D. R. Ernst
A5018798656- Magnetic confinement fusion research
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Solar and Space Plasma Dynamics
- Nuclear reactor physics and engineering
- Fluid Dynamics and Turbulent Flows
- Electromagnetic Launch and Propulsion Technology
- Laser-induced spectroscopy and plasma
- Semiconductor materials and devices
- Dust and Plasma Wave Phenomena
- Advanced Data Storage Technologies
- Statistical Mechanics and Entropy
- Metal and Thin Film Mechanics
- Silicon and Solar Cell Technologies
- Non-Destructive Testing Techniques
- Semiconductor Quantum Structures and Devices
- High-Energy Particle Collisions Research
- Atomic and Subatomic Physics Research
- Plasma and Flow Control in Aerodynamics
- Physics of Superconductivity and Magnetism
- Traffic control and management
Massachusetts Institute of Technology
2015-2024
Plasma Technology (United States)
2013-2024
Fusion Academy
2013-2024
Fusion (United States)
2007-2022
Princeton Plasma Physics Laboratory
1994-2016
General Atomics (United States)
1997-2016
University of Wisconsin–Madison
1994-2016
University of Colorado Boulder
2016
University of California, Los Angeles
2016
University of California, San Diego
2016
The object of this review is to summarize the achievements research on Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] place that in context quest for practical fusion energy. a compact, high-field tokamak, whose unique design operating parameters have produced wealth new important results since it began operation 1993, contributing data extends tests critical physical models into parameter ranges regimes. Using only...
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...
Wall conditioning in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] by injection of lithium pellets into plasma has resulted large improvements deuterium–tritium fusion power production (up to 10.7 MW), Lawson triple product 1021 m−3 s keV), and energy confinement time 330 ms). The maximum current for access high-performance supershots been increased from 1.9 2.7 MA, leading stable operation at stored values greater than 5 MJ. amount on limiter...
Nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence, within an internal particle transport barrier, are performed and compared with experimental data. The results provide a mechanism for barrier control on-axis radio frequency heating, as demonstrated in Alcator C-Mod experiments [S. J. Wukitch et al., Phys. Plasmas 9, 2149 (2002)]. Off-axis heating produces energy after the transition to enhanced Dα high confinement mode. foot reaches half-radius, peak density 2.5...
Peak fusion power production of 6.2\ifmmode\pm\else\textpm\fi{}0.4 MW has been achieved in TFTR plasmas heated by deuterium and tritium neutral beams at a total 29.5 MW. These have an inferred central alpha particle density 1.2\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$ without the appearance either disruptive magnetohydrodynamics events or detectable changes Alfv\'en wave activity. The measured loss rate energetic particles agreed with...
The capability to inject deuterium pellets from the magnetic high field side (HFS) has been added DIII-D tokamak [J. L. Luxon and G. Davis, Fusion Technol. 8, 441 (1985)]. It is observed that injected HFS lead deeper mass deposition than identical outside midplane, in spite of a factor 4 lower pellet speed. have used generate peaked density profile plasmas [peaking (ne(0)/〈ne〉) excess 3] develop internal transport barriers when centrally heated with neutral beam injection. are formed...
A set of key properties for an ideal dissipation scheme in gyrokinetic simulations is proposed, and implementation a model collision operator satisfying these described. This based on the exact linearized test-particle operator, with approximations to field-particle terms that preserve conservation laws H-theorem. It includes energy diffusion, pitch-angle scattering, finite Larmor radius effects corresponding classical (real-space) diffusion. The numerical continuum code GS2 [Kotschenreuther...
The MIT Plasma Science and Fusion Center collaborators are proposing a high-performance Advanced Divertor RF tokamak eXperiment (ADX)-a specifically designed to address critical gaps in the world fusion research programme on pathway next-step devices: nuclear science facility (FNSF), pilot plant (FPP) and/or demonstration power (DEMO). This high-field (>= 6.5 T, 1.5 MA), high density (P/S similar MW m(-2)) will test innovative divertor ideas, including an 'X-point target divertor' concept,...
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...
After many years of fusion research, the conditions needed for a D–T reactor have been approached on Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For first time unique phenomena present in plasma are now being studied laboratory plasma. The magnetic experiments to study plasmas using nearly equal concentrations deuterium and tritium carried out TFTR. At maximum power 10.7 MW, 39.5 MW neutral-beam heating, supershot discharge 6.7 high-βp following current rampdown....
Abstract Nonlinear gyrokinetic simulations of impurity transport are compared to experimental for the first time. The GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) was used perform global, nonlinear a standard Alcator C-Mod, L-mode discharge. laser blow-off technique combined with soft x-ray measurements single charge state calcium provide time-evolving profiles this non-intrinsic, non-recycling over radial range 0.0 ⩽ r / 0.6. Experimental coefficient their uncertainties were...
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...
