A5058355047- Magnetic confinement fusion research
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Semiconductor materials and devices
- Advanced Data Storage Technologies
- Earthquake Detection and Analysis
- Metal and Thin Film Mechanics
- Silicon Carbide Semiconductor Technologies
- Seismic Waves and Analysis
- Silicon and Solar Cell Technologies
- Atomic and Subatomic Physics Research
- Geophysical Methods and Applications
- Thin-Film Transistor Technologies
- Iterative Learning Control Systems
- Solar and Space Plasma Dynamics
- Diamond and Carbon-based Materials Research
- Particle Accelerators and Free-Electron Lasers
- Seismology and Earthquake Studies
- Magnetic Field Sensors Techniques
- Geophysics and Sensor Technology
- Physics of Superconductivity and Magnetism
General Atomics (United States)
2011-2024
Northwestern University
2024
University of Utah
2023
DIII-D National Fusion Facility
1999-2015
San Jose State University
2014-2015
Ames Research Center
2014-2015
Search for Extraterrestrial Intelligence
2014-2015
Fusion (United States)
2015
Culham Centre for Fusion Energy
2005
Princeton Plasma Physics Laboratory
2005
The development of techniques for neoclassical tearing mode (NTM) suppression or avoidance is crucial successful high beta/high confinement tokamaks. Neoclassical modes are islands destabilized and maintained by a helically perturbed bootstrap current represent significant limit to performance at higher poloidal beta. confinement-degrading can be reduced completely suppressed precisely replacing the “missing” in island O-point interfering with fundamental helical harmonic pressure....
New experiments on JET, COMPASS-D and DIII-D have identified the critical scalings of error field sensitivity harmonic content effects, enabling predictions to be made requirements for larger devices such as ITER. Thresholds are lowest at low density, a regime proposed H mode access Results suggest moderate (δB/B ≈ 10-4) ITER, comparable with size its intrinsic error, although there uncertainties in scaling behaviour. Other studies show that sideband harmonics (2, 1) component play an...
Otherwise stable discharges can become nonlinearly unstable to disruptive locked modes when subjected a resonant m=2, n=1 error field from irregular poloidal coils, as in DIII-D [Nucl. Fusion 31, 875 (1991)], or magnetic perturbation coils COMPASS-C [Proceedings of the 18th European Conference on Controlled and Plasma Physics, Berlin (EPS, Petit-Lancy, Switzerland, 1991), Vol. 15C, Part II, p. 61]. Experiments Ohmically heated deuterium with q≊3.5, n̄ ≊ 2 × 1019 m−3 BT 1.2 T show that much...
Locked n = 1 tearing modes are observed over a wide range of parameter space in DIII-D and other tokamaks. Much the difficulty with low density operation is attributed to locked they also as precursors limit disruptions. From observations consistent mode toroidal phase, it appears that locking small field perturbation caused by slight irregularities location one or more vertical coils respect coil. By intentionally producing an external coil, was possible influence onset q, plasmas. The...
Using newly developed techniques and improved diagnostics, rotating wall-stabilized discharges have been maintained in the DIII-D tokamak for 30 characteristic resistive wall decay times---significantly longer than was previously achieved. The terminating mode has directly identified using internal fluctuation its correlation with slowdown plasma rotation is established.
The authors' data indicate that the L-mode to H-mode transition in DIII-D tokamak is associated with sudden reduction anomalous, fluctuation-connected transport across outer midplane of plasma. In addition edge density and magnetic fluctuations observed at transition, radial electric field becomes more negative after transition. They have determined scaling power threshold various plasma parameters; roughly linear increase toroidal are particularly significant. Control ELM frequency duration...
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...
Sustained stabilization of the n=1 kink mode by plasma rotation at beta approaching twice stability limit calculated without a wall has been achieved in DIII-D combination error field reduction and sufficient drive. Previous experiments have transiently exceeded no-wall limit. However, demonstration sustained rotational remained elusive because found to decay whenever is stabilized. Recent theory [Boozer, Phys. Rev. Lett. 86, 5059 (2001)] predicts resonant response fields marginal low-n...
Values of the normalized plasma pressure up to twice free-boundary stability limit predicted by ideal magnetohydrodynamic (MHD) theory have been sustained in DIII-D tokamak. Long-wavelength modes are stabilized resistive wall and rapid toroidal rotation. High rotation speed is maintained minimization nonaxisymmetric magnetic fields, overcoming a long-standing impediment [E. J. Strait, Phys. Rev. Lett. 74, 2483 (1995)]]. The ideal-MHD calculated with an observed as operational pressure.
Fusion power has been increased by a factor of 3 in DIII-D tailoring the pressure profile to avoid kink instability $H$-mode plasmas. The resulting plasmas are found have neoclassical ion confinement. This reduction transport losses beam-heated with negative central shear is correlated dramatic density fluctuations. Improved magnetohydrodynamic stability achieved controlling plasma width. In deuterium highest gain $Q$ (the ratio fusion input power), was 0.0015, corresponding an equivalent...
A set of twelve coils for stability control has recently been installed inside the DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] vacuum vessel, offering faster time response and a wider range applied mode spectra than previous external coils. Stabilization n=1 ideal kink is crucial to many high beta, steady-state tokamak scenarios. resistive wall converts slowly growing (RWM). With feedback-controlled error field correction, rotational stabilization RWM sustained more 2.5 s. Using...
