A5047037076- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Nuclear reactor physics and engineering
- Solar and Space Plasma Dynamics
- Tropical and Extratropical Cyclones Research
- Nuclear Physics and Applications
- Geophysical Methods and Applications
- Ocean Waves and Remote Sensing
- Atomic and Molecular Physics
- Metal and Thin Film Mechanics
- X-ray Spectroscopy and Fluorescence Analysis
- Meteorological Phenomena and Simulations
- Atomic and Subatomic Physics Research
- Laser-Matter Interactions and Applications
- High-pressure geophysics and materials
- Diamond and Carbon-based Materials Research
- Geophysics and Gravity Measurements
- Geological and Tectonic Studies in Latin America
- Synthetic Aperture Radar (SAR) Applications and Techniques
- Ion-surface interactions and analysis
University of Oxford
2020-2025
Fusion (United States)
2015-2020
Plasma Technology (United States)
2015-2020
Fusion Academy
2015-2020
Massachusetts Institute of Technology
2020
University of California, San Diego
2020
General Atomics (United States)
2020
Princeton Plasma Physics Laboratory
2020
University of California, Davis
2020
University of Wisconsin–Madison
2020
Abstract As part the DTE2 campaign in JET tokamak, we conducted a parameter scan T and D-T complementing existing pulses H D. For different main ion masses, type-I ELMy H-modes at fixed plasma current magnetic field can have pedestal pressure varying by factor of 4 total changing from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo>...
Abstract Nonlinear multiscale gyrokinetic simulations of a Joint European Torus edge pedestal are used to show that electron-temperature-gradient (ETG) turbulence has rich three-dimensional structure, varying strongly according the local magnetic-field configuration. In plane normal magnetic field, steep electron temperature gradient gives rise anisotropic with radial (normal) wavelength much shorter than in binormal direction. parallel direction, location and extent determined by variation...
Abstract Plasma turbulence on disparate spatial and temporal scales plays a key role in defining the level of confinement achievable tokamaks, with development reduced numerical models for cross-scale effects informed by experimental measurements an essential step. MAST-U is well-equipped facility having instruments to measure ion electron scale at plasma edge. However, measurement core challenging, especially H mode. Using novel synthetic diagnostic approach, we present simulated...
We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfvén mode in magnetically confined plasma. Core-localized modes frequency inside toroidicity-induced gap (and its harmonics) exhibit three-wave coupling interactions with fluctuation. The observation consistent theoretical and numerical predictions zonal modes, correlated increase deep core ion temperature, temperature gradient, confinement factor <a:math...
The phenomenon of focusing microwave beams in a plasma near turning-point caustic is discussed by exploiting the analytical solution to Gaussian beam-tracing equations two-dimensional (2-D) linear-layer problem. location maximum beam and width at that are studied terms initial conditions. This must be taken into account interpret Doppler backscattering (DBS) measurements. We find filter function characterises scattering intensity contribution along path through inversely proportional width,...
A linear response, local model for the DBS amplitude applied to gyrokinetic simulations shows that radial correlation Doppler reflectometry measurements (RCDR, Schirmer et al., Plasma Phys. Control. Fusion 49 1019 (2007)) are not sensitive average turbulence length, but a length depends on binormal wavenumber $k_\perp$ selected by backscattering (DBS) signal. Nonlinear show naturally exhibits non-separable power law spectrum in space, leading dependence of with $l_r \sim C k_\perp^{-\alpha}...
Abstract The mission of the low aspect ratio spherical tokamak NSTX-U is to advance physics basis and technical solutions required for optimizing configuration next-step steady-state fusion devices. will ultimately operate at up 2 MA plasma current 1 T toroidal field on axis 5 s, has available 15 MW neutral beam injection power different tangency radii 6 high harmonic fast wave heating. With these capabilities develop understanding control tools ramp-up sustain performance fully...
Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the gyro-scale, k⊥ρe ≲ 1, can be responsible for anomalous thermal transport in NSTX. Electron scale (high-k) is diagnosed NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report stabilization effects of density electron-scale fluctuations set neutral beam injection heated H-mode plasmas. We found absence from measurements correlated large...
Abstract In magnetic confinement fusion devices, the ratio of plasma pressure to field energy, β , can become sufficiently large that electromagnetic microinstabilities unstable, driving turbulence distorts or reconnects equilibrium field. this paper, a theory is proposed for electromagnetic, electron-driven linear instabilities have current layers localised mode-rational surfaces and binormal wavelengths comparable ion gyroradius. The model retains axisymmetric toroidal geometry with...
