Steep Potential Gradients Research Articles

Atom Interferometric Imaging of Differential Potentials Using an Atom Laser.

Interferometry is a prime technique for modern precision measurements. Atoms, unlike light, have significant interactions with electric, magnetic, and gravitational fields, making their use in interferometric applications particularly versatile. Here, we demonstrate atom interferometry to image optical and magnetic potential landscapes over an area exceeding 240 μm×600 μm. The differential potentials employed in our experiments generate phase imprints in an atom laser that are made visible through a Ramsey pulse sequence. We further demonstrate how advanced pulse sequences can enhance desired imaging features, e.g., to image steep potential gradients. A theoretical discussion is presented that provides a semiclassical analysis and matching numerics.

Carrier-Transport Mechanism in Organic Antiambipolar Transistors Unveiled by Operando Photoemission Electron Microscopy.

Organic antiambipolar transistors (AATs) have partially overlapped p-n junctions. At room temperature, this p-n junction induces a negative differential transconductance in an AAT. However, the detailed carrier-transport mechanism remains unclear. Herein, an operando photoemission electron microscopy is used to tackle this issue owing to the technique's ability to visualize conductive electrons in real time during transistor operation. Notably, it is observed that when the AAT is on, a depletion layer forms at the lateral p-n junction. The visualized depletion layer shows that both p- and n-type channels have pinch-off states in the gate voltage range when the AAT is in on state. The steep potential gradient at the lateral p-n interface enhances the electron conduction from n-type to p-type semiconductor. Another significant finding is that most electrons are considered to recombine with the accumulated holes in the p-type semiconductor, affording the reduction of photoemission intensity by ≈80%. This technique provides a thorough understanding of carrier transport in AATs, further improving the device performance.

Improvement of performance and sensitivity of 2D and 3D image reconstruction in EIT using EFG forward model

This paper presents a pure element-free Galerkin method (EFGM) forward model for image reconstruction in 2D and 3D electrical impedance tomography (EIT) using an adaptive current injection method. In EIT systems with the adapting current injection method, both static and dynamic images can be reconstructed; however, determination of electrode contact impedances in the complete electrode model is difficult and the Gap model is used. In this paper, in the EIT forward problem a weak form functional based on the Gap model and a pure EFGM approach are developed, and in the EIT inverse problem, Jacobian matrix is computed by the EFGM, and a fast integration technique is introduced to calculate the entries of the Jacobian matrix within an adequate computation time. The influence of increasing the density of nodes at and near the electrodes with steep electric potential gradients on the accuracy of FEM and EFGM forward solutions is investigated, and the performance of the image reconstruction algorithm with the proposed fast integration technique is examined. The numerical results reveal that the proposed EFGM forward model with the fast integration technique has an efficient performance both in terms of mean relative imaging errors and computational time.

Tunability of Interactions between the Core and Shell in Rattle-Type Particles Studied with Liquid-Cell Electron Microscopy.

Yolk–shell or rattle-type particles consist of a core particle that is free to move inside a thin shell. A stable core with a fully accessible surface is of interest in fields such as catalysis and sensing. However, the stability of a charged nanoparticle core within the cavity of a charged thin shell remains largely unexplored. Liquid-cell (scanning) transmission electron microscopy is an ideal technique to probe the core–shell interactions at nanometer spatial resolution. Here, we show by means of calculations and experiments that these interactions are highly tunable. We found that in dilute solutions adding a monovalent salt led to stronger confinement of the core to the middle of the geometry. In deionized water, the Debye length κ–1 becomes comparable to the shell radius Rshell, leading to a less steep electric potential gradient and a reduced core–shell interaction, which can be detrimental to the stability of nanorattles. For a salt concentration range of 0.5–250 mM, the repulsion was relatively long-ranged due to the concave geometry of the shell. At salt concentrations of 100 and 250 mM, the core was found to move almost exclusively near the shell wall, which can be due to hydrodynamics, a secondary minimum in the interaction potential, or a combination of both. The possibility of imaging nanoparticles inside shells at high spatial resolution with liquid-cell electron microscopy makes rattle particles a powerful experimental model system to learn about nanoparticle interactions. Additionally, our results highlight the possibilities for manipulating the interactions between core and shell that could be used in future applications.

