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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Exploration of magnetic perturbation effects on advanced divertor configurations in NSTX-U

The control of divertor heat loads—both steady state and transient—remains a key challenge for the successful operation of ITER and FNSF. Magnetic perturbations provide a promising technique to control ELMs (Edge Localized Modes) (transients), but understanding their detailed impact is difficult due to their symmetry breaking nature. One approach for reducing steady state heat loads is so called “advanced divertors” which aim at optimizing the magnetic field configuration: the snowflake and the (super-)X-divertor. It is likely that both concepts—magnetic perturbations and advanced divertors—will have to work together, and we explore their interaction based on the NSTX-U setup. An overview of different divertor configurations under the impact of magnetic perturbations is presented, and the resulting impact on plasma edge transport is investigated with the EMC3-EIRENE code. Variations in size of the magnetic footprint of the perturbed separatrix are found, which are related to the level of flux expansion on the divertor target. Non-axisymmetric peaking of the heat flux related to the perturbed separatrix is found at the outer strike point, but only in locations where flux expansion is not too large.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Phase coherence of parametric-decay modes during high-harmonic fast-wave heating in the National Spherical Torus Experiment

Third-order spectral analysis, in particular, the auto bicoherence, was applied to probe signals from high-harmonic fast-wave heating experiments in the National Spherical Torus Experiment. Strong evidence was found for parametric decay of the 30 MHz radio-frequency (RF) pump wave, with a low-frequency daughter wave at 2.7 MHz, the local majority-ion cyclotron frequency. The primary decay modes have auto bicoherence values around 0.85, very close to the theoretical value of one, which corresponds to total phase coherence with the pump wave. The threshold RF pump power for onset of parametric decay was found to be between 200 kW and 400 kW.

Carlsson, J. A. (ORCID:0000000346148150)↗
DOE OSTI2016

Preliminary design of a tangentially viewing imaging bolometer for NSTX-U

The infrared imaging video bolometer (IRVB) measures plasma radiated power images using a thin metal foil. Two different designs with a tangential view of NSTX-U are made assuming a 640 × 480 (1280 × 1024) pixel, 30 (105) fps, 50 (20) mK, IR camera imaging the 9 cm × 9 cm × 2 μm Pt foil. The foil is divided into 40 × 40 (64 × 64) IRVB channels. This gives a spatial resolution of 3.4 (2.2) cm on the machine mid-plane. The noise equivalent power density of the IRVB is given as 113 (46) μW/cm{sup 2} for a time resolution of 33 (20) ms. Synthetic images derived from Scrape Off Layer Plasma Simulation data using the IRVB geometry show peak signal levels ranging from ∼0.8 to ∼80 (∼0.36 to ∼26) mW/cm{sup 2}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Time-dependent analysis of visible helium line-ratios for electron temperature and density diagnostic using synthetic simulations on NSTX-U

Helium line-ratios for electron temperature (T{sub e}) and density (n{sub e}) plasma diagnostic in the Scrape-Off-Layer (SOL) and edge regions of tokamaks are widely used. Due to their intensities and proximity of wavelengths, the singlet, 667.8 and 728.1 nm, and triplet, 706.5 nm, visible lines have been typically preferred. Time-dependency of the triplet line (706.5 nm) has been previously analyzed in detail by including transient effects on line-ratios during gas-puff diagnostic applications. In this work, several line-ratio combinations within each of the two spin systems are analyzed with the purpose of eliminating transient effects to extend the application of this powerful diagnostic to high temporal resolution characterization of plasmas. The analysis is done using synthetic emission modeling and diagnostic for low electron density NSTX SOL plasma conditions by several visible lines. Quasi-static equilibrium and time-dependent models are employed to evaluate transient effects of the atomic population levels that may affect the derived electron temperatures and densities as the helium gas-puff penetrates the plasma. The analysis of a wider range of spectral lines will help to extend this powerful diagnostic to experiments where the wavelength range of the measured spectra may be constrained either by limitations of the spectrometer or by other conflicting lines from different ions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Plasma diagnostics in spherical tokamaks with silicon charged-particle detectors

