A5057334541- Magnetic confinement fusion research
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Particle accelerators and beam dynamics
- Nuclear Physics and Applications
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- Integrated Circuits and Semiconductor Failure Analysis
- Advanced Materials Characterization Techniques
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- Acoustic Wave Resonator Technologies
- Optical Systems and Laser Technology
- Electron and X-Ray Spectroscopy Techniques
- Laser-Matter Interactions and Applications
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- Diamond and Carbon-based Materials Research
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Massachusetts Institute of Technology
2014-2024
Plasma Technology (United States)
2009-2024
Fusion Academy
2006-2024
Fusion (United States)
1994-2024
General Atomics (United States)
2001-2022
University of California, Los Angeles
2009-2019
The University of Texas at Austin
2019
Lawrence Livermore National Laboratory
2016-2019
University of Wisconsin–Madison
2016-2019
University of Colorado Boulder
2016
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,...
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...
Edge conditions in DIII-D are being quantified order to provide insight into the physics of H mode regime. Several studies show that electron temperature is not key parameter controls L-H transition. Gradients edge and pressure much more promising candidates for elements such parameters. They systematically increase during L phases discharges which make a transition mode, these increases typically larger than underlying quantities. The quality confinement strongly correlated with height...
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...
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...
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.
Phase contrast imaging (PCI) is an internal reference beam interferometry technique which provides a direct image of line integrated plasma density fluctuations. The method has been used with great success to measure waves and turbulence in magnetically confined high temperature plasmas. principle PCI was developed optics the 1930s by Dutch physicist Zernike, leading development phase-contrast microscopy. allows one detect variation index refraction dielectric medium (such as plasma) due...
Recent advances in gyrokinetic simulation of core turbulence and associated transport requires an intensified experimental effort to validate these codes using state the art synthetic diagnostics compare simulations with data. A phase contrast imaging (PCI) diagnostic [M. Porkolab, J. C. Rost, N. Basse et al., IEEE Trans. Plasma Sci. 34, 229 (2006)] is used study H-mode plasmas Alcator C-Mod Greenwald, D. Andelin, Nucl. Fusion 45, S109 (2005)]. The PCI system capable measuring density...
New experimental studies and modelling of the coherent edge harmonic oscillation (EHO), which regulates conventional Quiescent H-mode (QH-mode) edge, validate proposed hypothesis rotational shear in destabilizing low-n kink-peeling mode as additional drive mechanism for EHO. The observed minimum E × B required EHO decreases linearly with pedestal collisionality , is favorable operating QH-mode machines low rotation such ITER. In addition, regime DIII-D has recently been found to bifurcate...
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...
Abstract Nonlinear gyrokinetic simulations correctly predict particle as well ion and electron energy fluxes of high confinement plasmas with a negative triangularity cross sectional shape, showing that core transport in these is described by standard models. Experimentally inferred power balance are mostly reproduced within one deviation across wide portion the minor radius. Experimental conditions scale simulations, without need to include density temperature profile curvature effects. The...
Substantial progress has been made towards both understanding and control of internal transport barriers (ITBs) on DIII-D, resulting in the discovery a new sustained high performance operating mode termed quiescent double barrier (QDB) regime. The QDB regime combines core with ELM-free H edge (termed QH mode), giving rise to separate (double) barriers. are mutually compatible do not merge, broad profiles an pedestal. is characterized by behaviour continuous multiharmonic MHD activity...
Recent advances in gyrokinetic simulation have allowed for quantitative predictions of core turbulence and associated transport. However, numerical codes must be tested against experimental results both In this paper, we present recent from ohmic plasmas the Alcator C-Mod tokamak using phase contrast imaging (PCI) diagnostic, which is capable measuring density fluctuations with wave numbers up to 55 cm−1. The experiments were carried out over range densities covering 'neo-Alcator' (linear...