Localized nonlinear solution strategies for efficient simulation of unconventional reservoirs

Accurate and efficient numerical simulation of unconventional reservoirs is challenging. Long periods of transient flow and steep potential gradients occur due to the extreme conductivity contrast between matrix and fracture. Detailed near-well/near-fracture models are necessary to provide sufficient resolution, but they are computationally impractical for field cases with multiple hydraulic-fracture stages.Previous works in the literature of unconventional simulations mainly focus on the gridding level that adapts to wells and fractures. Limited research has been conducted on nonlinear strategies that exploit locality across timesteps and nonlinear iterations. It was reported that an individual Newton update is typically sparse and nonlinear convergence is constrained by a small portion of the model. To perform localized computations, an a-prioristrategy is essential to first determine the active subset of simulation cells for the subsequent iteration. The active set flags the cells that will be updated, and then the corresponding localized linear system is solved.The objective of this work is to develop localization methods that are readily applicable to complex fracture networks and flow physics in unconventional reservoirs. By utilizing the diffusive nature of pressure updates, an adaptive algorithm is proposed to make adequate estimates for the active domains. In addition, we further develop a localized solver based on nonlinear domain decomposition (DD). Compared to a standard DD method, domain partitions are dynamically constructed. The new solver provides effective partitioning that adapts to flow dynamics and Newton updates.We evaluate the developed methods using several complex problems with discrete fracture networks. The problems consider multi-phase and compositional fluid systems with phase changes. The results show that large degrees of solution locality present across timesteps and iterations. Compared to a standard Newton solver, the new solvers enable superior computational performance. Moreover, Newton convergence behavior is preserved, without any impact on solution accuracy.

Local Deformation-Controlled Fast Directional Metal Outflow in Metal/Ceramic Nanolayer Sandwiches upon Low Temperature Annealing.

Precise nanoindentation on AlN/Cu/AlN nanolayer sandwiches has been conducted by using an atomic force microscope to promote fast and directional metal (Cu) outflow upon heating at low temperatures. Local plastic deformation during indentation results in the generation of high defect densities and stress gradients, which not only effectively reduce the activation energies for fast in-plane diffusion but also direct the in-plane transport of confined Cu to the indent location. In addition, a steep chemical potential gradient of O will be established across the AlN barrier upon exposure to air, which drives fast outward diffusion of Cu along defective pathways in the top AlN layer at the indent location. Selective and fast Cu metal outflow can thus be achieved at the indent locations upon annealing at a relatively low temperature of 350 °C for 5 min in air. The microstructures and phase boundaries of the AlN barrier and confined Cu nanolayers are unperturbed outside the plastically deformed region and remain metastable after annealing at 350 °C. By changing the surface processing modes, patterned nanoparticles and isolated nanowire structures can be fabricated straightforwardly. Such local deformation-controlled directional mass transport phenomena can be utilized to manipulate materials down to the atomic scale for designing functional nanoarchitectures for nanophotonic and nanoelectronic applications.

Development of Operando Confocal Microprobe X-ray Fluorescence Techniques to Measure Cation Transport in PEM Fuel Cells

