W. J. Waganaar

A high density field reversed configuration (FRC) target for magnetized target fusion: First internal profile measurements of a high density FRC

Magnetized target fusion (MTF) is a potentially low cost path to fusion, intermediate in plasma regime between magnetic and inertial fusion energy. It requires compression of a magnetized target plasma and consequent heating to fusion relevant conditions inside a converging flux conserver. To demonstrate the physics basis for MTF, a field reversed configuration (FRC) target plasma has been chosen that will ultimately be compressed within an imploding metal liner. The required FRC will need large density, and this regime is being explored by the FRX–L (FRC-Liner) experiment. All theta pinch formed FRCs have some shock heating during formation, but FRX–L depends further on large ohmic heating from magnetic flux annihilation to heat the high density (2–5×1022 m−3), plasma to a temperature of Te+Ti≈500 eV. At the field null, anomalous resistivity is typically invoked to characterize the resistive like flux dissipation process. The first resistivity estimate for a high density collisional FRC is shown here. Th...

Intense ion beam optimization and characterization with infrared imaging

We have developed two-dimensional calorimetry with infrared imaging of beam targets to optimize and measure the energy-density distribution of intense ion beams. The technique, which measures a complete energy-density distribution on each machine firing, has been used to rapidly develop and characterize two very different beams—a 400 keV beam used to study materials processing and an 80 keV beam used for magnetic fusion diagnostics. Results of measurements, using this technique, varying the diode applied magnetic field strength and geometry, anode material type and configuration, and anode-cathode gap spacing are presented and correlated with other observations. An assessment of calorimeter errors due to target ablation is made by comparison with Faraday cup measurements and computer modeling of beam-target interactions.

Preparation of diamondlike carbon films by high‐intensity pulsed‐ion‐beam deposition

Diamondlike carbon (DLC) films were prepared by high‐intensity pulsed‐ion‐beam ablation of graphite targets. A 350 keV, 35 kA, 400 ns beam, consisting primarily of hydrogen, carbon, and oxygen ions was focused onto a graphite target at a fluence of 15–45 J/cm2. Amorphous carbon films were deposited at up to 30 nm per pulse, corresponding to an instantaneous deposition rate greater than 1 mm/s. Electrical resistivities were between 1 and 1000 Ω cm. Raman spectra indicate that diamondlike carbon is present in most of the films. Electron‐energy‐loss spectroscopy indicates significant amounts of sp3‐bonded carbon, consistent with the presence of DLC. Scanning electron microscopy showed most films contain 100 nm features, but micron size particles were deposited as well. Initial tests revealed favorable electron field‐emission behavior.

Confinement analyses of the high-density field-reversed configuration plasma in the field-reversed configuration experiment with a liner

The focus of the field-reversed configuration (FRC) experiment with a liner (FRX-L) is the formation of a target FRC plasma for magnetized target fusion experiments. An FRC plasma with density of 1023m−3, total temperature in the range of 150–300 eV, and a lifetime of ≈20μs is desired. Field-reversed θ-pinch technology is used with programed cusp fields at θ-coil ends to achieve non-tearing field line reconnections during FRC formation. Well-formed FRCs with density between (2–4)×1022m−3, lifetime in the range of 15–20μs, and total temperature between 300–500 eV are reproducibly created. Key FRC parameters have standard deviation in the mean of 10% during consecutive shots. The FRCs are formed at 50 mTorr deuterium static fill using 2 kG net reversed bias field inside the θ-coil confinement region, with external main field unexpectedly ranging between 15–30 kG. The high-density FRCs confinement properties are approximately in agreement with empirical scaling laws obtained from previous experiments with fi...

Large-scale implantation and deposition research at Los Alamos National Laboratory

This paper provides a review of research performed at two novel, large-scale ion implantation and deposition facilities developed within the High Energy-Density Physics Group at Los Alamos National Laboratory: the Plasma Source Ion Implantation (PSII) facility, where large-area (several m2) workpieces are being implanted with nitrogen and carbon for tribological applications using a 100 kV, 60 A pulse modulator, and the High Intensity Pulsed Ion Beam (HIPIB) facility, where high-temperature superconductor and diamond-like carbon films are being deposited from substrate material evaporated with a 300 keV, 30 kA ion beam capable of energy fluences of 30 kJ/cm2 per pulse over an area of 25 cm2.

Cratering behavior in single- and poly-crystalline copper irradiated by an intense pulsed ion beam

