Performance characteristics of a magnetic annular arc.
Magnetic annular arc thrust and current-voltage characteristics, using various working fluids
THRUST MEASUREMENT↗
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Effects of near-Earth stochastic acceleration and reflections of magnetotail ions on the formation of auroral arcs
Findings obtained from global kinetic simulations of magnetotail plasma are discussed. A region of strongly nonadiabatic ion acceleration (known as the 'wall' region) exists in the near earth tail and demarcates two very different regimes of ion motion: adiabatic and quasi-adiabatic. After convection through the wall, ion distributions rapidly become isotropized and thermalized. A strong enhancement of the cross tail current occurs on the tailward side of the wall. Comparison of numerical and adiabatic pressure profiles indicates that nonadiabatic processes operating in this region may contribute significantly to a pressure balance relief in the course of quasi-steady magnetospheric convection.
Ashour-Abdalla, Maha↗
Experimental breakdown of selected anodized aluminum samples in dilute plasmas
Anodized aluminum samples representative of Space Station Freedom structural material were tested for electrical breakdown under space plasma conditions. In space, this potential arises across the insulating anodized coating when the spacecraft structure is driven to a negative bias relative to the external plasma potential due to plasma-surface interaction phenomena. For anodized materials used in the tests, it was found that breakdown voltage varied from 100 to 2000 volts depending on the sample. The current in the arcs depended on the sample, the capacitor, and the voltage. The level of the arc currents varied from 60 to 1000 amperes. The plasma number density varied from 3 x 10 exp 6 to 10 exp 3 ions per cc. The time between arcs increased as the number density was lowered. Corona testing of anodized samples revealed that samples with higher corona inception voltage had higher arcing inception voltages. From this it is concluded that corona testing may provide a method of screening the samples.
Grier, Norman T.↗
A snapshot of high-entropy alloy processing techniques and their effects on resulting mechanical properties
High-entropy alloys (HEAs) exhibit exceptional strength, corrosion resistance, and thermal stability, making them promising candidates for nuclear, aerospace, and other extreme applications. While most prior work has focused on compositional design, manufacturing techniques themselves can alter microstructure and mechanical properties as dramatically as alloy chemistry. This review compiles and compares the effects of processing routes—including arc melting, induction melting, mechanical alloying with spark plasma sintering, and additive manufacturing—on the structure and properties of HEAs. Quantitative comparisons highlight, for example, that SPS-processed alloys can achieve ∼20–45 % higher yield and tensile strength than arc-melted counterparts, while Bridgman solidification produces nearly single-crystal structures with elongation to failure exceeding 80 %. Additive manufacturing routes such as selective laser melting offer fine microstructures but also introduce anisotropy and porosity, leading to yield strengths spanning 100–600 MPa for the same composition. By synthesizing such results, this review provides actionable insight into how processing routes interact with HEA core effects (high entropy, lattice distortion, sluggish diffusion, and cocktail effect) to determine performance, thereby offering a practical guide for optimizing manufacturing strategies.
36 MATERIALS SCIENCE↗
Transients on Arc and Convertor Currents in the Multi-cusp Cesiated Surface Conversion H-Source at LANSCE
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Accelerator Design, Technology, and Operations↗
Practical aspects of plasma processes in thermionic energy converters
Over a decade of cesium vapor thermionic converter research has yielded sufficient understanding of the basic plasma processes to permit application of this understanding to improvement of converter performance. A performance index is defined which relates such converter improvements directly to increases in system performance. A prime practical objective of current research is to reduce or eliminate the arc potential drop presently required to sustain the plasma in the ignited cesium diode. This will substantially increase the energy conversion efficiency, and will permit operation at substantially lower emitter temperatures without requiring lower collector (heat rejection) temperature. Present work is concentrating on evaluating and reducing to practice the several methods employing auxiliary ion sources to eliminate the arc drop which were demonstrated over a decade ago: i.e., various ignited and unignited triode concepts, and the pulse-enhanced diode and triode. These methods are reviewed in light of present understanding and recent experimental data.