Detection of charged fusion products, such as protons and tritons resulting from D(d, p) t reactions, can be used to determine the position and time dependent fusion reaction rate profile in spherical tokamak plasmas with neutral beam heating. We have developed a prototype instrument consisting of 6 ion-implanted-silicon surface barrier detectors combined with collimators in such a way that each detector can accept 3 MeV protons and 1 MeV tritons and thus provides a curved view across the plasma cross section. The combination of the results from all six detectors will provide information on the spatial distribution of the fusion reaction rate. The expected time resolution of about 1 ms makes it possible to study changes in the reaction rate due to slow variations in the neutral beam density profile, as well as rapid changes resulting from MHD instabilities. Details of the new instrument, its data acquisition system, simulation results, and electrical noise testing results are discussed in this paper. First experimental data are expected to be taken during the current experimental campaign at NSTX-U.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Design and characterization of a prototype divertor viewing infrared video bolometer for NSTX-U

The InfraRed Video Bolometer (IRVB) is a powerful tool to measure radiated power in magnetically confined plasmas due to its ability to obtain 2D images of plasma emission using a technique that is compatible with the fusion nuclear environment. A prototype IRVB has been developed and installed on NSTX-U to view the lower divertor. The IRVB is a pinhole camera which images radiation from the plasma onto a 2.5 μm thick, 9 × 7 cm{sup 2} Pt foil and monitors the resulting spatio-temporal temperature evolution using an IR camera. The power flux incident on the foil is calculated by solving the 2D+time heat diffusion equation, using the foil’s calibrated thermal properties. An optimized, high frame rate IRVB, is quantitatively compared to results from a resistive bolometer on the bench using a modulated 405 nm laser beam with variable power density and square wave modulation from 0.2 Hz to 250 Hz. The design of the NSTX-U system and benchtop characterization are presented where signal-to-noise ratios are assessed using three different IR cameras: FLIR A655sc, FLIR A6751sc, and SBF-161. The sensitivity of the IRVB equipped with the SBF-161 camera is found to be high enough to measure radiation features in the NSTX-U lower divertor as estimated using SOLPS modeling. The optimized IRVB has a frame rate up to 50 Hz, high enough to distinguish radiation during edge-localized-modes (ELMs) from that between ELMs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Compact and multi-view solid state neutral particle analyzer arrays on National Spherical Torus Experiment-Upgrade

A compact and multi-view solid state neutral particle analyzer (SSNPA) diagnostic based on silicon photodiode arrays has been successfully tested on the National Spherical Torus Experiment-Upgrade. The SSNPA diagnostic provides spatially, temporally, and pitch-angle resolved measurements of fast-ion distribution by detecting fast neutral flux resulting from the charge exchange (CX) reactions. The system consists of three 16-channel subsystems: t-SSNPA viewing the plasma mid-radius and neutral beam (NB) line #2 tangentially, r-SSNPA viewing the plasma core and NB line #1 radially, and p-SSNPA with no intersection with any NB lines. Due to the setup geometry, the active CX signals of t-SSNPA and r-SSNPA are mainly sensitive to passing and trapped particles, respectively. In addition, both t-SSNPA and r-SSNPA utilize three vertically stacked arrays with different filter thicknesses to obtain coarse energy information. The experimental data show that all channels are operational. The signal to noise ratio is typically larger than 10, and the main noise is x-ray induced signal. The active and passive CX signals are clearly observed on t-SSNPA and r-SSNPA during NB modulation. The SSNPA data also indicate significant losses of passing particles during sawteeth, while trapped particles are weakly affected. Fluctuations up to 120 kHz have been observed on SSNPA, and they are strongly correlated with magnetohydrodynamics instabilities.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Far-infrared tangential interferometer/polarimeter design and installation for NSTX-U

