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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Collisionless fast-particle confinement in high-{beta} W7-X equilibria

Fast-particle collisionless confinement in Wendelstein 7-X is revisited exploring the configurational space given by the currents in the modular and auxiliary coils and a two-parameter pressure profile. Preliminary results indicate that at Left-Pointing-Angle-Bracket {beta} Right-Pointing-Angle-Bracket {approx} 0.04 the core-plasma loss cone usually present in stellarators can be approximately eliminated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Impact of toroidal magnetic field direction on integrated ELM-stable operation and divertor power exhaust via boron powder injection in EAST

We report the first in-depth comparison of the impact of toroidal magnetic field direction on solid boron injection used for Edge-Localized Mode (ELM) control, power exhaust, and core high-Z impurity control in the Experimental Advanced Superconducting Tokamak. With favorable ion ∇B drift towards the upper X-point in an upper-single-null configuration, boron injection effectively suppresses ELMs, produces a detachment of the inner divertor target, and leads to improved energy confinement. ELM suppression in this configuration is accompanied by the excitation of an Edge Harmonic Mode. In contrast, with unfavorable ion ∇B drift away from the upper X-point, boron injection also suppresses ELMs but leads to a more symmetric detachment state of both the inner and outer divertor targets, while plasma energy confinement is slightly degraded despite similar boron injection levels; a different low-frequency coherent mode without multiple harmonics is observed. Measurements from toroidally separated views show that the divertor response to boron injection is essentially toroidally symmetric, supporting the use of two-dimensional SOLPS-ITER modeling with a toroidally uniform impurity source. These experimental observations are qualitatively consistent with SOLPS-ITER simulations, which highlight the critical role of E × B drift effects in setting the Bt-dependent in–out asymmetry of detachment and in asymmetrically transporting particles and injected impurities within the scrape-off layer and private-flux region. These findings underscore the importance of drift physics and real-time wall conditioning in controlling low-Z impurity transport and optimizing edge solutions for integrated, ELM-stable, high-performance tokamak operation.

E × B drift↗
DOE OSTI2012

New mechanism of runaway electron diffusion due to microturbulence in tokamaks

Chaotic transport of runaway electrons in a toroidal system in the presence of a weak small-scale magnetic turbulent field with a wide mode spectrum is studied. Using a fast running mapping, the radial profiles of turbulent diffusion coefficients are calculated. It is found that at large Kubo numbers the chaotic transport of the electrons is described by a fractal-like radial dependence of the diffusion coefficients with reduced or zero values near low-order rational drift surfaces which form transport barriers. The latter can be one of the main reasons of the improved confinement of runaway electrons in tokamaks. One can expect that this effect may lead to the formation of the nested beams of runaway electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium

This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2011

Lower hybrid current drive at plasma densities required for thermonuclear reactors

Driving current in high-density plasmas is essential for the progress of thermonuclear fusion energy research based on the tokamak concept. The lower hybrid current drive (LHCD) effect, is potentially the most suitable tool for driving current at large plasma radii, consistent with the needs of ITER steady state scenario. Unfortunately, experiments at reactor grade high plasma densities with kinetic profiles approaching those required for ITER, have shown problems in penetration of the LH power into the core plasma. These plasmas represent a basic reference for designing possible methods useful for assessing the LHCD concept in ITER. On the basis of the phenomenology observed during LHCD experiments carried out in different machines, and model of the spectral broadening effect due to parametric instability, an interpretation and possible solution of the related important problem is presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Fast ion stabilization of tilt in large radius FRCs

The field reversed configuration (FRC) has been a curious case in plasma physics research in that early MHD analysis suggested FRCs should be grossly unstable, while experimental results contradicted that prediction. Later, this theory was able to resolve this contradiction by understanding that finite Larmor radius effects largely negated the MHD predictions. Similarly, previous theoretical studies of beam driven FRCs predicted that such system would be unstable to beam driven modes while, again, experimental results indicated the contradiction. In this paper, we reconcile the theoretical understanding of beam driven modes with experimental observations of stability in these systems. By self-consistently capturing fast ion generation from neutral beam injection and its impact on the plasma equilibrium, we show that low amplitude perturbations in the magnetic field, driven by betatron particles, modify the precession frequencies of the betatron particles such that the drive for compressional Alfvén waves in the thermal plasma is reduced. Finally, we are able to demonstrate, for the first time, stable beam driven FRC evolution at high S*/E in 3D kinetic simulations.

