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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Ion temperature gradient instability at sub-Larmor radius scales with non-zero ballooning angle

Linear gyro-kinetic stability calculations predict unstable toroidal ion temperature gradient modes (ITGs) with normalised poloidal wave vectors well above one (k{sub {theta}}{rho}{sub i}>1) for standard tokamak parameters with adiabatic electron response. These modes have a maximum amplitude at a poloidal angle {theta} that is shifted away from the low field side ({theta}{ne}0). The physical mechanism is clarified through the use of a fluid model. It is shown that the shift of the mode away from the low field side reduces the effective drift frequency which allows for the instability to develop. Numerical tests using the gyro-kinetic model confirm this physical mechanism. Furthermore, it is shown that modes localized away from the low field side can be important also for k{sub {theta}}{rho}{sub i}<1 close to the threshold of the ITG. In fact, modes with maximum amplitude at {theta}{ne}0 can exist for normalised temperature gradient lengths below the threshold of the ITG obtained for the case with the maximum at {theta}=0.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Suppression of the asymmetric competition mode in the relativistic Ku-band coaxial transit-time oscillator

A relativistic Ku-band coaxial transit-time oscillator has been proposed in our previous work. In the experiments, we find that the asymmetric competition mode in the device limits the microwave power with the increase of the input electric power. For solving such a problem, the methods for analysis and suppression of the asymmetric competition mode in the device are investigated theoretically and experimentally. It is shown that the structure and the material of the collector, the concentricity, and the electron emission uniformity play an important part in the suppression of the asymmetric competition mode in the relativistic Ku-band transit-time oscillator. In the subsequent experiments, the asymmetric mode was suppressed effectively. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 1 GW, frequency of 14.3 GHz close to the simulation one, and efficiency of 20% was generated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Conference Report on the 8th International Symposium on Liquid Metals Applications for Fusion (ISLA-8)

The International Symposium on Liquid Metals Applications for Fusion (ISLA) aims to assemble scientists and engineers engaged in research on lithium and liquid metal applications for fusion devices, facilitating discussions on recent advancements and challenges in an open forum to support the development of viable fusion reactors. The 8th International Symposium on Liquid Metals Applications for Fusion (ISLA-8) was organized by the Institute of Plasma Physics, Chinese Academy of Sciences, from 8 to 12 September 2024, in Hefei, China. The symposium was attended by over 70 participants, marking one of the highest attendance figures in the series. A total of 68 presentations were delivered, including 59 presented on-site, while the remainder were conducted online. The participants represented 10 countries, namely China, Japan, the Netherlands, Russia, the USA, the Czech Republic, Italy, Thailand, Spain, and Germany. The symposium covered 10 topics, structured into 13 sessions. Additionally, an opening session provided an overview of the current symposium, while a closing session summarized reports from each session chair.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2004

Demonstration of Separation Delay with Glow-Discharge Plasma Actuators

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modern low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2 percent) and high (2.5 percent) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.↗
NASA NTRSDate not supplied

Wavelength Calibration of the Full-sun Ultraviolet Rocket SpecTrograph: (FURST)

The Sun has a well-known periodicity in sunspot number and magnetic field variation. The underlying cause of this 11-year cycle is not fully understood and has yet to be connected with those processes in other stellar objects. The Full-sun Ultraviolet Rocket SpecTrograph (FURST) is a sounding rocket payload being developed by Montana State University (MSU) alongside the Marshall Space Flight Center (MSFC) solar physics group. Scheduled to launch from White Sands Missile Range (WSMR) in 2022, this instrument is unique in that it will provide the connection between stellar observatories with measurements of our Sun. It will achieve this through extremely high-resolution full-disk spectroscopy in EUV. We aim to obtain a wavelength resolution R > 10,000 in the 115 - 181 nm range, on par with that of the Hubble (HST) Space Telescope Imaging Spectrograph (STIS). The Lyman Alpha line (121 nm) is known to oversaturate most CCD electronics and is of particular challenge for this spectral range. In addition, this resolution goal will allow us to study the 3 km/s motion (a Doppler-shift of about 0.01 Angstroms) of the relatively low-temperature plasma in the chromosphere and lower corona. This paper will present the results of our simulation of the diagnostic lamp signal to be used in this wavelength calibration. To test the viability of this precise of a device, we are building a collimator capable of calibrating the FURST instrument under these strict radiometric requirements. By way of a diagnostic lamp simulation, we will account for photon noise, CCD electronic readout noise, and statistical error. These will lead to the development of our pre- and post-launch calibration plan. Future work includes absolute radiometric and wavelength calibration with this new collimator. In addition, the ability of FURST to measure extremely small Doppler-shifts will provide capabilities for planetary atmospheric scientists. This impact is coupled with the diverse international partnership created by the closely-knit Sounding Rocket teams across the globe. These Sounding Rockets have an even broader impact, as they encourage future satellite missions under the prospect of long-term observations.

