Electron Density Measurements Research Articles

On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

AbstractElectron density and Neutral Wind (ENWi) probe and/or Langmuir probe were flown on three different rocket flights from equatorial station Thumba (8.5°N, 77°E), during daytime, eclipse time, and post sunset time respectively, of low solar activity period, to study ionization irregularities in the E region of the ionosphere. The spectral characteristics observed using the payloads were analyzed during the three different rocket flights. The 15 January 2010 solar eclipse event and “SOUREX 1” wind and electron density measurements confirm the validity of the wind shear theory for equatorial regions during the eclipse and post sunset periods, when electrojet is weak, using wind and electron density irregularity measurements from the same instrument (ENWi) for the first time. The spectral indices in the range of −1.2 to −1.78 and the strong wind shear due to gravity wave winds during the eclipse time as well as the post sunset time, confirm the role of neutral turbulence in the generation of irregularities in the 95–112 km altitude region. The spectral index of −2.0 to −2.7 and the presence of irregularities in the negative gradient regions establishes the role of wind‐driven gradient drift instability (GDI) in generating irregularities during the SOUREX 1 post sunset flight for altitudes below 93 km. Further, the role of gradient drift instability in triggering ionization irregularities during the daytime on 14 January 2010 is unraveled by the spectral index of −2.03 and the presence of irregularities in the positive gradient regions alone.

Accelerating σ-Bond Metathesis at Sn(II) Centers.

Molecular main-group hydride catalysts are attractive as cheap and Earth-abundant alternatives to transition-metal analogues. In the case of the latter, specific steric and electronic tuning of the metal center through ligand choice has enabled the iterative and rational development of superior catalysts. Analogously, a deeper understanding of electronic structure-activity relationships for molecular main-group hydrides should facilitate the development of superior main-group hydride catalysts. Herein, we report a modular Sn-Ni bimetallic system in which we systematically vary the ancillary ligand on Ni, which, in turn, tunes the Sn center. This tuning is probed using Sn L1 XAS as a measure of electron density at the Sn center. We demonstrate that increased electron density at Sn centers accelerates the rate of σ-bond metathesis, and we employ this understanding to develop a highly active Sn-based catalyst for the hydroboration of CO2 using pinacolborane. Additionally, we demonstrate that engineering London dispersion interactions within the secondary coordination sphere of Sn allows for further rate acceleration. These results show that the electronics of main-group catalysts can be controlled without the competing effects of geometry perturbations and that this manifests in substantial reactivity differences.

Quasi-thermal Noise Spectroscopy Analysis of Parker Solar Probe Data: Improved Electron Density Model for Solar Wind

We present a comprehensive analysis of electron density measurements in the solar wind using quasi-thermal noise (QTN) spectroscopy applied to data from the first 15 encounters of the Parker Solar Probe mission (2018 November–2023 March). Our methodology involves the identification of the plasma line frequency and the calculation of plasma density based on in situ measurements. By analyzing over 2.1 million data points, we derive a power-law model for electron density as a function of radial distance from the Sun in the range of 13 to 50 R ☉: n e(r) = (343,466 ± 19921) × r (−1.87±0.11). This model provides improved estimates for localizing interplanetary solar radio bursts. Moreover, obtained electron densities can be used for calibrating particle instruments on board the Parker Solar Probe. We discuss its limitations and potential for further refinement with additional Parker Solar Probe encounters.

Deep learning assisted microwave-plasma interaction based technique for plasma density estimation

The electron density is a key parameter to characterize any plasma. Most of the plasma applications and research in the area of low-temperature plasmas (LTPs) are based on the accurate estimations of plasma density and plasma temperature. The conventional methods for electron density measurements offer axial and radial profiles for any given linear LTP device. These methods have major disadvantages of operational range (not very wide), cumbersome instrumentation, and complicated data analysis procedures. The article proposes a deep learning (DL) assisted microwave-plasma interaction-based non-invasive strategy, which can be used as a new alternative approach to address some of the challenges associated with existing plasma density measurement techniques. The electric field pattern due to microwave scattering from plasma is utilized to estimate the density profile. The proof of concept is tested for a simulated training data set comprising a low-temperature, unmagnetized, collisional plasma. Different types of symmetric (Gaussian-shaped) and asymmetrical density profiles, in the range 1016–1019 m−3, addressing a range of experimental configurations have been considered in our study. Real-life experimental issues such as the presence of noise and the amount of measured data (dense vs sparse) have been taken into consideration while preparing the synthetic training data-sets. The DL-based technique has the capability to determine the electron density profile within the plasma. The performance of the proposed DL-based approach has been evaluated using three metrics- structural similarity index, root mean square logarithmic error, and mean absolute percentage error. The obtained results show promising performance in estimating the 2D radial profile of the density for the given linear plasma device and affirms the potential of the proposed machine learning-based approach in plasma diagnostics.

