in influencing voltage breakdown threshold, statistical time lag, and reproducibility under high voltage conditions with and without external ultraviolet stimulation. We are investigating whether field emission at triple points can sufficiently minimize variance in atmospheric breakdown.

The success of dynamic materials properties research at Sandia National Laboratories has led to research into ultralow impedance, compact pulsed power systems capable of multi-MA shaped current pulses with rise times ranging from 220 to 500 ns. The Genesis design consists of two hundred and forty 200 kV, 80 kA modules connected in parallel to a solid dielectric disk transmission line and is capable of producing 280 kbar of magnetic pressure (>; 500 kbar pressure in high Z materials) in a 1.75 nH, 20-mm wide stripline load. Stripline loads operating under these conditions expand during the experiment resulting in a time-varying load that can impact the performance and lifetime of the system. This paper provides analysis of time-varying stripline loads and the impact of these loads on system performance. Further, an approach to reduce dielectric stress levels through active damping is presented as a means to increase system reliability and lifetime.

This paper discusses the penetration and coupling of a lightning return stroke through a hole in a metal barrier to a conductor located behind the hole. Indirect field coupling (electric and magnetic) and direct discharges are considered both analytically and experimentally. Although here we consider the hole to be preexisting, one application of this work is lightning return stroke coupling through holes burned in metallic barriers by the continuing current component of lightning. The goal is to develop an understanding of the mechanisms and expected penetrant levels in lightning burnthrough.

An electromagnetic analysis is performed on the ITER shield modules under different plasma-disruption scenarios using the OPERA-3d software. The models considered include the baseline design as provided by the International Organization and an enhanced design that includes the more realistic geometrical features of a shield module. The modeling procedure is explained, electromagnetic torques are presented, and results of the modeling are discussed.

This paper describes the eddy current computation and the resultant forces and torques on selected shield modules assigned to the US team that occur due to plasma disruption. The plasma disruption considered is referred to as major disruption (MD) and is one of the disruption cases defined by the International Organization (IO). This paper identifies the applicability of geometrical simplifications for future design analyses. In particular it is shown that cutting a module in half does not preserve the physics of the eddy current generation and resultant calculations while modeling a full module including the nearest modules does preserve the fundamental physics. The force results are shown for shield modules 7 and 13 exposing the validity of geometrical simplifications. The computed torque for these two modules is also presented.

A new way to connect pulsed-power modules to a common load is presented. Unlike previous connectors, the clam shell magnetically insulated transmission line (CSMITL) has magnetic nulls only at large radius where the cathode electric field is kept below the threshold for emission, has only a simply connected magnetic topology to avoid plasma motion along magnetic field lines into highly stressed gaps, and has electron injectors that ensure efficient electron flow even in the limiting case of self-limited MITLs. Multilevel magnetically insulated transmission lines with a posthole convolute are the standard solution but associated losses limit the performance of state-of-the-art accelerators. Mitigating these losses is critical for the next generation of pulsed-power accelerators. A CSMITL has been successfully implemented on the Saturn accelerator. A reference design for the Z accelerator is derived and presented. The design conservatively meets the design requirements and shows excellent transport efficiency in three simulations of increasing complexity: circuit simulations, electromagnetic fields only with Emphasis, fields plus electron and ion emission with Quicksilver.

Particle-in-cell simulations often suffer from load-imbalance on parallel machines due to the competing requirements of the field-solve and particle-push computations. We propose a new algorithm that balances the two computations independently. The grid for the field-solve computation is statically partitioned. The particles within a processor's sub-domain(s) are dynamically balanced by migrating spatially-compact groups of particles from heavily loaded processors to lightly loaded ones as needed. The algorithm has been implemented in the quicksilver electromagnetic particle-in-cell code. We provide details of the implementation and present performance results for quicksilver running models with up to a billion grid cells and particles on thousands of processors of a large distributed-memory parallel machine.