A new extensive validation study performed for a modest-beta National Spherical Torus eXperiment (NSTX) neutral beam injection-heated H-mode discharge predicts that electron thermal transport can be entirely explained by short-wavelength electron-scale turbulence fluctuations driven the temperature gradient mode (ETG), both in conditions of strong and weak ETG drive. Quantitative comparisons between high-k fluctuation measurements (Smith et al 2008 Rev. Sci. Instrum. 79 123501) simulations...
We use the beam model of Doppler backscattering (DBS), which was previously derived from tracing and reciprocity theorem, to shed light on mismatch attenuation. This attenuation backscattered signal occurs when wavevector probe beam's electric field is not in plane perpendicular magnetic field. Correcting for this effect important determining amplitude actual density fluctuations. Previous preliminary comparisons between Mega-Ampere Spherical Tokamak (MAST) plasmas were promising. In work,...
Two synthetic diagnostics are implemented for the high-k scattering system in NSTX (Smith et al 2008 Rev. Sci. Instrum. 79 123501) allowing direct comparisons between and experimentally detected frequency wavenumber spectra of electron-scale turbulence fluctuations. Synthetic formulated real-space space, deployed realistic simulations carried out with GYRO code (Candy Waltz 2003 J. Comput. Phys. 186 545). A highly unstable electron temperature gradient (ETG) mode regime a modest-β NBI-heated...
An extensive validation effort performed for a modest-beta NSTX NBI-heated H-mode discharge predicts that electron thermal transport can be entirely explained by electron-scale turbulence fluctuations driven the temperature gradient mode (ETG), both in conditions of strong and weak ETG drive. Thermal power-balance estimates computed TRANSP as well shape high-k density fluctuation wavenumber spectrum level ratio between strongly weakly ETG-turbulence matched nonlinear gyrokinetic simulations...
We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfv\'en mode in magnetically confined plasma. Core-localized bidirectional modes frequency inside toroidicity-induced gap (and its harmonics) exhibit three-wave coupling interactions with fluctuation. The observation consistent theoretical and numerical predictions zonal modes, correlated increase deep core ion temperature, temperature gradient, confinement factor $H_{89,P}$. Despite energetic...
The phenomenon of beam focusing microwaves in a plasma near turning-point caustic is discussed the context analytical solution to Gaussian beam-tracing equations 2D linear-layer problem. location maximum and width at that are studied terms initial conditions. analytic used study effect this on Doppler backscattering (DBS). We find filter function characterises scattering intensity contributions along path through inversely proportional width, predicting enhanced from region. show DBS signal...
Toroidal Alfv\'en eigenmodes (TAEs) can transport fusion-born energetic particles out of the plasma volume, thereby decreasing self-heating efficiency and possibly damaging reactor walls. Therefore, understanding TAE destabilisation identifying saturation mechanisms is crucial to achieving burning plasma. While TAEs have been studies extensively in past using kinetic-MHD codes, here a fully gyrokinetic study employed which allows for additional physics. In case studied, primary drive...
Toroidal Alfvén eigenmodes (TAEs) can transport fusion-born energetic particles out of the plasma volume, thereby decreasing self-heating efficiency and possibly damaging reactor walls. Therefore, understanding TAE destabilization identifying saturation mechanisms are crucial to achieving burning plasma. Here, a fully gyrokinetic study is employed. In case studied, primary drive mechanism identified as resonance between magnetic drifts TAE, this seen be disrupted by equilibrium flow shear,...
Results of experiments studying the effect a ringing 10 kA current prepulse on 160 kA, 7 μm carbon fibre z-pinch are presented. A duration 100–300 ns was found to radically alter pinch behaviour. delayed onset in x-ray and optical emission with respect main observed. There marked improvement axial uniformity pinch. large soft pulse, ten twenty times larger than discharges without recorded. An electron temperature 250±50 eV measured which considerably higher prepulse.
A new pseudolocal tomography algorithm is developed for soft X-ray(SXR) imaging measurements of the turbulent electron temperature fluctuations (δ Te) in tokamaks and stellarators. The overcomes constraints limited viewing ports on vessel wall (viewing angle) number lines sight (LOS). This accomplished by increasing LOS locally a region interest. Numerical modeling demonstrates that wavenumber spectrum turbulence can be reliably reconstructed, with an acceptable angles suitable low SNR...