External impurity injection into L mode edge discharges in DIII-D has produced clear confinement improvement (a factor of 2 energy and neutron emission), reduction all transport channels (particularly ion thermal diffusivity to the neoclassical level), simultaneous long wavelength turbulence. Suppression turbulence are attributed synergistic effects induced enhancement E × B shearing rate toroidal drift wave growth rate. A prompt density fluctuations local at beginning appears result from an...
The divertor of the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] routinely radiates a large fraction power entering scrape-off layer. This dissipative operation occurs whether is detached or not, and volumetric radiative emissivities, up to 60 MW m−3 in ion cyclotron range frequency (ICRF) heated discharges, have been measured using bolometer arrays. An analysis both Ohmic ICRF-heated discharges has demonstrated some relative merits versus high-recycling operation. advantage that...
Transport in ohmically heated plasmas Alcator C-Mod was studied both the linear (LOC) and saturated (SOC) ohmic L-mode confinement regimes importance of turbulent transport region r/a = 0.5–0.8 established. After an extensive analysis with TGLF GYRO, it is found that using effective impurity ion species Zi = 8, moderately high Zeff (2.0–5.6), LOC regime electron becomes dominant due to TEM turbulence. The key ingredient present results observation dilution main (deuterium) by moderate charge...
A novel rotating mask system has been designed and implemented on the DIII-D phase contrast imaging (PCI) diagnostic to produce first spatially localized PCI measurements of a tokamak plasma. The localization technique makes use variation in magnetic field component perpendicular viewing chord as function height. This new capability provides range 2<k<30 cm(-1), 10 kHz<f<10 MHz, 0.7<r/a<1. spatial resolution cm at k=15 cm(-1) can realistically provide rate profiles/s. Calibration show...
Experiments on the DIII-D tokamak have identified a new sustained high-performance operating mode, termed quiescent double barrier (QDB) regime. The QDB regime combines internal transport barriers (ITBs) with quiescent, edge localized mode (ELM)-free H-mode edge, QH-mode, giving rise to separate core and barriers. These been maintained for {>}3.5 s (~25τE), demonstrating long-pulse, quasi-steady-state capability. combination of ITBs temperature pedestals results in plasmas; βN H89 product 7...
A “synthetic diagnostic” has been developed to calculate the expected experimental response of phase contrast imaging (PCI), a scattering diagnostic used measure density fluctuations in laboratory plasmas, tokamak discharge modeled with GYRO nonlinear gyrokinetic code [J. Candy and R. Waltz, J. Comput. Phys. 186, 545 (2003)]. The synthetic PCI includes spatial diagnostic, primarily implemented as line integral plasma along beam path, minimum maximum wavenumber resulting from detection...
Abstract More than 0.6 MW of rf power at 476 MHz has been coupled to DIII-D plasmas by launching helicon (whistler) waves with a traveling-wave antenna (comb-line) in the fast-wave polarization (Van Compernolle et al 2021 Nucl. Fusion 61 116034) which resulted observation electron heating core plasma single-pass absorption based on ray-tracing L-mode discharges. The coupling performance 1.5 m wide 30-element comb-line consistent expectations 2015–2016 experiments low-power 12-element...
A population of suprathermal ions has been observed in the scrape off layer during injection power ion cyclotron frequency range on Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. These generated energetic neutrals which were measured with a charge exchange neutral particle analyzer. In hydrogen minority heating regime, fast particles only when injected was above 500 kW. Fast at low level rf multiple layer. The deposited edge always less than five percent and...
In this work, a novel combined diagnostic capable of measuring multiscale density fluctuations that extend from magnetohydrodynamic (MHD) to the lower range electron temperature gradient turbulence has been designed, installed, and operated at DIII-D. The was constructed by adding heterodyne interferometer pre-existing phase contrast imaging (PCI) system, both which measure line-integrated fluctuations. port-space footprint is minimized via use single 10.6 μm probe beam. With temporal...