FURST↗
DOE OSTI2023

Density wavenumber spectrum measurements, synthetic diagnostic development, and tests of quasilinear turbulence modeling in the core of electron-heated DIII-D H-mode plasmas

Abstract Measurements of the turbulent density wavenumber spectrum, δ n ˆ e ( k ⊥ ) , using the Doppler Back-Scattering (DBS) diagnostic are reported from DIII-D H-mode plasmas with electron cyclotron heating as the only auxiliary heating method. These electron-heated plasmas have low collisionality, ν e ∗ < 1 , T e / T i > 1 , and zero injected torque—a regime expected to be relevant for future fusion devices. We probe density fluctuations in the core ( ρ ≈ 0.7) over a broad wavenumber range, 0.5 ⩽ k ⊥ ⩽ 16 cm −1 ( 0.1 ⩽ k ⊥ ρ s ⩽ 5 ), to characterize plasma instabilities and compare with theoretical predictions. We present a novel synthetic DBS diagnostic to relate the back-scattered power spectrum, P s ( k ⊥ ) —which is directly measured by DBS—to the underlying electron density fluctuation spectrum, δ n ˆ e ( k ⊥ ) . The synthetic DBS P s ( k ⊥ ) spectrum is calculated by combining the SCOTTY beam-tracing code with a model δ n ˆ e ( k ⊥ ) predicted either analytically or numerically. In this work we use the quasi-linear code Trapped Gyro-Landau Fluid (TGLF) to approximate the δ n ˆ e ( k ⊥ ) spectrum. We find that TGLF, using the experimental profiles, is capable of closely reproducing the DBS measurements. Both the DBS measurements and the TGLF-DBS synthetic diagnostic show a wavenumber spectrum with variable decay. The measurements show weak decay ( k −0.6 ) for k < 3.5 cm −1 , with k −2.6 at intermediate- k ( 3.5 ⩽ k ⩽ 8.5 cm −1 ), and rapid decay ( k −9.4 ) for k > 8.5 cm −1 . Scans of physics parameters using TGLF suggest that the normalized ∇ T e scale-length, R / L T e , is an important factor for distinguishing microturbulence regimes in these plasmas. A combination of DBS observations and TGLF simulations indicate that fluctuations remain peaked at ITG-scales (low k ) while R / L T e -driven TEM/ETG-type modes (intermediate/high k ) are marginally sub-dominant.

synthetic diagnostics↗
DOE OSTI2024

Self‐consistent transport simulation of boron dust particle injection in the peripheral plasma in Large Helical Device

Abstract The trajectories and the ablation positions of boron dust particles dropped from an impurity powder dropper in the peripheral plasma in the Large Helical Device (LHD) were calculated using a three‐dimensional edge plasma simulation code (EMC3‐EIRENE) and a dust transport simulation code (DUSTT). The simulation shows that the trajectory of the boron dust particles is deflected at the upper divertor leg due to the effect of the hydrogen plasma flow, and the ablation positions of the dust particles in an ergodic layer change toward the outboard side of the torus for higher plasma densities. The effect of the boron ion flow in the divertor leg on the deflection is investigated by coupling the two codes self‐consistently. The simulation predicts that the boron ions in the divertor leg, which are produced by sputtering on the divertor plates, which do not affect the change in the ablation positions. It also shows that the ablation positions move toward the inboard side and approach the Last Closed Flux Surface (LCFS) in case of increased boron dust drop rates, which is caused by the lowered plasma flow in the upper divertor leg due to the lowered electron temperature by radiation cooling by the dropped dust particles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Fast Fiber-Coupled Imaging Devices