Several seemingly unrelated effects in Alcator C-Mod ohmic L-mode plasmas are shown to be closely connected: non-local heat transport, core toroidal rotation reversals, energy confinement saturation and up/down impurity density asymmetries. These phenomena all abruptly transform at a critical value of the collisionality. At low densities linear regime, with collisionality ?*???0.35 (evaluated inside q?=?3/2 surface), transport exhibits behaviour, is directed co-current, edge profiles...
Ohmic energy confinement saturation is found to be closely related core toroidal rotation reversals in Alcator C-Mod tokamak plasmas. Rotation occur at a critical density, depending on the plasma current and magnetic field, which coincides with density separating linear regime from saturated regime. The directed co-current low abruptly changes direction counter-current when saturates as increased. Since there bifurcation of this reversal very sensitive indicator determination change. results...
The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated the study of deuterium–tritium D–T plasmas containing significant populations energetic alpha particles, spanned over two decades from conception completion. During design TFTR, key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, reactivity. Energetic particle was given less...
The Tomamak Fusion Test reactor has performed initial high-power experiments with the plasma fueled nominally equal densities of deuterium and tritium. Compared to pure plasmas, energy stored in electron ions increased by \ensuremath{\sim}20%. These increases indicate improvements confinement associated use tritium possibly heating electrons \ensuremath{\alpha} particles created D-T fusion reactions.
Trapped electron mode (TEM) turbulence exhibits a rich variety of collisional and zonal flow physics. This work explores the parametric variation flows underlying mechanisms through series linear nonlinear gyrokinetic simulations, using both particle-in-cell continuum methods. A new stability diagram for modes is presented, identifying critical boundary at ηe=1, separating long short wavelength TEMs. novel parity test used to separate TEMs from temperature gradient driven modes. scan ηe...
Multi-channel transport experiments have been conducted in auxiliary heated (Ion Cyclotron Range of Frequencies) L-mode plasmas at Alcator C-Mod [Marmar and Group, Fusion Sci. Technol. 51(3), 3261 (2007)]. These provide good diagnostic coverage for measurements kinetic profiles, impurity transport, turbulence (electron temperature density fluctuations). In the experiments, a steady sawtoothing plasma with 1.2 MW on-axis RF heating is established scanned by 20%. Measured rotation profiles...
The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without accompanying particle and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate at edge.
In transport barriers, particularly H-mode edge pedestals, radial scale lengths can become comparable to the ion orbit width, causing neoclassical physics radially nonlocal. this work, resulting changes flow and current are examined both analytically numerically. Steep density gradients considered, with poloidal gyroradius, together strong electric fields sufficient electrostatically confine ions. Attention is restricted relatively weak temperature (but permitting arbitrary electron...
The first measurements of long wavelength (kyρs < 0.3) electron temperature fluctuations in Alcator C-Mod made with a new correlation cyclotron emission diagnostic support long-standing hypothesis regarding the confinement transition from linear ohmic (LOC) to saturated (SOC). Electron decrease significantly (∼40%) crossing LOC SOC, consistent change trapped mode (TEM) turbulence domination ion gradient (ITG) as density is increased. Linear stability analysis performed GYRO code (Candy and...
A series of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] low torque quiescent H-mode experiments show that density gradient driven trapped electron mode (DGTEM) turbulence dominates the inner core plasmas during strong cyclotron heating (ECH). Adding 3.4 MW ECH doubles Te/Ti from 0.5 to 1.0, which halves linear DGTEM critical gradient, locally reducing peaking, while transport in all channels displays extreme stiffness gradient. This suggests fusion α-heating may degrade confinement...
Main ion dilution has been predicted by gyrokinetic simulations to have a significant effect on thermal transport in C-Mod ohmic plasmas. This was verified experimentally with specific set of experiments which deuterium plasmas across the linear confinement (LOC) through saturated (SOC) regimes were diluted seeding nitrogen gas (Z = 7) injection. The observed increase normalized temperature gradients (ITGs) up 30% without corresponding gyrobohm energy flux, indicating change either stiffness...
The confinement and heating of supershot plasmas are significantly enhanced with tritium beam injection relative to deuterium in the Tokamak Fusion Test Reactor [Plasma Phys. Controlled 26, 11 (1984)]. global energy local thermal transport analyzed for fueled quantify their dependence on average mass hydrogenic ions. Radial profiles densities determined from D–T fusion neutron emission profile. inferred scalings isotopic quite strong, τE∝〈A〉0.85±0.20, τEthermal∝〈A〉0.89±0.20,...
Long wavelength turbulence as well heat and momentum transport are significantly reduced in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] a result of neon seeding low confinement mode negative central shear discharge. Correspondingly, energy time increases by up to 80%. Fully saturated measurements near ρ=0.7 (ρ=r/a) wave number range 0.1⩽k⊥ρs⩽0.6, obtained with beam emission spectroscopy, exhibit...