Rasor, N. S.↗
Coordinated analysis of data
All Sky Cameras (ASCA) observations were made at the field line conjugate of the ATS-5 Satellite. The field of view of these cameras covered the region of the magnetosphere from L=5 to L=ll at the approximate longitude of the ATS field line conjugate. Definite statements are made concerning the correlation of the auroras observed by the ASCA's and the magnetospheric trapped fluxes. No auroras are observed at the field line conjugate, on quiet days when the hot plasma does not penetrate into the magnetosphere far enough to reach the ATS-5 orbit. On more disturbed days, when the ATS-5 enters the plasma sheet containing plasma clouds, an equatorward motion of the lowest latitude auroral arc is observed. Significant qualitative correlation between the ASCA data and the trapped fluxes is observed when a local plasma injection event occurs near ATS-5. The clearest signature of the injection event is magnetic and is most pronounced as a recovery of a negative bay at the ATS-5 magnetometer. The most significant correlations are observed with the intensification of the diffuse uniform glow which intensifies during the injection event.
Mende, S. B.↗
Formation of Imploding Plasma Liners for HEDP and MIF Application
Plasma jets with high density and velocity have a number of important applications in fusion energy and elsewhere, including plasma refueling, disruption mitigation in tokamaks, magnetized target fusion, injection of momentum into centrifugally confined mirrors, plasma thrusters, and high energy density plasmas (HEDP). In Magneto-Inertial Fusion (MIF), for example, an imploding material liner is used to compress a magnetized plasma to fusion conditions and to confine the resulting burning plasma inertially to obtain the necessary energy gain. The imploding shell may be solid, liquid, gaseous, or a combination of these states. The presence of the magnetic field in the target plasma suppresses thermal transport to the plasma shell, thus lowering the imploding power needed to compress the target to fusion conditions. This allows the required imploding momentum flux to be generated electromagnetically using off-the-shelf pulsed power technology. Practical schemes for standoff delivery of the imploding momentum flux are required and are open topics for research. One approach for accomplishing this, called plasma jet driven magneto-inertial fusion (PJMIF), uses a spherical array of pulsed plasma guns to create a spherically imploding shell of very high velocity, high momentum flux plasma. This approach requires development of plasma jet accelerators capable of achieving velocities of 50-200 km/s with very precise timing and density profiles, and with high total mass and density. Low-Z plasma jets would require the higher velocities, whereas very dense high-Z plasma shells could achieve the goal at velocities of only 50-100 km/s. In this report, we describe our work to develop the pulsed plasma gun technology needed for an experimental scientific exploration of the PJMIF concept, and also for the other applications mentioned earlier. The initial goal of a few hundred of hydrogen at 200 km/s was eventually replaced with accelerating 8000 μg of argon or xenon to 50 km/s for the Plasma Liner Experiment (PLX) at Los Alamos National Laboratory (LANL). Initial work used existing computational and analytical tools to develop and refine a specific plasma gun concept having a novel tapered coaxial electromagnetic accelerator contour with an array of symmetric ablative plasma injectors. The profile is designed to suppress the main barrier to success in coaxial guns, namely the blow-by instability in which the arc slips past and outruns the bulk of the plasma mass. Efforts to begin developing a set of annular non-ablative plasma injectors for the coaxial gun, in order to accelerate pure gases, resulted in development of linear parallel-plate MiniRailguns that turned out to work well as plasma guns in their own right and we subsequently chose them for an initial plasma liner experiment on the PLX facility at LANL. This choice was mainly driven by cost and schedule for that particular experiment, while longer term goals still projected use of coaxial guns for reactor-relevant applications for reasons of better symmetry, lower impurities, more compact plasma jet formation, and higher gun efficiency. Our efforts have focused mainly on 1) developing various plasma injection systems for both coax and linear railguns and ensuring they work reliably with the accelerator section, 2) developing a suite of plasma and gun diagnostics, 3) performing computational modeling to design and refine the plasma guns, 4) establishing a research facility dedicated to plasma gun development, and finally, 5) developing plasma guns and associated pulse power systems capable of achieving these goals and installing and testing the first two gun sets on the PLX facility at LANL. During the second funding cycle for this program, HyperV joined in a collaborative effort with LANL, the University of Alabama at Huntsville, and the University of New Mexico to perform a plasma liner experiment (PLX) to investigate the physics and technology of forming