Developing the Pulsed Fission-Fusion (PuFF) Engine

In September 2013 the NASA Innovative Advanced Concept (NIAC) organization awarded a phase I contract to the PuFF team. Our phase 1 proposal researched a pulsed fission-fusion propulsion system that compressed a target of deuterium (D) and tritium (T) as a mixture in a column, surrounded concentrically by Uranium. The target is surrounded by liquid lithium. A high power current would flow down the liquid lithium and the resulting Lorentz force would compress the column by roughly a factor of 10. The compressed column would reach criticality and a combination of fission and fusion reactions would occur. Our Phase I results, summarized herein, review our estimates of engine and vehicle performance, our work to date to model the fission-fusion reaction, and our initial efforts in experimental analysis

Pulsed Fission-Fusion (PuFF)

In September 2013 the NASA Innovative Advanced Concept (NIAC) organization awarded a phase I contract to the PuFF team. Our phase 1 proposal discussed a pulsed fission-fusion propulsion system that injected gaseous deuterium (D) and tritium (T) as a mixture in a column, surrounded concentrically by gaseous uranium fluoride (UF6) and then an outer shell of liquid lithium. A high power current would flow down the liquid lithium and the resulting Lorentz force would compress the column by roughly a factor of 10. The compressed column would reach criticality and a combination of fission and fusion reactions would occur. The fission reactions would further energize the fusion center, and the fusion reactions would generate neutrons that promote more complete burnup of the fission fuel. The lithium liner provides some help as a neutron reflector but also acts as a propulsive medium, being converted to plasma which is then expanded against a magnetic nozzle for thrust. The expansion of the (primarily) lithium plasma against the nozzle's magnetic field inducts a current that is used to charge the system for the next pulse. Our concept also included secondary injection of a Field Reversed Configuration (FRC) plasmoid that would provide a secondary compression direction, axially against the column, and push the column away from the injection manifold, increasing the manifold's survivability.Our phase 1 proposal included modeling the above process first under steady state assumptions and second under a time variant integration. We proposed including these results into a Mars concept vehicle and finally proposing promising conditions to be evaluated experimentally in Phase II. In phase I we quickly realized that we needed to modify our approach. Our steady state work was completed as proposed, and the results indicated that one, a two stage compression system was not needed and two, that we wanted to move away from UF6. The steady state model shows much more margin than expected, to the point that we may well reach breakeven with the Charger 1 facility, a 572 kJ Marx bank currently under refurbishment at UAH. Additionally we found that using gaseous D-T and UF6, provided a relatively simple prospect of using a pulsed injector, made reaching criticality more difficult. The introduction of large amounts of fluorine meant a radiative sink, sapping power from the fusion plasma and was harder to handle. Therefore we moved to a solid uranium target that held D-T under pressure. In so doing we could move our target closer to criticality and remove any material that did not sustain the reaction

Design of Z-Pinch and Dense Plasma Focus Powered Vehicles

Z-pinch and Dense Plasma Focus (DPF) are two promising techniques for bringing fusion power to the field of in-space propulsion. A design team comprising of engineers and scientists from UAHuntsville, NASA's George C. Marshall Space Flight Center and the University of Wisconsin developed concept vehicles for a crewed round trip mission to Mars and an interstellar precursor mission. Outlined in this paper are vehicle concepts, complete with conceptual analysis of the mission profile, operations, structural and thermal analysis and power/avionics design. Additionally engineering design of the thruster itself is included. The design efforts adds greatly to the fidelity of estimates for power density (alpha) and overall performance for these thruster concept

Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept

Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. Magneto-Inertial Fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small fusion reactor/engine assembly (1). The Z-Pinch dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an estimated axial current of approximately 100 MA. Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4) (2). The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this is repeated over short timescales (10(exp -6) sec). This plasma formation is widely used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, as well as in fusion energy research. There is a wealth of literature characterizing Z-Pinch physics and existing models (3-5). In order to be useful in engineering analysis, a simplified Z-Pinch fusion thermodynamic model was developed to determine the quantity of plasma, plasma temperature, rate of expansion, energy production, etc. to calculate the parameters that characterize a propulsion system. The amount of nuclear fuel per pulse, mixture ratio of the D-T and nozzle liner propellant, and assumptions about the efficiency of the engine, enabled the sizing of the propulsion system and resulted in an estimate of the thrust and Isp of a Z-Pinch fusion propulsion system for the concept vehicle. MIF requires a magnetic nozzle to contain and direct the nuclear pulses, as well as a robust structure and radiation shielding. The structure, configuration, and materials of the nozzle must meet many severe requirements. The configuration would focus, in a conical manner, the Deuterium-Tritium (D-T) fuel and Lithium-6/7 liner fluid to meet at a specific point that acts as a cathode so the Li-6 can serve as a current return path to complete the circuit. In addition to serving as a current return path, the Li liner also serves as a radiation shield. The advantage to this configuration is the reaction between neutrons and Li-6 results in the production of additional Tritium, thus adding further fuel to the fusion reaction and boosting the energy output. To understand the applicability of Z-Pinch propulsion to interplanetary travel, it is necessary to design a concept vehicle that uses it. The propulsion system significantly impacts the design of the electrical, thermal control, avionics, radiation shielding, and structural subsystems of a vehicle. The design reference mission is the transport of crew and cargo to Mars and back, with the intention that the vehicle be reused for other missions. Several aspects of this vehicle are based on a previous crewed fusion vehicle study called Human Outer Planet Exploration (HOPE), which employed a Magnetized Target Fusion (MTF) propulsion concept. Analysis of this propulsion system concludes that a 40-fold increase of Isp over chemical propulsion is predicted. This along with a greater than 30% predicted payload mass fraction certainly warrants further development of enabling technologies. The vehicle is designed for multiple interplanetary missions and conceivably may be suited for an automated one-way interstellar voyage

Foot-and-Mouth Disease Virus Serotype A in Egypt

We describe the characterization of a foot-and-mouth disease (FMD) serotype A virus responsible for recent outbreaks of disease in Egypt. Phylogenetic analysis of VP1 nucleotide sequences demonstrated a close relationship to recent FMD virus isolates from East Africa, rather than to viruses currently circulating in the Middle East

Interest in employment among people with schizophrenia

There are divergent findings about the level of employment interest among community residents with schizophrenia. In addition, little is known about interest in other socially valued roles, such as formal education and training, self-development, living independently, and other forms of rehabilitation. Interest in employment is important as an indicator of demand for effective supported employment services. Data for this analysis were provided by a large and well-defined community sample of 255 persons with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder. Role functioning was investigated with the Socially-Valued Role Classification Scale. Interest in employment was high, with 85% of the participants being either employed or interested in employment as a future goal. In addition, 95% of participants were either performing, or interested in performing, two other socially valued roles (education and training or rehabilitation). This is more encouraging than some previous studies suggest and indicates that 95% of all community residents with schizophrenia and schizoaffective disorder are candidates for effective rehabilitation programs. Further research is needed to understand the importance of interest in socially valued roles and how appropriate assistance can develop both interest and lack of interest into motivation and action within each role domain

Correlates of employment interest among adults with schizophrenia

Background/Aims: Role functioning is an important part of recovery and psychiatric rehabilitation for people with schizophrenia. However, little is known about why some people and not others return to socially valued roles such as employment. While the demographic and clinical correlates of employment have been extensively studied, little is known about how employment interest forms and develops into actual employment activity. The aim was to compare demographic and clinical correlates of employment interest to correlates of actual employment participation. Methods: A community sample of 255 working-age adults with schizophrenia or schizoaffective disorder were interviewed about their current employment status and current employment interest. Univariate logistic regression was used to examine the demographic and clinical correlates of both employment interest and participation. Findings: Age, employment history and severity of current hallucinations were associated with both employment interest and participation, while illness severity pattern, illness course, severity of disability, and severity of avolition were associated only with employment participation. Conclusions: Resilience of employment interest to the clinical symptoms of schizophrenia is a promising finding. Those with more severe illness patterns and more impaired functioning can remain good candidates for vocational rehabilitation, because interest and motivation for employment may be unaffected

Removal of copper and zinc from ground water by granular zero-valent iron : a mechanistic study

Designing water treatment systems with contaminant removal based on zero-valent iron (ZVI) requires an understanding of the formation of a series of iron oxyhydroxides produced during corrosion of the thermodynamically unstable ZVI core. X-ray diffractometry (XRD) and geochemical modelling were used to investigate the mechanisms of copper and zinc removal and the formation of iron oxyhydroxides in batch experiments at 4 and 25°C, over a period of 349 days. Copper removal was predominantly associated with a mineral product, which was unstable in an aerobic environment. Zinc and some copper were sequestered into the iron oxyhydroxide structure and did not redissolve when the pH was reduced. X-ray diffractometry and geochemical modelling suggest that ZVI reacted to form magnetite and lepidocrocite, with lepidocrocite being the most stable mineral observed under the experimental conditions. However, XRD analysis did not allow the identification of poorly crystalline intermediate or substituted products which were most likely also present. Capsule Abstract During zero-valent iron treatment heavy metal contaminants are sequestered into iron oxyhydroxide structures formed during corrosion.9 page(s