A5091062314- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Fusion materials and technologies
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Semiconductor materials and devices
- Solar and Space Plasma Dynamics
- Magnetic Field Sensors Techniques
- Advanced Data Storage Technologies
- Electrostatic Discharge in Electronics
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
- Advancements in Semiconductor Devices and Circuit Design
- Non-Destructive Testing Techniques
- Nuclear reactor physics and engineering
- Laser-induced spectroscopy and plasma
- Magnetic Properties and Applications
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General Atomics (United States)
2015-2024
Fusion Academy
2023-2024
Fusion (United States)
1999-2024
University of Wisconsin–Madison
1976-2021
University of California, Los Angeles
2004-2021
The University of Texas at Austin
1997-2021
University of California, San Diego
2009-2021
Predictive Science (United States)
2019
Columbia University
2003-2017
Princeton Plasma Physics Laboratory
1996-2017
Progress in the area of MHD stability and disruptions, since publication 1999 ITER Physics Basis document (1999 Nucl. Fusion 39 2137–2664), is reviewed. Recent theoretical experimental research has made important advances both understanding control tokamak plasmas. Sawteeth are anticipated baseline ELMy H-mode scenario, but tools exist to avoid or them through localized current drive fast ion generation. Active other instabilities will most likely be also required ITER. Extrapolation from...
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...
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 maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed short pulse and predicted by the ideal MHD theory. Recent experiments, particular those simulating International Thermonuclear Experimental Reactor (ITER) [M. Rosenbluth et al., Plasma Physics Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1995), Vol. 2, p. 517] scenarios with νe*, are often limited low-m/n nonideal...
DIII-D discharges with values of beta (the ratio plasma pressure to magnetic pressure) up 12.5% demonstrate that a resistive wall can stabilize low- $n$ magnetohydrodynamic (MHD) modes. In broad current profiles, exceeds the ideal MHD stability limit by at least factor 1.3 assuming no wall, but remains below calculated under assumptions vacuum vessel is perfectly conducting wall. Plasma rotation essential stabilization, and instabilities resembling predicted ``resistive mode'' appear only...
Neutral beams were injected into low field (B = 0.7-1.0 T) deuterium plasmas in an attempt to destabilize toroidicity induced Alfvén eigenmodes (TAE modes). When the parallel beam velocity approached and volume averaged beta exceeded 2%, localized, propagating modes with n 2-10 observed. As much as 45% of power was lost a result modes. The threshold for TAE instability is at least one order magnitude higher than that predicted by Fu VanDam (Phys. Fluids B 1 (1989) 1949).
AbstractAbstractPhysics elements and advances crucial for the development of axisymmetric magnetohydrodynamic equilibrium reconstruction to support plasma operation data analysis in DIII-D tokamak are reviewed. A response function formalism a Picard linearization scheme used efficiently combine fitting iterations search optimum solution vector. Algorithms incorporate internal current pressure profile measurements, topological constraints, toroidal rotation into described. Choice basis...
Energetic ions can drive Alfv\'en gap modes unstable, causing large losses of fast ions. Toroidicity-induced eigenmodes (TAE) were expected to disappear into the shear continuum and become stable as plasma beta increased. Although TAE may disappear, another dangerous instability with similar properties but approximately half frequency appears in a spectral that is created by finite effects. The measured new mode agrees theoretical beta-induced eigenmodes.
The development of techniques for neoclassical tearing mode (NTM) suppression or avoidance is crucial successful high beta/high confinement tokamaks. Neoclassical modes are islands destabilized and maintained by a helically perturbed bootstrap current represent significant limit to performance at higher poloidal beta. confinement-degrading can be reduced completely suppressed precisely replacing the “missing” in island O-point interfering with fundamental helical harmonic pressure....
It is shown that the theoretical predictions and experimental observations of toroidicity-induced Alfvén eigenmodes (TAE’s) are now in good agreement, with particularly detailed agreement mode frequencies. Calculations driving damping rates predict importance continuum for low toroidal numbers this confirmed experimentally. However, calculations finite-β, shaped discharges existence other global modes, particular ellipticity-induced eigenmode (EAE) a new mode, beta-induced (BAE). The BAE...