Plasmasphere Control of ULF Wave Distribution at Different Geomagnetic Conditions

AbstractMagnetic storms and substorms cause global disturbances in the Earth's magnetosphere. Plasma clouds injected from the magnetotail during storm or substorm drift around the Earth and generate ultra‐low frequency (ULF) waves via various mechanisms. At the same time, the inner part of the magnetosphere called plasmasphere is filled with cold particles and its characteristics are sensitive to the geomagnetic activity level. Previous theoretical and some observational studies suggested plasmasphere and its boundary, plasmapause, are special regions for ULF waves to interact with charged particles. We present a statistical analysis of ULF waves during different geomagnetic conditions. We utilized Arase satellite magnetic field and electron density measurements from March 2017 to December 2020 to investigate spatial distribution of ULF waves and its dependence on the plasmapause location. A 1–2 RE gap between the plasmapause and a region of high transverse waves occurrence rate was found. This gap keeps during quiet geomagnetic conditions when plasmasphere expands, and we concluded that the plasmapause controls the ULF wave distribution in the magnetosphere. ULF wave occurrence rate significantly decreases at quiet time, but dayside and dawnside maxima still occur for poloidal and compressional, and toroidal waves, respectively. Thus, we can distinguish internally and externally excited waves. Average wave frequency distribution revealed field‐line resonance character of toroidal waves as frequency increases toward the Earth. Poloidal and compressional waves distributions clearly distinguish low frequency externally excited waves and high frequency storm‐time pulsations.

New O Partial Photoionization Cross Sections Resolve Ionospheric EUV Remote Sensing Issues

AbstractThe ionospheric O+ number density can be measured remotely during the day by observing its optically thick 83.4 nm radiance. Some ambiguity is present in the process of retrieving the density due to uncertainties in the initial excitation rate. This can be removed by observing a companion optically thin emission at 61.7 nm originating from the O+(3s 2P) state, providing that the ratio of the initial excitation rates is known. Analyses of ICON EUV data using an 83.4/61.7 emission ratio of order 10 result in O+ densities lower by ∼2 than other measurements. Key to relating the two emissions is accurate knowledge of the partial photoionization cross sections and the spectroscopy of O+—the topic of this paper. Up to now, no independent evaluation of the ratio of the 83.4/61.6 emission ratio exists. The recent availability of state‐of‐the‐art calculations of O partial photoionization cross sections into a variety of O+ states presents an opportunity to evaluate the O+(2p4 4P)/O+(3s 2P) ionization rate ratio. We calculate excitation of these parent states of the emissions including both direct and cascade excitation from higher lying O+ energy states. The resulting theoretical prediction gives ratios that range from 13.5 to 12 from solar minimum to maximum, larger than the value of 10 used by the ICON 83.4 and 61.7 nm algorithm. The higher theoretical values for the ratio reconcile the ∼2 discrepancy between simultaneous ICON and other electron density measurements.

Edge Thomson scattering diagnostic with compact polychromators on the HL-3 Tokamak

The edge Thomson scattering (ETS) diagnostic with compact polychromators on the HL-3 Tokamak was developed recently. The energy and repetition frequency of the Nd: YAG laser are 2.0 J and 30 Hz, respectively. The laser beam propagates vertically through the plasma region and the scattered light is observed horizontally. The projected scattering region at the plasma midplane is from 0.6 < r/a < 1.0. The 5-channel compact polychromator (width 432 mm, depth 472 mm and height 88 mm) is developed to measure the Thomson scattering spectra. Modular design in the power supply and the amplifier circuits simplifies the assembly and maintenance of the polychromator. By using the new narrow band filters with cut-off depth larger than OD 4, the stray light resulted from Nd: YAG laser has been suppressed by the polychromator. The signal to noise ratio (SNR) range of each channel is from 10 to 200 depending on plasma parameters. The designed electron temperature measurement range is from 5 to 1000 eV and electron density measurement range is from 5 × 1018 to 1 × 1020 m-3. New measurement results of electron temperature by ETS are compared with that from the electron cyclotron emission (ECE) radiometer. The time evolution of ETS and ECE matches with each other in different plasma discharges. Combined with the data from the core Thomson scattering diagnostic system, the plasma electron temperature profile on the HL-3 tokamak is presented for the first time.

