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(EX/W-4) Physics of Electron Cyclotron Current Drive on DIII-D

C.C. Petty1), R. Prater1), T.C. Luce1), R.A. Ellis2), R.W. Harvey3), J.E. Kinsey4), L.L. Lao1), J. Lohr1), M.A. Makowski5), K.L. Wong2)
1) General Atomics, San Diego, USA
2) Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA
3) CompX, Del Mar, California, USA
4) Lehigh University, Bethelehem, Pennsylvania, USA
5) Lawrence Livermore National Laboratory, Livermore, California, USA

Abstract.  Recent experiments on DIII-D have focused on determining the effect of trapped particles on the electron cyclotron current drive (ECCD) efficiency. Using measurements from the motional Stark effect diagnostic, driven currents as small as 1% of the total plasma current can be accurately measured, allowing the physics of ECCD to be explored in unprecedented detail. The ECCD efficiency was measured for co, counter, and radial injection, with little current drive observed for the latter case as expected. The measured ECCD efficiency increased with increasing electron beta, which can be explained due to reduced electron trapping effects. The beta dependence was stronger for more off-axis ECCD since the trapped particle fraction increased with radius. Owing to this favorable beta dependence, high ECCD efficiencies are expected in advanced tokamak plasmas. The measured ECCD has been compared to both the linear theory (TORAY-GA) as well as a Fokker-Planck model (CQL3D). The experimental ECCD was found to be in better agreement with the more complete Fokker-Planck calculation. *Supported by U.S. DOE Contracts DE-AC03-99ER55463, W-7405-ENG-48, Grants DE-FG03-99ER54541, DE-FG02-92ER54141.

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IAEA 2003