A5083103072- Magnetic confinement fusion research
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Solar and Space Plasma Dynamics
- Atomic and Molecular Physics
- Laser-induced spectroscopy and plasma
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
- Fluid Dynamics and Turbulent Flows
- Nuclear reactor physics and engineering
- Semiconductor materials and devices
- Nuclear Physics and Applications
- Electrostatic Discharge in Electronics
- Dust and Plasma Wave Phenomena
- Advancements in Semiconductor Devices and Circuit Design
- Semiconductor Quantum Structures and Devices
- Advanced Data Storage Technologies
- High-Energy Particle Collisions Research
- Spectroscopy and Laser Applications
- Silicon and Solar Cell Technologies
- Plasma and Flow Control in Aerodynamics
General Atomics (United States)
2016-2025
Princeton University
1986-2022
Oak Ridge National Laboratory
2009-2022
University of California, Los Angeles
1990-2022
Princeton Plasma Physics Laboratory
1986-2022
Columbia University
2017-2022
University of Wisconsin–Madison
1979-2022
The University of Texas at Austin
2022
Ain Shams University
2022
University of California, Irvine
2012-2018
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.
An efficient method is given for self-consistent reconstruction of the tokamak current profiles and their associated magnetic topology using magnetohydrodynamic (MHD) equilibrium constraint from external measurements, kinetic profile internal poloidal field topological information soft X-ray (SXR) measurements. Illustrative examples beam heated H-mode divertor discharges in DIII-D are presented, experimentally measured data existing diagnostics. Comparative reconstructions various...
Marked changes in the edge radial electric field ${\mathit{E}}_{\mathit{r}}$ and poloidal rotation velocity ${\mathit{v}}_{\mathrm{\ensuremath{\theta}}}$ are important signatures of L-H transition DIII-D tokamak. Shear exists increases from L mode to H mode. A comparison experiment with theory shows that shear is sufficient suppress fluctuations, ion-orbit loss large enough be source ${\mathit{v}}_{\mathrm{\ensuremath{\theta}}}$, may play a causal role transition.
We develop and test a model, EPED1.6, for the H-mode pedestal height width based upon two fundamental calculable constraints: (1) onset of non-local peeling–ballooning modes at low to intermediate mode number, (2) nearly local kinetic ballooning high number. Calculation these constraints allows unique, predictive determination both width. The present version model is first principles, in that no parameters are fit observations, includes important non-ideal effects. Extensive successful...
The pressure at the top of edge transport barrier (or “pedestal height”) strongly impacts tokamak fusion performance. Predicting pedestal height in future devices such as ITER [ITER Physics Basis Editors, Nucl. Fusion 39, 2137 (1999)] remains an important challenge. While uncertainties remain, magnetohydrodynamic stability calculations intermediate wavelength (the “peeling-ballooning” model), accounting for diamagnetic stabilization, have been largely successful determining observed maximum...
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...
Explicit expressions for the neoclassical poloidal and toroidal rotation speeds of primary ion impurity species are derived via Hirshman Sigmar moment approach. The can be significantly different from those impurities in various interesting cases. rapid increase edge region H-mode discharges tokamaks explained by a steepening pressure gradient. Depending on collisionality, speed ions at quite small flow direction may opposite to that impurities. This cast considerable doubts current L H...
Parametric scalings of the intrinsic (spontaneous, with no external momentum input) toroidal rotation observed on a large number tokamaks have been combined an eye towards revealing underlying mechanism(s) and extrapolation to future devices. The velocity has found increase plasma stored energy or pressure in JET, Alcator C-Mod, Tore Supra, DIII-D, JT-60U TCV, decrease increasing current some these cases. Use dimensionless parameters led roughly unified scaling MA ∝ βN, although variety Mach...
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...
The L to H transition in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. I, p. 159] is associated with two clear signatures: edge density fluctuations are abruptly suppressed (in ≊100 μsec), while poloidal rotation velocity vθ increases, implying that radial electric field Er becomes more negative. Detailed new spectroscopic profile measurements show changes generate a region of sheared flow width ≊3–5 cm. This develops...
