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(EX8/1) Highly Localized Electron Cyclotron Heating and Current Drive and Improved Core Transport in DIII-D

R. Prater1), M. E. Austin2), S. Bernabei3), K. H. Burrell1), R. W. Callis1), W. P. Cary1), J. S. deGrassie1), C. Fuchs4), C. M. Greenfield1), Y. Gorelov1), R. W. Harvey5), J. C. Hosea3), A. Isayama6), J. Jayakumar7), R. J. La Haye1), L. L. Lao1), R. A. Legg1), Y. R. Lin-Liu1), J. Lohr1), T. C. Luce1), M. A. Makowski7), C. C. Petty1), R. I. Pinsker1), D. Ponce1), S. G. E. Pronko1), S. Raftopoulos3), E. J. Strait1), and K. L. Wong3)
1) General Atomics, San Diego, California USA
2) University of Texas-Austin, Austin, Texas USA
3) Princeton Plasma Physics Laboratory, Princeton, New Jersey USA
4) Max Planck Institute fur Plasmaphysik, Garching, Federal Republic of Germany
5) CompX, Del Mar, California USA
6) Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, IbaRaki-ken, Japan
7) Lawrence Livermore National Laboratory, Livermore, California USA

Abstract.  Electron cyclotron heating (ECH) and current drive (ECCD) are widely recognized as methods of depositing highly localized power and current in a plasma, based on calculations of wave absorption. The experiments reported here demonstrate through direct analysis of the poloidal field pitch angles measured by the motional Stark effect diagnostic that ECCD can be as localized as theory predicts. This very narrow profile of driven current has been verified even for ELMing H-mode discharges, and observation of full stabilization of neoclassical tearing modes tends to corroborate the calculations of ECCD far off axis even in plasmas with large MHD activity present. The electron heating by EC waves can have dramatic effects on the plasma, creating high central electron temperatures even with very modest ECH power and generating a strong transport barrier in the electron fluid in discharges with strongly reversed central magnetic shear. The electron diffusivity is much smaller than ion neoclassical diffusivity in the narrow barrier which develops just outside the heating location.

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IAEA 2001