The performance of a 15-cm-radius applied-magnetic-field ion diode was investigated on the PBFA II accelerator at a power of 23 TW. The power coupling between the accelerator and diode was measured and compared with numerical simulations that show the effects of the electron flow in the MITL. The power coupled to the cathode of the diode was 18 MW. Measurements of the lithium beam generated from an electric-field-emission LiF anode showed a lithium beam power of 9 TW. The lithium beam was ballistically focused in a gas cell filled with 2 torr argon. The resultant focused power density was ∼1.8 TW/cm2 equivalent on a cylindrical target at the centerline of the diode. The focused power was limited by the 20- to 30-mR divergence of the beam caused by the LiF source used and by virtual cathode instabilities in the anode–cathode gap. The ion mode instability in the virtual cathode was studied extensively by measurement of waves in the ion emission pattern from the anode and of the E-P0 correlation between variations in the beam energy and transverse momentum. The instability Played a dominant role in the limitation of the focused lithium power.

A lightning flash consists of multiple, high-amplitude but short duration return strokes. Between the return strokes is a lower amplitude, continuing current which flows for longer duration. If the walls of a Faraday cage are made of thin enough metal, the continuing current can melt a hole through the metal in a process called burnthrough. A subsequent return stroke can couple energy through this newly-formed hole. This LDRD is a study of the protection provided by a Faraday cage when it has been compromised by burnthrough. We initially repeated some previous experiments and expanded on them in terms of scope and diagnostics to form a knowledge baseline of the coupling phenomena. We then used a combination of experiment, analysis and numerical modeling to study four coupling mechanisms: indirect electric field coupling, indirect magnetic field coupling, conduction through plasma and breakdown through the hole. We discovered voltages higher than those encountered in the previous set of experiments (on the order of several hundreds of volts).

The computational tools used in the investigation of light-ion diode physics at Sandia National Laboratories are described. Applied-B ion diodes are used to generate intense beams of ions and focus these beams onto targets as part of Sandia's inertial confinement fusion program. Computer codes are used to simulate the energy storage and pulse forming sections of the accelerator and the power flow and coupling into the diode where the ion beam is generated. Other codes are used to calculate the applied magnetic field diffusion in the diode region, the electromagnetic fluctuations in the anode-cathode gap, the subsequent beam divergence, the beam propagation, and response of various beam diagnostics. These codes are described and some typical results are shown.

We have developed a new type of convolute called the Clam Shell MITL (CSMITL) to couple multi-level accelerators to a common load. The CSMITL has magnetic nulls only at large radius where the cathode electric field is kept below the threshold for emission, has only a simply connected magnetic topology to avoid plasma motion along magnetic field lines into highly stressed gaps, and has electron injectors that ensure efficient electron flow even in the limiting case of self-limited MITLs. We report the first experimental results on a CSMITL, which convolutes two disk feeds on the Saturn accelerator into a single disk feed. Experiments with a high impedance electron beam load operating at twice the self-limited impedance of the CSMITL confirm key design features and demonstrate robust operation.

The prediction of electromagnetic loads on the ITER blanket modules during a plasma disruption is considered for two different blanket modules and different disruption events.

This report documents calculations conducted to determine if 42 low-power transmitters located within a metallic enclosure can initiate electro-explosive devices (EED) located within the same enclosure. This analysis was performed for a generic EED no-fire power level of 250 mW. The calculations show that if the transmitters are incoherent, the power available is 32 mW - approximately one-eighth of the assumed level even with several worst-case assumptions in place.

Recent advances in the analytic theory and numerical simulation of applied-B ion diodes in general and, in particular, the diodes being tested experimentally on the Particle Beam Fusion Accelerator II at Sandia National Laboratories, Albuquerque, NM, are described. Numerical simulation of these diodes using the three-dimensional particle-in-cell code QUICKSILVER and analytic stability analysis have provided new insight into the physics governing instability-induced beam divergence. Experimental evidence of these instabilities is described and compared with the theory. When simulation parameters are chosen to model present experiments, QUICKSILVER calculates beam divergence near the measured value. A new understanding of the nature of the electromagnetic instabilities and their effects on beam divergence has led to suggestions for improved diode design. A simulation of one of these design concepts shows divergence levels in the vicinity of 10 mrad, a level considered adequate for ignition experiments. >

An electromagnetic analysis is performed on the ITER shield modules under different plasma disruption scenarios using the OPERA-3d software. The modeling procedure is explained, electromagnetic torques are presented, and results of the modeling are discussed.

