Hypersonic Plasma Jets Research Articles

Hypersonic Plasma Setup for Oxidation Testing of Ultrahigh Temperature Ceramic Composites

Abstract In this study, a hypersonic plasma setup was constructed based on a vortex plasma heater with prenozzle gas-dynamic insertion. The prenozzle allows the improvement of the characteristics of the vacuum system according to the necessities of the experiments. The plasma setup produces a hypersonic thermal flow, which is capable to test the thermal oxidation of ultrahigh temperature ceramics (UHTC) composites, such as zirconium diboride (ZrB2). Thereby, ZrB2 samples were prepared with a variation of 10, 20, and 30% of silicon carbide (SiC) in volume, in order to investigate the oxidation mechanisms and microstructural properties of the samples tested under hypersonic thermal flow. The results of the oxidation tests showed that the samples with 10 and 30% of SiC undergo to the active oxidation and forms an unstable and fragile ZrO2 oxide. The formed ZrO2 does not withstand the drag force and the thermal flux of the hypersonic plasma jet, partially volatilizing the oxide layer, causing an accentuated loss of mass. For the oxidation tests of the sample with 20% of SiC, the gain of mass was observed due to the formation of ZrSiO4 passivation layer, which is a stable oxide and promotes mechanical resistance, and low degradation rate. These results can be associated with the variation of SiC, which demonstrates an ideal proportion of 20% of SiC in ZrB2, which influences the oxidation mechanisms and produce a protective layer.

Experimental characterization of a section of a spherically imploding plasma liner formed by merging hypersonic plasma jets

We report experimental results on merging of hypersonic plasma jets, which is the fundamental building block for forming spherically imploding plasma liners as a potential standoff compression driver for magneto-inertial fusion. Jets are formed and launched by contoured-gap coaxial plasma guns mounted at the six vertices and the center of a hexagon covering approximately one-tenth of the surface area of a 9-ft-diameter spherical chamber. First, from experiments with two and three merging jets of four different species (N, Ar, Kr, and Xe), we show that (1) density spatial non-uniformities can be large (with electron-density jumps ranging from 2.9 for N to 6.6 for Xe) when shocks form upon jet merging, but smaller (density jumps <2) when shocks do not form; (2) jet impurities (20% Ti in these experiments) can increase the level of density spatial non-uniformity by increasing the collisionality of jet merging, leading to shock formation rather than potentially more desirable shockless jet merging; and (3) the liner Mach number can remain high (≳10), as required for plasma liners to be an effective compression driver. Second, from experiments with six and seven merging jets using Ar, we present results with improved jet-to-jet mass balance of <2% across jets, including (1) evidence of substantially increased balance in the jet merging and symmetry of the liner structure and (2) potentially favorable changes in the jet-merging morphology with the addition of the seventh jet. For both experiments, we present comparisons between experimental and synthetic data from three-dimensional hydrodynamic codes.

Experimental study of ion heating in obliquely merging hypersonic plasma jets

In this experiment, we measure ion temperature evolution of collisional plasma shocks and colliding supersonic plasma flows across a range of species (Ar, Kr, Xe, and N), Mach numbers, and collisionalities. Shocks are formed via the collision of discrete plasma jets relevant to plasma-jet-driven magneto-inertial fusion (PJMIF). We observe nearly classical ion shock heating and ion-electron equilibration, with peak temperatures attained consistent with collisional shock heating. We also observe cases where this heating occurs in a smooth merged structure with reduced density gradients due to significant intepenetration of the plasma jets. In application to PJMIF liners, we find that Mach number degradation due to ion shock heating will likely not be significant at the typical full-scale conditions proposed, and that a degree of interpenetration may be an attractive condition for PJMIF and similar approaches which seek to form uniform merged structures from discrete supersonic plasma jets.

Neutronics Calculations for a Hypothetical Plasma-Jet-Driven Magneto-Inertial-Fusion Reactor

We present neutronics calculations for a hypothetical fusion reactor based on the repetitively pulsed concept of plasma-jet-driven magneto-inertial fusion (PJMIF). A PJMIF reactor is envisioned to have a replaceable, 3-m-radius spherical metal first wall exposed to 14.1-MeV neutrons; a fast-flowing FLiBe liquid blanket (with thickness 0.75 m) behind the first wall serving as the primary coolant and tritium-breeding medium; and finally an outer structural spherical wall shielded by the blanket. Cylindrical penetrations through both walls and the flowing blanket allow for hundreds of plasma gun drivers to inject hypersonic plasma jets that form both the deuterium-tritium plasma target and high-Z spherically imploding plasma liner to compress the target. This research is the first to conduct Monte Carlo N-Particle (MCNP6.2) and CINDER2008 neutronics calculations relevant to the PJMIF reactor configuration, with the primary objectives of determining (1) the neutron flux as a function of blanket thickness in the blanket and key reactor components and (2) the tritium production rate in the liquid blanket. These results will be used to estimate other quantities of interest, such as first-wall and gun-electrode lifetimes based on displacements per atom (dpa) accumulation, optimum blanket thickness, activation level of the outer wall and xenon liner, and achievable tritium-breeding ratios. Energy-dependent flux tallies were used to calculate neutron flux inside the FLiBe blanket and outer wall, as well as the cylindrical ports where plasma guns are located. Tally multipliers of the flux in MCNP6.2 estimated tritium breeding ratio, dpa, and nuclear heating, while the depletion code CINDER2008 was used to compare tritium breeding ratios with MCNP6.2 and calculate activation of the outer wall and xenon liner. These calculations provide a baseline for blanket requirements necessary for power production in a PJMIF reactor.

