A. Hubbard
A5061702002- Magnetic confinement fusion research
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Metal and Thin Film Mechanics
- Nuclear reactor physics and engineering
- Electromagnetic Launch and Propulsion Technology
- Engineering Applied Research
- Solar and Space Plasma Dynamics
- High-pressure geophysics and materials
- Nuclear Physics and Applications
- Dust and Plasma Wave Phenomena
- Laser-induced spectroscopy and plasma
- Semiconductor materials and devices
- Physics of Superconductivity and Magnetism
- Nuclear Materials and Properties
- Atomic and Molecular Physics
- Silicon and Solar Cell Technologies
- Fluid Dynamics and Turbulent Flows
- Diamond and Carbon-based Materials Research
- Particle Accelerators and Free-Electron Lasers
- Metallurgical Processes and Thermodynamics
Massachusetts Institute of Technology
2015-2025
Fusion (United States)
2016-2025
Plasma Technology (United States)
2016-2025
Fusion Academy
2016-2025
Caris Life Sciences (United States)
2024
Royal Military Academy
2020
IIT@MIT
2009-2017
University of York
2015-2017
Princeton Plasma Physics Laboratory
2001-2016
The University of Texas at Austin
2015-2016
The understanding and predictive capability of transport physics plasma confinement is reviewed from the perspective achieving reactor-scale burning plasmas in ITER tokamak, for both core edge regions. Very considerable progress has been made understanding, controlling predicting tokamak across a wide variety conditions regimes since publication Physics Basis (IPB) document (1999 Nucl. Fusion 39 2137–2664). Major areas considered here follow. (1) Substantial improvement content, reliability...
Early operation of the Alcator-C-MOD tokamak [I.H. Hutchinson, Proceedings IEEE 13th Symposium on Fusion Engineering, Knoxville, TN, edited by M. Lubell, Nestor, and S. Vaughan (Institute Electrical Electronic Engineers, New York, 1990), Vol. 1, p. 13] is surveyed. Reliable operation, with plasma current up to 1 MA, has been obtained, despite massive conducting superstructure associated error fields. However, vertical disruptions are not slowed long vessel time constant. With pellet fueling,...
An improved energy confinement regime, I-mode, is studied in Alcator C-Mod, a compact high-field divertor tokamak using ion cyclotron range of frequencies (ICRFs) auxiliary heating. I-mode features an edge transport barrier without accompanying particle barrier, leading to several performance benefits. H-mode obtained core impurity accumulation, resulting reduced radiation with high-Z metal wall and ICRF has stationary temperature pedestal localized modes typically absent, while plasma...
Abstract High-temperature superconductors (HTS) promise to revolutionize high-power applications like wind generators, DC power cables, particle accelerators, and fusion energy devices. A practical HTS cable must not degrade under severe mechanical, electrical, thermal conditions; have simple, low-resistance, manufacturable electrical joints; high stability; rapid detection of runaway quench events. We designed experimentally qualified a vacuum pressure impregnated, insulated, partially...
The SPARC Toroidal Field Model Coil (TFMC) Program was a three-year effort between 2018 and 2021 that developed novel Rare Earth Barium Copper Oxide (REBCO) superconductor technologies then successfully utilized these to design, build, test first-in-class, high-field (∼20 T), representative-scale (∼3 m) superconducting toroidal field (TF) coil. program executed jointly by the MIT Plasma Science Fusion Center (PSFC) Commonwealth Systems (CFS) as technology enabler of pathway fusion energy,...
The SPARC Toroidal Field Model Coil (TFMC) is the first large-scale (∼3 m), high-field (∼20 T) superconducting fusion magnet based on Rare Earth Yttrium Barium Copper Oxide (REBCO). Its objective was to retire risk for toroidal field in tokamak, a burning plasma class magnetic confinement energy device. Weighing 10,058 kg and utilizing 270 km of REBCO, TFMC non-insulated, stack-in-plate style magnet. It has three main components: (1) winding pack; (2) structural case; (3) case extensions, or...
Plasma profiles and flows in the low- high-field side scrape-off-layer (SOL) regions Alcator C-Mod are found to be remarkably sensitive magnetic separatrix topologies (upper-, lower- double-null) impose topology-dependent flow boundary conditions on confined plasma. Near-sonic plasma along field lines observed SOL, with magnitude direction clearly dependent X-point location. The principal drive mechanism for is a strong ballooning-like poloidal transport asymmetry: parallel arise so as...
The pressure at the top of edge transport barrier (or ‘pedestal height’) strongly impacts fusion performance, while large localized modes (ELMs), driven by free energy in pedestal region, can constrain material lifetimes. Accurately predicting height and ELM behavior ITER is an essential element prediction optimization performance. Investigation intermediate wavelength MHD ‘peeling–ballooning’ modes) has led to improved understanding important constraints on mechanism for ELMs. combination...
A series of experiments, examining the confinement properties ion cyclotron range frequencies (ICRF) heated H mode plasmas, has been carried out on Alcator C-Mod tokamak. is a compact tokamak that operates at high particle, power and current densities toroidal fields up to 8 T. Under these conditions plasma essentially thermal with very little contribution stored energy from energetic ions (typically no more than 5%) Ti~Te. Most data were taken machine in single null `closed' divertor...
