Linear induction cells driven by bipolar solid-state pulsed power have accelerated a kiloamp electron beam using active reset of the magnetic core material. Four 25 kV bipolar pulsers accelerated the FXR beam in double pulse mode, resetting the magnetic core between each pulse. The integration of the active reset system into a production facility enables continued development toward cinematographic radiography. The flexibility of the solid-state active reset system to generate an arbitrary number of pulses will allow access to more physics during a single experiment. The design and capabilities of the active reset system will be presented.

This article examines the mechanical design tolerances for the Scorpius injector using a 3-D particle-in-cell (PIC) code. In order to meet its objective as a high-fidelity, multipulse flash X-ray source, the accelerator has requirements for the electron beam in order to minimize the spot size of the beam focused onto a foil target to create high fluence X-rays at energies greater than 10 MeV. The requirements for alignment of the cathode, anode beam pipe, focusing solenoids, and transport solenoids specified using Trak and AMBER are independently verified using a 3-D electrostatic/magnetostatic model of the Scorpius injector, including transverse magnetic field errors that arise from mechanical alignment errors. It is predicted that the injector will meet the performance requirements for radiographic operation and has a design margin to correct for potentially unforeseen operating conditions.

We have developed a thin-film coating for neutron generator targets that can be loaded with deuterium or tritium at low temperatures (100°C), and at gas/Ti ratios greater than 1.7. The key to this improvement is the addition of a thin palladium overcoat at the end of the titanium deposition. This overcoat prevents the oxidation of the titanium film, yet still allows loading to take place at low temperatures. A palladium overcoat of just 50–100Å is sufficient to protect the titanium, while presenting a minimal energy loss to incident ions. We have just begun producing targets using this method, and see the possibility of substantial improvement in neutron generator efficiencies.

The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions from a ~cm length interaction. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We are exploring the mechanisms behind these large accelerating gradients using fully kinetic simulations of a DPF Z-pinch and ion probe beam measurements. Our particle-in-cell simulations have successfully predicted ion beams and neutron yield from kJ-scale DPFs 1 , which past fluid simulations have not reproduced. To access the regime of MJ-scale devices within computational resources, we have developed a handoff simulation starting from a fluid calculation near the end of rundown and continuing fully kinetic through the pinch. To probe the accelerating fields in our tabletop experiment, we inject a 4 MeV deuteron beam along the z-axis. For the first time, we have directly measured the gradients in the DPF and the acceleration of an injected ion beam. We observe > 50 MV/m acceleration gradients during 800 J operation using a fast capacitive driver 2 . In addition, we have now experimentally measured and observed in simulations for the first time, electric field oscillations near the lower hybrid frequency. This is suggestive that the lower hybrid drift instability, long speculated to be the cause of the anomalous plasma resistivity that produces large DPF gradients, is playing an important role. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.

Dense-plasma-focus (DPF) Z-pinch devices are sources of copious high-energy electrons and ions, x rays, and neutrons. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood and past optimization efforts of these devices have been largely empirical. Previously we reported on fully kinetic simulations of a DPF and compared them with hybrid and fluid simulations of the same device. Here we present detailed comparisons between fully kinetic simulations and experimental data on a 1.2 kJ DPF with two electrode geometries, including neutron yield and ion beam energy distributions. A more intensive third calculation is presented which examines the effects of a fully detailed pulsed power driver model. We also compare simulated electromagnetic fluctuations with direct measurement of radiofrequency electromagnetic fluctuations in a DPF plasma. These comparisons indicate that the fully kinetic model captures the essential physics of these plasmas with high fidelity, and provide further evidence that anomalous resistivity in the plasma arises due to a kinetic instability near the lower hybrid frequency.

Active interrogation using neutrons is an effective method for detecting shielded nuclear material. A lightweight, lunch-box-sized, battery-operated neutron source would enable new concepts of operation in the field. We have developed at-scale components for a highly portable, completely self-contained, pulsed Deuterium-Tritium (DT) neutron source producing 14 MeV neutrons with average yields of 107 n/s. A gated, field ionization ion source using etched electrodes has been developed that produces pulsed ion currents up to 500 nA. A compact Cockcroft-Walton high voltage source is used to accelerate deuterons into a metal hydride target for neutron production. The results of full scale DT tests using the field ionization source are presented.

We are seeking to gain a better fundamental understanding of the ion beam acceleration and neutron production dense plasma focus (DPF) device. Experiments were performed on a kilojoule level, fast rise time DPF located at LLNL. Ion beam spectra and neutron yield were measured for deuterium pinches. Visible light images of the pinch are used to determine the pinch length. In addition, an RF probe was placed just outside the cathode to measure fluctuations in E-z up to 6 GHz, which is within the range of the lower hybrid frequencies. We find these oscillations arise at a characteristic frequency near 4 GHz during the pinch. Comparisons of the neutron yield and ion beam characteristics are presented. The neutron yield is also compared to scaling laws.