Betatrons↗
DOE OSTI2016

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P{sub 2}), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Importance of gyrokinetic exact Fokker-Planck collisions in fusion plasma turbulence

Gyrokinetic simulations of turbulence are fundamental to understanding and predicting particle and energy loss in magnetic fusion devices. Previous works have used model collision operators with approximate field-particle terms of unknown accuracy and/or have neglected collisional finite Larmor radius effects. This research moves beyond models to demonstrate important corrections using a gyrokinetic Fokker-Planck collision operator with the exact field-particle terms, in realistic simulations of turbulence in magnetically confined fusion plasmas. The exact operator shows significant corrections for temperature-gradient-driven trapped electron mode turbulence and zonal flow damping, and for microtearing modes in a Joint European Torus pedestal under ITER-like wall conditions. Analysis of the corrections using parameter scans motivates an accurate model which closely reproduces the exact results while reducing computational demands.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Taylor-Couette flow of unmagnetized plasma

Differentially rotating flows of unmagnetized, highly conducting plasmas have been created in the Plasma Couette Experiment. Previously, hot-cathodes have been used to control plasma rotation by a stirring technique [C. Collins et al., Phys. Rev. Lett. 108, 115001 (2012)] on the outer cylindrical boundary—these plasmas were nearly rigid rotors, modified only by the presence of a neutral particle drag. Experiments have now been extended to include stirring from an inner boundary, allowing for generalized circular Couette flow and opening a path for both hydrodynamic and magnetohydrodynamic experiments, as well as fundamental studies of plasma viscosity. Plasma is confined in a cylindrical, axisymmetric, multicusp magnetic field, with T{sub e} < 10 eV, T{sub i} < 1 eV, and n{sub e}<10{sup 11} cm{sup −3}. Azimuthal flows (up to 12 km/s, M = V∕c{sub s} ∼ 0.7) are driven by edge J × B torques in helium, neon, argon, and xenon plasmas, and the experiment has already achieved Rm ∼ 65 and Pm∼0.2−12. We present measurements of a self-consistent, rotation-induced, species-dependent radial electric field, which acts together with pressure gradient to provide the centripetal acceleration for the ions. The maximum flow speeds scale with the Alfvén critical ionization velocity, which occurs in partially ionized plasma. A hydrodynamic stability analysis in the context of the experimental geometry and achievable parameters is also explored.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Carbon ablator areal density at fusion burn: Observations and trends at the National Ignition Facility

For inertial confinement fusion experiments, the pusher is composed of a high-density deuterium tritium cyrogenic fuel layer and an ablator, often made of carbon. In an ideal, no-mix implosion, increasing the areal density of the pusher transfers more pressure to the hot spot and increases the hot spot confinement time. There has been a lack of knowledge about the final compressed state of the ablator for implosions at the National Ignition Facility. 14 MeV fusion neutrons inelastically scattering on the remaining carbon ablator excites a nuclear metastable state that emits a prompt 4.4 MeV gamma ray. The gamma reaction history diagnostic data, when reduced by a new data analysis technique, can isolate and measure the carbon gamma rays, which are proportional to the areal density of the ablator during fusion burn. The trends over many National Ignition Facility campaigns show that the ablator areal density is weakly sensitive to the maximum shell velocity, the cold fuel radius, the ablator mass remaining, or the laser picket intensity. Controlled parameter scans reveal that, for specific campaigns, ablator compression has a strong dependence on laser coast time, high Z dopants, and the laser drive foot duration. Using a model of the compressed ablator density profile reveals that the greatest variation of the ablator areal density comes from its thickness, with highly compressed, thin layers having high areal density values. The compression and thickness of the ablator are other metrics that designers should understand to differentiate the types of capsule degradation and maximize the inertial confinement fusion performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Towards Real-Time Detection and Tracking of Spatio-Temporal Features: Blob-Filaments in Fusion Plasma [Spatio-Temporal Features in Large Irregular Data: Blob-Filaments in Fusion Plasma]