Temperature-stable Ba0.8Sr0.2CuSi2O6 microwave dielectric ceramics for LTCC application achieved with the addition of LBSCA and LBBS glass

Ba0.8Sr0.2CuSi2O6 ceramics have a low dielectric constant, which is useful for low-latency 5G communication. To enable the preparation of Ba0.8Sr0.2CuSi2O6 low-temperature co-fired ceramic (LTCC) materials, LBSCA and LBBS were used in this paper to reduce the sintering temperature of Ba0.8Sr0.2CuSi2O6. The effects of LBSCA and LBBS on the phase composition, densification, microscopic morphology, and vibrational characteristics of the ceramics were investigated by X-ray diffraction, scanning electron microscopy, density measurements, and Raman spectroscopy, and the causal factors influencing the microwave dielectric properties with the addition of glass were analyzed. It was found that 0.4 wt% LBSCA glass and 1 wt% LBBS glass reduced the sintering temperature to 925 °C, and these prepared ceramics had excellent microwave dielectric properties. The ceramic prepared with 0.4 wt% LBSCA glass had an εr value of 7.672, Q × f value of 37193 GHz, and τf value of −14.93 ppm/°C, while the ceramic prepared with 1 wt% LBBS glass had an εr value of 7.512, Q × f value of 32136 GHz, and τf value of −13.92 ppm/°C. The phase composition of the ceramics did not significantly change, indicating that neither glass reacted with the ceramics. The εr value was affected by both density and Raman shift, the trend in the Q × f values was consistent with the density, and the τf value decreased with increasing glass content, which was attributed to the liquid phase generated by the glass in the ceramic. In addition, co-firing these glass-doped ceramics with Ag at a low temperature resulted in good chemical compatibility. Combined with the near-zero τf, these results demonstrate the excellent promise of these two ceramics as alternative materials for LTCC microwave devices and their application in 5G communication.

Two-Dimensional Thomson Scattering in Laser-Produced Plasmas

We present two-dimensional (2D) optical Thomson scattering measurements of electron density and temperature in laser-produced plasmas. The novel instrument directly measures ne(x,y) and Te(x,y) in two dimensions over large spatial regions (cm2) with sub-mm spatial resolution, by automatically translating the scattering volume while the plasma is produced repeatedly by irradiating a solid target with a high-repetition-rate laser beam (10 J, ∼1012 W/cm2, 1 Hz). In this paper, we describe the design and motorized auto-alignment of the instrument and the computerized algorithm that autonomously fits the spectral distribution function to the tens-of-thousands of measured scattering spectra, and captures the transition from the collective to the non-collective regime with distance from the target. As an example, we present the first 2D scattering measurements in laser-driven shock waves in ambient nitrogen gas at a pressure of 0.13 mbar.

A sheath correction method for electron density measurements with the microwave resonant curling probe

A correction method accounting for plasma sheath effects that appear when performing an electron density measurement with a microwave resonant probe immersed in plasma is described. The diagnostic is the novel curling probe (CP) that has already shown promising capabilities in various plasma sources. The correction method is based on the evaluation of two effects relative to the resonant probe operation and its interface with the plasma. First, the characteristic decay length of the electromagnetic field emitted by the CP, which defines the probed volume, has been characterized for the different harmonic resonance modes. Second, a semi-analytical model has been adapted to describe the plasma structure forming near the probe, which quantitatively describes the electron density profiles across the sheath structure. The correction method is then developed uniquely from numerical simulations and is independent of other diagnostics. Experimental results inside two plasma sources, an inductively coupled plasma and an electron cyclotron resonance plasma thruster, are presented and discussed. The validity of the method is assessed (i) by comparing CP corrected densities with Langmuir probe results, (ii) by varying the probe orientation to the expanding plasma flow, and (iii) by using two harmonics of the probe. The method is shown to significantly improve the accuracy of electron density measurements. Possible improvements to the method are also discussed.

