N. T. Howard
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View article: Efficient dataset construction using active learning and uncertainty-aware neural networks for plasma turbulent transport surrogate models
Efficient dataset construction using active learning and uncertainty-aware neural networks for plasma turbulent transport surrogate models Open
This work demonstrates a proof-of-principle for using uncertainty-aware architectures, in combination with active learning techniques and an in-the-loop physics simulation code as a data labeler, to construct efficient datasets for data-dr…
View article: Integrated modeling of SPARC H-mode scenarios: exploration of the impact of modeling assumptions on predicted performance
Integrated modeling of SPARC H-mode scenarios: exploration of the impact of modeling assumptions on predicted performance Open
In this paper an extensive database of SPARC H-modes confinement predictions has been provided, to assess its variability with respect to few input assumptions. The simulations have been performed within the ASTRA framework, using the quas…
View article: Gyrokinetic profile prediction and validation of a negative triangularity plasma in ASDEX Upgrade
Gyrokinetic profile prediction and validation of a negative triangularity plasma in ASDEX Upgrade Open
In this work, gyrokinetic simulations are performed with the CGYRO code (Candy et al 2016 J. Comput. Phys. 324 73–93) for a negative triangularity H-mode plasma in ASDEX Upgrade, and compared with experimental measurements. The PORTALS fra…
View article: High confinement regimes on SPARC: operational conditions for access and avoidance
High confinement regimes on SPARC: operational conditions for access and avoidance Open
This work examines H-mode and I-mode access on the SPARC tokamak, combining new simulations of core L-mode power balance with the best empirical scalings available for L–H and L–I thresholds. Scalings applied to SPARC for the first time in…
View article: Integrated Modeling of SPARC H-mode Scenarios: Exploration of the Impact of Modeling Assumptions on Predicted Performance
Integrated Modeling of SPARC H-mode Scenarios: Exploration of the Impact of Modeling Assumptions on Predicted Performance Open
In this paper an extensive database of SPARC H-modes confinement predictions has been provided, to assess its variability with respect to few input assumptions. The simulations have been performed within the ASTRA framework, using the quas…
View article: Prediction of performance and turbulence in ITER burning plasmas via nonlinear gyrokinetic profile prediction
Prediction of performance and turbulence in ITER burning plasmas via nonlinear gyrokinetic profile prediction Open
Burning plasma performance, transport, and the effect of hydrogen isotope (H, D, D-T fuel mix) on confinement has been predicted for ITER baseline scenario (IBS) conditions using nonlinear gyrokinetic profile predictions. Accelerated by su…
View article: Enhancing predictive capabilities in fusion burning plasmas through surrogate-based optimization in core transport solvers
Enhancing predictive capabilities in fusion burning plasmas through surrogate-based optimization in core transport solvers Open
This work presents the PORTALS framework (Rodriguez-Fernandez et al 2022 Nucl. Fusion 62 076036), which leverages surrogate modeling and optimization techniques to enable the prediction of core plasma profiles and performance with nonlinea…
View article: Simulating energetic ions and enhanced fusion rates from ion-cyclotron resonance heating with a full-wave/Fokker–Planck model
Simulating energetic ions and enhanced fusion rates from ion-cyclotron resonance heating with a full-wave/Fokker–Planck model Open
Reproducing fast-ion enhanced fusion rates from ion-cyclotron resonance heating (ICRH) in tokamaks requires the self-consistent coupling of a full-wave solver and a Fokker–Planck solver, which evolves multiple simultaneously resonant ion s…
View article: Core performance predictions in projected SPARC first-campaign plasmas with nonlinear CGYRO
Core performance predictions in projected SPARC first-campaign plasmas with nonlinear CGYRO Open
This work characterizes the core transport physics of SPARC early-campaign plasmas using the PORTALS-CGYRO framework. Empirical modeling of SPARC plasmas with L-mode confinement indicates an ample window of breakeven (Q > 1) without the…
View article: Fusion plasma turbulence research beyond the burning plasma era: perspectives on transport model validation in fusion and fission
Fusion plasma turbulence research beyond the burning plasma era: perspectives on transport model validation in fusion and fission Open
