A.C. Sontag
A5044122042- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Nuclear reactor physics and engineering
- Atomic and Subatomic Physics Research
- Nuclear Physics and Applications
- Laser-Plasma Interactions and Diagnostics
- Particle Detector Development and Performance
- Advanced Data Storage Technologies
- Astro and Planetary Science
- Spacecraft and Cryogenic Technologies
- Gamma-ray bursts and supernovae
- Distributed and Parallel Computing Systems
- Particle Accelerators and Free-Electron Lasers
- Advanced MRI Techniques and Applications
- Astronomy and Astrophysical Research
- Semiconductor materials and devices
- Geomagnetism and Paleomagnetism Studies
- Advancements in Semiconductor Devices and Circuit Design
- Laser-induced spectroscopy and plasma
- Geophysics and Gravity Measurements
University of Wisconsin–Madison
1998-2025
Oak Ridge National Laboratory
2009-2020
Columbia University
2005-2009
Higashihiroshima Medical Center
2006
Hiroshima University
2006
Lawrence Livermore National Laboratory
2006
University of California, Irvine
2006
University of Washington
2006
University of Rochester
2006
University of California, Los Angeles
2006
Dissipation of plasma toroidal angular momentum is observed in the National Spherical Torus Experiment due to applied nonaxisymmetric magnetic fields and their plasma-induced increase by resonant field amplification resistive wall mode destabilization. The measured decrease profile compared calculations nonresonant drag torque based on theory neoclassical viscosity. Quantitative agreement between experiment found when effect toroidally trapped particles included.
The National Spherical Torus Experiment (NSTX) has demonstrated the advantages of low aspect ratio geometry in accessing high toroidal and normalized plasma beta, βN ≡ 108⟨βt⟩ aB0/Ip. Experiments have reached βt = 39% 7.2 through boundary profile optimization. High plasmas can exceed ideal no-wall stability limit, βNno−wall, for periods much greater than wall eddy current decay time. Resistive mode (RWM) physics is studied to understand stabilization these plasmas. spectrum unstable RWMs...
The resistive-wall mode is actively stabilized in the National Spherical Torus Experiment high-beta plasmas rotating significantly below critical rotation speed for passive stability and range predicted International Thermonuclear Experimental Reactor. Variation of feedback stabilization parameters shows excitation or suppression. Stabilization toroidal number unity did not lead to instability two. can become unstable by deforming poloidally, an important consideration system design.
The low-aspect ratio, low magnetic field and wide range of plasma beta NSTX plasmas provide new insight into the origins effects errors. An extensive array sensors has been used to analyse error fields, measure error-field amplification detect resistive wall modes (RWMs) in real time. measured normalized threshold for onset locked shows a linear scaling with density, weak inverse dependence on toroidal positive shear. These results extrapolate favourable ITER. For these low-beta locked-mode...
The DIII-D tokamak magnetic diagnostic system [E. J. Strait, Rev. Sci. Instrum. 77, 023502 (2006)] has been upgraded to significantly expand the measurement of plasma response intrinsic and applied non-axisymmetric “3D” fields. placement design 101 additional sensors allow resolution toroidal mode numbers 1 ≤ n 3, poloidal wavelengths smaller than MARS-F, IPEC, VMEC magnetohydrodynamic model predictions. Small 3D perturbations, relative equilibrium field (10−5 < δB/B0 10−4), require...
A new small angle slot (SAS) divertor concept has been developed to enhance neutral cooling across the target by coupling a closed structure with appropriate shaping. Initial tests on DIII-D find strong interplay between such anticipated 'SAS' effects and cross-field drifts, favouring operation ion B × ∇B drift away from X-point, as currently employed for advanced tokamaks. This offers following key improvements relative DIII-D's open lower or partially-closed upper divertor: (i) SAS allows...
Dedicated experiments in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion, 42, 614 (2002)], Joint European Torus (JET) [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Fusion 25, 1011 (1985)], National Spherical Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. Peng et al., 40, 557 (2000)] reveal commonalities of resistive wall mode (RWM) stabilization by sufficiently fast toroidal plasma rotation devices different size aspect ratio. In each device weakly damped n=1 RWM manifests itself resonant field...
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...
Saturated internal kink modes have been observed in many of the highest toroidal β discharges National Spherical Torus Experiment (NSTX). These often cause rotation flattening plasma core, can degrade fast-ion confinement and some cases contribute to complete loss angular momentum stored energy. Characteristics are measured using soft x-ray, kinetic profile magnetic diagnostics. Toroidal flows approaching Alfvenic speeds, island pressure peaking enhanced viscous diamagnetic effects...
The major objective of the National Spherical Torus Experiment (NSTX) is to understand basic toroidal confinement physics at low aspect ratio and high βT in order advance spherical torus (ST) concept. In do this, NSTX utilizes up 7.5 MW neutral beam injection, 6 harmonic fast waves (HHFWs), it operates with plasma currents 1.5 MA elongations 2.6 a field 0.45 T. New facility, diagnostic modelling capabilities developed over past two years have enabled research team make significant progress...