We have designed and built a Dense Plasma Focus (DPF) Z-pinch device using a kJ-level capacitor bank and a hollow anode, and fueled by a cylindrically symmetric gas puff. Using this device, we have measured peak deuteron beam energies of up to 400 keV at 0.8 kJ capacitor bank energy and pinch lengths of ∼6 mm, indicating accelerating fields greater than 50 MV/m. Neutron yields of on the order of 10(7) per shot were measured during deuterium operation. The cylindrical gas puff system permitted simultaneous operation of DPF with a radiofrequency quadrupole accelerator for beam-into-plasma experiments. This paper describes the machine design, the diagnostic systems, and our first results.

A palm sized, portable neutron source would be useful for widespread implementation of detection systems for shielded, special nuclear material. We present progress towards the development of the components for an ultra-compact neutron generator using a pulsed, meso-scale field ionization source, a deuterated (or tritiated) titanium target driven by a negative high voltage lithium tantalate crystal. Neutron production from integrated tests using an ion source with a single, biased tungsten tip and a 3x1 cm, vacuum insulated crystal with a plastic deuterated target are presented. Component testing of the ion source with a single tip produces up to 3 nA of current. Dielectric insulation of the lithium tantalate crystals appears to reduce flashover, which should improve the robustness. The field emission losses from a 3 cm diameter crystal with a plastic target and 6 cm diameter crystal with a metal target are compared.

We present first experimental results on ion beam injection along the z-axis of a Z-pinch plasma with MV/cm gradients and the first fully kinetic simulations of such beam-plasma systems. Multi-MeV, kilo-Ampere ion beams have been produced by 100 kJ class, centimeter scale, Dense Plasma Focus (DPF) Z-pinches. We have now demonstrated > 50 MV/m acceleration gradients in an 800J DPF using a fast capacitive driver1. Understanding the mechanisms behind these high gradients is essential for optimizing the device for unique compact accelerator applications. We employ an RFQ accelerator to produce a 4 MeV deuteron beam to probe the DPF plasma. Using this beam we seek to directly measure the gradients and demonstrate acceleration of an injected ion beam for the first time. Our fully kinetic, particle-in-cell simulations have reproduced observed DPF ion beams2. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability. These are the first steps to enabling a technologically simple, compact, high-current, plasma-based accelerator.

Accelerator driven fusion gammas and fast neutrons could provide unique radiography capabilities due to their ability to produce both high and low energy mono-energetic gammas and neutrons compared with broadband bremsstrahlung based x-ray sources. The possibility of simultaneously obtaining both gamma and neutron radiographs using one source could allow complex objects composed of a large range of low to high Z materials to be imaged. In this paper we review a 4 MV RFQ accelerator driven radiography test-bed at LLNL designed to study the physics involved in applying these dual output fusion reactions for radiography applications. First experimental neutron images from a carbon target are presented.

The rearrangement of plasma due to turbulence is among the most important processes that occur in planetary magnetospheres and in experiments used for fusion energy research. Remarkably , fluctuations that occur in active magnetospheres drive particles inward and create centrally peaked profiles. Until now, the strong peaking seen in space has been undetectable in the laboratory because the loss of particles along the magnetic field is faster than the net driven flow across the magnetic field. Here, we report the first laboratory measurements in which a strong superconducting magnet is levitated and used to confine high temperature plasma in a configuration that resembles planetary magnetospheres. Levitation eliminates field-aligned particle loss, and the central plasma density increases dramatically. The build-up of density characterizes a turbulent pinch and is found equal to the rate predicted from measured electric field fluctuations. Our observations show that dynamic principles describing magnetospheric plasma are relevant to plasma confined by a levitated dipole. 1 Since the discovery of the Earth's radiation belts more than fifty years ago, observations of energetic particles trapped in the Earth's dipole magnetic field have illustrated a remarkable and non-intuitive process: random, low-frequency fluctuations caused by solar activity creates diffusion that drives particles inward towards the Earth and increases particle density 1–4. Instead of flattening density gradients, diffusion causes particles trapped in a magnetic dipole to become peaked. The central peaking of particle density–occurring in opposition to the usual direction of diffusion–characterizes a " turbulent pinch. " In strongly magnetized plasma, charged particles have gyro-radii very much smaller than the radius of the Earth 5 , and plasma motion along the magnetic field is fundamentally different from motion across the field 6. Low frequency fluctuations cause the random radial motion of entire populations of particles contained within field-aligned tubes of magnetic flux, and this motion links the geometry of the magnetic field to the particle density profile. For the Earth's dipolar magnetic field, the volume enclosed by tubes of a given flux decreases rapidly as the plasma moves inward. During active periods of the magnetosphere, radial diffusion equalizes the number of particles within volumes of equal magnetic flux (and not within equivalent volumes of space), and this causes the density of inward diffusing energetic particles to increase dramatically 3, 8–10. While laboratory experiments have observed space-related plasma phenomena before 7 , the study of the cross-field transport of plasma trapped in a dipole …