A5090600476- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
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- Fusion materials and technologies
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- Physics of Superconductivity and Magnetism
- Fluid Dynamics and Turbulent Flows
- Laser-induced spectroscopy and plasma
- Electrostatic Discharge in Electronics
- Advancements in Semiconductor Devices and Circuit Design
- Gyrotron and Vacuum Electronics Research
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University of California, Los Angeles
2016-2025
General Atomics (United States)
2002-2024
University of Wisconsin–Madison
2010-2021
The University of Texas at Austin
1987-2021
University of York
2021
Fusion (United States)
1993-2019
Plasma Technology (United States)
1992-2019
Fusion Academy
1991-2019
University of California, San Diego
1995-2019
Princeton Plasma Physics Laboratory
2008-2019
A stochastic magnetic boundary, produced by an applied edge resonant perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement ($H$-mode) plasmas. The resulting $H$ mode displays rapid, small oscillations with a bursty character modulated coherent 130 Hz envelope. transport barrier and core are unaffected the despite threefold drop toroidal rotation. These results demonstrate that boundaries compatible may be attractive for ELM control next-step fusion tokamaks.
The understanding and predictive capability of transport physics plasma confinement is reviewed from the perspective achieving reactor-scale burning plasmas in ITER tokamak, for both core edge regions. Very considerable progress has been made understanding, controlling predicting tokamak across a wide variety conditions regimes since publication Physics Basis (IPB) document (1999 Nucl. Fusion 39 2137–2664). Major areas considered here follow. (1) Substantial improvement content, reliability...
Direct evidence of zonal flow (ZF) predator-prey oscillations and the synergistic roles ZF- equilibrium $\mathbit{E}\ifmmode\times\else\texttimes\fi{}\mathbit{B}$ shear in triggering low- to high-confinement (L- H-mode) transition DIII-D tokamak is presented. Periodic turbulence suppression first observed a narrow layer at just inside separatrix when shearing rate transiently exceeds decorrelation rate. The final H mode with sustained transport reduction controlled by due increasing ion...
The paradigm of shear suppression turbulence as the mechanism for low to high confinement mode (L H) transition is examined by quantitative comparison predictions with experimental results from DIII-D tokamak [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. L H trigger V×B rotation, not main ion pressure gradient. radial electric field Er increases before fluctuation suppression, consistent increasing cause suppression. spatial...
Combined theoretical and experimental work has resulted in the creation of a paradigm which allowed semi-quantitative understanding edge confinement improvement that occurs H-mode. Shear E*B flow fluctuations plasma can lead to decorrelation fluctuations, decreased radial correlation lengths reduced turbulent transport. Changes electric field, density transport consistent with shear stabilization turbulence have been seen several tokamaks. The purpose this paper is discuss most recent data...
High-confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced physics. This choice, however, comes at a significant cost both and tokamaks because of effects edge localized modes (ELMs). ELMs can produce erosion in divertor affect beta limit reduced core transport regions needed operation. Experimental results from DIII-D [J. L. Luxon et al., Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency,...
The electrostatic fluctuations are decorrelated in the region of a naturally occurring ${\mathbf{E}}_{\mathit{r}}$\ifmmode\times\else\texttimes\fi{}B velocity shear close to outermost closed flux surface regular Ohmic TEXT discharges. concomitant local steepening density profile and suppression consistent with theoretical predictions. high-confinement mode found other tokamaks shows, exaggerated form, similar characteristics, could thus be related same mechanism leading locally improved confinement.
Large sub-millisecond heat pulses due to Type-I edge localized modes (ELMs) have been eliminated reproducibly in DIII-D for periods approaching nine energy confinement times (τE) with small dc currents driven a simple magnetic perturbation coil. The current required eliminate all but few isolated ELM impulses during coil pulse is less than 0.4% of plasma current. Based on field line modelling, the fields resonate flux surfaces across most pedestal region (0.9 ⩽ ψN 1.0) when q95 = 3.7 ± 0.2,...
A quantitative comparison of the fluctuation-induced energy flux with total has been made in edge region TEXT tokamak using fluctuation measurements from Langmuir, heavy-ion-beam, and magnetic probes. At all but lowest densities convected due to electrostatic fluctuations dominates losses caused by plasma transport. Energy loss through is insignificant region.
This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of fluctuations and measure particle heat flux caused by electrostatic are presented. Furthermore, study nonlinear coupling process turbulence redistribution energy among different modes discussed. The impact on fusion research is demonstrated with results collected Langmuir probes, heavy-ion beam laser scattering in tokamak TEXT....
H-mode operation is the choice for next-step tokamak devices based either on conventional or advanced physics. This choice, however, comes at a significant cost both and tokamaks because of effects edge-localized modes (ELMs). ELMs can produce erosion in divertor affect β limit reduced core transport regions needed operation. Recent experimental results from DIII-D have demonstrated new operating regime, quiescent which solves these problems. We achieved ELM-free yet has good density...