State-of-the-art polymer electrolyte membrane (PEM) fuel cells often use PtM (M= Co or Ni) as cathode catalysts and Ce-based additives in the membrane to enhance their performance and durability. During operation, however, the transition metals dissolve and Co2+ and Ce3+ cations transport from their initial positions, which decreases their efficacy and can cause fouling of ionomer regions, resulting in performance losses and local membrane failure.1 Despite general knowledge of cation transport through diffusion, migration, and convection, a thorough accounting of the cation positions and concentrations has not been available owing to an inability to monitor these processes under realistic MEA operating conditions and cell geometries. Our approach has been to leverage the unique capabilities of synchrotron microprobe X-ray fluorescence (µXRF), which enable point data collection on the millisecond-scale with spot sizes of <0.25 µm. Here, we report the development of techniques to directly observe transient, µm-scale migration of cations, in operando. An initial cell design to isolate 1-D through-thickness cation transport was tested using traditional µXRF at the Advanced Photon Source (APS). These experiments resulted in unexpected depletion of cations from the analysis surface of the cell, more preferentially from cathode side. Results agreed qualitatively with 3-D cell modeling, which suggested that steep potential gradients form between the air/cell interface and the interior of the cell, which drives cation migration deep into the cell.2 In order to map ions beyond the front cell edge, follow-on experiments utilized the confocal µXRF capabilities at the Cornell High Energy Synchrotron Source (CHESS). This setup relies on Si collimating optics to define a fluorescent voxel which can be controlled to generate 3-D elemental maps, enabling the measurement of cation transport in the interior of the cell. Steady state depth scans taken at 50 mA/cm2 show the depletion of ions from the surface (Figure 1a, inset), more preferentially from the cathode side, in agreement with the APS experiments. As shown in Figure 1, these depth profile scans were used to determine an optimized depth of ~180 µm, where depth profiles converged and were located far enough away to avoid edge effects, but near enough to the surface to get sufficient signal (~90% attenuation measured at a depth of 200 µm). Transient scans at this optimized depth were performed at 80°C and 50% RH with a current density of 100 mA/cm2. These measurements, shown in Figure 1b, reveal that Ce3+ cations initially situated in the PEM migrate from there into cathode catalyst layer (cCL), forming a gradient in the PEM after 15 minutes. Upon removal of load, Ce3+ rapidly diffuses and equilibrates between ionomer regions of the CL and PEM. These results demonstrate that cation transport in the MEA has a rapid response to the operating condition and generates concentration gradients under load, which validates the model findings and improves the understanding of the root cause of the performance loss. For the first time in fuel cell study, 3-D cation transport inside the MEA was monitored during cell operation. The findings and techniques developed in this study have significant implications for future designs of cell geometry and operating conditions. These results demonstrate that cation transport in the MEA has a rapid response to the operating condition and generates concentration gradients under load, which validates the model findings and improves the understanding of the root cause of the performance loss. For the first time in fuel cell study, 3-D cation transport inside the MEA was monitored during cell operation. The findings and techniques developed in this study have significant implications for future designs of cell geometry and operating conditions. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos and Technical Development Manager: Greg Kleen). This work is based upon research conducted at the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357 and the Cornell High Energy Synchrotron Source (CHESS) which is supported by the National Science Foundation under award DMR-1332208. References A. M. Baker, R. Mukundan, D. Spernjak, E. J. Judge, S. G. Advani, A. K. Prasad, and R. L. Borup, J. Electrochem. Soc., 163, F1023–F1031 (2016).Y. Cai, J. M. Ziegelbauer, A. M. Baker, W. Gu, R. S. Kukreja, A. Kongkanand, M. F. Mathias, R. Mukundan, and R. L. Borup, J. Electrochem. Soc., 165, F3132–F3138 (2018). Figure 1

Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System

AbstractSubglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, hat is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from single‐conduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3–7 days, while tremor produced by single‐conduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.

Off-Axis Ions Extraction Simulation in Tubular Electron String Ion Source (TESIS)

Tubular Electron String Ion Source (TESIS) – improved version of Electron String Ion Source (ESIS) aiming for nearly 200-fold increase in ion yield – is under development at JINR. TESIS advantages over ESIS are discussed and their characteristics are compared. Basic scheme of TESIS operation is presented. One of the crucial processes in TESIS – off-axis ion extraction – requires special confilguration of output electrodes providing steep potential gradient. Numerical simulations of ion extraction trajectories for two different electrode confilgurations are compared and the optimal one is discussed. The obtained results will be useful for TESIS design and construction.