Regimes of high-confinement mode have been studied in the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. with no edge localized modes (ELM-free) compared detail to a new regime, enhanced Dα (EDA). EDA discharges only slightly lower energy confinement than comparable ELM-free ones, but show markedly reduced impurity confinement. Thus do not accumulate impurities and typically fraction radiated power. The gradients seem be relaxed by continuous process rather an...
High-resolution charge-exchange recombination spectroscopic measurements of B5+ ions have enabled the first spatially resolved calculations radial electric field (Er) in Alcator C-Mod pedestal region [E. S. Marmar, Fusion Sci. Technol. 51, 261 (2006)]. These observations offer new challenges for theory and simulation provide important comparisons with other devices. Qualitatively, structure observed on is similar to that tokamaks. However, narrow high-confinement mode (H-mode) Er well widths...
The goal of the Lower Hybrid Current Drive (LHCD) system on Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] is to investigate current profile control under plasma conditions relevant future experiments. Experimental observations a LHCD "density limit" for are presented in this paper. Bremsstrahlung emission from relativistic fast electrons core drops suddenly above line averaged densities 1020 m−3 (ω/ωLH∼3–4), well below density limit previously observed other...
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...
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...
A set of external coils (A-coils) capable producing nonaxisymmetric, predominantly n=1, fields with different toroidal phase and a range poloidal mode m spectra has been used to determine the threshold amplitude for locking over plasma parameters in Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda, P. Bonoli, S. Fairfax, C. Fiore, J. Goetz, Golovato, Granetz, M. Greenwald et al., Phys. Plasmas 1, 1511 (1994)]. The perturbations parametric scalings, expressed terms (B21∕BT), are...
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas. The time evolution of core impurity toroidal rotation velocity profiles measured with a tangentially viewing crystal x-ray spectrometer array. Following the L-mode to EDA (enhanced Dα) H-mode transition both Ohmic and ion cyclotron range frequencies heated discharges, ensuing co-current velocity, which is generated absence any external source, propagate from edge plasma timescale order energy confinement time,...
Intrinsic rotation has been observed in $I$-mode plasmas from the $C$-Mod tokamak, and is found to be similar that $H$ mode, both its edge origin scaling with global pressure. Since have $\ensuremath{\nabla}T$, but completely different $\ensuremath{\nabla}n$, it may concluded drive of intrinsic $\ensuremath{\nabla}T$ rather than $\ensuremath{\nabla}P$. Evidence suggests connection between gradients residual stress, a for conversion free energy macroscopic flow calculated.
We report extended studies of the I-mode regime [Whyte et al., Nucl. Fusion 50, 105005 (2010)] obtained in Alcator C-Mod tokamak [Marmar Sci. Technol. 51(3), 3261 (2007)]. This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle barrier. Steady I-modes have now been favorable by using specific plasma shapes, as well drift over wider range shapes and parameters. With power thresholds are close to standard scaling for...
Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas the Alcator C-Mod [I. H. Hutchinson Plasmas 1, 1511 (1994)] tokamak, which characterized by a strong thermal transport barrier while providing little or no to both bulk impurity particles. Although previous work showed clear geodesic-acoustic modes (GAM) on C-Mod, using newly implemented, gas-puff-imaging based time-delay-estimate velocity...
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,...
With fusion device performance hinging on the edge pedestal pressure, it is imperative to experimentally understand physical mechanism dictating characteristics and validate improve predictive models. This Letter reports direct evidence of density magnetic fluctuations showing stiff onset an instability leading saturation Alcator C-Mod tokamak. Edge stability analyses indicate that unstable both ballooning mode kinetic in agreement with observations.
Direction reversals of intrinsic toroidal rotation have been observed in Alcator C-Mod ohmic L-mode plasmas following modest electron density or magnetic field ramps. The reversal process occurs the plasma interior, inside q = 3/2 surface. For low plasmas, is co-current direction, and can reverse to counter-current direction an increase above a certain threshold. Reversals from co- are correlated with sharp decrease fluctuations k R ⩾ 2 cm −1 frequencies 70 kHz. at which reverses increases...
Transport barrier formation and its relation to sheared flows in fluids plasmas are of fundamental interest various natural laboratory observations critical importance achieving an economical energy production a magnetic fusion device. Here we report the first observation edge transport event gyrokinetic simulation carried out realistic tokamak geometry. The results show that turbulent Reynolds stress driven ExB act concert with neoclassical orbit loss quench form just inside last closed...
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...
Abstract The ‘Super H-Mode’ regime is predicted to enable pedestal height and fusion performance substantially higher than standard H-Mode operation. This exists due a bifurcation of the pressure, as function density, that by EPED model occur in strongly shaped plasmas above critical density. Experiments on Alcator C-Mod DIII-D have achieved access Super (and Near H) regime, obtained very high including highest tokamak ( p ped ~ 80 kPa) experiments operating near ITER magnetic field. H...