Influence of plasma parameters on low-k SiCOH film grown by plasma-enhanced chemical vapor deposition using dimethyldimethoxysilane

Here, we report the influence of the electron density and the electron temperature on the reduction of dielectric constant in the SiCOH thin film using dimethyldimethoxysilane (DMDMS) as a function of pressure. The measured electron density and electron temperature decreased as increasing the pressure. The decrease in the measured electron density with increasing pressure can be attributed to local electron kinetics. Moreover, the decreasing electron temperature is caused by increased inelastic collisions between electrons and neutral species in the chamber. It is identified that CH3 radicals are less dissociated from DMDMS molecular at higher pressure by a quadrupole mass spectroscopy. As increasing pressure, the increase of the Si–CH3 bonds in SiCOH thin films is confirmed by Fourier transform infrared spectroscopy. As a result, the dielectric constant and refractive index of the SiCOH films are reduced at low electron density and electron temperature.

High-speed plasma measurements with a plasma impedance probe

Plasma impedance probes (PIPs) are a type of RF probe that primarily measures electron density. This work introduces two advancements: a streamlined analytical model for interpreting PIP-monopole measurements and techniques for achieving ≥1 MHz time-resolved PIP measurements. The model’s improvements include introducing sheath thickness as a measurement and providing a more accurate method for measuring electron density and damping. The model is validated by a quasi-static numerical simulation, which compares the simulation with measurements, identifies sources of error, and provides probe design criteria for minimizing uncertainty. The improved time resolution is achieved by introducing higher-frequency hardware, updated analysis algorithms, and a more rigorous approach to RF calibration. Finally, the new model and high-speed techniques are applied to two datasets: a 4 kHz plasma density oscillation resolved at 100 kHz with densities ranging between 2 × 1014 and 3 × 1015 m−3, and a 150 kHz oscillation resolved at 4 MHz with densities ranging between 4 × 1014 and 6 × 1014 m−3.

Coupled experimental and theoretical study of hydroxyapatite ceramics

Hydroxyapatite is a biomaterial that has great importance in the medical field and is commonly used as an implant to replace amputated bone in tissue and organ transplants and in drug delivery systems. Quantum chemistry is based on the density functional theory (DFT), which is an important tool for understanding structural arrangements and explaining the physicochemical properties of complexes. This work is mainly based on the synthesis of hydroxyapatite using the double-decomposition method. Fine hydroxyapatite powder was characterized by different techniques such as infrared spectroscopy, the X-ray diffraction method, scanning electron microscopy and density measurement. The crystalline microstructure of hydroxyapatite is hexagonal with lattice parameters a = b = 9.4260 Å and c = 6.8850 Å and space group P63/m. Hydroxyapatite has a porous surface particle morphology with a regular spherical shape. An agreement between the energies and the vibrational frequency of connection which are characteristic of the infrared spectrum. The geometry of the complex isolated using the DFT method was optimized in open air and in various solvents. Different functionals were chosen to determine the energies of excitation and the forces of the associated oscillator of the studied complex. Theoretical absorption spectra were obtained using the GaussView and Origin software programs.

Dependence of electron and neutral vapor density distributions on anode mode of high current vacuum arc

The vacuum arc discharge makes transition to a footpoint mode, anode spot type 1 (type 1) mode and anode spot type 2 (type 2) mode under high current conditions. The mode dependence of the electron and metal vapor densities were experimentally quantified using dichroic Shack–Hartmann type laser wavefront sensors. In the type 1 mode, the electron and metal vapor densities were about 2.5 times higher than the footpoint mode. The electron density of the type 2 mode was three times higher than that of the type 1 mode, while significant difference was not found in the metal vapor density. Such higher electron density for the type 2 mode than the type 1 mode was coherent with a previous result obtained by Stark broadening. The present electron and metal vapor density measurement demonstrated that the amount of the electrode erosion was in the following order: footpoint mode < type 1 mode < type 2 mode, which agreed with a previous study.