Edge conditions in DIII-D are being quantified order to provide insight into the physics of H mode regime. Several studies show that electron temperature is not key parameter controls L-H transition. Gradients edge and pressure much more promising candidates for elements such parameters. They systematically increase during L phases discharges which make a transition mode, these increases typically larger than underlying quantities. The quality confinement strongly correlated with height...
A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases particle transport, thereby allowing control with no ELM-induced pulsed divertor heat load. The barrier resembles those usually seen low (L) mode edge, without degradation often associated ELMs. barriers separated narrow region of high zero crossing E x B shearing rate.
Fusion power has been increased by a factor of 3 in DIII-D tailoring the pressure profile to avoid kink instability $H$-mode plasmas. The resulting plasmas are found have neoclassical ion confinement. This reduction transport losses beam-heated with negative central shear is correlated dramatic density fluctuations. Improved magnetohydrodynamic stability achieved controlling plasma width. In deuterium highest gain $Q$ (the ratio fusion input power), was 0.0015, corresponding an equivalent...
The confinement and the stability properties of DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms rotational magnetic shear, with an emphasis on recent experimental results obtained from negative central shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside region accompanied by reduction fluctuation...
Externally applied magnetic fields are used on the Texas Experimental Tokamak (TEXT) to study possibility of controlling particle, impurity and heat fluxes at plasma edge. Fields with toroidal mode number n = 2 or 3 multiple poloidal numbers m (dominantly 7) used, a poloidally toroidally averaged ratio radial field components 〈|br/Bø〉 ≅0. 1%. Calculations show that it is possible produce mixed islands stochastic regions edge (r/a ≥ 0.8) without affecting interior. The expected structure...
Recent QH-mode research on DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] has used the peeling-ballooning modes model of edge magnetohydrodynamic stability as a working hypothesis to organize data; several predictions this theory are consistent with experimental results. Current ramping results indicate that QH operate near current limit set by peeling modes. This operating point...
The spectra, magnitude and spatial distribution of low-frequency (ω ≪ ωci) density fluctuation have been measured by two independent experimental methods in the edge plasma TEXT tokamak. Good agreement between far-infrared laser scattering Langmuir probe measurements has achieved strengths each technique are evaluated. probes used to directly determine particle flux induced fluctuations (Γ ∝ ⟨ñ×B⟩) collective Thomson permits an extension these observations interior. Results presented for...
A low amplitude (δbr∕BT=1 part in 5000) edge resonant magnetic field perturbation with toroidal mode number n=3 and poloidal numbers between 8 15 has been used to suppress most large type I localized modes (ELMs) without degrading core plasma confinement. ELMs have suppressed for periods of up 8.6 energy confinement times when the safety factor q95 is 3.5 4. The are replaced by packets events (possibly II ELMs) small amplitude, narrow radial extent, a higher level density fluctuations,...
For the first time, profiles (0.3<ρ<0.9) of electron temperature and density fluctuations in a tokamak have been measured simultaneously results compared to nonlinear gyrokinetic simulations. Electron neutral beam-heated, sawtooth-free low confinement mode (L-mode) plasmas DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] are found be similar frequency normalized amplitude, with amplitude increasing radius. The radial profile two fluctuation fields allows for new rigorous...
Particle transport in an ohmically heated tokamak plasma was investigated the Texas Experimental Tokamak (TEXT). Spectroscopic measurements of electron source were used with density to derive particle confinement times from continuity equation. Scalings developed for time density, current, toroidal field, and positioning. Simultaneous measurement electrostatic fluctuations Langmuir probes may suggest a correlation between edge TEXT turbulence. In addition, two major features isolated. First,...
Doppler backscattering has emerged in recent years as a powerful diagnostic tool high temperature fusion plasmas. The technique is sensitive to plasma turbulence flow and been utilized determine radial electric field study geodesic acoustic modes, zonal flows, intermediate scale density turbulence. current manuscript describes novel for creating stable, multichannel system covering the V-band frequency range (50-75 GHz) which enables simultaneous monitoring of turbulent flows fluctuation...
A series of carefully designed experiments on DIII-D have taken advantage a broad set turbulence and profile diagnostics to rigorously test gyrokinetic simulations. In this paper the goals, tools performed in these validation studies are reviewed specific examples presented. It is found that predictions transport fluctuation levels mid-core region (0.4 < ρ 0.75) better agreement with experiment than those outer (ρ ⩾ where edge coupling effects may become increasingly important multiscale...
Long-wavelength turbulence increases dramatically in the outer regions of DIII-D plasmas with application resonant magnetic field perturbations (RMPs) that suppress edge-localized modes (ELMs). Correspondingly, transport and global energy confinement decreases these low-collisionality RMP-ELM suppressed discharges. The core pedestal density are sharply reduced, while ion electron temperatures may change only slightly. Low wavenumber (k⊥ρi < 1) range 60–300 kHz, measured beam emission...
Robust validation of predictive turbulent transport models requires quantitative comparisons to experimental measurements at multiple levels, over a range physically relevant conditions. Toward this end, series carefully designed experiments has been performed on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] obtain comprehensive multifield, multipoint, multiwavenumber fluctuation and their scalings with key dimensionless parameters. The results two representative studies are...