The use of stripline, rather than coaxial, load configurations for isentropic compression experiments (ICE) on Sandia's Z accelerator has recently become commonplace. Such loads offer many advantages over previously-developed coaxial loads, but also introduce new issues. In this paper, we will describe the behavior of these stripline loads and examine some of the issues that arise through their use.

An electromagnetic analysis is performed on different first wall designs for the ITER device. The electromagnetic forces and torques present due to a plasma disruption event are calculated and compared for the different designs.

Charged-particle simulations in three dimensions are now performed routinely in the Pulsed Power Sciences Directorate at Sandia with the QUICKSILVER suite of codes. QUICKSILVER is a multitasked, finite-difference, three-dimensional, fully relativistic, electromagnetic, particle-in-cell code developed at Sandia. It is targeted for use on current and near-term supercomputers, such as the Cray Y-MP/864 or the Cray X-MP/416, which are characterized by large, shared central memories and multiple processors. QUICKSILVER has already been used to simulate ion diodes, magnetically insulated transmission lines, microwave devices, and electron beam propagation. Before describing the suite in detail, it is worthwhile to highlight some salient architectural features of the QUICKSILVER simulation code. All grid-related quantities (electromagnetic fields and current density, for example) are stored in central memory and particle information may be stored out of memory if there is not sufficient central memory. In order to minimize the use of central memory, large conductor volumes in which fields are always zero must not be stored. This necessitates constructing the simulation region from blocks'' logically connected along arbitrary planes. The overhead required to accomplish this block connection in the field-solving routines uses a very small percentage of the total processing time. After the grid-related arrays have beenmore » allocated in memory, additional central memory is used to cache particle information. When this cache is full, it is necessary to shuffle particle information in and out of the memory cache and onto disk or other out-of-memory storage. 8 refs.« less

Initial experiments to investigate coupling of the four-stage HELIA linear-induction accelerator to a uniformly insulated applied-B ion diode in planar extraction geometry are reported. Results describing the efficient operation of an applied-B extraction ion diode coupled to the HELIA linear induction accelerator operated in positive polarity are reported. Operation of a close-coupled, undermatched, applied-B diode on HELIA was consistent with magnetically insulated transmission line (MITL) electron flow intermediate between locally emitted flow and generalized flow, rather than with full-gap flow. Peak ion coupling efficiencies of 60-70% and peak ion power levels of 0.3-0.4 TW have been achieved. >

Summary form only given. Electromagnetic simulations of the gas switch proposed for the new ZR accelerator have been revisited. The switch is designed for operation at 6 MV. The original simulations incorporated a model for cascade-gap arc formation that allowed the full cascade to make the transition from insulator to electrical conductor (cascade "run time") in about 9 ns from the time of the trigger-gap breakdown. Recent streak camera data from the cascade section of the ZR gas switch as well as careful analysis of laser-trigger-gap timing and downstream electrical measurements from recent gas switch test shots have indicated a much longer cascade run time of about 35 nanoseconds. This difference was expected to impact the electric field strength that develops on the gas-housing surface at switch closing, affecting switch reliability and lifetime. Two components of the individual gap breakdown time (and therefore of full cascade run time) are incorporated into the prescription for cascade-gap conductance evolution to enable the study of the effect of each: aft, streamer production time, or arc formation time, and cgt, conductivity growth time. Different combinations of aft and cgt that produce cascade run times (14-37 ns) covering the range seen experimentally were investigated. We find that for a given run time, longer cgt lessens the electric field on the inside of the gas housing after switch closing.

