A5054077336- 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
- Atomic and Subatomic Physics Research
- Solar and Space Plasma Dynamics
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Physics of Superconductivity and Magnetism
- Dust and Plasma Wave Phenomena
- Fluid Dynamics and Turbulent Flows
- Nuclear Physics and Applications
- Spectroscopy and Laser Applications
- Semiconductor materials and devices
- Electrostatic Discharge in Electronics
- Nuclear reactor physics and engineering
- Advanced Data Storage Technologies
- Diamond and Carbon-based Materials Research
- Semiconductor Quantum Structures and Devices
- Quantum, superfluid, helium dynamics
- Laser Design and Applications
- Advancements in Semiconductor Devices and Circuit Design
University of Iowa Health Care
2024
General Atomics (United States)
2013-2022
Oak Ridge National Laboratory
1981-2021
Princeton Plasma Physics Laboratory
2011-2021
University of California, Los Angeles
1991-2019
The University of Texas at Austin
1997-2019
University of California, Irvine
2012-2018
Oak Ridge Associated Universities
2012-2017
Tech-X Corporation (United States)
2017
VTT Technical Research Centre of Finland
2017
One of the scientific success stories fusion research over past decade is development E×B shear stabilization model to explain formation transport barriers in magnetic confinement devices. This was originally developed barrier formed at plasma edge tokamaks after L (low) H (high) transition. concept has universality needed seen limiter and divertor tokamaks, stellarators, mirror machines. More recently, this been applied further improvement from mode VH (very high) some where becomes wider....
Peaked pressure profiles and central ion temperatures up to 20 keV are observed in DIII-D $H$-mode discharges with a region of strongly reversed magnetic shear. Short wavelength ballooning modes stabilized by access the second stable regime, longer conducting wall possibly rotational Values normalized beta, ${\ensuremath{\beta}}_{N}=\frac{\ensuremath{\beta}\mathrm{aB}}{I}$, 4 (%-$m$-T/MA), energy confinement factor 3 better than $L$ mode, at least 50% noninductive plasma current this regime...
The suppression of turbulence by the E×B flow shear and parallel is studied in an arbitrary shape finite aspect ratio tokamak plasma using two point nonlinear analysis previously utilized a high [Phys. Plasmas 1, 2940 (1994)]. result shows that only responsible for flute-like fluctuations. This occurs regardless rotation direction is, therefore, relevant very (VH) mode core as well (H) edge. Experimentally observed in–out asymmetry fluctuation reduction behavior can be addressed context flux...
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.
Large Type-I edge localized modes (ELMs) are completely eliminated with small n = 3 resonant magnetic perturbations (RMP) in low average triangularity, , plasmas and ITER similar shaped (ISS) plasmas, relevant collisionalities . Significant differences the RMP requirements properties of ELM suppressed found when comparing two triangularities. In ISS current required to suppress ELMs is approximately 25% higher than triangularity plasmas. It also that width q95 window for suppression smaller...
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...
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...
Understanding the physics of edge pedestal and localized modes (ELMs) is great importance for ITER optimization tokamak concept. The peeling–ballooning model has quantitatively explained many observations, including ELM onset constraints, in standard H-mode regime. ELITE code been developed to efficiently evaluate stability comparison with observation predictions future devices. We briefly review recent progress model, experimental validation height predictions, nonlinear 3D simulations...
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...
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...
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...
In this paper the manipulation of power deposition on divertor targets at DIII-D by application resonant magnetic perturbations (RMPs) for suppression large type-I edge localized modes (ELMs) is analysed. We discuss modification ELM characteristics RMP applied. It shown that width pattern in ELMy H-mode depends linearly deposited energy, whereas phase discharge those patterns are controlled externally induced perturbation. was also found heat transport due to small, plasma pedestal electron...
We present the first evidence for existence of a neoclassical toroidal rotation driven in direction counter to plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta and with large injected neutral beam momentum, field torque slows down toward ``offset'' rate. With small is accelerated offset rotation, resulting improvement global energy confinement time. The observed magnitude, direction, radial profile are consistent theory predictions [A. J. Cole et al., Phys. Rev....
The application of static, non-axisymmetric, nonresonant magnetic fields (NRMFs) to high beta DIII-D plasmas has allowed sustained operation with a quiescent H-mode (QH-mode) edge and both toroidal rotation neutral beam injected torque near zero. Previous studies have shown that QH-mode can be accessed only if sufficient radial shear in the plasma flow is produced edge. In past experiments, this was using injection (NBI) provide torque. recent nearly completely replaced by from applied...
A beam emission spectroscopy system has been installed on DIII-D to provide localized density fluctuation measurements for long-wavelength turbulent modes with k⩽3 cm−1 which are typically associated anomalous radial transport. High signal-to-noise fluctuations accomplished through use of high speed electronics maintain a frequency response over 500 KHz and cryogenically cooled amplifiers detectors reduce electronic noise. The optics neutral beam-sightline geometry have optimized allow...
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...
A prime goal in physics research is the development of theories which have universality needed to explain a wide range observations. Developed over past decade, model turbulence decorrelation and stabilization by sheared E×B flow has reduction confinement improvement seen edge core magnetic devices. Because shear, turbulence, transport are all intimately intertwined multiple feedback loops, devising experiments test whether shear causes change been major challenge for experimentalists. Over...
The authors' data indicate that the L-mode to H-mode transition in DIII-D tokamak is associated with sudden reduction anomalous, fluctuation-connected transport across outer midplane of plasma. In addition edge density and magnetic fluctuations observed at transition, radial electric field becomes more negative after transition. They have determined scaling power threshold various plasma parameters; roughly linear increase toroidal are particularly significant. Control ELM frequency duration...