A5082096794- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Fluid Dynamics and Turbulent Flows
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
- Computational Fluid Dynamics and Aerodynamics
- Laser-induced spectroscopy and plasma
- Electrostatic Discharge in Electronics
- Dust and Plasma Wave Phenomena
- Nuclear Physics and Applications
- Gyrotron and Vacuum Electronics Research
- Crystallography and molecular interactions
- Spectroscopy and Laser Applications
- Acoustic Wave Resonator Technologies
- Silicon Carbide Semiconductor Technologies
- Magnetic Field Sensors Techniques
- Nonlinear Photonic Systems
- Electromagnetic Launch and Propulsion Technology
- GaN-based semiconductor devices and materials
University of Wisconsin–Madison
2016-2025
General Atomics (United States)
2010-2024
Princeton University
2022
Princeton Plasma Physics Laboratory
2011-2022
University of California, Los Angeles
2010-2022
University of California, San Diego
2006-2021
The University of Texas at Austin
2010-2021
University of York
2021
Lawrence Livermore National Laboratory
2017-2020
Beijing Polytechnic
2020
Periods of edge localized mode (ELM)-free H-mode with increased pedestal pressure and width were observed in the DIII-D tokamak when density fluctuations to region near separatrix present. Injection a powder 45 µm diameter lithium particles duration enhanced phases up 350 ms, also likelihood transition phase. Lithium injection at level sufficient for triggering extended resulted significant plasma core, but carbon other higher Z impurities as well radiated power levels reduced. Recycling...
Experiments on HL-2A, DIII-D and EAST show that turbulence just inside the last closed flux surface (LCFS) acts to reinforce existing sheared ExB flows in this region.This flow drive gets stronger as heating power is increased L-mode, leads development of a strong oscillating shear which can transition into H-mode regime when rate energy transfer from exceeds threshold.These effects become compressed time during an L-H transition, but key role turbulent still observed.The results compare...
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...
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...
Long-wavelength turbulence increases dramatically in the outer regions of DIII-D plasmas with application resonant magnetic field perturbations (RMPs) that suppress edge-localized modes (ELMs). Correspondingly, transport and global energy confinement decreases these low-collisionality RMP-ELM suppressed discharges. The core pedestal density are sharply reduced, while ion electron temperatures may change only slightly. Low wavenumber (k⊥ρi < 1) range 60–300 kHz, measured beam emission...
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...
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...
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...
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...
Abstract Since the last IAEA Fusion Energy Conference in 2018, significant progress of experimental program HL-2A has been achieved on developing advanced plasma physics, edge localized mode (ELM) control physics and technology. Optimization confinement performed. In particular, high- β N H-mode plasmas exhibiting an internal transport barrier have obtained (normalized pressure reached up to 3). Injection impurity improved confinement. ELM using resonance magnetic perturbation or injection a...
Experimental conditions obtained on the DIII-D tokamak in ITER Similar Shape (ISS) have been compared extensively with nonlinear gyrokinetic simulation using CGYRO code [Candy et al., J. Comput. Phys. 324, 73–93 (2016)] comparisons spanning ion and electron heat fluxes, impurity particle transport, turbulent fluctuation levels characteristics. Bayesian optimization techniques [Rodriguez-Fernandez Nucl. Fusion 62(7), 076036 (2022)], combined gyrokinetics, used to obtain simultaneously Qi, Qe,...
Multimachine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing power densities that require mitigation. In the experiments presented, width of this is nearly doubled using actuators to increase turbulent transport plasma edge. This achieved low collisionality, confinement edge pedestals with their gradients limited by instead large-scale, coherent instabilities. The flux profile and divertor leg diffusive spreading both double...
Abstract Viable magnetic fusion devices necessitate combining good confinement with effective power flux handling. A major concern for ITER, and beyond, is the divertor heat load width, which sets peak boundary loads on plasma-facing materials. Current estimates of width are narrow future reactors. Here, we demonstrate how pedestal turbulence can expand into, or entrain, stable scrape-off-layer so broaden beyond these neoclassical predictions. Employing combined theoretical, computational,...
A set of high frequency coherent (HFC) modes ($f=80--250\text{ }\text{ }\mathrm{kHz}$) is observed with beam emission spectroscopy measurements density fluctuations in the pedestal a strongly shaped quiescent H-mode plasma on DIII-D, characteristics predicted for kinetic ballooning (KBM): propagation ion-diamagnetic drift direction; near 0.2--0.3 times frequency; inferred toroidal mode numbers $n\ensuremath{\sim}10--25$; poloidal wave...