Summary form only given. The Z pulsed power driver at Sandia National Laboratories is used to develop high energy density Z-pinch X-ray sources for inertial confinement fusion research and radiation effects testing, and drive megabar pressures in material samples for equation of state studies. The pulsed power system is in the process of being replaced, improving reliability and increasing energy delivered to the load. The upgraded pulsed power system will deliver more than nine megajoules of forward wave energy in the first one hundred nanoseconds of its pulse. The system is comprised of thirty-six nominally identical modules, each producing a 3.3-terawatt pulse in 6Omega water-insulated transmission lines. The peak forward-going voltage is about 5 MV. The pulse rise time is -75 ns; the full width at half maximum is -190 ns. The thirty-six modules are combined in parallel and drive twenty to twenty-five MA into the single load. In such a system, reliable insulation and precise switching are primary concerns. We show key components of the system and results from a test module. We also show performance results from the energy storage, triggering, and pulse-forming systems. We also show the differing constraints of power flow from the 175 kA from each Marx generator, to currents in excess of 24 MA in the final feed to the load.

This paper describes the electromagnetic analysis that has been completed using the OPERA-3d product to characterize the forces on the ITER shield modules as part of the conceptual design. These forces exist due to the interaction of the eddy currents induced in the shield modules and the large magnetic fields present in the tokamak.

EIGERtrade is a general-purpose, 3D frequency-domain electromagnetics code suite consisting of a pre-processor (Jungfrau), the physics code (EIGER), and post processor (Moench). In order to better enable collaborative development, EIGERtrade version 2.0 has been approved for release as open source software under a GNU Public License. EIGERtrade is primarily an integral-equation code for both frequency-domain electromagnetics and electrostatics. This version includes the following Green's functions: 2D and 3D free space, symmetry-planes, periodic and layered media. There is a thin-wire algorithm as well as junction basis functions for attachment of a wire to a conducting surface, and also thin-slot models for coupling into cavities. The code is written in Fortran 90 using object-oriented design and has the capability to run both in parallel and serial.

This report constructs simple circuit models for a hairpin shaped resonant plasma probe. Effects of the plasma sheath region surrounding the wires making up the probe are determined. Electromagnetic simulations of the probe are compared to the circuit model results. The perturbing effects of the disc cavity in which the probe operates are also found.

An applied B-field ion diode on PBFA II has produced a 17 TW proton beam for investigation of beam generation and transport physics pertinent to inertial confinement fusion experiments. Power was led to the diode via two conical self-magnetically-insulated transmission lines that incorporated plasma opening switches. The diode utilized a pair of B-field coils in disc shaped cathodes to produce a 3 T axial B-field that insulated the 16 mm anode-cathode gap from electron loss. The 15-cm-radius anode was configured with a 5.5-cm-tall curved ion emitting region. A 2.6 MA ion beam originated from this region, was accelerated to 6 MV in the anode-cathode gap, and then transported ballistically toward the axis in a current neutralizing gas cell. The best transport (75%) occurred with narrow 5.5-cm-tall anode sources in which a 180 kJ proton beam was observed within 1.2 cm of the diode centerline. The FWHM of the beam focused at the centerline of the diode was 5 to 7 mm. This beam gave a peak proton power density of approximately 5 TW/cm/sup 2/.

The ZR accelerator is a refurbishment of Sandia National Laboratories Z accelerator [1]. The ZR accelerator components were designed using electrostatic and circuit modeling tools. Transient electromagnetic modeling has played a complementary role in the analysis of ZR components [2]. In this paper we describe a 3D transient electromagnetic analysis of the ZR water convolute and stack using edge-based finite element techniques.

