PPPL-3590 is available in <a href="PPPL-3590.pdf">pdf</a> or 
<a href="PPPL-3590.ps">postscript</a> formats.

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<b>High Performance Plasmas on the National Spherical Torus Experiment</b>
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<b>Authors:</b> D.A. Gates, M.G. Bell, R.E. Bell, J. Bialek, T. Bigelow, M. Bitter, P. Bonolid, D. Darrow, P. Efthimion, J. Ferron, E. Fredrickson, L. Grisham, J. Hosea, D. Johnson, R. Kaita, S. Kaye, S. Kubota, H. Kugel, B. LeBlanc, R. Maingi, J. Manickam, T.K. Mau, R.J. Maqueda, E. Mazzucato, J. Menard, D. Mueller, B. Nelson, N. Nishino, M. Ono, F. Paoletti, S. Paul, Y-K.M. Peng, C.K. Phillips, R. Raman, P. Ryan, S.A. Sabbagh, M. Schaffer, C.H. Skinner, D. Stutman, D. Swain, E. Synakowski, Y. Takase, J. Wilgen, J.R. Wilson, W. Zhu, S. Zweben, A. Bers, M. Carter, B. Deng, C. Domier, E. Doyle,  M. Finkenthal, K. Hill, T. Jarboe, S. Jardin, H. Ji, L. Lao, K.C. Lee, N. Luhmann, R. Majeski, H. Park, T. Peebles, R.I. Pinsker, G. Porter, A. Ram, M. Rensink, T. Rognlien, D. Stotler, B. Stratton, G. Taylor, W. Wampler, G.A. Wurden, X.Q. Xu, L. Zeng, and the NSTX Team
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<b>Date of PPPL Report:</b> July 2001
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<b>Presented at:</b> the 13th International Pulsed Power Plasma Science Conference and the 28th IEEE International Conference on Plasma Science, Las Vegas, Nevada, June 18-22, 2001.
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The National Spherical Torus Experiment has produced toroidal plasmas at low aspect ratio (A = R/a = 0.86m/0.68m <FONT FACE = "symbol">~</FONT FACE = "symbol">1.3, where R is the major radius and a is the minor radius of the torus) with plasma currents of 1.4 MA. The rapid development of the machine has led to very exciting physics results during the first full year of physics operation. Pulse lengths in excess of 0.5 s have been obtained with inductive current drive. Up to 4 MW of High Harmonic Fast Wave (HHFW) heating power has been applied with 6 MW planned. Using only 2 MW of HHFW heating power clear evidence of electron heating is seen with HHFW, as observed by the multi-point Thomson scattering diagnostic. A nonnductive current drive concept known as Coaxial Helicity Injection (CHI) has driven 260 kA of toroidal current. Neutral beam heating power of 5 MW has been injected. Plasmas with <FONT FACE = "symbol">b</FONT FACE = "symbol"><sub>t</sub> (= 2<FONT FACE = "symbol">m<sub>0</sub></FONT>&#60p&#62/B<sup>2</sup> = a measure of magnetic confinement efficiency) of 22% have been achieved, as calculated using the EFIT equilibrium reconstruction code. <FONT FACE = "symbol">b </FONT>-limiting phenomena have been observed, and the maximum<FONT FACE = "symbol"> b</FONT><sub>t</sub> scales with I<sub>p</sub>/aB<sub>t</sub>. High frequency (>MHz) magnetic fluctuations have been observed. H-mode plasmas are observed with confinement times of >100 ms. Beam-heated plasmas show energy confinement times in excess of those predicted by empirical scaling expressions. Ion temperatures in excess of 2.0 keV have been measured, and power balance suggests that the power loss from the ions to the electrons may exceed the calculated classical input power to the ions.



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