A remarkable degree of consistency experimental results from tokamaks throughout the world has developed with regard to phenomenology transition L-mode H-mode confinement in tokamaks. The is initiated a narrow layer at plasma periphery where density fluctuations are suppressed and steep gradients temperature form region large first second radial derivatives vE=(E×B)/B2 flow velocity. These qualitatively consistent theories which predict suppression by shear or curvature vE. required vE...
The pressure at the top of edge transport barrier (or ‘pedestal height’) strongly impacts fusion performance, while large localized modes (ELMs), driven by free energy in pedestal region, can constrain material lifetimes. Accurately predicting height and ELM behavior ITER is an essential element prediction optimization performance. Investigation intermediate wavelength MHD ‘peeling–ballooning’ modes) has led to improved understanding important constraints on mechanism for ELMs. combination...
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,...
Following boronization, tokamak discharges in DIII-D have been obtained with confinement times up to a factor of 3.5 above the ITER89-P L-mode scaling and 1.8 greater than DIII-D/JET H-mode relation. Very high phases are characterized by relatively central density ${\mathit{n}}_{\mathit{e}}$(0)\ensuremath{\approxeq}1\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$, ion temperatures 13.6 keV at moderate plasma currents (1.6 MA) heating powers (12.5--15.3...
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,...
The hypothesis of stabilization turbulence by shear in the E×B drift speed successfully predicts observed reduction and confinement improvement seen at L (low)–H (high) transition; addition, levels significantly exceed value theoretically required to stabilize turbulence. Furthermore, this same is best explanation date for further plasma core when goes from H mode VH (very high) mode. Consequently, most fundamental question H-mode studies now is: How electric field Er formed? radial force...
The EPED model predicts the H-mode pedestal height and width based upon two fundamental calculable constraints: (1) onset of non-local peeling-ballooning modes at low to intermediate mode number, (2) nearly local kinetic ballooning high number. We present detailed tests in discharges with edge localized (ELMs), employing new resolution measurements, finding good quantitative agreement across a range parameters. is then applied for first time quiescent (QH), similar level between predicted...
Rapid bifurcations in the plasma response to slowly varying $n=2$ magnetic fields are observed as transitions into and out of edge-localized mode (ELM) suppression. The rapid transition ELM suppression is characterized by an increase toroidal rotation a reduction electron pressure gradient at top pedestal that reduces perpendicular flow there near zero. These events occur simultaneously with inner-wall response. observations consistent strong resonant field penetration onset suppression,...
Recent DIII-D [J. L. Luxon et al., Nucl. Fusion 43, 1813 (2003)] experiments show a correlation between the extent of overlap magnetic islands induced in edge plasma by perturbation coils and complete suppression Type-I localized modes (ELMs) plasmas with ITER-like electron pedestal collisionality νe*∼0.1, flux surface shape low safety factor (q95≈3.6). With fixed amplitude n=3 resonant (RMP), ELM is obtained only finite window (q95) consistent maximizing component applied helical field....
Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear that develops $\ensuremath{\sim}100\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ prior to the low-confinement ($L$ mode) high-confinement ($H$ transition appears trigger it. These changes are localized narrow layer 1--2 cm inside magnetic boundary. Increasing heating power increases Reynolds stress, energy transfer from poloidal flow, edge shearing rate then...
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...
Poloidal and toroidal rotation of the main ions (${\mathrm{He}}^{2+}$) impurity (${\mathrm{C}}^{6+}$ ${\mathrm{B}}^{5+}$) in H-mode helium plasmas have been measured via charge exchange recombination spectroscopy DIII-D tokamak. It was discovered that ion poloidal is diamagnetic drift direction while electron direction, qualitative agreement with neoclassical theory. The deduced radial electric field edge same negative-well shape regardless which species used, validating fundamental nature...
The structure and scaling of the H-mode (high mode) pedestal are examined for discharges in DIII-D tokamak [Plasma Physics Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. For typical conditions, values ion electron temperatures Ti Te comparable. Measurements main C6+ profiles indicate that pressure gradient barrier is 50%–100% deuterium plasmas. magnitude often exceeds predictions infinite-n ballooning mode theory by a factor 2. Moreover, via bootstrap...