spherically imploding plasma liners. HyperV’s tasks focused on developing the plasma guns and associated pulse power systems required for the 30 gun experiment at LANL. Unfortunately, funding for the entire PLX collaborative project was terminated after only two years of the four year project due to program funding realignments which necessitated recompeting the project in midstream. Despite the loss of funding, HyperV installed two Mark1 guns and pulsed power systems on PLX, and jet characterization and merging experiments were subsequently successfully performed at LANL by the PLX Team. In parallel with those PLX experiments, HyperV continued its efforts to develop a plasma gun capable of meeting the PLX goal of 8 mg of argon at 50 km/s. HyperV was ultimately successful in this effort, demonstrating 10.8 mg at 52.8 km/s and 7.5 mg at 62.4 km/s with the Mark2 MiniRailgun.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The Concept of a Hybrid Pulsed Plasma Thruster for Small-Size Space Satellites
A concept of a hybrid plasma source to be used as a micro satellite thruster is proposed, where the propellant is a liquid gallium–indium alloy. The plasma source operates in two modes: 1) generation of laser ablation plasma and 2) generation of plasma in a laser-triggered, low-voltage vacuum-arc discharge. The cathode in the discharge cell of the source represents a stainless-steel capillary filled with the working liquid. The laser beam target is the working liquid meniscus. Without any voltage in the discharge gap, only laser-ablated plasma is generated. Upon application of even a relatively low voltage (<1 kV), the ablation initiates a high-current vacuum-arc discharge. In the experiments, the discharge current and voltage waveforms were recorded and so were the images of plasma glow obtained with a HSFC-Pro 4-channel high-speed camera. Regularities of current flow in the high-current vacuum-arc discharge, initiated by the cathode laser ablation, are investigated.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Voyager 1 planetary radio astronomy observations near Jupiter
Results from the first low-frequency radio receiver to be transported into the Jupiter magnetosphere are reported. Dramatic new information was obtained, both because Voyager was near or in Jupiter's radio emission sources and because it was outside the relatively dense solar wind plasma of the inner solar system. Extensive radio spectral arcs, from above 30 to about 1 MHz, occurred in patterns correlated with planetary longitude. A newly discovered kilometric wavelength radio source may relate to the plasma torus near Io's orbit. In situ wave resonances near closest approach define an electron density profile along the Voyager trajectory and form the basis for a map of the torus. Detailed studies are in progress and are outlined briefly.
Warwick, J. W.↗
Coordinated ATS-5 electron flux and simultaneous auroral observations, appendix B
All Sky Cameras (ASCA) magnetosphere observations were made at the field line conjugate of the ATS-5 Satellite. The magnetosphere region examined was L=5 to L=11. The correlation of the auroras observed by the ASCA's and the magnetospheric trapped fluxes was studied. It is shown that auroral forms are not simply correlated with the synchronous altitude electron fluxes. The presence of hot plasma at the ATS-5 satellite is a necessary but not sufficient condition for the occurrence of local auroras. On quiet days the hot plasma does not penetrate into the magnetosphere far enough to reach the ATS-5 orbit. Under these conditions no auroras are observed at the field line conjugate, but auroras are usually observed on higher latitude field lines. On more disturbed days, auroral arcs are observed at lower latitudes when the plasma sheet penetrates into the ATS-5 orbit. Significant qualitative correlation between the ASCA data and the trapped fluxes was observed when a local plasma injection event occurred near ATS-5. Magnetograms are shown.
Mende, S. B.↗
Optimization of the thermal efficiency of the magnetic annular arc.
Propulsion efficiency of magnetic annular arc /MAARC/
PLASMA ACCELERATOR↗
Three-dimensional calculation of shuttle charging in polar orbit
The charged particles environment in polar orbit can be of sufficient intensity to cause spacecraft charging. In order to gain a quantitative understanding of such effects, the Air Force is developing POLAR, a computer code which simulates in three dimensions the electrical interaction of large space vehicles with the polar ionospheric plasma. It models the physical processes of wake generation, ambient ion collection, precipitating auroral electron fluxes, and surface interactions, including secondary electron generation and backscattering, which lead to vehicle charging. These processes may be followed dynamically on a subsecond timescale so that the rapid passage through intense auroral arcs can be simulated. POLAR models the ambient plasma as isotropic Maxwellian electrons and ions (0+, H+), and allows for simultaneous precipitation of power-law, energetic Maxwellian, and accelerated Gaussian distributions of electrons. Magnetic field effects will be modeled in POLAR but are currently ignored.