Accurate measurement of effective atomic number and electron density with X-ray attenuation coefficient spectrum

Energy spectra of X-ray attenuation coefficients, μ(E)s, are measured using a system comprising a laboratory X-ray source and a photon-counting-type detector with an accuracy of 3% or less. We propose a method to derive the electron density (ρe) and effective atomic number (Zeff) of an object from measured μ(E) values. The method is based on a simple approximation in which an atomic cross-section of attenuation is expressed by a linear equation of Z4 and experimental calibration using standard materials. The μ(E) values of aqueous ethanol and acetic acid aqueous solutions are measured to get the ρes and Zeffs. The proposed method yielded a ρe value with an accuracy of 1.4% despite the use of standard materials, whereas it yielded a Zeff value with an accuracy of 1.1% for standard materials whose values of Z are similar to that of the sample.

Unraveling the role of fullerene encapsulation driven CO2 capture in square pillared Bio-HOF under humid condition by advanced molecular simulation

Despite several interesting adsorbent materials, it is difficult to capture CO2 from point sources in industrial settings without removing humidity. Herein, we investigated the detailed adsorption of CO2 in the presence of humidity for a specifically designed material, which is known as Bio-Hydrogen bonded Organic Framework (Bio-HOFs). Specifically, the designed Bio-HOFs are made up of purine bases as organic ligands, supported with SiF6 pillar and connected via intermolecular hydrogen bonds. The strength of H-bonds in Bio-HOFs is screened with the aid of electron density measurement (Atom in Molecule) of optimized structure from advanced Density Functional Theory (DFT). Subsequently, Grand canonical Monte Carlo (GCMC) simulation was employed to estimate the CO2 uptake of Bio-HOFs and performed co-adsorptions in the presence of humidity at 298 K. Further, novel HOFs are envisaged by incorporating C60 fullerene to enhance zig-zag channels in Bio-HOFs. The resulting Bio-HOF@C60 further exhibits anomalous selectivity with higher values of screening parameters. In addition, the impact of the insertion of C60 fullerene in Bio-HOFs on the uptake of CO2 and the exceptional retention span of CO2 over N2 in SIFSIX-Cu-Adenine@C60 in the presence of humidity are highlighted.

Thomson scattering measurements of electron temperature and electron density in laser-driven Gd plasmas

In this study, we demonstrate the laser intensity scaling of electron temperature in Gd laser-produced plasmas (LPPs) through experiment and simulation. The spatial and temporal profiles of electron density ne and temperature Te in Gd LPPs were directly measured during a drive laser pulse duration of 7 ns at a laser wavelength of 1064 nm using collective Thomson scattering. We found that the measured maximum Te value in Gd LPPs increases with increasing laser intensity IL , with the dependence , in the IL range of 1010–. Radiation-hydrodynamic simulation code of the STAR-2D was performed under identical conditions to those used in the experiment, and extended further to higher laser intensities of up to ; the simulated Te was found to be in good agreement with the experimental data over the used IL range. The simulation indicates that higher overall maximum Te typically exists 50–70 above the target and modifies the dependence as . Experiments reveal that a laser intensity of is required to achieve the optimum condition ( 100 eV and ion charge states , at –) for efficient beyond extreme ultraviolet (EUV) light source. In addition, two spot sizes (150 and 250 in diameter) were used to study the effect of the spot size on the Te profile. Our experimental findings, supported by the simulations, show that larger spots can create uniform Te profiles, higher maximum Te , and larger high-Te regions in LPPs. The results and scaling laws presented in this study provide important information for developing more powerful and energy-efficient EUV light sources.

VUV to IR Emission Spectroscopy and Interferometry Diagnostics for the European Shock Tube for High-Enthalpy Research

The European Shock Tube for High-Enthalpy Research is a new state-of-the-art facility, tailored for the reproduction of spacecraft planetary entries in support of future European exploration missions, developed by an international consortium led by Instituto de Plasmas e Fusão Nuclear and funded by the European Space Agency. Deployed state-of-the-art diagnostics include vacuum-ultraviolet to ultraviolet, visible, and mid-infrared optical spectroscopy setups, and a microwave interferometry setup. This work examines the specifications and requirements for high-speed flow measurements, and discusses the design choices for the main diagnostics. The spectroscopy setup covers a spectral window between 120 and 5000 nm, and the microwave interferometer can measure electron densities up to 1.5 × 1020 electrons/m3. The main design drivers and technological choices derived from the requirements are discussed in detail herein.