Laser-induced fluorescence measurements of acceleration zone scaling in the 12.5 kW HERMeS Hall thruster

We present laser-induced fluorescence measurements of acceleration zone scaling with discharge voltage (Vd), magnetic field strength (B), and facility background pressure (PBG) in NASA’s 12.5 kW Hall Effect Rocket with Magnetic Shielding. At fixed discharge current, the plasma potential profiles at discharge voltages from 300 to 600 V approximately overlapped in the region with plasma potential less than 300 V; ion acceleration began further upstream at higher Vd because the region with a steep potential gradient was broader. The radial divergence of mean ion velocity vectors in the outer half of the channel and near plume increased with decreasing Vd. At fixed Vd, the acceleration zone was located further upstream at higher B and at higher PBG. Bimodal ion velocity distribution functions (IVDFs) were measured along the channel centerline in the acceleration zone at high discharge voltages; this effect was attributed to time-averaging over movement of the acceleration zone during large-amplitude discharge current oscillations. At lower discharge voltages, the broadening of the IVDFs in the near plume could not be fully explained by ionization within the acceleration region. These results have implications for understanding front pole erosion, which can be an important wear mechanism over the long lifetimes of magnetically shielded thrusters, and they provide baseline data for validating first principles models of cross-field electron transport.

Structural basis of proton translocation and force generation in mitochondrial ATP synthase.

ATP synthases produce ATP by rotary catalysis, powered by the electrochemical proton gradient across the membrane. Understanding this fundamental process requires an atomic model of the proton pathway. We determined the structure of an intact mitochondrial ATP synthase dimer by electron cryo-microscopy at near-atomic resolution. Charged and polar residues of the a-subunit stator define two aqueous channels, each spanning one half of the membrane. Passing through a conserved membrane-intrinsic helix hairpin, the lumenal channel protonates an acidic glutamate in the c-ring rotor. Upon ring rotation, the protonated glutamate encounters the matrix channel and deprotonates. An arginine between the two channels prevents proton leakage. The steep potential gradient over the sub-nm inter-channel distance exerts a force on the deprotonated glutamate, resulting in net directional rotation.

The State of the Atomic Lattice of Structure Materials: Pre NDE Indication Assessments

The lattice of structural alloys possesses electronic characteristics which offer NDE predictions of potential failures in materials and structural assemblies. The atomic lattice represents a periodic potential which provide electronic wave descriptions that appear to be free. Any distortion in the periodic lattice (potentials) will achieve electronic and/or elastic interactions giving advance NDE waves tools possibility to assess stability of engineering materials at the atomic level during service life. Furthermore, the small dimensional defects (i.e. dislocations and interfaces) will produce steep potential gradients resulting in electronic and / or elastic physical properties changes that can be also measured. These collective potential and electronics signatures could be used as pre NDE lattice indications to produce awareness of potential degradations (i.e. susceptibility of fatigue, strain enhanced corrosion and cracking). The proper selection, utilization and assessment will increase both reliability and the NDE economics. A new approach to the next generation of nondestructive evaluations based on the electronic and elastic wave signals and analyses will be presented.

Femtosecond Heterodyne Transient-Grating Studies of Nonradiative Decay of the S2 (1(1)Bu(+)) State of β-Carotene: Contributions from Dark Intermediates and Double-Quantum Coherences.

Femtosecond transient-grating spectroscopy with heterodyne detection was employed to characterize the nonradiative decay pathway in β-carotene from the S2 (1(1)Bu(+)) state to the S1 (2(1)Ag(-)) state in benzonitrile solution. The results indicate definitively that the S2 state populates an intermediate state, Sx, on an ultrafast time scale prior to nonradiative decay to the S1 state. Numerical simulations using the response function formalism and the multimode Brownian oscillator model were used to fit the absorption and dispersion components of the transient-grating signal with a common set of parameters for all of the relevant Feynman pathways, including double-quantum coherences. The requirement for inclusion of the Sx state in the nonradiative decay pathway is the observed fast rise time of the dispersion component, which is predominantly controlled by the decay of the stimulated emission signal from the optically prepared S2 state. The finding that the excited-state absorption spectrum from the Sx state is significantly red-shifted from that of S2 and S1 leads to a new assignment for the spectroscopic origin of the Sx state. Rather than assigning Sx to a discrete electronic state, such as the (1)Bu(-) state suggested in previous work, it is proposed that the Sx state corresponds to a transition-state-like structure on the S2 potential surface. In this hypothesis, the 12 fs time constant for the decay of the S2 state corresponds to a vibrational displacement of the C-C and C═C bond-length alternation coordinates of the conjugated polyene backbone from the optically prepared Franck-Condon structure to a potential energy barrier on the S2 surface that divides planar and torsionally displaced structures. The lifetime of the Sx state would be associated with a subsequent relaxation along torsional coordinates over a steep potential energy gradient toward a conical intersection with the S1 state. This hypothesis leads to the idea that twisted structures with intramolecular charge-transfer character along the S2 torsional gradient are active in excitation energy-transfer mechanisms to (bacterio)chlorophyll acceptors.