HyperV Technologies Corp. has successfully designed, built and experimentally demonstrated a full scale 1024 pixel 100 MegaFrames/s fiber coupled camera with 12 or 14 bits, and record lengths of 32K frames, exceeding our original performance objectives. This high-pixel-count, fiber optically-coupled, imaging diagnostic can be used for investigating fast, bright plasma events. In Phase 1 of this effort, a 100 pixel fiber-coupled fast streak camera for imaging plasma jet profiles was constructed and successfully demonstrated. The resulting response from outside plasma physics researchers emphasized development of increased pixel performance as a higher priority over increasing pixel count. In this Phase 2 effort, HyperV therefore focused on increasing the sample rate and bit-depth of the photodiode pixel designed in Phase 1, while still maintaining a long record length and holding the cost per channel to levels which allowed up to 1024 pixels to be constructed. Cost per channel was 53.31 dollars, very close to our original target of $50 per channel. The system consists of an imaging "camera head" coupled to a photodiode bank with an array of optical fibers. The output of these fast photodiodes is then digitized at 100 Megaframes per second and stored in record lengths of 32,768 samples with bit depths of 12 to 14 bits per pixel. Longer record lengths are possible with additional memory. A prototype imaging system with up to 1024 pixels was designed and constructed and used to successfully take movies of very fast moving plasma jets as a demonstration of the camera performance capabilities. Some faulty electrical components on the 64 circuit boards resulted in only 1008 functional channels out of 1024 on this first generation prototype system. We experimentally observed backlit high speed fan blades in initial camera testing and then followed that with full movies and streak images of free flowing high speed plasma jets (at 30-50 km/s). Jet structure and jet collisions onto metal pillars in the path of the plasma jets were recorded in a single shot. This new fast imaging system is an attractive alternative to conventional fast framing cameras for applications and experiments where imaging events using existing techniques are inefficient or impossible. The development of HyperV's new diagnostic was split into two tracks: a next generation camera track, in which HyperV built, tested, and demonstrated a prototype 1024 channel camera at its own facility, and a second plasma community beta test track, where selected plasma physics programs received small systems of a few test pixels to evaluate the expected performance of a full scale camera on their experiments. These evaluations were performed as part of an unfunded collaboration with researchers at Los Alamos National Laboratory and the University of California at Davis. Results from the prototype 1024-pixel camera are discussed, as well as results from the collaborations with test pixel system deployment sites.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Structure of the runaway electron loss during induced disruptions in TEXTOR

The loss of runaway electrons during an induced disruption is recorded by a synchrotron imaging technique using a fast infrared CCD camera. The loss is predominantly diffuse. During the “spiky-loss phase”, when the runaway beam moves close to the wall, a narrow channel between the runaway column and a scintillator probe is formed and lasts until the runaway beam is terminated. In some cases, the processed images show a stripe pattern at the plasma edge. A comparison between the MHD dominated disruptions and the MHD-free disruption is performed. A new mechanism of plasma disruptions with the runaway electron generation and a novel model which reproduces many characteristic features of the plasma beam evolution during a disruption is briefly described.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Initial operation of a newly developed multichord motional Stark effect diagnostic in KSTAR

A photo-elastic modulator based 25-chord motional Stark effect (MSE) diagnostic has been successfully developed and commissioned in Korea Superconducting Tokamak Advanced Research. The diagnostic measures the radial magnetic pitch angle profile of the Stark splitting of a D-alpha line at 656.1 nm by the electric field associated with the neutral deuterium heating beam. A tangential view of the neutral beam provides a good spatial resolution of 1–3 cm for covering the major radius from 1.74 m to 2.28 m, and the time resolution is achieved at 10 ms. An in-vessel calibration before the vacuum closing as well as an in situ calibration during the tokamak operation was performed by means of specially designed polarized lighting sources. In this work, we present the final design of the installed MSE diagnostic and the first results of the commissioning.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Validation of full-wave simulations for mode conversion of waves in the ion cyclotron range of frequencies with phase contrast imaging in Alcator C-Mod

Mode conversion of fast waves in the ion cyclotron range of frequencies (ICRF) is known to result in current drive and flow drive under optimised conditions, which may be utilized to control plasma profiles and improve fusion plasma performance. To describe these processes accurately in a realistic toroidal geometry, numerical simulations are essential. Quantitative comparison of these simulations and the actual experimental measurements is important to validate their predictions and to evaluate their limitations. The phase contrast imaging (PCI) diagnostic has been used to directly detect the ICRF waves in the Alcator C-Mod tokamak. The measurements have been compared with full-wave simulations through a synthetic diagnostic technique. Recently, the frequency response of the PCI detector array on Alcator C-Mod was recalibrated, which greatly improved the comparison between the measurements and the simulations. In this study, mode converted waves for D-{sup 3}He and D-H plasmas with various ion species compositions were re-analyzed with the new calibration. For the minority heating cases, self-consistent electric fields and a minority ion distribution function were simulated by iterating a full-wave code and a Fokker-Planck code. The simulated mode converted wave intensity was in quite reasonable agreement with the measurements close to the antenna, but discrepancies remain for comparison at larger distances.