The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system has been refurbished and is being reinstalled on the National Spherical Torus Experiment—Upgrade (NSTX-U) to supply real-time line-integrated core electron density measurements for use in the NSTX-U plasma control system (PCS) to facilitate real-time density feedback control of the NSTX-U plasma. Inclusion of a visible light heterodyne interferometer in the FIReTIP system allows for real-time vibration compensation due to movement of an internally mounted retroreflector and the FIReTIP front-end optics. Real-time signal correction is achieved through use of a National Instruments CompactRIO field-programmable gate array.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Design of microwave broadband CMOS transmitter and receiver circuits for MIR and ECEI plasma diagnostics

To efficiently determine the plasma electron density fluctuations using the MIR diagnostic technique, a 55–75 GHz 65 nm-CMOS transmitter has been developed where four separate intermediate frequency (IF) signals are up-converted, amplified, and then combined to generate an 8-tone RF output; a broadband 90 nm-CMOS receiver has also been constructed, which consists of an RF-low noise amplifier (LNA), mixer, and IF amplifier. The circuits and their corresponding modules will soon be deployed on the DIII-D and NSTX-U fusion devices. A 110–140 GHz 65 nm-CMOS receiver has also been designed, which is suitable for measuring the deep-core temperature fluctuations in the DIII-D tokamak using the electron cyclotron emission imaging diagnostic system. In addition to the RF-LNA/balun, mixer, and IF amplifier, an LO balun/tripler and driving amplifier are now included in this highly integrated circuit chip. By adopting the microwave and millimeterwave system-on-chip concept in the front-end system design, this paper demonstrates that compact transmitter and receiver modules can be easily built, which, in turn, facilitates array implementation and maintenance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Modeling of carbon pellets disruption mitigation in an NSTX-U plasma

Single carbon pellet disruption mitigation simulations using M3D-C1 were conducted for an NSTX-U-like plasma to support the electromagnetic pellet injection concept (EPI). A carbon ablation model has been implemented in M3D-C1 and tested with available data. 2D simulations were conducted in order to estimate the amount of carbon needed to quench the plasma, finding that the content in a 1 mm radius vitreous carbon pellet (~3.2x10E20 atoms) would be enough if it is entirely ablated. 3D simulations were performed, scanning over pellet velocity and parallel thermal conductivity, as well as different injection directions and pellet concepts (solid pellets and shell pellets). The sensitivity of the thermal quench and other related quantities to these parameters has been evaluated. A 1 mm radius solid pellet only partially ablates at velocities of 300 m/s or higher, thus being unable to fully quench the plasma. To further enhance the ablation, approximations to an array of pellets and the shell pellet concept were also explored. 3D field line stochastization plays an important role in both quenching the center of the plasma and in heat flux losses, thus lowering the amount of carbon needed to mitigate the plasma when compared to the 2D case. This study constitutes an important step forward in `predict-first' simulations for disruption mitigation in NSTX-U and other devices, such as ITER.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Study of MHD Stability, Active Mode Control, and Disruption Avoidance in NSTX-U