This work was originally motivated the need to identify and track blob filaments, a feature often associated with instability in magnetically confined fusion plasma. Understanding and mitigating such instability would improve fusion reactors and make fusion a truly inexhaustible source of clean energy. Similar spatio-temporal features are important in many other applications, for example, ignition kernels in combustion and tumor cells in a medical image. This work presents an approach for extracting these features by dividing the overall task into three steps: local identification of feature cells, grouping feature cells into extended feature, and tracking movement of feature through overlapping in space. Through our extensive work in parallelization, we demonstrate that this approach can effectively make use of a large number of compute nodes to detect and track blobs in fusion plasma. On a set of 4.3TB data, we observed linear speedup on 1024 processes and completed blob detection in less than three milliseconds using Edison, a Cray XC30 system at NERSC.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Confinement effects of shock waves on laser-induced plasma from a graphite target

The spatial confinement effects of shock waves on the laser-induced plasma (LIP) from a graphite target in air were studied by probe beam deflection (PBD) measurements and optical emission spectroscopy (OES). A clear relationship between the confinement of the LIP by the shock wave and the effects on the LIP emission was observed, and the underlying mechanisms are discussed. PBD monitoring revealed that the laser-ablation induced shock wave could be well analogized to the shock wave generated by a point explosion and would be reflected by a block. OES measurements indicated that the optical emission of the LIP exhibited significant variations with the block placement. A first enhancement and then a fast decay of CN molecular emission as well as a suppression of carbon atomic emission were observed in the presence of the block. The results revealed that the reflected shock wave spatially confined the expansion of the LIP and compressed the LIP after encountering it, pushing back the species of the LIP and changing the density of the LIP species including luminous carbon atoms and CN molecules. It is suggested that the change of the LIP emission is attributed to the density variation of the LIP species due to the compression of the LIP and the reactions occurring in the plasma.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Design, development, and results from a charge-collector diagnostic for a toroidal electron plasma experiment

A suitable charge-collector has been designed and developed to estimate charge-content of electron plasmas in a Small Aspect Ratio Toroidal Experiment in a C-shaped trap (SMARTEX-C). The electrons are periodically injected and held in the trap with the aid of electrostatic end-fields and a toroidal magnetic field. After a preset “hold” time, the trapped charges are dumped onto a grounded collector (by gating it). As the charges flow along the magnetic field lines onto the collector, the integrated current gives the charge-content of the plasma at the instant of dump. In designing such a charge collector, several challenges peculiar to the geometry of the trap and the nature of the plasma had to be addressed. Instantaneous charge measurements synchronised with the E × B drift of the plasma, along with fast transit times of electrons to the collector (few 100 ns or less) (due to the low aspect ratio of the trap) essentially require fast gating of the collector. The resulting large capacitive transients alongside low charge content (few nC) of such plasmas further lead to increasing demands on response and sensitivity of the collector. Complete cancellation of such transients is shown to be possible, in principle, by including the return path in our measurement circuit but the “non-neutrality” of the plasma acts as a further impediment. Ultimately, appropriate shielding and measurement circuits allow us to (re)distribute the capacitance and delineate the paths of these currents, leading to effective cancellation of transients and marked improvement in sensitivity. Improved charge-collector has thus been used to successfully estimate the time evolution of total charge of the confined electron plasma in SMARTEX-C.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Transient plasma-detachment events induced by multiple gas puffs in ADITYA-U tokamak

