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3 results on '"null M.H. Redi"'

1. Characterization of Fast Ion Absorption of the High Harmonic Fast Wave in the National Spherical Torus Experiment

Author

null A.L. Rosenberg, null J.E. Menard, null J.R. Wilson, null S. Medle, null C.K. Phillips, null R. Andre, null D.S. Darro, null R.J. Dumont, null B.P. LeBlanc, null M.H. Redi, null T.K. Mau, null E. F. Jaeger, null P.M. Ryan, null D.W. Swain, null R.W. Harvey, null J. Egedal, and null the NSTX Team

Subjects
Physics, education.field_of_study, Thomson scattering, Population, Neutron detection, Torus, Neutron, Atomic physics, Absorption (electromagnetic radiation), education, Neutral particle, Ion
Abstract

Ion absorption of the high harmonic fast wave in a spherical torus is of critical importance to assessing the viability of the wave as a means of heating and driving current. Analysis of recent National Spherical Torus Experiment (NSTX) shots has revealed that under some conditions when neutral beam and radio-frequency (RF) power are injected into the plasma simultaneously, a fast ion population with energy above the beam injection energy is sustained by the wave. In agreement with modeling, these experiments find the RF-induced fast ion tail strength and neutron rate at lower B-fields to be less enhanced, likely due to a larger beta profile, which promotes greater off-axis absorption where the fast ion population is small. Ion loss codes find the increased loss fraction with decreased B insufficient to account for the changes in tail strength, providing further evidence that this is an RF interaction effect. Though greater ion absorption is predicted with lower k(sub)||, surprisingly little variation in the tail was observed, along with a small neutron rate enhancement with higher k(sub)||. Data from the neutral particle analyzer, neutron detectors, X-ray crystal spectrometer, and Thomson scattering is presented, along with results from the TRANSP transport analysis code, ray-tracing codes HPRT and CURRAY, full-wave code and AORSA, quasi-linear code CQL3D, and ion loss codes EIGOL and CONBEAM.

Published
2003

2. Results of NSTX Heating Experiments

Author

null D. Mueller, null M. Ono, null M.G. Bell, null R.E. Bell, null M. Bitter, null C. Bourdelle, null D.S. Darrow, null P.C. Efthimion, null E.D. Fredrickson, null D.A Gates, null R.J. Goldston, null L.R. Grisham, null R.J. Hawryluk, null K.W. Hill, null J.C. Hosea, null S.C. Jardin, null H. Ji, null S.M. Kaye, null R. Kaita, null H.W. Kugel, null D.W. Johnson, null B.P. LeBlanc, null R. Majeski, null E. Mazzucato, null S.S. Medley, null J.E. Menard, null H.K. Park, null S.F. Paul, null C.K. Phillips, null M.H. Redi, null A.L. Rosenberg, null C.H. Skinner, null V.A. Soukhanovskii, null B. Stratton, null E.J Synakowski, null G. Taylor, null J.R. Wilson, null S.J. Zweben, null Y-K.M. Peng, null R. Barry, null T. Bigelow, null C.E. Bush, null M. Carter, null R. Maingi, null M. Menon, null P.M. Ryan, null D.W. Swain, null J. Wilgen, and null 37 additional authors

Subjects
Physics, Toroid, Physics::Plasma Physics, Beta (plasma physics), Torus, Plasma, Magnetohydrodynamics, Atomic physics, Scaling, Neutral beam injection, Bootstrap current
Abstract

The National Spherical Torus Experiment (NSTX) at Princeton is designed to assess the potential of the low-aspect-ratio spherical torus concept for magnetic plasma confinement. The plasma has been heated by up to 5 MW of neutral beam injection, NBI, at an injection energy of 90 keV and up to 6 MW of high harmonic fast wave, HHFW, at 30 MHz. NSTX has achieved beta T of 32%. A variety of MHD phenomena have been observed to limit eta. NSTX has now begun addressing E scaling, eta limits and current drive issues. During the NBI heating experiments, a broad Ti profile with Ti up to 2 keV, Ti > Te and a large toroidal rotation. Transport analysis suggests that the impurity ions have diffusivities approaching neoclassical. For L-Mode plasmas, E is up to two times the ITER-89P L-Mode scaling and exceeds the ITER-98pby2 H-Mode scaling in some cases. Transitions to H-Mode have been observed which result in an approximate doubling of tE. after the transition in some conditions. During HH FW heating, Te > Ti and Te up to 3.5 keV were observed. Current drive has been studied using coaxial helicity injection (CHI), which has produced 390 kA of toroidal current and HHFW, which has produced H-modes with significant bootstrap current fraction at low Ip, high q and high{sub etap}.

Published
2002

3. MHD Stability Calculations of High-Beta Quasi-Axisymmetric Stellarators

Author

null C. Kessel, null G.Y. Fu, null L.P. Ku, null M.H. Redi, null N. Pomphrey, and null et al

Subjects
Physics, Rotational symmetry, Plasma, Mechanics, Kink instability, Bootstrap current, Physics::Fluid Dynamics, Classical mechanics, Physics::Plasma Physics, Beta (plasma physics), Astrophysics::Solar and Stellar Astrophysics, Magnetohydrodynamics, Axial symmetry, Plasma stability, Astrophysics::Galaxy Astrophysics
Abstract

The MHD stability of quasi-axisymmetric compact stellarators is investigated. It is shown that bootstrap current driven external kink modes can be stabilized by a combination of edge magnetic shear and appropriate 3D plasma boundary shaping while maintaining good quasi-axisymmetry. The results demonstrate that there exists a new class of stellarators with quasi-axisymmetry, large bootstrap current, high MHD beta limit, and compact size.

Published
1999

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