The National Spherical Torus Experiment (NSTX) Research Program and Progress Towards High Beta, Long Pulse Operating Scenarios
Authors: E.J. Synakowski, M.G. Bell, R.E. Bell, T. Bigelow, M. Bitter, W. Blanchard, J. Boedo, C. Bourdelle, C. Bush, D.S. Darrow, P.C. Efthimion, E.D. Fredrickson, D.A. Gates, M. Gilmore, L.R. Grisham, J.C. Hosea, D.W. Johnson, R. Kaita, S.M. Kaye, S. Kubota, H.W. Kugel, B.P. LeBlanc, K. Lee, R. Maingi, J. Manickam, R. Maqueda, E. Mazzucato, S.S. Medley, J. Menard, D. Mueller, B.A. Nelson, C. Neumeyer, M. Ono, F. Paoletti, H.K. Park, S.F. Paul, Y.-K.M. Peng, C.K. Phillips, S. Ramakrishnan, R. Raman, A.L. Roquemore, A. Rosenberg, P.M. Ryan, S.A. Sabbagh, C.H. Skinner, V. Soukhanovskii, T. Stevenson, D. Stutman, D.W. Swain, G. Taylor, A. Von Halle, J. Wilgen, M. Williams, J.R. Wilson, X. Xu, S.J. Zweben, R. Akers, R.E. Barry, P. Beiersdorfer, J.M. Bialek, B. Blagojevic, P.T. Bonoli, R. Budny, M.D. Carter, J. Chrzanowski, W. Davis, B. Deng, E.J. Doyle, L. Dudek, J. Egedal, R. Ellis, J.R. Ferron, M. Finkenthal, J. Foley, E. Fredd, A. Glasser, T. Gibney, R.J. Goldston, R. Harvey, R.E. Hatcher, R.J. Hawryluk, W. Heidbrink, K.W. Hill, W. Houlberg, T.R. Jarboe, S.C. Jardin, H. Ji, M. Kalish, J. Lawrance, L.L. Lao, K.C. Lee, F.M. Levinton, N.C. Luhmann, R. Majeski, R. Marsala, D. Mastravito, T.K. Mau, B. McCormack, M.M. Menon, O. Mitarai, M. Nagata, N. Nishino, M. Okabayashi, G. Oliaro, D. Pacella, R. Parsells, T. Peebles, B. Peneflor, D. Piglowski, R. Pinsker, G.D. Porter, A.K. Ram, M. Redi, M. Rensink, G. Rewoldt, J. Robinson, P. Roney, M. Schaffer, K. Shaing, S. Shiraiwa, P. Sichta, D. Stotler, B.C. Stratton, Y. Takase, X. Tang, R. Vero, W.R. Wampler, G.A. Wurden, X.Q. Xu, J.G. Yang, L. Zeng, and W. Zhu
Date of PPPL Report: October 2002
Presented at: the Nineteenth IAEA Fusion Energy Conference in Lyon, France, October 14-19, 2002
Published in: Nucl. Fusion 43 (December 2003) 1653-1664
A major research goal of the National Spherical Torus Experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed over the last two years, including neutral beam (up to 7 MW) and high harmonic fast wave heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with <bT> up to 35%. Normalized beta values often exceed the no wall limit, and studies suggest that passive wall mode stabilization is enabling this for broad pressure profiles characteristic of H-mode plasmas.
The viability of long, high bootstrap current fraction operations has been established for ELMing H-mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fueling are likely contributing to a reduction in H-mode power thresholds. Electron thermal conduction is the dominant thermal loss channel in auxiliary-heated plasmas examined thus far.
High harmonic fast wave (HHFW) effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is by comparing of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. A peak heat flux of 10 MW/m2 has been measured in the H-mode, with large asymmetries in the power deposition being observed between the inner and outer strike points. Noninductive plasma start-up studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.