STDEM is the structured mesh time-domain electromagnetic and plasma physics component of Emphasis/Nevada. This report provides a guide on using STDEM. Emphasis, the electromagnetic physics analysis system, is a suite of codes for the simulation of electromagnetic and plasma physics phenomena. The time-dependent components of Emphasis have been implemented using the Nevada framework [1]. The notation Emphasis/Nevada is used to highlight this relationship and/or distinguish the time-dependent components of Emphasis. In theory the underlying framework should have little influence on the user's interaction with the application. In practice the framework tends to be more invasive as it provides key services such as input parsing and defines fundamental concepts and terminology. While the framework offers many technological advancements from a software development point of view, from a user's perspective the key benefits of the underlying framework are the common interface for all framework physics modules as well as the ability to perform coupled physics simulations. STDEM is the structured time-domain electromagnetic and plasma physics component of Emphasis/Nevada. STDEM provides for the full-wave solution to Maxwell's equations on multi-block three-dimensional structured grids using finite-difference time-domain (FDTD) algorithms. Additionally STDEM provides for the fully relativistic, self-consistent simulation of charged particles using particle-in-cell (PIC) algorithms.

Transverse electromagnetic (TEM) wave analysis is used to estimate the efficiencies of the coax to triplate transition in Sandia's Z-20 test module. The structure of both the TEM mode and higher order TE modes in the triplate transmission line are characterized. In addition, three dimensional time domain simulations are carried out and used in conjunction with the modal analysis to provide insight into the wave structure excited in the triplate transmission line.

Models for predicting the penetration of cable shields have a long history and have had considerable success. However, occasionally, modifications to cable topology call into question the use of these models. It would thus be useful to assemble a first principles model of the shield, not only to handle changes in topology from the standard geometry, but also to form a theoretical underpinning for the existing models. The paper discusses the progress on a first principles model of a braided shield. A planar approximation to the cylindrical braid is used to reduce the number of parameters involved in the braid description. The model uses Ewald summation techniques to sum efficiently over the periodicity of the braid. Connections between the electrostatic potential behind the planar braid shield and the transfer capacitance, and also between the magnetic flux behind the shield and transfer inductance, are derived to connect planar quantities with the transfer immittances of the cylindrical braid. The braid wires are taken to be perfect electrical conductors (i.e., losses are not considered at present). Moment methods are used to calculate the static potentials about the braid wires and match the boundary conditions on the wires. The field from the net current on the wire is represented by a vector potential.

A summary of recent progress and the present status of the PBFA-II (Particle Beam Fusion Accelerator II) light-ion beam fusion program is given. An analytic theory of applied-B ion diodes has been developed that correctly predicts the diode operating points at peak power, and there is agreement between simulations and experiment for the ion beam transport to the diode axis. The anode plasma has been identified as an area for study to improve the ion beam focusing and diode impedance behavior further. An extensive array of ion beam diagnostics has been developed and proven to operate well in the harsh X-ray environment of PBFA II. Work on interpreting data from these diagnostics has provided insights into the physics of beam generation and transport and has stimulated advances in both analytic and calculational modeling of the processes. Three plasma opening switch configurations have been identified and tested. Efficient ion beam generation has been demonstrated, and a focal spot diameter of >

The US Department of Energy has supported a substantial research program in Inertial Confinement Fusion (ICF) since the early 1970s. Over the ensuing 25 years, pulsed power approaches to inertial fusion have remained of interest primarily because of the high energy, efficiency, and relatively low cost of the technology when compared to the mainline ICF approach involving large glass lasers. These compelling advantages, however, have been tempered with the difficulty in concentrating the energy in space and time to create the high energy and power density required to achieve temperatures useful in indirect drive ICF. Since the Beams '96 meeting, the situation has changed dramatically, and extremely high X-ray power (290 TW) and energy (1.8 MJ) have been produced in fast z-pinch implosions on the Z accelerator. These sources have been utilized to heat hohlraums to >150 eV and have opened the door to important ICF capsule experiments. Although light ion beams offer a long term potential for fusion energy, we are suspending our ion beam research this year to maximize progress with z pinches.