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 OSTI2020

Physics-guided machine learning approaches to predict the ideal stability properties of fusion plasmas

One of the biggest challenges to achieve the goal of producing fusion energy in tokamak devices is the necessity of avoiding disruptions of the plasma current due to instabilities. The disruption event characterization and forecasting (DECAF) framework has been developed in this purpose, integrating physics models of many causal events that can lead to a disruption. Two different machine learning approaches are proposed to improve the ideal magnetohydrodynamic (MHD) no-wall limit component of the kinetic stability model included in DECAF. First, a random forest regressor (RFR), was adopted to reproduce the DCON computed change in plasma potential energy without wall effects for a large database of equilibria from the national spherical torus experiment (NSTX). This tree-based method provides an analysis of the importance of each input feature, giving an insight into the underlying physics phenomena. Secondly, a fully-connected neural network has been trained on sets of calculations with the DCON code, to get an improved closed form equation of the no-wall β limit as a function of the relevant plasma parameters indicated by the RFR. The neural network has been guided by physics theory of ideal MHD in its extension outside the domain of the NSTX experimental data. The estimated value has been incorporated into the DECAF kinetic stability model and tested against a set of experimentally stable and unstable discharges. Moreover, the neural network results were used to simulate a real-time stability assessment using only quantities available in real-time. Finally, the portability of the model was investigated, showing encouraging results by testing the NSTX-trained algorithm on the mega ampere spherical tokamak (MAST).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Perpendicular currents and electric fields in fully and partially ionized magnetized plasma

Perpendicular currents and self-consistent electric fields in fully and partially ionized plasma in strong magnetic field are analyzed. In fully ionized plasma, the analyses are concentrated on closing of viscosity driven currents. For partially ionized plasma, it is demonstrated that the perpendicular currents could be expressed through the total pressure gradient (including the pressure gradient of neutral particles) and viscosity of neutrals. The self-consistent electric fields and corresponding E(vector sign)×B(vector sign) could be quite large, which is important for various applications, in particular, for the divertor plasma of a tokamak in the detached regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Relative intensity calibration of the DIII-D charge-exchange recombination spectroscopy system using neutral beam injection into gas

A new calibration method for the DIII-D charge-exchange spectroscopy system produces a smoother impurity density profile compared to previous techniques, thus improving the accuracy of the impurity density profile reconstruction. The relative intensity calibration between the chords of the DIII-D charge-exchange recombination spectroscopy system is performed by firing neutral beams into the evacuated vacuum vessel pre-filled with neutral gas. Relative calibration is required in order to account for uncertainty in the 3D geometry of the neutral beam. Previous methods using helium gas have been improved by using xenon, which emits an emission line close to the commonly used carbon wavelength 5290.5 Å, as well as improved timing of the gas injection, inclusion of variations in the vessel pressure, and timing of neutral beam injection. Photoemission spectra recorded by 112 sightlines viewing 6 neutral beams are compared and used to form a relative calibration factor for each sightline. This relative calibration is shown to improve the quality of the measured ion density profile.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Real-time avoidance of the L-mode and H-mode density limit via machine-learned stability metrics

Reliable operation of burning plasma tokamaks will require robust control strategies to avoid macroscopic instability limits such as the L-mode and H-mode density limits (LDL, HDL). In this work, we explore closed-loop avoidance of these phenomena at DIII-D using machine-learned risk metrics. Feedback control is implemented via the ‘DL Supervisor’ scheme, which regulates the chosen risk metric by reducing the density target or increasing NBI heating in real-time. Using the LDL 25 risk metric, the LDL is reproducibly suppressed. We also introduce an HDL risk metric in this study, HDL 25 , which reduces the False Positive Rate by 2x compared to the Greenwald fraction. Applying this scaling to a plasma current ramp-down, we successfully avoid an HDL-driven H/L back-transition. These experiments constitute the first demonstration of real-time DL avoidance using machine-learned risk metrics. These instability metrics outline a path to safer high-density operation, more reliable ramp-down scenarios, and improved off-normal control for next-step devices such as ITER and SPARC.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Shock formation induced by poloidal flow and its effects on the edge stability in tokamaks

In the high confinement mode of tokamaks, magnitude of the radial electric field increases at the edge. Thus, the poloidal flow inside the transport barrier can be sonic when the edge pressure gradient is not steep enough to make the poloidal flow subsonic. When the poloidal Mach number is close to unity, a shock appears in the low field side and causes a large density perturbation. In this study, we describe a shock induced by the sonic poloidal plasma flow. Then, an entropy production across the shock is calculated. Finally, we introduce a simple model for Type III edge localized modes using the poloidal density variation driven by the sonic poloidal flow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