A5021281539- Magnetic confinement fusion research
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The University of Texas at Austin
2016-2025
Fusion Academy
2014-2025
Fusion (United States)
2015-2025
General Atomics (United States)
2002-2024
Australian and New Zealand Intensive Care Society
2023
Florida State University
2022
University of California, Los Angeles
2005-2021
University of Wisconsin–Madison
2010-2021
University of York
2021
Princeton Plasma Physics Laboratory
2013-2019
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...
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,...
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...
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...
DIII-D experiments at low density (n_{e}∼10^{19} m^{-3}) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with intensity (hard x-ray emission level), occurs novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The frequencies scale magnetic field strength electron as expected from dispersion relation. modes are stabilized increasing field, which consistent wave-particle...
The negative triangularity tokamak (NTT) is a unique reactor concept based on 'power-handling-first' philosophy with the heat exhaust problem as leading concern. present paper exposes using L-mode edge NTT configuration, providing merits of no (or very weak) edge-localized modes, larger particle flux and large major radius for power handling. It shown that reasonably compact (Rp from 9 m to 7 m) possible by achieving higher confinement improvement (HH = 1.5) and/or utilizing magnetic field...
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...
In a series of high performance diverted discharges on DIII-D, we demonstrate that strong negative triangularity (NT) shaping robustly suppresses all edge-localized mode (ELM) activity over wide range plasma conditions: ⟨n⟩=0.1-1.5×10^{20} m^{-3}, P_{aux}=0-15 MW, and |B_{t}|=1-2.2 T, corresponding to P_{loss}/P_{LH08}∼8. The full dataset is consistent with the theoretical prediction magnetic shear in NT edge inhibits access ELMing H-mode regimes; experimental pressure profiles are found be...
Abstract Strongly-shaped diverted negative triangularity (NT) plasmas in the DIII-D tokamak demonstrate simultaneous access to high normalized density, current, pressure, and confinement. NT are shown exist across an expansive parameter space compatible with fusion power production, revealing surprisingly good core stability properties that compare favorably conventional positive DIII-D. Non-dimensionalizing key parameters, expanded operating spaces featuring edge safety factors below 3,...
Abstract Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV DIII-D tokamaks motivated installation of graphite-tile armor lower outer wall DIII-D. A dedicated multiple-week experimental campaign was conducted qualify scenario future reactors. During...
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...
The electron cyclotron emission (ECE) heterodyne radiometer diagnostic on DIII-D has been upgraded with the addition of eight channels for a total 40. new, higher frequency allow measurements temperature into magnetic axis in discharges at maximum field, 2.15 T. complete set now extends over full usable range second harmonic frequencies 2.0 T, covering radii from outer edge inward to location third overlap high-field side. Full coverage permits measurement heat pulses and magnetohydrodynamic...
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.
The spatial structure of toroidal Alfv\'en eigenmodes and reversed shear in DIII-D is obtained from electron-cyclotron-emission measurements. Peak measured temperature perturbations are similar magnitude for both found to be $\ensuremath{\delta}{T}_{e}/{T}_{e}\ensuremath{\approx}0.5%$. Simultaneous measurements density fluctuations using beam-emission spectroscopy indicate $\ensuremath{\delta}{n}_{e}/{n}_{e}\ensuremath{\approx}0.25%$. Predictions the perturbation profiles as well...
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...
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...
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...
Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The first application fast-ion D_{alpha} (FIDA) spectroscopy to Alfvén-eigenmode physics shows that profile is anomalously flat inner half discharge. Neutron equilibrium measurements corroborate FIDA data. current density driven by fast ions also strongly modified. Calculations based on measured mode amplitudes do not...
Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvénic activity including toroidicity-induced Alfvén eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete penetration results in high central safety factor increased drive due to multiple higher order resonances. Scans injected 80 keV neutral power on showed transition from classical AE dominated fast ion transport and, as previously...
Two techniques were developed at DIII-D [J. L. Luxon, Nucl. Fusion 42, 64 (2002)] to tackle ITER-specific aspects of neoclassical tearing mode (NTM) control, namely, (1) the relatively small size rotating islands, smaller than electron cyclotron current drive (ECCD) deposition region, and (2) increased tendency compared present devices, lock wall or residual error field, in a position not necessarily accessible ECCD. Modulated ECCD is known suppress islands more efficiently, when “broad,”...
Linear gyrokinetic simulation of fusion plasmas finds a radial localization the toroidal Alfv\'en eigenmodes (TAEs) due to nonperturbative energetic particle (EP) contribution. The EP-driven TAE has mode width much smaller than that predicted by magnetohydrodynamic theory. position stays around strongest EP pressure gradients when profile evolves. contribution is also main cause for breaking symmetry ballooning structure and dependence frequency on number. These phenomena are beyond picture...
Abstract This paper describes joint ITPA studies of the I-mode regime, which features an edge thermal barrier together with L-mode-like particle and impurity transport no localized modes (ELMs). The regime has been demonstrated on Alcator C-Mod, ASDEX Upgrade DIII-D tokamaks, over a wide range device parameters pedestal conditions. Dimensionless at show overlap across devices extend to low collisionality. When they are matched, temperature profiles also similar. Pedestals stable...
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...