Learning how to achieve sustained operation at high plasma pressure is an important goal of the National Spherical Torus Upgrade (NSTX-U) program and is critically important to any future fusion power plant. This research addresses high priority stability and control issues outlined by the NSTX-U Program. Reduced models of the stabilization physics learned continue to be created and tested against actual plasma operation in NSTX, NSTX-U, and other tokamak devices. This research is forming physics-based models for disruption forecasting that aims to unify results across different fusion machines for more confident extrapolation of the techniques studied to future devices including ITER. The Disruption Event Characterization and Forecasting (DECAF) code was expanded to analyze data from the TCV tokamak, including real-time MHD analysis signals. The presence of a mode and likelihood of its m/n numbers can be tracked, as well as the mode frequency, although a limitation at low frequency does not yet allow tracking modes to the locking point in TCV. Initial analyses of NSTX-U operation were conducted using the DECAF code. The timing of sawtooth oscillations was investigated taking advantage of the more extensive L-mode operation of the device in its first run campaign. An initial investigation of thermal collapses in NSTX-U was also conducted with specific comparison to the Greenwald density limit. A local island power balance model to explain the density limit in tokamaks has been tested with NSTX data and is being evaluated as a potential disruption forecaster in the DECAF code, presently showing similarities to the global Greenwald density evolution and limit. A module was written for the DECAF code that generalizes magnetic spectrogram analysis of MHD modes. This new portable code, written in Python, discriminates the toroidal mode number of instabilities and can track each mode as a DECAF event, monitoring the evolution of the mode through bifurcation and locking points. This is a critical new capability to allow disruption event characterization for general tokamak databases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Advances in boronization on NSTX-Upgrade

Boronization has been effective in reducing plasma impurities and enabling access to higher density, higher confinement plasmas in many magnetic fusion devices. The National Spherical Torus eXperiment, NSTX, has recently undergone a major upgrade to NSTX-U in order to develop the physics basis for a ST-based Fusion Nuclear Science Facility (FNSF) with capability for double the toroidal field, plasma current, and NBI heating power and increased pulse duration from 1–1.5 s to 5–8 s. A new deuterated tri-methyl boron conditioning system was implemented together with a novel surface analysis diagnostic. We report on the spatial distribution of the boron deposition versus discharge pressure, gas injection and electrode location. The oxygen concentration of the plasma facing surface was measured by in-vacuo XPS and increased both with plasma exposure and with exposure to trace residual gases. Furthermore, this increase correlated with the rise of oxygen emission from the plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Advances in boronization on NSTX-Upgrade

Boronization has been effective in reducing plasma impurities and enabling access to higher density, higher confinement plasmas in many magnetic fusion devices. The National Spherical Torus eXperiment, NSTX, has recently undergone a major upgrade to NSTX-U in order to develop the physics basis for a ST-based Fusion Nuclear Science Facility (FNSF) with capability for double the toroidal field, plasma current, and NBI heating power and increased pulse duration from 1–1.5 s to 5–8 s. A new deuterated tri-methyl boron conditioning system was implemented together with a novel surface analysis diagnostic. We report on the spatial distribution of the boron deposition versus discharge pressure, gas injection and electrode location. The oxygen concentration of the plasma facing surface was measured by in-vacuo XPS and increased both with plasma exposure and with exposure to trace residual gases. This increase correlated with the rise of oxygen emission from the plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U

Three-dimensional nonlinear simulations of Alfvén eigenmodes in the subcyclotron frequency range demonstrate a robust physical stabilizing mechanism via modest off-axis beam injection, in agreement with experimental observations from the National Spherical Torus Experiment (NSTX-U). Experimental results from NSTX-U have demonstrated that neutral beam injection from the new beam sources with large tangency radii deposits beam ions with large pitch, which can very effectively stabilize all unstable Global Alfvén Eigenmodes (GAEs). Beam-driven GAEs have been linked to enhanced electron transport in NSTX, and the ability to control these modes will have significant implications for NSTX-U, ITER, and other fusion devices where super-Alfvénic fast ions might be present. Nonlinear simulations using the HYM code have been performed to study the excitation and stabilization of GAEs in the NSTX-U right before and shortly after the additional off-axis beam injection. The simulations reproduce the experimental finding, namely, it is shown that off-axis neutral beam injection reliably and strongly suppresses all unstable GAEs. Before additional beam injection, the simulations show unstable counter-rotating GAEs with toroidal mode numbers and frequencies that match the experimentally determined modes. Additional off-axis beam injection has been modeled by adding beam ions with large pitch and varying density. The complete stabilization occurs at less than 7% of the total beam ion inventory. New analytical theory of GAE (de)stabilization has also been derived, indicating a different interpretation for the GAE stabilization mechanism compared to previous publications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Two-fluid equilibrium with flow: FLOW2