Cooke, D. L.↗
Theoretical and experimental investigation on magneto-hydrodynamics of plasma window
As a new device, plasma window has been designed to use plasma discharge to separate atmosphere from vacuum with high difference of pressure. It has many excellent properties, being able to be used as available passage for ion beam with negligible energy loss, also impervious to radiation damage and thermal damage. Normally beam focusing by accelerators is not that easy to achieve within channel of small cross section. 10 mm diameter plasma window's experimental realization could contribute to its further application in accelerator system. In this paper, 10 mm diameter 60 mm long plasma window has first been designed and managed to generate arc discharge with argon gas experimentally. The result proves that it has the ability to separate at least 28.8 kPa (not the upper limit) from 360 Pa with 50 A direct current and 2.5 kW power supplied. Current increase leads to linear inlet pressure increase obviously, while it has less impact on outlet pressure and voltage, coming to the conclusion that the higher current of plasma discharge, the larger pressure difference it creates. Theoretical analysis of 10 mm diameter plasma window in axis symmetrical configuration using argon also has been provided, in which a numerical 2D FLUENT-based magneto-hydrodynamic simulation model is settled. It has a good agreement with experimental result on voltage and mass flow rate when inlet pressure is increased.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Vacuum ultraviolet radiometry with a stabilized hydrogen arc.
Use of the spectral radiation emitted from a dense hydrogen plasma of at least 12,000 K, which is in local thermodynamic equilibrium (LTE), as a light source for vacuum UV radiometry. Its spectroscopic qualities are exactly known, and except for a few strongly Stark-broadened Lyman lines, its spectrum in the vacuum UV is essentially continuous. The calculated continuum output of this source for typical operating conditions is compared with the UV output of the tungsten strip lamp and the carbon arc.
Ott, W. R.↗
Flow field characteristics and performance limitations of quasi-steady magnetoplasmadynamic accelerators
Measurements of terminal voltage, exhaust velocity, current and potential distributions in a quasi-steady MPD arc operating over a range of currents from 3 to 25 kA countervene previous indications of basic limitations on MPD performance. Terminal voltage fluctuations, previously used as an indicator of a unique limiting value of the parameter current squared over mass flow, are shown to be related to cathode surface area rather than to interelectrode plasma phenomena. With improved electrodes and insulators, satisfactory arc operation at specific impulses somewhat beyond previously proposed limits has been demonstrated, and the significant thrust producing mechanisms in such arcs have been identified.
Boyle, M. J.↗
Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel
This study demonstrates that using spin-polarized deuterium-tritium (D-T) fuel with more deuterium than tritium can increase tritium burn efficiency (TBE) by at least an order of magnitude without compromising fusion power output, compared to unpolarized fuel. Although previous studies show that a low tritium fraction can enhance TBE, this strategy resulted in reduced fusion power density. The surprising improvement in TBE at fixed power reported here is due to the TBE increasing nonlinearly with decreasing tritium fraction but the fusion power density increasing roughly linearly with D-T cross section. A study is performed for an ARC-like tokamak producing 481 MW of fusion power with unpolarized 53:47 D-T fuel, finding the minimum startup tritium inventory (I startup,min ) is 0.69 kg. By spin-polarizing half of the fuel and using a 60:40 D-T mix, I startup,min is reduced to 0.08 kg, and fully spin-polarizing the fuel with a 63:37 D-T mix further reduces I startup,min to 0.03 kg. Some ARC-like scenarios are predicted to achieve plasma ignition with relatively modest spin polarization. These findings indicate that, with advancements in helium divertor pumping efficiency, TBE values of approximately 10%–40% could be achieved using low-tritium-fraction and spin-polarized fuel with minimal power loss. This would dramatically lower tritium startup inventory requirements and reduce the amount of on-site tritium. More generally than just for spin-polarized fuels, increased plasma performance can be used to increase TBE. This strongly motivates the development of spin-polarized fuels and low-tritium-fraction operation for burning plasmas.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