Joint experiment/theory/modelling research has led to increased confidence in predictions of the pedestal height ITER. This work was performed as part a US Department Energy Research Target FY11 identify physics processes that control H-mode structure. The study included experiments on C-Mod, DIII-D and NSTX well interpretation experimental data with theory-based modelling codes. provides ability models for peeling–ballooning stability, bootstrap current, width scaling make correct...
Abstract A stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D reactor relevant edge parameters no ELMs. As the injected neutral beam torque is ramped down E × B shear reduces, transition from standard QH to QH-mode occurs. At transition, coherent harmonic oscillations (EHO) that usually regulate cease broadband MHD modes appear along rapid increase in pressure height (by ⩽60%) width ⩽50%). We posit...
Experiments have been executed in the DIII-D tokamak to extend suppression of Edge Localized Modes (ELMs) with Resonant Magnetic Perturbations (RMPs) ITER-relevant levels beam torque. The results support hypothesis for RMP ELM based on transition from an ideal screened response a tearing at resonant surface that prevents expansion pedestal unstable width [Snyder et al., Nucl. Fusion 51, 103016 (2011) and Wade 55, 023002 (2015)]. In ITER baseline plasmas I/aB = 1.4 ν* ∼ 0.15, ELMs are readily...
Global electromagnetic gyrokinetic simulations show the existence of near threshold conditions for both a high-$n$ kinetic ballooning mode (KBM) and an intermediate-$n$ version peeling-ballooning (KPBM) in edge pedestal two DIII-D H-mode discharges. When magnetic shear is reduced narrow region steep pressure gradient, KPBM significantly stabilized, while KBM weakly destabilized hence becomes most-unstable mode. Collisions decrease KBM's critical $\ensuremath{\beta}$ increase growth rate.
A critical gradient threshold has been observed for the first time in a systematic, controlled experiment locally measured turbulent quantity core of confined high-temperature plasma. In an DIII-D tokamak where L(T(e))(-1) = |∇T(e)|/T(e) and toroidal rotation were varied, long wavelength (k(θ)ρ(s) ≲ 0.4) electron temperature fluctuations exhibit L(T(e))(-1): below, they change little; above, steadily increase. The increase δT(e)/T(e) is concurrent with increased heat flux transport...
Abstract In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHOs) play an important role in avoiding transient localized mode (ELM) power fluxes by providing benign and continuous particle transport. A detailed theoretical, experimental modeling comparison has been made of low- n ( ⩽ 5) EHO DIII-D QH-mode plasmas. The calculated linear eigenmode structure from extended magentoohydrodynamics (MHD) code M3D-C1 matches closely coherent properties external magnetics data...
The mission of HL-2A is to explore the key physical topics relevant ITER and advanced tokamak operation (e.g. future HL-2M), such as access H-mode, energetic particle physics, edge-localized mode (ELM) mitigation/suppression disruption mitigation. Since 2016 Fusion Energy Conference, team has focused on investigations following areas: (i) pedestal dynamics L–H transition, (ii) techniques ELM control, (iii) turbulence transport, (iv) physics. results demonstrated that increase mean shear flow...
Abstract Negative Triangularity (NT) plasmas have demonstrated robustly ELM-free high-performance operation and provide a unique testbed to study how plasma shaping affects turbulent transport. The Beam Emission Spectroscopy (BES) diagnostic provides localized 2D measurements of low-k ($k_{\theta} \rho_s < 1$) density fluctuations. In sweep upper triangularity at fixed power, H-mode access is suppressed an NT-edge observed. turbulence amplitude ($\tilde{n}/n$) shown decrease by $\sim50\%$...
Abstract The dynamics of the L-H transition is not fully understood, with many parameters changing threshold power to enter H-mode and self-regulation between zonal flows turbulence in plasma edge. This paper primarily a presentation experimental results for DIII-D H-L transitions speculation on observations made. Power analysis measurements pedestal temperatures these are presented. A comparison made an comparable P sep exhibiting oscillatory behaviour, showing symmetry forward backward...
Recent high-poloidal-beta (high-βP) experiments on DIII-D and EAST have made coordinated breakthroughs for high confinement quality at density near the Greenwald limit. Density gradient amplification of turbulence suppression βP can explain both these achievements. Experiments achieved fraction (fGr = line-averaged density/Greenwald density) above 1 simultaneously with normalized energy (H98y2) around 1.5, as required in fusion reactor designs but never before verified tokamak divertor...
A method for measuring nonlinear energy transfer in the frequency domain using a two-field model of drift turbulence is proposed, and theoretical motivation experimental results are presented. The approach based on cross-bispectral analysis quadratic nonlinearities turbulent internal kinetic balance equations directly derived from fluid plasma continuity momentum equations. Application technique to data laboratory experiment reveals weak collisional turbulence; show density fluctuation...