Simulation study of the influence of experimental variations on the structure and quality of plasma liners

Simulation studies of a section of a spherically imploding plasma liner, formed by the merger of six hypersonic plasma jets, have been performed at conditions relevant to the Plasma Liner Experiment (PLX) [S. C. Hsu et al., IEEE Trans. Plasma Sci. 46, 1951–1961 (2018)]. The main aim of simulations was to study the sensitivity of the detailed structure of plasma liners and their global properties to experimental mass variations and timing jitter across the six plasma jets. Experimentally observable synthetic quantities have been computed using simulation data and compared with the available experimental data. Simulations predicted that the primary oblique shock wave structure is preserved at small experimental variations. At later phases of the liner implosion, primary shocks and, especially, secondary shocks are more sensitive to experimental variations. These conclusions follow from the simulation data and experimental CCD camera images. Small displacements of shock wave structures may also cause significant changes in the synthetic interferometer data at early time. Our studies showed that such global properties of the plasma liners such as the averaged Mach number and averaged ram pressure along the leading edges of plasma liners are less sensitive to experimental variations. Simulation data of the liner structure were largely confirmed by the PLX experimental data.

Optimization of the TiB2 plasma dynamic synthesis

Titanium Diboride (TiB2) nanoparticles were obtained by plasma dynamic synthesis in a hypersonic plasma jet. The aim of the work was to optimize synthesis of TiB2 nanoparticles. Firstly, three series of experiments with different ways of a discharge initiation were implemented: 1) using titanium conductors; 2) using carbon fibers; 3) using graphite aerosol (graphitization). Secondly, experiments with different atmosphere gas, which filled the volume of the reactor chamber – Ar and N2 were implemented. Thirdly, there were experiments with different mass ratio of Ti:B precursors using graphitization (26.7:73.3; 45.5:54.5; 61.1:38.9; 86.4:13.6). And finally experiments with 16.9 kJ released energy were implemented. The results showed, that the best of way of initiation an arc discharge is graphitization using Ar with mass ratio Ti:B 26.7:73.3 and input energy − 33.9 kJ. The yield of TiB2 was 93.2% with the smallest particles 56.1 nm.

Magnetized Plasma Target for Plasma-Jet-Driven Magneto-Inertial Fusion

We identify the desired characteristics and parameters of a beta>1 magnetized plasma, possibly with highly tangled, open field lines, that could be a suitable target to be compressed to fusion conditions by a spherically imploding plasma liner [S. C. Hsu et al., IEEE Trans. Plasma Sci. 40, 1287 (2012)] formed by merging hypersonic plasma jets. This concept is known as plasma-jet-driven magneto-inertial fusion (PJMIF). We set requirements on the target and liner such that (a) compressional heating dominates over thermal transport in the target, and (b) magnetic amplification due to compression dominates over dissipation over the entire implosion. We also evaluate the requirements to avoid drift-instability-induced anomalous transport and current-driven anomalous resistivity in the target. Next, we describe possible approaches to create such a magnetized, beta>1 plasma target. Finally, assuming such a target can be created, we evaluate the feasibility of a proof-of-concept experiment using presently achievable plasma jets to demonstrate target compressional heating at a plasma-liner kinetic energy of <~ 100 kJ (a few hundred times below that needed in a PJMIF reactor).

The Influence of the Ratio of Precursors on the Powdered Product of Plasmodynamic Synthesis in the System Ti-B

The present work reported a novel way of making nanocrystalline Ti-B phases (titanium boride and titanium diboride) in a hypersonic plasma jet. According to the purpose to synthesize nanosized Ti-B phases, experiments with different mass proportions of precursors were implemented. The optimal ratio of precursors, which leads to the yield of titanium diboride is 93.2% and the average particle size, doesn`t exceed 56.1 nm, is the ratio of Ti: B of 26.7: 73.3.

Physics Criteria for a Subscale Plasma Liner Experiment

Spherically imploding plasma liners, formed by merging hypersonic plasma jets, are a proposed standoff driver to compress magnetized target plasmas to fusion conditions [S. C. Hsu et al., IEEE Trans. Plasma Sci. 40, 1287 (2012)]. In this paper, the parameter space and physics criteria are identified for a subscale, plasma-liner-formation experiment to provide data, e.g., on liner ram-pressure scaling and uniformity, that are relevant for addressing scientific issues of full-scale plasma liners required to achieve fusion conditions. Based on these criteria, we quantitatively estimate the minimum liner kinetic energy and mass needed, which informed the design of a subscale plasma liner experiment now under development.