Control of Oxygen Permeability in Alumina under Oxygen Potential Gradients at High Temperature by Dopant Configurations

The oxygen permeability of polycrystalline α‐alumina wafers, which served as models for alumina scales on alumina‐forming alloys, under steep oxygen potential gradients () was evaluated at 1873 K. Oxygen permeation occurred by the grain‐boundary (GB) diffusion of oxygen from the higher‐oxygen‐partial‐pressure () surface to the lower‐ surface, along with the simultaneous GB diffusion of aluminum in the opposite direction. The fluxes of oxygen and aluminum at the outflow side of the wafer were significantly larger than at the inflow side. Furthermore, Lu and Hf segregation at the GBs selectively reduced the mobility of oxygen and aluminum, respectively. A wafer with a bilayer structure, in which a Lu‐doped layer was exposed to a lower and an Hf‐doped layer was exposed to a higher , decreased the oxygen permeability. When the sign of was reversed, however, the oxygen permeability of the wafer was comparable to that of a nondoped wafer. Co‐doping with both Lu and Hf markedly increased the oxygen permeation, presumably because the Lu‐stabilized HfO2 particles that were segregated at the GBs acted as extremely fast diffusion paths for oxygen through the large number of oxygen vacancies introduced by the solid solution of Lu in the particles.

Laminar shocks in high power laser plasma interactions

We propose a theory to describe laminar ion sound structures in a collisionless plasma. Reflection of a small fraction of the upstream ions converts the well known ion acoustic soliton into a structure with a steep potential gradient upstream and with downstream oscillations. The theory provides a simple interpretation of results dating back more than forty years but, more importantly, is shown to provide an explanation for recent observations on laser produced plasmas relevant to inertial fusion and to ion acceleration.

Effect of Dopants on the Distribution of Aluminum and Oxygen Fluxes in Polycrystalline Alumina Under Oxygen Potential Gradients at High Temperatures

The oxygen permeability of Lu‐, Y‐, and Hf‐doped polycrystalline alumina wafers under steep oxygen potential gradients was evaluated at temperatures above 1773 K. Oxygen permeation occurred by the grain‐boundary (GB) diffusion of oxygen from the higher oxygen partial pressure (PO2) surface to the lower PO2 surface, and was coincident with GB diffusion of aluminum in the reverse direction. Lu‐ and Y‐doping both suppressed oxygen permeation to the same extent, owing to the decrease in oxygen mobility, but neither had any significant effect on aluminum mobility. Hf‐doping had the opposite effect. The fluxes of oxygen and aluminum at the inflow side in all wafers were significantly smaller than those at the outflow side, regardless of whether or not these dopants were added. Consequently, the intersection of the fluxes shifted to the lower PO2 side upon Lu‐ and Y‐doping, and to the higher PO2 side upon Hf‐doping. Furthermore, the effect of dopants on the mass transfer in scales formed by oxidation of FeCrAl‐based alloys at 1300–1500 K was analyzed through predictions of the flux distributions of oxygen and aluminum in the scales.

Modeling the Impact of Reset Depth on Vacancy-Induced Filament Perturbations in ${\rm HfO}_{2}$ RRAM

Random telegraph noise in resistive switching memory devices is governed by two distinct mechanisms-oxygen vacancy perturbations in the filament as well as the electron trapping-detrapping phenomenon. In this letter, we focus on the dominant role of vacancies in governing the stability of the filament in the high resistance state and characterize the dependence of the read disturb voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DIST</sub> ) on the depth of the reset level during switching. Our slow voltage ramp read disturb tests at different reset levels indicate the possibility of filamentary instability even for read voltages lower than the standard value of 0.10 V. These experimental trends can be well explained using the quantum point contact model for conduction in the filament, as deeper reset levels induce very steep potential gradients at the two ends of the constriction that make the filaments highly unstable and susceptible to structural modifications due to vacancy generation and/or transport during memory read operation.

