Current drive with fast waves, electron cyclotron waves, and neutral injection in the DIII-D tokamak

Current drive experiments have been performed on the DIII-D tokamak using fast waves, electron cyclotron waves, and neutral injection. Fast wave experiments were performed using a 4-strap antenna with 1 MW of power at 60 MHz. These experiments showed effective heating of electrons, with a global heating efficiency equivalent to that of neutral injection even when the single pass damping was calculated to be as small as 5%. The damping was probably due to the effect of multiple passes of the wave through the plasma. Fast wave current drive experiments were performed with a toroidally directional phasing of the antenna straps. Currents driven by fast wave current drive (FWCD) in the direction of the main plasma current of up to 100 kA were found, not including a calculated 40 kA of bootstrap current. Experiments with FWCD in the counter current direction showed little current drive. In both cases, changes in the sawtooth behavior and the internal inductance qualitatively support the measurement of FWCD. Experiments on electron cyclotron current drive have shown that 100 kA of current can be driven by 1 MW of power at 60 GHz. Calculation with a Fokker-Planck code show that electron cyclotron current drive (ECCD) can be well predicted when the effects of electron trapping and of the residual electric field are included.

[1]  Nathaniel J. Fisch,et al.  Theory of current-drive in plasmas , 1987 .

[2]  F. Wagner,et al.  Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak , 1982 .

[3]  Hoffman,et al.  Absorption of fast waves by electrons on the DIII-D tokamak. , 1992, Physical review letters.

[4]  J. Ongena,et al.  Ion cyclotron resonance heating of a tokamak plasma using an antenna without a Faraday shield , 1991 .

[5]  Yamazaki,et al.  Electron cyclotron current drive at the second harmonic in the WT-3 tokamak. , 1988, Physical review letters.

[6]  Snider,et al.  Electron-cyclotron-current-drive experiments in the DIII-D tokamak. , 1992, Physical review. A, Atomic, molecular, and optical physics.

[7]  Lao,et al.  Neutral-beam current-driven high-poloidal-beta operation of the DIII-D tokamak. , 1988, Physical review letters.

[8]  P. T. Bonoli,et al.  Numerical modelling of lower hybrid RF heating and current drive experiments in the Alcator C tokamak , 1988 .

[9]  Lao,et al.  Regime of very high confinement in the boronized DIII-D tokamak. , 1991, Physical review letters.

[10]  L. L. Lao,et al.  Very high confinement discharges in DIII‐D after boronization , 1992 .

[11]  Bell,et al.  Bootstrap current in TFTR. , 1988, Physical review letters.

[12]  J. Cordey,et al.  Observation of a plasma current driven by rf waves at the electron cyclotron resonance in the Culham Levitron , 1982 .

[13]  M. Porkolab,et al.  Theory of fast wave current drive for tokamak plasmas , 1989 .

[14]  Allen H. Boozer,et al.  Creating an asymmetric plasma resistivity with waves , 1980 .

[15]  L. Lao,et al.  Reconstruction of current profile parameters and plasma shapes in tokamaks , 1985 .

[16]  J. Ongena,et al.  Comparison of the performance of ICRF antennas with and without Faraday shield on TEXTOR , 1992 .