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1) General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA 2) Lawrence Livermore National Laboratory, Livermore, California 94550, USA 3) Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 4) Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA 5) EPFL CRPP-Lausanne, Lausanne, Switzerland 6) Euratom/UKAEA(More)
One of the goals of the National Spherical Torus Experiment (NSTX) is to investigate the physics of global mode stabilization in a low aspect ratio device. NSTX has a major radius R0 = 0.86 m, a midplane half-width of 0.7 m, and an on-axis vacuum toroidal field B0 0.6 T and has reached a plasma current Ip = 1.5 MA. Experiments have established the(More)
The plasma material interface in Demo will be more challenging than that in ITER, due to requirements for approximately four times higher heat flux from the plasma and approximately five times higher average duty factor. The scientific and technological solutions employed in ITER may not extrapolate to Demo. The key questions to be resolved for Demo and the(More)
A novel mechanism that directly transfers energy from super-Alfvénic energetic ions to thermal ions in high- beta plasmas is described. The mechanism involves the excitation of compressional Alfvén eigenmodes in the frequency range with omega less than approximetely omega(ci). The broadband turbulence resulting from the large number of excited modes causes(More)
New observations of the formation and dynamics of long-lived impurity-induced helical "snake" modes in tokamak plasmas have recently been carried out on Alcator C-Mod. The snakes form as an asymmetry in the impurity ion density that undergoes a seamless transition from a small helically displaced density to a large crescent-shaped helical structure inside(More)
A suite of novel high-resolution spectroscopic imaging diagnostics has facilitated the identification and localization of molybdenum impurities as the main species during the formation and lifetime of m = 1 impurity-induced snake-modes on Alcator C-Mod. Such measurements made it possible to infer, for the first time, the perturbed radiated power density(More)
A motional Stark effect diagnostic has been utilized to reconstruct the parallel current density profile in a spherical-torus plasma for the first time. The measured current profile compares favorably with neoclassical theory when no large-scale magnetohydrodynamic instabilities are present in the plasma. However, a current profile anomaly is observed(More)
A model-based feedback system is presented enabling the simultaneous control of the stored energy through βn and the toroidal rotation profile of the plasma in National Spherical Torus eXperiment Upgrade device. Actuation is obtained using the momentum from six injected neutral beams and the neoclassical toroidal viscosity generated by applying(More)