Understanding helicon plasmas

This paper presents a comprehensive overview of work on the helicon plasmas and also discusses various aspects of RF power deposition in such plasmas. Some of the work presented here is a review of earlier work on theoretical [A. Ganguli et al., Phys. Plasmas 14, 113503 (2007)] and experimental [A. Ganguli et al., Plasma Sources Sci. Technol. 20(1), 015021 (2011)] investigations on helicon plasmas in a conducting cylindrical waveguide for m = −1 mode. This work also presents an approach to investigate the mechanisms by which the helicon and associated Trivelpiece-Gould (TG) waves are responsible for RF power deposition in Helicon discharges. Experiment design adopts the recent theory of damping and absorption of Helicon modes in conducting waveguides [A. Ganguli et al., Phys. Plasmas 14, 113503 (2007)]. The effort has also been made to detect the warm electrons, which are necessary for ionization, because Helicon discharges are of high density, low Te discharges and the tail of the bulk electron population may not have sufficient high-energy electrons. Experimental set up also comprises of the mirror magnetic field. Measurements using RF compensated Langmuir probes [A. Ganguli et al., Plasma Sources Sci. Technol. 17, 015003 (2008)], B-dot probe and computations based on the theory shows that the warm electrons at low pressure (0.2–0.3 mTorr) Helicon discharges, are because of the Landau damping of TG waves. In collisional environment, at a pressure ≈10 mTorr, these high-energy electrons are due to the acceleration of bulk electrons from the neighboring regions across steep potential gradients possibly by the formation of double layers.

Ussing's conundrum and the search for transport mechanisms in plants

Plant transport physiologists have developed a range of models describing the movement of ions across cell membranes. However, while substantial progress has been made towards providing precise descriptions of the mechanisms underlying these fluxes, important instances remain in which the prevailing models cannot account for repeated observations, particularly in terms of energy transformations. As we shall show, disagreements with experimental findings may entail a revision of the proposed models, similarly to what has been required in animal transport studies (Ussing, 1994; see below). We present, as a key example, the futile cycling of sodium under toxic conditions (see Britto & Kronzucker, 2006, and discussed later), and show that unidirectional flux magnitudes measured by several groups, including our own, cannot be explained energetically by current models. We attempt to explain these observations by proposing alternative mechanisms of Na + transport across the root-cell plasma membrane. The influx/efflux cycle of Na + in plants has been attributed to the sophisticated activity of distinct transport proteins in

Evidence of nonclassical plasma transport in hollow cathodes for electric propulsion

Measurements, simplified analyses, and two-dimensional numerical simulations with a fluid plasma model show that classical resistivity cannot account for the elevated electron temperatures and steep plasma potential gradients measured in a 25–27.5A electric propulsion hollow cathode. The cathode consisted of a 1.5cm hollow tube with an ∼0.28cm diameter orifice and was operated with 5.5SCCM (SCCM denotes cubic centimeter per minute at STP) of xenon flow using two different anode geometries: a segmented cone and a circular flat plate. The numerical simulations show that classical resistivity yields as much as four times colder electron temperatures compared to the measured values in the orifice and near-plume regions of the cathode. Classical transport and Ohm’s law also predict exceedingly high electron-ion relative drift speeds compared to the electron thermal speed (&amp;gt;4). It is found that the addition of anomalous resistivity based on existing growth rate formulas for electron-ion streaming instabilities improves qualitatively the comparison between the numerical results and the time-averaged measurements. Simplified analyses that have been based largely on the axial measurements support the conclusion that additional resistivity is required in Ohm’s law to explain the measurements. The combined results from the two-dimensional simulations and the analyses bound the range of enhanced resistivity to be 3–100 times the classical value.