Verification and validation of the open-source plasma fluid code: Zapdos

Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. This paper outlines Zapdos verification, benchmarking, and validation efforts for 1D and 2D RF capacitively-coupled plasma discharge models for mid-range pressures (0.1 - 1 Torr). The verification process involved using the method of manufactured solutions to assess Zapdos spatial and temporal error convergence. L2 errors ranged from 10−2 to 10−4, while the convergence's slope were in agreement with the predicted slopes for the tested variable and time integration orders. The benchmarking process involved comparisons to previously results from the validated finite element code, LSODI [1–3]. These works included 1D and 2D simulations for a range of plasma parameters (densities, temperatures, voltage, etc.). For the 1D cases, Zapdos and LSODI results were in very good agreement. In the 2D cases, variable behaviors matched, with slight discrepancies in peak values. The validation process involved comparisons to experimental works including electron density measurements by microwave interferometry [4] and metastable density measurements by planar laser-induced fluorescence imaging [5]. Results shown reasonable agreement at higher pressure, with results starting to diverge at low pressures. Probable causes for this diverges are the limitation of the fluid assumption for plasmas at low pressure, or the need for more robust boundary conditions. Overall, Zapdos shown reasonable results for the verification, benchmarking, and validation efforts, and Zapdos can be downloaded at https://github.com/shannon-lab/zapdos. Program summaryProgram Title: ZapdosCPC Library link to program files:https://doi.org/10.17632/j76jr9m66p.1Developer's repository link:https://github.com/shannon-lab/zapdosLicensing provisions: LGPL-2.1Programming language: C++, PythonSupplementary material:shannon-lab.github.io/zapdosNature of problem: For the plasma computational community, multiphysics packages are needed for the highly couple physics seen in plasma problems (e.g. chemistry, fluid flow, heat transfer, electromagnetic, etc.). One limiting factor for these types of computational research is the high cost to purchase the licenses needed for established multiphysics packages, such as COMSOL. An additional problem that can arise is the limited ability to add new physics to these existing frameworks, in such a way that new physics can be easily coupled to current models. For any new software that wants to tackle these problems, the question of verification and validation for these codes needs to be addressed.Solution method: Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. MOOSE (Multiphysics Object Oriented Simulation Environment) solves highly nonlinear, tightly coupled sets of partial differential equations (PDEs) and houses multiple physics applications that can be easily coupled together. Zapdos, along with the MOOSE ecosystem, is all free, open-source, and completing customizable with no black box components. Zapdos has gone through verification and validation for applications common in the plasma computational community.Additional comments including restrictions and unusual features: Zapdos, along with MOOSE and other MOOSE applications, require an Unix based operating system.

Enhancing densification in binder jet additive manufacturing of magnesium via nanoparticles as sintering aids

Additive manufacturing technologies for magnesium alloys have been developing faster than before, but many challenges are on the horizon. The native oxide film covering each Mg powder particle remains a significant challenge to overcome for further advancing sinter-based AM of Mg alloys. The present study investigated if, and how, adding calcium-containing sintering aids can push the sintering boundaries of binder-jet printed Mg powder towards a faster densification rate. Calcium-containing nanoparticles were mixed with Mg-ZnZr powder to prepare feedstock for binder jetting and sintering. The as-printed and as-sintered samples were investigated using various characterization methods, including scanning electron microscopy, vibrational spectroscopy, density measurement, chemical analysis, and mechanical tests. The results showed that adding the sintering aid to Mg powder improved its densification rate by up to 25 %. Compared to the monolithic Mg counterpart, the physical and mechanical properties of the Mg-0.2 wt% Ca sample increased (i.e., the relative density ∼7 %, tensile strength ∼30 %, compressive strength ∼15 %, elastic modulus ∼18 %, and elongation ∼185 %). These improvements are discussed in the context of consumption mechanisms of calcium interacting with the Mg powder, its MgO film, and the other alloying elements. The current study has taken the first step towards developing a targeted nano-alloying approach to enhance the printing and post-printing processes for Mg alloys fabricated by binder jetting and fused filament fabrication.