PPPL-3700 is available in <a href="PPPL-3700.pdf">pdf</a> format (296 KB).

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<b>Operational Regimes of the National Spherical Torus Experiment</b>
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<b>Authors:</b> D. Mueller, M.G. Bell, R.E. Bell, M. Bitter, T. Bigelow, P. Bonoli, M. Carter, J. Ferron, E. Fredrickson, D. Gates, L. Grisham, J.C. Hosea, D. Johnson, R. Kaita, S.M. Kaye, H. Kugel, B.P. LeBlanc, R. Maingi, R. Majeski, R. Maqueda, J. Menard, M. Ono, F. Paoletti, S. Paul, C.K. Phillips, R. Pinsker, R. Raman, S.A. Sabbagh, C.H. Skinner, V.A. Soukhanovskii, D. Stutman, D. Swain, Y. Takase, J. Wilgen, J.R. Wilson, G.A. Wurden, and S. Zweben 
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<b>Date of PPPL Report:</b> June 2002
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<b>Presented at:</b> the 28th EPS Conference on Plasma Physics and Controlled Fusion, June 18-22, 2001. Papers to be published in a special issue of Plasma Physics and Controlled Fusion.</p>


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The National Spherical Torus Experiment (NSTX) is a proof-of-principle experiment designed to study the physics of Spherical Tori (ST), i.e., low-aspect-ratio toroidal plasmas. Important issues for ST research are whether the high-beta stability and reduced transport theoretically predicted for this configuration can be realized experimentally.  In NSTX, the commissioning of a digital real-time plasma control system, the provision of flexible heating systems, and the application of wall conditioning techniques were instrumental in achieving routine operation with good confinement. NSTX has produced plasmas with R/a ~ 0.85 m/0.68 m, A ~ 1.25, I<sub>p</sub> less than or equal to 1.1 MA, B<sub>T</sub> = 0.3-0.45 T, <font face = "symbol">k</font face = "symbol"> less than or equal to 2.2, <font face = "symbol">d</font face = "symbol"> less than or equal to 0.5, with auxiliary heating by up to 4 MW of High Harmonic Fast Waves, and 5 MW of 80 keV D<sup>0</sup> Neutral Beam Injection (NBI). The energy confinement time in plasmas heated by NBI has exceeded 100 ms and a toroidal beta (<font face = "symbol">b</font face = "symbol"><sub>T</sub> = 2<font face = "symbol">m</font face = "symbol"><sub>0</sub>&#60;p&#62;/B<sub>T0</sub><sup>2</sup>, where B<sub>T0</sub> is the central vacuum toroidal magnetic field) up to 22&#37; has been achieved. HHFW power of 2.3 MW has increased the electron temperature from an initial 0.4 keV to 0.9 keV both with and without producing a significant density rise in the plasma. The early application of both NBI and HHFW heating has slowed the penetration of the inductively produced plasma current, modifying the current profile and, thereby, the observed MHD stability.




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