AbstractThe use of a fusion component testing facility to study and establish, during the ITER era, remaining scientific technical knowledge needed by Demo is considered described in this paper. This aims test components an integrated nuclear environment, for first time, discover understand underpinning physical properties, develop improved further testing, time-efficient manner. It requires design with extensive modularization remote handling activated components, flexible hot-cell...
The deuterium-deuterium (D-D) fusion reaction rate in a spherically convergent ion focus is observed to significantly exceed the predicted by collisionless flow model. However, careful consideration of ion-neutral collisions and trapped neutral density cathode account for extra reactivity without invoking anomalous trapping converged core region. This conclusion supported proton collimation measurements, which indicate that bulk originates outside In addition, classical model, where charge...
The National Spherical Torus Experiment (NSTX) offers an operational space characterized by high-beta (β t = 39%, β N > 7, ) and low aspect ratio ( A 1.27) to leverage the plasma parameter dependences of RWM stabilization rotation damping physics giving greater confidence for extrapolation ITER. Significant new capability research has been added device with commissioning a set six non-axisymmetric magnetic field coils, allowing generation fields dominant toroidal mode number, n , 1–3....
Characterizations of the pedestal parameter dynamics throughout edge localized mode (ELM) cycles are performed on National Spherical Torus Experiment (NSTX, (Ono et al 2000 Nucl. Fusion 40 557)). A clear buildup height between ELMs is observed for three different plasma currents. This tends to saturate at low and medium Similarly, width increases with no evidence saturation during an ELM cycle. The maximum gradient as a function current, reaches nominal value after crash, remains constant...
Determining the toroidal rotation for future tokamaks like ITER is a challenging and important problem. By combining empirical scalings intrinsic at top of pedestal with expected neutral beam torque modeling momentum transport, profile predicted TGYRO using TGLF (SAT0 SAT1). On axis exceeds 20 krad s−1 shear significant enough to reduce turbulent transport significantly increase confinement fusion power when comparing cases that ignore effect rotation. The prediction made increased...
The resistive wall mode (RWM) poses a limit to the maximum β that can be sustained in magnetic fusion experiments. RWM stabilization physics at low aspect ratio is studied high-β National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. Peng et al., Nucl. Fusion 40, 557 (2000)] plasmas (βt up 39%; βN 6.8) understand and alleviate this constraint. Plasmas with increased q NSTX have been maintained above computed ideal no-wall for more than 20 times no signs of growth cases where...
The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER.Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents 0.7 MA with non-inductive fractions above 65% while simultaneously achieving β T N values 17% 5.7 (%m -1 ), respectively.A newly available motional Stark effect diagnostic...
Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into tokamaklike topology where maximum sustained determined by helicity balance and requirements for relaxation.
The compact (R0~1.2-1.3m) Fusion Nuclear Science Facility (FNSF) is aimed at providing a fully integrated, continuously driven fusion nuclear environment of copious neutrons. This facility would be used to test, discover, and understand the complex challenges plasma material interactions, tritium fuel management, power extraction. Such properly designed provide, initially JET-level pressure (~30%T2) conditions (e.g., Hot-Ion H-Mode, Q<1)), an outboard neutron flux 0.25 MW/m2 while requiring...
Calculations of the plasma response to applied non-axisymmetric fields in several DIII-D discharges show that predicted displacements depend strongly on edge current density. This result is found using both a linear two-fluid-MHD model (M3D-C1) and nonlinear ideal-MHD (VMEC). Furthermore, it observed probability discharge being localized mode (ELM)-suppressed most closely related density, as opposed pressure gradient. It with stronger kink are closer peeling–ballooning stability limit ELITE...
The filterscope diagnostic on DIII-D utilizes photomultiplier tubes to measure visible light emission from the plasma. system has undergone a substantial upgrade since previous attempts cross-calibrate with other spectroscopic diagnostics were unsuccessful. optics now utilize dichroic mirror initially split at nearly 99% transmission or reflectance for below above 550 nm. This allows Dα without degrading plasma wavelengths nm (to Dβ, Dγ, W–I, C-III, etc.). Additional optimization of optical...
The National Spherical Torus Experiment (NSTX) has explored the effects of shaping on plasma performance as determined by many diverse topics including stability global magnetohydrodynamic (MHD) modes (e.g., ideal external kinks and resistive wall modes), edge localized (ELMs), bootstrap current drive, divertor flux expansion, heat transport. Improved capability been crucial to achieving βt∼40%. Precise shape control achieved NSTX using real-time equilibrium reconstruction. simultaneously...
Analysis with the SOLPS code suite (Schneider R. et al 1992 J. Nucl. Mater. 196 810; Wiesen S. 2015 463 480–4; Bonnin X. 2016 Plasma Fusion Res. 11 1403102) explains differences in pedestal structure associated different ion drift directions DIII-D. Core transport models predict that fusion power scales roughly as square of pressure at top pedestal, so understanding effects determine steady-state operational scenarios is important to help project developed DIII-D ITER and other devices. Both...