The effects of finite macroscopic velocities on axisymmetric ideal equilibria are examined using the two-fluid (ions and electrons) model. A new equilibrium solver, the code FLOW2, is introduced for the two-fluid model and used to investigate the importance of various flow patterns on the equilibrium of tight aspect ratio (NSTX) and regular tokamak (DIII-D) configurations. Several improvements to the understanding and calculation of two-fluid equilibria are presented, including an analytical and numerical proof of the single-fluid and static limits of the two-fluid model, a discussion of boundary conditions, a user-friendly free-function formulation, and the explicit evaluation of velocity components normal to magnetic surfaces.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Flowing liquid lithium plasma-facing components – Physics, technology and system analysis of the LiMIT system

The use of low atomic number liquid metals has been shown to have the potential to solve many of the prevalent problems like erosion and radiation losses associated with the interaction of fusion plasma with the plasma facing component (PFC) structures in tokamaks. Since the first evidence of lithium increasing plasma performance in TFTR [1], the benefits of using lithium in fusion environments have been seen in many devices, including CDX-U [2], NSTX [3], LTX [4], and DIII-D [5]. While both fast flow and slow flow concepts have been studied with regards to liquid lithium first wall alternatives, this report will focus on efforts placed on fast flow research and will mainly focus on advancements in the LiMIT device that help to eliminate concerns over the broad use of liquid lithium. Due to the promising TFTR results along with results obtained at the University of Illinois at Urbana-Champaign [6], suitably designed trench structures holding liquid lithium could be an appropriate fast flow candidate for PFC modules in future fusion devices. There are four potential shortcomings of this approach: (1) Droplet ejection, (2) Wetting control, (3) Tritium retention, and (4) Limited heat flux handling. Droplet ejection is discussed in a companion publication [7], while this paper addresses the topics of wetting control and heat flux handling. Limitations in wetting and prevention of lithium creep (i.e. getting and keeping the lithium only where it should be) have been solved by laser-texturing the base material with extreme short laser pulses (pico – femto second) of high power (several 10 s of W). Micro- and nano-structuring results indicate that the textured substrates displayed significant change in their wetting properties, increasing the temperature needed to wet from 310 °C to 390 °C. Lastly, initial designs for the Lithium Metal Infused Trenches (LiMIT) [6] showed dryout above 3 MW/m 2 , but new designs of the trench shaping show potential to be able to handle up to 10 MW/m 2 . Dryout is accompanied by lithium evaporation which is shown to mitigate the incident heat flux, which may be viewed as beneficial [8]. The advances shown here will increase the viability of the LiMIT system in large-scale testing, and allow for extensive design iteration to begin tackling the large powers and heat fluxes present in reactor-relevant systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A dual wavelength imaging system for plasma-surface interaction studies on the National Spherical Torus Experiment Upgrade

A two-channel spectral imaging system based on a charge injection device radiation-hardened intensified camera was built for studies of plasma-surface interactions on divertor plasma facing components in the National Spherical Torus Experiment Upgrade (NSTX-U) tokamak. By means of commercially available mechanically referenced optical components, the two-wavelength setup images the light from the plasma, relayed by a fiber optic bundle, at two different wavelengths side-by-side on the same detector. Remotely controlled filter wheels are used for narrow bandpass and neutral density filters on each optical path allowing for simultaneous imaging of emission at wavelengths differing in brightness up to 3 orders of magnitude. Applications on NSTX-U will include the measurement of impurity influxes in the lower divertor strike point region and the imaging of plasma-material interaction on the head of the surface analysis probe MAPP (Material Analysis and Particle Probe). The diagnostic setup and initial results from its application on the lithium tokamak experiment are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