Application of periodic short bursts of gas leads to periodic separation of the plasma column edge from the limiter in the Ohmically heated discharges of ADITYA-U tokamak. After every gas-puff, injecting around 10 17 –10 18 m −3 molecules of fuel gas in the edge of the plasma column, a significant reduction in plasma density, temperature, H α emission intensity and an increase in the H β /H α ratio is observed in the vicinity of the limiter radius for a certain time duration before these parameters regain their pre-gas puff values. A decline in the ion-flux to the limiter is also observed simultaneously. The global confinement of plasma also increases after each gas-puff. These observations, which repeat after each gas-injection, imply that the plasma–neutral interaction occurs further away from the limiters after the gas-injection and indicate a periodic plasma separation from the limiter surface. Further investigation revealed that the gas-injection modifies the radial and toroidal electric field, which may be playing a role in the separation of the plasma column from the limiter surface. It was further demonstrated by an electrode bias experiment in the absence of gas-injection that an application of an external radial electric field can result in obtaining a separated plasma state.

Physics - Plasma physics↗
DOE OSTI2024

Diocotron modes in pure electron plasmas in the APEX levitating dipole trap

Abstract Observations of persistent toroidal modes in dipole-trapped pure electron plasmas are presented. Non-neutral electron plasmas were confined by the poloidal magnetic field of the APEX (A Positron Electron eXperiment) levitating dipole trap. The negative bias of the electron emitter was gated to control the filling time. Large amplitude, narrow-band oscillations were consistently observed in wall probe measurements after the fill. The oscillatory image-charge currents induced by the trapped electron plasma typically persisted for many seconds with fundamental frequencies, f 0 = 50 to 500 kHz, that scale with the E → × B → drift velocity. We attribute this feature to the dipole-equivalent of the diocotron mode that is commonly observed in non-neutral plasmas in linear traps.

Deller, A. (ORCID:0000000234301501)↗
DOE OSTI2016

Faraday-effect polarimeter diagnostic for internal magnetic field fluctuation measurements in DIII-D

Motivated by the need to measure fast equilibrium temporal dynamics, non-axisymmetric structures, and core magnetic fluctuations (coherent and broadband), a three-chord Faraday-effect polarimeter-interferometer system with fast time response and high phase resolution has recently been installed on the DIII-D tokamak. A novel detection scheme utilizing two probe beams and two detectors for each chord results in reduced phase noise and increased time response [δb ∼ 1G with up to 3 MHz bandwidth]. First measurement results were obtained during the recent DIII-D experimental campaign. Simultaneous Faraday and density measurements have been successfully demonstrated and high-frequency, up to 100 kHz, Faraday-effect perturbations have been observed. Preliminary comparisons with EFIT are used to validate diagnostic performance. Principle of the diagnostic and first experimental results is presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Staircases of passive and active scalar concentration in cellular flow

This paper develops a unified model for staircase formation in both passive and active scalar systems, building upon prior numerical studies by offering new heuristic and physical insights. While prior studies primarily reported numerical results, they did not explore the underlying unifying physics that governs both types of scalar transport; this work addresses that gap by identifying shared mechanisms across both cases. Results of studies of passive and active scalar staircase formation in cellular flows are presented. Staircase formation in cellular flows occurs due to the interplay of fast mixing within cells and slow transport across the inter-cell boundary. The cell boundary emerges as a de facto transport barrier. Special attention is focused on the effects of cellular fluctuations and noise upon staircase structure. A forced, fluctuating vortex array model is used to drive the underlying flow structure. Cellular Peclet number and staircase profile curvature are identified as figures-of-merit to quantify the resiliency of layering. These are related to simple, multi-scatterer scalar random walk models. Results for Peclet number and curvature scaling with flow excitation are presented. We also study staircases of magnetic potential evolving in two-dimensional magnetohydrodynamics as examples of layering of active scalar concentration. Formation of magnetic potential staircases is indeed observed. Flux expulsion inhibits the intercellular transport of magnetic potential and strengthens staircase barriers. Magnetic staircases can be supported against resistive decay by magnetic potential noise forcing. Implications for staircase formation in magnetic confinement experiments are discussed.

Control theory↗