As part of the ITER Design Review and in response to issues identified by Science Technology Advisory Committee, physics requirements were reviewed as appropriate updated. The focus this paper will be on recent work affecting design with special emphasis topics near-term procurement arrangements. This describe results on: sensitivity studies, poloidal field coil requirements, vertical stability, effect toroidal ripple thermal confinement, material choice heat load for plasma-facing...
Toroidicity induced Alfven eigenmodes (TAE) are observed in the DIII-D tokamak when energetic beam ions ( approximately 75 keV) used to destabilize mode. Measurements of neutron emission indicate that up 70% injected power is lost during strong TAE activity. poloidal distribution fast ion losses suggest greatest near vessel midplane. Fast discharges with combined fishbones and bursts 1.5 2 times greater than fishbone without TAB The scaling MHD mode amplitude exhibits no threshold amplitude,...
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...
External measurements of the magnetic field surrounding a hot, magnetically confined plasma yield important information about state plasma, since external is generated in part by electric currents within itself. Therefore, diagnostics are an essential both operation and physics experiments tokamaks other confinement devices. The diagnostic system DIII-D tokamak includes approximately 250 inductive sensors various types: axisymmetric poloidal flux loops, diamagnetic-flux probes saddle loops...
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,...
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....
Density pumpout and edge-localized mode (ELM) suppression by applied $n=2$ magnetic fields in low-collisionality DIII-D plasmas are shown to be correlated with the magnitude of plasma response driven on high-field side (HFS) axis but not low-field (LFS) midplane. These distinct responses a direct measurement multimodal response, each structure preferentially excited different spectrum detected LFS or HFS. Ideal resistive magneto-hydrodynamic (MHD) calculations find that is primarily...
Intense axisymmetric oscillations driven by suprathermal ions injected in the direction counter to toroidal plasma current are observed DIII-D tokamak. The modes appear at nearly half ideal geodesic acoustic mode frequency, plasmas with comparable electron and ion temperatures elevated magnetic safety factor (${q}_{\mathrm{min}}\ensuremath{\ge}2$). Strong bursting frequency chirping observed, concomitant large (10%--15%) drops neutron emission. Large density fluctuations...
DIII-D experiments on rapid shutdown runaway electron (RE) beams have improved the understanding of processes involved in RE beam control and dissipation. Improvements feedback enabled stable confinement out to volt-second limit ohmic coil, as well enabling a ramp down zero current. Spectroscopic studies shown that neutrals tend be excluded from centre. Measurements energy distribution function indicate broad with mean order several MeV peak energies 30–40 MeV. The appears more skewed...
High repetition rate injection of deuterium pellets from the low-field side (LFS) DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up $12\ifmmode\times\else\texttimes\fi{}$ low natural ELM frequency in $H$-mode plasmas designed match ITER baseline configuration shape, normalized beta, and input power just above threshold. The pellet size, velocity, location were chosen limit penetration outer 10% plasma. resulting perturbations plasma density energy...
Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, normalized fusion performance increased by ≥30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled improved understanding of 'relaxation oscillations', previously attributed repetitive ITB collapses, and fast ion behavior this regime. It found that...
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...
Locked n = 1 tearing modes are observed over a wide range of parameter space in DIII-D and other tokamaks. Much the difficulty with low density operation is attributed to locked they also as precursors limit disruptions. From observations consistent mode toroidal phase, it appears that locking small field perturbation caused by slight irregularities location one or more vertical coils respect coil. By intentionally producing an external coil, was possible influence onset q, plasmas. The...
Using newly developed techniques and improved diagnostics, rotating wall-stabilized discharges have been maintained in the DIII-D tokamak for 30 characteristic resistive wall decay times---significantly longer than was previously achieved. The terminating mode has directly identified using internal fluctuation its correlation with slowdown plasma rotation is established.