In fusion, the validation of turbulent transport models is undertaken with the goals of making basic physics discoveries as well as for development of new predictive models to improve the operation and enhance the performance of existing a…
View article: Prediction of Performance and Turbulence in ITER Burning Plasmas via Nonlinear Gyrokinetic Profile Prediction
Prediction of Performance and Turbulence in ITER Burning Plasmas via Nonlinear Gyrokinetic Profile Prediction Open
Burning plasma performance, transport, and the effect of hydrogen isotope on confinement has been predicted for ITER baseline scenario (IBS) conditions using nonlinear gyrokinetic profile predictions. Accelerated by surrogate modeling [P. …
View article: Core performance predictions in projected SPARC first-campaign plasmas with nonlinear CGYRO
Core performance predictions in projected SPARC first-campaign plasmas with nonlinear CGYRO Open
This work characterizes the core transport physics of SPARC early-campaign plasmas using the PORTALS-CGYRO framework. Empirical modeling of SPARC plasmas with L-mode confinement indicates an ample window of breakeven (Q>1) without the need…
View article: Overview of multiscale turbulence studies covering ion-to-electron scales in magnetically confined fusion plasma
Overview of multiscale turbulence studies covering ion-to-electron scales in magnetically confined fusion plasma Open
Turbulent transport in magnetically confined fusion plasma has conventionally been analyzed at the ion gyroradius scale based on the microturbulence theory. However, ion-scale turbulence analysis sometimes fails to predict the turbulent tr…
View article: Simultaneous reproduction of experimental profiles, fluxes, transport coefficients, and turbulence characteristics via nonlinear gyrokinetic profile predictions in a DIII-D ITER similar shape plasma
Simultaneous reproduction of experimental profiles, fluxes, transport coefficients, and turbulence characteristics via nonlinear gyrokinetic profile predictions in a DIII-D ITER similar shape plasma Open
Experimental conditions obtained on the DIII-D tokamak in the ITER Similar Shape (ISS) have been compared extensively with nonlinear gyrokinetic simulation using the CGYRO code [Candy et al., J. Comput. Phys. 324, 73–93 (2016)] with compar…
View article: Enhancing predictive capabilities in fusion burning plasmas through surrogate-based optimization in core transport solvers
Enhancing predictive capabilities in fusion burning plasmas through surrogate-based optimization in core transport solvers Open
This work presents the PORTALS framework, which leverages surrogate modeling and optimization techniques to enable the prediction of core plasma profiles and performance with nonlinear gyrokinetic simulations at significantly reduced cost,…
View article: Development of compact tokamak fusion reactor use cases to inform future transport studies
Development of compact tokamak fusion reactor use cases to inform future transport studies Open
The OMFIT STEP (Meneghini et al. , Nucl. Fusion , vol. 10, 2020, p. 1088) workflow has been used to develop inductive and steady-state H-mode core plasma scenario use cases for a $B_0 = 8 \, {\rm T}$ , $R_0 = 4 \, {\rm m}$ machine to help …
View article: Predictions of improved confinement in SPARC via energetic particle turbulence stabilization
Predictions of improved confinement in SPARC via energetic particle turbulence stabilization Open
The recent progress in high-temperature superconductor technologies has led to the design and construction of SPARC, a compact tokamak device expected to reach plasma breakeven with up to 25 MW of external ion cyclotron resonant heating (I…
View article: Validation of IMEP on Alcator C-Mod and JET-ILW ELMy H-mode plasmas
Validation of IMEP on Alcator C-Mod and JET-ILW ELMy H-mode plasmas Open
The recently developed integrated model based on engineering parameters (IMEP) (Luda et al 2020 Nucl. Fusion 61 126048; Luda et al 2021 Nucl. Fusion 60 036023), so far validated on ASDEX Upgrade, has been tested on a database of 3 Alcator …
View article: Investigation of core impurity transport in DIII-D diverted negative triangularity plasmas
Investigation of core impurity transport in DIII-D diverted negative triangularity plasmas Open
Tokamak operation at negative triangularity has been shown to offer high energy confinement without the typical disadvantages of edge pedestals (Marinoni et al 2021 Nucl. Fusion 61 116010). In this paper, we examine impurity transport in D…
View article: A Conformer-based Waveform-domain Neural Acoustic Echo Canceller Optimized for ASR Accuracy
A Conformer-based Waveform-domain Neural Acoustic Echo Canceller Optimized for ASR Accuracy Open