Interaction of the jet from the neutron star with the interstellar medium

The interaction between the hypersonic plasma jet from the accreting neutron star and the ambient interstellar medium is studied. It is assumed that the jet is launched from the accretion disk via the open magnetic field anchored in the disk. The analytical investigation for the structure of the working surface of the jet is carried out. The estimates of the volume stream functions in the region of the interaction between the jet and the interstellar medium are derived. The obtained results allow to examine the distribution of the plasma velocity fields in the interaction region.

Synthesis of silicon carbide nanopowders in free flowing plasma jet with different energy levels

Silicon carbide (SiC) nanopowders were produced by the synthesis in an electrodischarge plasma jet generated by a high-current pulsed coaxial magnetoplasma accelerator. The present work focuses on the experiments where the obtained hypersonic plasma jet flew into space of the reactor chamber without impact on a target. The energy level of experiments was changed from ∼10.0 to ∼30.0 kJ. Four experiments were carried out at different energy levels. The powder products synthesized by the plasmadynamic method were studied by such well-known methods: X-ray diffraction (XRD), transmission electron microscopy (TEM). All the powders mainly contain cubic silicon carbide (β-SiC) particles with clear crystal structures and triangular shapes. SiC content reaches its maximum value 95% at the energy level 21.0 kJ, then SiC content is decreased to 70% the energy level 27.8 kJ. The powder crystallites in different experiments have approximately the same average crystallite size because quasistationary time, which allows growing powder crystallites, is absent.

Production of radiatively cooled hypersonic plasma jets and links to astrophysical jets

We present results of high energy density laboratory experiments on the production of supersonic radiatively cooled plasma jets with dimensionless parameters (Mach number ∼30, cooling parameter ∼1 and density contrast ρj/ρa ∼ 10) similar to those in young stellar objects jets. The jets are produced using two modifications of wire array Z-pinch driven by 1 MA, 250 ns current pulse of MAGPIE facility at Imperial College, London. In the first set of experiments the produced jets are purely hydrodynamic and are used to study deflection of the jets by the plasma cross-wind, including the structure of internal oblique shocks in the jets. In the second configuration the jets are driven by the pressure of the toroidal magnetic field and this configuration is relevant to the astrophysical models of jet launching mechanisms. Modifications of the experimental configuration allowing the addition of the poloidal magnetic field and angular momentum to the jets are also discussed. We also present three-dimensional resistive magneto-hydrodynamic simulations of the experiments and discuss the scaling of the experiments to the astrophysical systems.

High Quality Ceramic Coatings Sprayed by High Efficiency Hypersonic Plasma Spraying Gun

This paper introduced the structure of the high efficiency hypersonic plasma spraying gun and the effects of hypersonic plasma jet on the sprayed particles. The optimised spraying process parameters for several ceramic powders such as Al2O3, Cr2O3, ZrO2, Cr3C2 and Co-WC were listed. The properties and microstructure of the sprayed ceramic coatings were investigated. Nano Al2O3-TiO2 ceramic coating sprayed by using the high efficiency hypersonic plasma spraying was also studied. Compared with the conventional air plasma spraying, high efficiency hypersonic plasma spraying improves greatly the ceramic coatings quality but at low cost.

Laboratory Astrophysics and Collimated Stellar Outflows: The Production of Radiatively Cooled Hypersonic Plasma Jets

We present the first results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent flows. The convergent flows are created by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch). Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Canto and collaborators as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe, and W) show that a highly supersonic (M ~ 20), well-collimated jet is generated when the radiative cooling rate of the plasma is significant. We discuss scaling issues for the experiments and their potential use for numerical code verification. The experiments also may allow direct exploration of astrophysically relevant issues such as collimation, stability, and jet-cloud interactions.

Possibilities of creating highly effective sources using frequency-doubled pulses based on discharge in hypersonic plasma jets

Possibilities of creating highly effective sources using frequency-doubled pulses based on discharge in hypersonic plasma jets

Homogeneous anisotropic turbulence in a weakly ionized gas

The statistics of the electron density of a plasma in a turbulent velocity field are of interest in connection with the frequency scaling of the wake radar cross sections of hypersonic re-entry vehicles and turbulent plasma jets. In this paper, the dynamic equations for the spectrum of the electron density fluctuations are derived under the reasonable assumption of an anisotropic but homogeneous fluctuation field affected by a turbulent velocity field and by ionization and recombination effects. The form of the equations indicates that: (1) The net excitation of fluctuations of the electron density is due to the interaction of the velocity-electron fluctuations and the gradients of the mean of the density if temperature fluctuations are negligible. (2) The shear of the mean velocity will affect both the large and the small electronic eddies. (3) The effects of recombination at most decrease the lifetime of the largest eddies.