A5025941890- Magnetic confinement fusion research
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- Physics of Superconductivity and Magnetism
- Solar and Space Plasma Dynamics
- Laser-induced spectroscopy and plasma
- Nuclear reactor physics and engineering
- Electrostatic Discharge in Electronics
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General Atomics (United States)
2015-2024
The University of Texas at Austin
2005-2021
University of California, Los Angeles
1996-2021
University of Wisconsin–Madison
2010-2021
University of York
2021
University of Mississippi Medical Center
2020
State Street (United States)
2020
American College of Allergy, Asthma and Immunology
2020
Fusion Academy
1986-2019
Fusion (United States)
1989-2019
Plasma discharges with a negative triangularity (δ=−0.4) shape have been created in the DIII-D tokamak significant normalized beta (βN=2.7) and confinement characteristic of high mode (H98y2=1.2) despite absence an edge pressure pedestal no localized modes (ELMs). These inner-wall-limited plasmas similar global performance as positive (δ=+0.4) ELMing H-mode discharge same plasma current, elongation cross sectional area. For cases both dominant electron cyclotron heating Te/Ti>1 neutral beam...
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....
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,...
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...
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...
Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold presence of many overlapping small-amplitude Alfv\'en eigenmodes (AEs). The is phase-space dependent and occurs when particle orbits become stochastic due to resonances with AEs. Above threshold, equilibrium density profiles are unchanged despite increased drive, intermittent losses observed. Fast-ion $\mathrm{D}\ensuremath{\alpha}$ spectroscopy indicates radially localized...
Diverted discharges at negative triangularity on the DIII-D tokamak sustain normalized confinement and pressure levels typical of standard H-mode scenarios (H98y2 ≃ 1, βN 3) without developing an edge pedestal, despite auxiliary power far exceeding L → H threshold expected from conventional scaling laws. The degradation is substantially weaker than ITER-89P scaling, resulting in a factor that improves with increasing power. absence pedestal beneficial several ways, such as eliminating need...
The first suppression of the important and deleterious m = 2/n 1 neoclassical tearing mode (NTM) is reported using electron cyclotron current drive (ECCD) to replace 'missing' bootstrap in island O-point. Experiments on DIII-D tokamak verify that maximum shrinkage occurs when ECCD location coincides with q 2 surface. plasma control system put into a 'search suppress' make small changes toroidal field find lock onto optimum position, based real time measurements dBθ/dt, for complete NTM by...
Peaked electron temperature profiles are observed in the DIII-D tokamak during cyclotron heating despite fact that >75% of input power is deposited significantly off axis. Power balance analysis indicates a net inward flow energy for electrons. An not compatible with diffusive or critical gradient models. A time-dependent perturbation technique employed to estimate conductive loss and nondiffusive part transport. The component transport appears only at radii smaller than location.
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...
We report the results of first experiments on DIII-D tokamak to examine dependence transport and stability characteristics ITER hybrid scenario plasmas toroidal flow (or rotation) plasma. With new capability independently vary neutral beam torque power, central rotation has been reduced by as much a factor 4.6 compared with discharges unidirectional beams. Although energy confinement decreases m/n = 3/2 NTM amplitude increases for low speed, fusion performance figure merit, , still exceeds...
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...
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...
Recent experiments in 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] have led to the discovery of a means modifying edge turbulence achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities with no net external torque input. Eliminating ELM-induced heat bursts controlling plasma stability at low rotation represent two great challenges for fusion...
Plasmas with a negative triangularity shape have been created on the DIII-D tokamak that, despite maintaining standard L-mode edge radial profiles, reach volume averaged pressure levels typical of H-mode scenarios. Within auxiliary power available for these experiments, plasmas exhibit near-zero degradation while sustaining βN = 2.7 and H98,y2 1.2 several energy confinement times. Detailed comparison matched discharges at positive indicates that Trapped Electron Modes are weakened...
Experimental evidence is reported of an internal kink instability driven by a new mechanism: barely trapped suprathermal electrons produced off-axis electron cyclotron heating on the DIII-D tokamak. It occurs in plasmas with evolving safety factor profile q(r) when q(min) approaches 1. This most active ECCD applied high field side flux surface. has bursting behavior poloidal/toroidal mode number = m/n 1/1. In positive magnetic shear plasmas, this becomes fishbone instability. observation can...
The scaling of cross-field heat transport with relative gyroradius ρ* was measured in low (L) and high (H) mode tokamak plasmas using the technique dimensionally similar discharges. scalings electron ion thermal diffusivities were determined separately a two-fluid analysis. For L-mode plasmas, diffusivity scaled as χe∝χBρ1.1±0.3* (gyro-Bohm-like) while χi∝χBρ−0.5±0.3* (worse than Bohm-like). results independent method auxiliary heating (radio frequency or neutral beam). Since fluids had...
Plasma turbulence characteristics, including radial correlation lengths, decorrelation times, amplitude profile and flow velocity, have been measured during a ρ* scan on DIII-D while all other transport relevant dimensionless quantities (e.g., β, ν*, κ, q, Te/Ti) are held nearly constant. The is by examining the properties of local long wavelength (k⊥ρi ≤ 1) density fluctuations, with beam emission spectroscopy. length Lc,r shown to scale ion gyroradius, ≈ 5ρi, times acoustic velocity as...
In DIII-D [J. L. Luxon and G. Davis, Fusion Technol. 8, 441 (1985)] tokamak plasmas with an internal transport barrier (ITB), the comparison of gyrokinetic linear stability (GKS) predictions experiments in both low strong negative magnetic shear provide improved understanding for electron thermal within plasma. Within a limited region just inside ITB, temperature gradient (ETG) modes appear to control and, consequently, transport. The increase temperaturegradient more strongly is consistent...
Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized beta βN, by varying the mix co (parallel to plasma current) and counter beams. Under balanced injection (i.e. zero total plasma), maintains significant rotation in co-direction. This 'intrinsic' can be modeled being due an offset 'anomalous torque'). anomalous appears have magnitude comparable one source. The presence such source must taken into account obtain meaningful...
A potential new standard in stationary tokamak performance is emerging from experiments on DIII-D. These have demonstrated the ability to operate near free boundary, n = 1 stability limit with good confinement quality under conditions. The normalized fusion at or above that projected for Qfus 10 operation International Thermonuclear Experimental Reactor (ITER) design over a wide operating range both edge safety factor (2.8–4.7) and plasma density (35–70% of Greenwald density). Projections...
A review of the application dimensionless parameter scaling techniques to magnetic fusion experiments is presented. Because methods this type analysis are not generally known, a detailed discussion basis for these given, including examples. The primary applications and successes in research area transport energy particles across surfaces constant flux. experimental justification use describe reviewed. two key techniques, identification underlying physical mechanisms that cause projection...
This paper presents new measurements of the cross-phase angle, αneTe, between long-wavelength (kθρs&lt;0.5) density, ñe, and electron temperature, T̃e, fluctuations in core DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamak plasmas. The coherency angle ñe T̃e are measured using coupled reflectometer correlation cyclotron emission diagnostics that view same plasma volume. In addition to experimental results, two sets local, nonlinear gyrokinetic turbulence simulations performed...
Recent experiments on DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment (NSTX) [M. Ono et al., 40, 557 (2000)] have focused investigating mechanisms of driving rotation in fusion plasmas. The so-called intrinsic is generated by an effective torque, driven residual stresses the plasma, which appears to originate plasma edge. A clear scaling this drive with H-mode pressure gradient observed. Coupled experimentally inferred pinch angular momentum, such...