D. C. Pace
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View article: DIII-D's role as a national user facility in enabling the commercialization of fusion energy
DIII-D's role as a national user facility in enabling the commercialization of fusion energy Open
The path to fusion in the United States requires partnership between public and private sector. While the private sector provides the vigor to take some of the major steps necessary, there is a depth of expertise and capability in the publ…
View article: Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma
Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma Open
The aim of this study is to analyze the effect of the neutral beam injector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs) in DIII-D plasma. The analysis is done using the linear and nonlinear versions of the…
View article: Polarized fusion and potential in situ tests of fuel polarization survival in a tokamak plasma
Polarized fusion and potential in situ tests of fuel polarization survival in a tokamak plasma Open
The use of spin-polarized fusion fuels would provide a significant boost towards the ignition of a burning plasma. The cross section for D + T → α + n, would be increased by 1.5 if the fuels were injected with parallel polarization. Furthe…
View article: Impact of β <sub> n </sub> and spectrum of n = 1 applied fields on fast ion losses in DIII-D
Impact of β <sub> n </sub> and spectrum of n = 1 applied fields on fast ion losses in DIII-D Open
The effect of n = 1 magnetic perturbations (MPs) on prompt fast ion losses in DIII-D has been investigated using the light ion beam probe technique. The effect of normalized beta, β n , and the plasma response to the MPs is studied for sev…
View article: Diverted negative triangularity plasmas on DIII-D: the benefit of high confinement without the liability of an edge pedestal
Diverted negative triangularity plasmas on DIII-D: the benefit of high confinement without the liability of an edge pedestal Open
Diverted discharges at negative triangularity on the DIII-D tokamak sustain normalized confinement and pressure levels typical of standard H-mode scenarios (H98y,2≅1, βN≅3) without developing an edge pressure pedestal, despite the auxiliar…
View article: Response of thermal and fast-ion transport to beam ion population, rotation and T <sub>e</sub>/T <sub>i</sub> in the DIII-D steady state hybrid scenario
Response of thermal and fast-ion transport to beam ion population, rotation and T <sub>e</sub>/T <sub>i</sub> in the DIII-D steady state hybrid scenario Open
The thermal and fast-ion transport properties of DIII-D steady-state hybrid discharges with normalized beta β N ≳ 3 are studied at low injected torque and an increased electron to ion temperature ratio T e / T i . Linear stability analysis…
View article: Central ion cyclotron emission in the DIII-D tokamak
Central ion cyclotron emission in the DIII-D tokamak Open
Collective ion cyclotron emission (ICE) at the ion cyclotron frequency and its harmonics is a potential passive diagnostic of the fast-ion distribution in fusion reactors. ICE is observed in most plasmas in the DIII-D tokamak and is most s…
View article: Feedback control of stored energy and rotation with variable beam energy and perveance on DIII-D
Feedback control of stored energy and rotation with variable beam energy and perveance on DIII-D Open
Design and testing of a new method for real-time control on DIII-D using the new voltage and perveance variation capability of DIII-D’s neutral beam injection system is presented. The approach enables control of power, torque, stored energ…
View article: Radio frequency measurements of energetic-particle-driven emission using the ion cyclotron emission diagnostic on the DIII-D tokamak
Radio frequency measurements of energetic-particle-driven emission using the ion cyclotron emission diagnostic on the DIII-D tokamak Open
The Ion Cyclotron Emission (ICE) diagnostic on the DIII-D tokamak consists of two outboard midplane systems. In the first system, straps of an ion cyclotron range of frequencies antenna are configured as receiving antennas. For the second …
View article: Experiments on helicons in DIII-D—investigation of the physics of a reactor-relevant non-inductive current drive technology
Experiments on helicons in DIII-D—investigation of the physics of a reactor-relevant non-inductive current drive technology Open
Experiments have begun in DIII-D to evaluate a toroidally-directed spectrum of helicon waves (also known as 'very high harmonic fast waves', 'fast waves in the lower hybrid range of frequencies', or 'whistlers') that can generate efficient…
View article: Dynamic neutral beam current and voltage control to improve beam efficacy in tokamaks
Dynamic neutral beam current and voltage control to improve beam efficacy in tokamaks Open
An engineering upgrade to the neutral beam system at the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables time-dependent programming of the beam voltage and current. Initial application of this capability involves pre-prog…
View article: Resolving runaway electron distributions in space, time, and energy
Resolving runaway electron distributions in space, time, and energy Open