Summary form only given. QUICKSILVER is a 3-D electromagnetic particle-in-cell simulation code developed and used at Sandia to model relativistic charged particle transport. It was originally written for shared-memory, multi-processor supercomputers such as the Cray X/MP. A new parallel version of QUICKSILVER has been developed to enable large-scale simulations to be efficiently run on massively-parallel distributed memory supercomputers with thousands of processors, such as the Intel Tflops and Cplant machines at Sandia. The new parallel code implements all the features of the original QUICKSILVER and can be run on any platform that supports the message-passing interface (MPI) standard as well as on single-processor workstations. The original QUICKSILVER code was based on a multiple-block grid, which provided a natural strategy for extending the code to partition a simulation among multiple processors. By adding the automated capability to divide QUICKSILVER's existing blocks into sub-blocks and then distribute those sub-blocks among processors, a simulation's spatial domain can be easily and efficiently partitioned. Based upon this partitioning scheme as well as QUICKSILVER's existing particle-handling infrastructure, an algorithm has been developed for dynamically rebalancing the particle workload on a timestep-by-timestep basis that has proven to be very efficient. This paper will elaborate on the strategies used and describe the algorithms developed to parallelize and dynamically load-balance the code. Results of several benchmark simulations will be presented that illustrate the code's performance and parallel efficiency for a wide variety of simulation conditions. These calculations have as many as 10/sup 8/ grid cells and 10/sup 9/ particles and were run on thousands of processors.

The dramatic increase in computational capability that has occurred over the last ten years has allowed fully electromagnetic simulations of large, complex, three-dimensional systems to move progressively from impractical, to expensive, and recently, to routine and widespread. This is particularly true for systems that require the motion of free charge to be self-consistently treated. The QUICKSILVER electromagnetic Particle-In-Cell (EM-PIC) code has been developed at Sandia National Laboratories to provide a general tool to simulate a wide variety of such systems. This tool has found widespread use for many diverse applications, including high-current electron and ion diodes, magnetically insulated power transmission systems, high-power microwave oscillators, high-frequency digital and analog integrated circuit packages, microwave integrated circuit components, antenna systems, radar cross-section applications, and electromagnetic interaction with biological material. This paper will give a brief overview of QUICKSILVER and provide some thoughts on its future development.

Summary form only given, as follows. In 1993 lithium beam intensities /spl ges/1 TW/cm/sup 2/ were achieved and lithium-driven target experiments at the /spl sim/1400 TW/g level were performed on the Particle Beam Fusion Accelerator II (PBFA II) at Sandia National Laboratories. Hohlraum radiation temperatures of up to 60 eV were achieved using this lithium beam. Our 1995 Light-Ion ICF program milestone of achieving a 100 eV radiation temperature in an ion-driven hohlraum will require a lithium beam intensity of 5/spl plusmn/1 TW/cm/sup 2/ on a 4 mm diameter cylindrical target: this will require both an increase in coupled lithium power and a decrease in total lithium beam divergence. The lithium beam power has been limited to /spl sim/5-6 TW by a so called "parasitic load". This parasitic current loss in our ion diodes has recently been identified as being carried by ions that are accelerated from plasmas that are formed when high voltage electrons are lost to anodes with many monolayers of hydrocarbon surface contamination. Control of anode and cathode plasmas on the SABRE accelerator using RF-discharge cleaning, anode heating, and cryogenic cooling of the cathode have increased the efficiency of the production of lithium current by a factor of 2-3. The principal cleaning technique uses an RF-assisted (13.5 MHz, DC bias/spl sim/100 V) Ar/O/sub 2/ glow discharge to chemically combust and sputter the hydrocarbons, followed by an Ar-only discharge to remove the remaining oxides via sputtering. Anode recontamination can be limited by heating the anode to /spl sim/450/spl deg/C to reduce the sticking coefficient and stimulate thermal desorption. A new ion diode incorporating glow discharge cleaning and titanium gettering pumps has been installed in PBFAII and will be tested in December 1994. Anode heaters should be available in January 1995. Circuit model calculations indicate that we can more than double our coupled lithium ion power on PBFA II by eliminating the parasitic current.