A comprehensive set of L–H transition experiments has been performed on DIII-D to determine the requirements for access H-mode plasmas in ITER's first (non-nuclear) operational phase with H and He second (activated) D plasmas. The power threshold, P TH , was evaluated different configurations auxiliary heating methods main ion species. Helium have significantly higher than deuterium at low densities all schemes, but similar as high except H-neutral beam injection-heated discharges, which are...
A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch ideal magnetohydrodynamic (MHD) kink under influence stabilizing wall, on DIII-D tokamak device [Plasma Phys. Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159; Plasmas 1, 1415 (1994)]. The RWM was successfully suppressed and high beta duration above no-wall limit extended more than 50 times flux diffusion time. It...
Using resonant magnetic perturbations with toroidal mode number n = 3, we have produced H-mode discharges without edge localized modes (ELMs) which run constant density and radiated power for periods up to about 2550 ms (17 energy confinement times). These ELM suppression results are achieved at pedestal collisionalities close those desired next step burning plasma experiments such as ITER provide a means of eliminating the rapid erosion divertor components in machines could be caused by...
Recent DIII-D experiments have shown that the growth of n = 1 resistive wall mode (RWM) can be influenced by an external magnetic field applied in closed loop feedback using a six element error correction coil (C coil). The RWM constitutes primary limitation to normalized beta recent advanced tokamak plasma experiments. toroidal rotation plasmas does not seem sufficient completely suppress RWM: very slowly growing (growth rate γ<<1/τw) or saturated is often observed at above no limit and...
Error field optimization on DIII-D tokamak (Luxon J.L. 2002 Nucl. Fusion 42 814) plasma discharges has routinely been done for the last ten years with use of external `n = 1 coil' or `C-coil'. The optimum level correction coil current is determined by ability to avoid locked mode instability and access previously unstable parameter space at low densities. typically toroidal poloidal numbers n m 2, respectively, it this component that initially phase. Realization importance nearby components...
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...
Tokamak discharges using the expanded boundary divertor in DIII-D device exhibit H-mode confinement. With neutral-beam power up to 6 MW, energy confinement remains comparable Ohmic value at a plasma current of 1 MA. Confinement is also independent density and toroidal field. increases with current, but exact functional dependence is, as yet, uncertain. These results show that H mode can be achieved reactor-compatible open configuration.
Discharges which can satisfy the high gain goals of burning plasma experiments have been demonstrated in DIII-D tokamak under stationary conditions at relatively low current (q95>4). A figure merit for fusion (βNH89/q952) has maintained values corresponding to Q = 10 operation a >6 s or 36τE and 2τR. The key element is relaxation profile state with qmin>1. In absence sawteeth fishbones, stable achieved up estimated no-wall β limit. Feedback control energy content particle inventory allow...
The stability of the resistive-wall mode (RWM) in DIII-D plasmas above conventional pressure limit, where toroidal plasma rotation order a few percent Alfv\'en velocity is sufficient to stabilize $n=1$ RWM, has been probed using technique active MHD spectroscopy at frequencies Hertz. measured frequency spectrum response externally applied rotating resonant magnetic fields well described by single-mode approach and provides an absolute measurement damping rate natural stable RWM.
Internal coils, 'I-Coils', were installed inside the vacuum vessel of DIII–D device to generate non-axisymmetric magnetic fields act directly on plasma. These are predicted stabilize resistive wall mode (RWM) branch long-wavelength external kink with plasma beta close ideal limit. Feedback using these I-Coils was found be more effective as compared coils located outside vessel. Locating allows for a faster response and coil geometry also better coupling helical structure. Initial results...
Recent DIII–D experiments show that ideal kink-modes can be stabilized at high beta by a resistive wall, with sufficient plasma rotation. However, the resonant response to static magnetic field asymmetries marginally stable wall mode lead strong damping of Careful reduction such has allowed plasmas well above MHD no-wall limit, and approaching ideal-wall sustained for durations exceeding 1 s. Feedback control improve stability direct stabilization or reducing asymmetry. Assisted rotation,...
Experimental results in the DIII-D tokamak demonstrate that discharges are more robust with regard to external nonaxisymmetric error fields as plasma fluid rotation is increased, but sensitive beta increased. In a series of discharges, and varied by number type ('tangential' and/or 'perpendicular') neutral beams. For each discharge, once kinetic energy equilibrated, an coil used slowly increase low m,n=1 resonant, static field until locked mode instability occurs. A larger critical needed...
Small non-axisymmetric magnetic fields are known to cause serious loss of stability in tokamaks, leading confinement and abrupt termination plasma current (disruptions). The best examples the locked mode resistive wall mode. Understanding underlying field anomalies (departures hardware-related from ideal toroidal poloidal on a single axis) interaction with them is crucial tokamak development. Results both experiments (Scoville J.T. La Haye R.J. 2003 Nucl. Fusion 43 250) (Garofalo A.M.,...
Rapid plasma toroidal rotation, sufficient for stabilization of the n = 1 resistive wall mode, can be sustained by improving axisymmetry magnetic field geometry DIII-D. The required symmetrization is determined experimentally both optimizing currents in external correction coils with respect to and use feedback detect minimize response non-axisymmetric fields as β increases. Both methods point an intrinsic ∼7 G (0.03% field), m/n 2/1 resonant helical at q 2 surface cause rotation slowdown...