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Effects of Flow and Flow Shear in NSTX
| Author: | Menard J.E. |
| Coauthor: | M.G. Bell, R.E. Bell, D.A. Gates, S.M. Kaye, B.P. LeBlanc, W. Park, S.A. Sabbagh, D. Stutman |
| Institution : | Princeton Plasma Physics Lab |
| Abstract text: | NSTX has achieved both high toroidal beta up to 35%, and high normalized beta approaching 7. In the highest toroidal beta discharges obtained at high I/aB > 6MA/mT, the central safety factor is typically near 1 and the limiting modes are most often n=1 pressure-driven internal kink instabilities. However, in the highest-beta discharges of NSTX with normalized beta = 5-6, these instabilities can saturate or even decay in amplitude for beta values well above the no-wall limit at mode onset. An important element in this saturation appears to be the high toroidal rotation velocity and strong rotational shear in NSTX plasmas with neutral beam heating. Stability analysis with the MARS and M3D codes indicates that growth times as long as 5ms are possible, and this relatively slow growth rate may contribute to reducing the deleterious impact of the mode on confinement. However, M3D simulations carried into the non-linear phase find that the flow profile typically flattens during the reconnection process allowing complete magnetic reconnection to occur. Similar flattening is observed in the experiment, yet for the highest-beta cases in NSTX, complete reconnection is apparently avoided. |
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