Areas of agreement and disagreement with present-day models of runaway electron (RE) evolution are revealed by measuring MeV-level bremsstrahlung radiation from runaway electrons (REs) with a pinhole camera. Spatially resolved measurements…
View article: Advances in the steady-state hybrid regime in DIII-D—a fully non-inductive, ELM-suppressed scenario for ITER
Advances in the steady-state hybrid regime in DIII-D—a fully non-inductive, ELM-suppressed scenario for ITER Open
Here, the hybrid regime with beta, collisionality, safety factor and plasma shape relevant to the ITER steady-state mission has been successfully integrated with ELM suppression by applying an odd parity n=3 resonant magnetic perturbation …
View article: Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks
Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks Open
Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the in…
View article: Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes
Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes Open
Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfv en eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold, leading to fast-ion density profile resilience and reduced fusio…
View article: Prediction of nonlinear evolution character of energetic-particle-driven instabilities
Prediction of nonlinear evolution character of energetic-particle-driven instabilities Open
A general criterion is proposed and found to successfully predict the\nemergence of chirping oscillations of unstable Alfv\\'enic eigenmodes in tokamak\nplasma experiments. The model includes realistic eigenfunction structure,\ndetailed ph…
View article: Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold
Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold Open
Experiments on the DIII-D tokamak have identified how multiple simultaneous Alfvén eigenmodes (AEs) lead to overlapping wave-particle resonances and stochastic fast-ion transport in fusion grade plasmas [C. S. Collins et al., Phys. Rev. Le…
View article: A path to stable low-torque plasma operation in ITER with test blanket modules
A path to stable low-torque plasma operation in ITER with test blanket modules Open
New experiments in the low-torque ITER Q = 10 scenario on DIII-D demonstrate that n = 1 magnetic fields from a single row of ex-vessel control coils enable operation at ITER performance metrics in the presence of applied non-axisymmetric m…
View article: Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks
Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks Open
A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak (Luxon 2002 Nucl. Fusion 42 614). Pre-programmed waveforms for…
View article: Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak
Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak Open
Spectra of passive fast-ion D-alpha (FIDA) light from beam ions that charge exchange with background neutrals are measured and simulated. The fast ions come from three sources: ions that pass through the diagnostic sightlines on their firs…
View article: Polarized fusion, its Implications and plans for Direct Measurements in a Tokamak
Polarized fusion, its Implications and plans for Direct Measurements in a Tokamak Open
A long-term energy option that is just approaching the horizon after decades of struggle, is fusion. Recent developments allow us to apply techniques from spin physics to advance its viability. The cross section for the primary fusion fuel…
View article: Applying the new gamma ray imager diagnostic to measurements of runaway electron Bremsstrahlung radiation in the DIII-D Tokamak (invited)
Applying the new gamma ray imager diagnostic to measurements of runaway electron Bremsstrahlung radiation in the DIII-D Tokamak (invited) Open
A new gamma ray imager (GRI) is developed to probe the electron distribution function with 2D spatial resolution during runaway electron (RE) experiments at the DIII-D tokamak. The diagnostic is sensitive to 0.5–100 MeV gamma rays, allowin…
View article: Gamma ray imager on the DIII-D tokamak
Gamma ray imager on the DIII-D tokamak Open
A gamma ray camera is built for the DIII-D tokamak [J. Luxon, Nucl. Fusion 42, 614 (2002)] that provides spatial localization and energy resolution of gamma flux by combining a lead pinhole camera with custom-built detectors and optimized …
View article: Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport
Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport Open
Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold in the presence of many overlapping small-amplitude Alfvén eigenmodes (AEs). The threshold is phase-space dependent and occurs…
View article: Diverse wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit
Diverse wave-particle interactions for energetic ions that traverse Alfvén eigenmodes on their first full orbit Open
Neutral-beam ions that are deflected onto loss orbits by Alfvén eigenmodes (AE) on their first bounce orbit and are detected by a fast-ion loss detector (FILD) satisfy the “local resonance” condition proposed by Zhang et al. [Nucl. Fusion …
View article: Investigation of He–W interactions using DiMES on DIII-D
Investigation of He–W interactions using DiMES on DIII-D Open
Tungsten button samples were exposed to He ELMing H-mode plasma in DIII-D using 2.3 MW of electron cyclotron heating power. Prior to the exposures, the W buttons were exposed to either He, or D, plasma in PISCES-A for 2000 s at surface tem…