Acoustic Echo Cancellation (AEC) is essential for accurate recognition of queries spoken to a smart speaker that is playing out audio. Previous work has shown that a neural AEC model operating on log-mel spectral features (denoted "logmel"…
View article: Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade
Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade Open
The I-mode confinement regime is promising for future reactor operation due to high energy confinement without high particle confinement. However, the role of edge turbulence in creating I-mode's beneficial transport properties is still un…
View article: Mask scalar prediction for improving robust automatic speech recognition
Mask scalar prediction for improving robust automatic speech recognition Open
Using neural network based acoustic frontends for improving robustness of streaming automatic speech recognition (ASR) systems is challenging because of the causality constraints and the resulting distortion that the frontend processing in…
View article: Nonlinear gyrokinetic predictions of SPARC burning plasma profiles enabled by surrogate modeling
Nonlinear gyrokinetic predictions of SPARC burning plasma profiles enabled by surrogate modeling Open
Multi-channel, nonlinear predictions of core temperature and density profiles are performed for the SPARC tokamak (Creely et al 2020 J. Plasma Phys. 86 865860502) accounting for both kinetic neoclassical and fully nonlinear gyro-kinetic tu…
View article: Overview of the SPARC physics basis towards the exploration of burning-plasma regimes in high-field, compact tokamaks
Overview of the SPARC physics basis towards the exploration of burning-plasma regimes in high-field, compact tokamaks Open
The SPARC tokamak project, currently in engineering design, aims to achieve breakeven and burning plasma conditions in a compact device, thanks to new developments in high-temperature superconductor technology. With a magnetic field of 12.…
View article: Interpreting radial correlation Doppler reflectometry using gyrokinetic simulations
Interpreting radial correlation Doppler reflectometry using gyrokinetic simulations Open
A linear response, local model for the DBS amplitude applied to gyrokinetic simulations shows that radial correlation Doppler reflectometry measurements (RCDR, Schirmer et al 2007 Plasma Phys. Control. Fusion 49 1019) are not sensitive to …
View article: A Conformer-Based ASR Frontend for Joint Acoustic Echo Cancellation, Speech Enhancement and Speech Separation
A Conformer-Based ASR Frontend for Joint Acoustic Echo Cancellation, Speech Enhancement and Speech Separation Open
We present a frontend for improving robustness of automatic speech recognition (ASR), that jointly implements three modules within a single model: acoustic echo cancellation, speech enhancement, and speech separation. This is achieved by u…
View article: A Conformer-based ASR Frontend for Joint Acoustic Echo Cancellation,\n Speech Enhancement and Speech Separation
A Conformer-based ASR Frontend for Joint Acoustic Echo Cancellation,\n Speech Enhancement and Speech Separation Open
We present a frontend for improving robustness of automatic speech\nrecognition (ASR), that jointly implements three modules within a single model:\nacoustic echo cancellation, speech enhancement, and speech separation. This is\nachieved b…
View article: Experimental inference of neutral and impurity transport in Alcator C-Mod using high-resolution x-ray and ultra-violet spectra
Experimental inference of neutral and impurity transport in Alcator C-Mod using high-resolution x-ray and ultra-violet spectra Open
We present experimental inferences of cross-field impurity transport coefficients for AlcatorC-Mod plasmas without edge-localized modes, leveraging a novel forward model for the entire Ca K α spectrum, including satellite lines within the …
View article: Modeling of particle transport, neutrals and radiation in magnetically-confined plasmas with Aurora
Modeling of particle transport, neutrals and radiation in magnetically-confined plasmas with Aurora Open
We present Aurora, an open-source package for particle transport, neutrals and radiation modeling in magnetic confinement fusion plasmas. Aurora's modern multi-language interface enables simulations of 1.5D impurity transport within high-p…
View article: Experimental Inference of Neutral and Impurity Transport in Alcator\n C-Mod Using High-Resolution X-Ray and Ultra-Violet Spectra
Experimental Inference of Neutral and Impurity Transport in Alcator\n C-Mod Using High-Resolution X-Ray and Ultra-Violet Spectra Open
We present experimental inferences of cross-field impurity transport\ncoefficients for Alcator C-Mod plasmas using a novel forward model for the\nentire Ca K-alpha spectrum, including satellite lines within the spectral\nrange, to compare …