When treated with intense pulsed ion beams (IPIB), many materials exhibit increased wear resistance, fatigue life, and hardness. However, this treatment often results in cratering and roughening of the surface. In this work, high purity single crystal and polycrystalline copper samples were irradiated with pulses from an IPlB to gain insight into the causes of this cratering behavior. Samples were treated with 1,2,5, and 10 shots at 2 J/cm2 and 5 J/cm2 average energy fluence per shot. Shots were about 400 ns in duration and consisted of a mixture of carbon, hydrogen, and oxygen ions at 300 keV. It was found that the single crystal copper cratered far less than the polycrystalline copper at the lower energy fluence. At the higher energy fluence, cratering was replaced by other forms of surface damage, and the single crystal copper sustained less damage at all but the largest number of shots. Molten debris from the Lucite anode (the ion source) was removed and redeposited on the samples with each shot. Introduction Intense Pulsed Ion Beams (IHB) have been under investigation for a number of years in Japan, the Former Soviet Union, Germany, and the United States for materials processing applications [I-71. Such PIE3 devices typically produce beams of 10’s of kiloamps current at 100’s to 1OOO’s of kilovolts, in pulses of 50 -lo00 ns. Although these are called “ion beams”, they are, in fact beams of neutral plasma although only the ions are initially accelerated, electrons are pulled off surfaces to provide quasi-neutrality. -I __ When treated with by PIE%, many materials exhibit increased wear resistance, fatigue life, and hardness. However, this treatment often results in cratering and roughening of the surface [8lo], which undergoes rapid melting and resolidification. Although FIB treatment of pure materials such as copper [8,9] and silicon [ 1 1 J has been studied, it is not clear whether this cratering damage results from alloy content, explosive behavior of impurities at grain boundaries, grain structure itself, or impact of debris on the molten surface. In the work reported here, high purity single crystal and polycrystalline copper samples were irradiated with pulses from an FIB to gain insight into the causes of this cratering behavior. Samples were treated with 1,2,5, and 10 shots of 400 ns duration at 2 J/cm2 and 5 Jkm2 average energy fluence per shot. Following treatment, the samples were examined for damage with a scanning electron microscope. Experimental Apparatus Experiments were performed on the Anaconda IPIB at Los Alamos National Laboratory (LANL) [ 123. Anaconda utilizes the ballistically focused, magnetically insulated ion diode shown in Figure 1. Ions are formed by the flashover of a conical annulus of Lucite attached to the anode electrode. Ions are accelerated across a 300 kV gap toward nested, truncated metal cones that form the cathode. Field emitted cathode electrons are prevented from shorting the anode-cathode gap by a transverse magnetic field generated by pulsed electromagnets which surround the cathode cone. The azimuthal ExB drift of electrons in the anodecathode gap causes them to stay confined. The diode is connected directly to a Marx generator operated to produce-a.3-00 keV, 30 kA, 400 ns beam of carbon, hydrogen, and oxygen ions. The ballistic focus of the diode produces a minimum spot size of about 100 cm2fyfetcfing energy fluences at focus of about 30 J/cm2. This energy fluence is sufficient to ablate material. Since we desired to rapidly melt and resolidify the surface, we placed the samples past OUTER COIL

FRC lifetime studies for the Field Reversed Configuration Heating Experiment (FRCHX)

The goal of the Field-Reversed Configuration Heating Experiment (FRCHX) is to demonstrate magnetized plasma compression and thereby provide a low cost approach to high energy density laboratory plasma (HEDLP) studies, which include such topics as magneto-inertial fusion (MIF). A requirement for the field-reversed configuration (FRC) plasma is that the trapped flux in the FRC must maintain confinement of the plasma within the capture region long enough for the compression process to be completed, which is approximately 20 microseconds for FRCHX. Current lifetime measurements of the FRCs formed with FRCHX show lifetimes of only 7 ∼ 9 microseconds once the FRC has entered the capture region.

Characterization and modeling of the ablation plumes formed by intense-pulsed ion beam impact on solid targets

An investigation of the properties of the ablation products from intense-pulsed ion beam impact on solid targets is described. Measurements and calculations of the properties of the ablation plume are presented and correlated with incident beam parameters. Experimental techniques include Thomson parabola particle spectroscopy to measure the incident ion beam atomic composition and the energy spectrum of each beam component, thermal imaging to measure the incident-beam energy density, time-resolved photography to measure the plume expansion time history and geometry, and time-resolved energy-density measurements of the plume. The results of a thermal transport model of the beam-target interaction are presented, and a detailed comparison with measurements is made.

Multichord optical interferometry of FRX-L’s field reversed configuration

A 0.633μm laser interferometer provides detailed time resolved information about the spatial distribution of the plasma density of field reversed configurations (FRC’s) produced by the FRX-L experiment at Los Alamos National Laboratory. This experiment is an effort to produce a magnetized plasma with closed field lines suitable for compression by a solid metal liner imploded by the Shiva Star capacitor bank at the Air Force Research Laboratory. The interferometer probes a fanned array of eight chords through the FRC midplane, measuring the line integrated free electron density via its effect on optical phase shift relative to eight reference beams as a function of time. The reference beams are given nominally identical optical paths, except that they are folded for compactness and given an 80MHz higher optical frequency by use of a Bragg cell beam splitter. After the beams are recombined, interference results in 80MHz electromagnetic beat waves with dynamic phase shifts equal to those of the corresponding...

Separatrix radius measurement of field-reversed configuration plasma in FRX-L

Magnetic pickup coils and single turn flux loops are installed on the FRX-L device. The combination of the two measurements provides the excluded flux radius that approximates the separatrix radius of the field-reversed configuration (FRC) plasma. Arrays of similar probes are used to map out local magnetic field dynamics beyond both ends of the theta-coil confinement region to help understand the effects of cusp locations on flux trapping during the FRC formation process. Details on the probe design and system calibrations are presented. The overall system calibration of excluded flux radius measurement is examined by replacing FRC plasma with a known radius aluminum conductor cylinder.