Description: To support the Advanced Tokamak (AT) operating regimes in the DIII-D tokamak, methods need to be developed to control the current and pressure profiles across the plasma discharge. In particular, AT plasmas require substantial off-axis current in contrast to normal tokamak discharges where the current peaks on-axis. An effort is under way to use Electron Cyclotron Current Drive (ECCD) as a method of sustaining the off-axis current in AT plasmas. The first step in this campaign is the installation of three megawatts of electron cyclotron heating power. This involves the installation of three rf systems operating at 110 GHz, the second harmonic resonance frequency on DIII-D, with each system generating nominally 1 MW. The three systems will use one GYCOM (Russian) gyrotron and two CPI (formerly Varian) gyrotrons, all with windowless evacuated corrugated low loss transmission lines. The first two of three 1 MW ECH systems is operating routinely at DIII-D with injected power at 110 GHz of approximately 1.5 MW with good power accountability. Transport experiments using modulated ECH have been performed confirming the power deposition location. On-axis and off-axis current drive experiments have been successfully performed with on-axis ECCD currents of 170 kA being observed.
Date: July 1998
Creator: Callis, R. W.; Lohr, J.; Ponce, D.; Harris, T. E.; O`Neill, R. C.; Remsen, D.B. et al.
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