Abstract
The ECH/ECCD system on DIII-D benefits from protective measures set in place in order to reduce the likelihood of refracted rf power potentially reaching sensitive areas of the vacuum vessel or diagnostics. In addition to installation of shutters and valves, a density interlock prevents the rf injection into overdense plasma. Visible light cameras, light detectors, Langmuir probes and reflected power sniffers complete the array of diagnostics used for EC protection. Besides the 110 GHz gyrotron, a new higher frequency gyrotron at 117.5 GHz was added to the system during the 2018 experimental campaign. The new frequency allows for operation at higher plasma density and with better current drive efficiency at higher magnetic field than for 110 GHz. Injection in O-mode was used in some of the high density plasmas where the X-mode is refracted.
Highlights
Recent years have seen an increase in the large variety of experiments involving injection of 110 GHz EC power into the DIII-D tokamak plasma, with operational regimes approaching or exceeding the density limits for X-mode second harmonic resonance absorption
In addition to operational limits for the line averaged plasma density, an array of diagnostics is used for EC protection, including visible light cameras which monitor the light in the launchers, light detectors, and reflected power sniffers, and Langmuir probes
A new gyrotron operating at a higher frequency of 117.5 GHz has been added alongside the other operational 110 GHz, 1.0 MW class gyrotrons in the existing electron cyclotron heating and current drive (ECH/ECCD) complex on the DIII-D tokamak [1], all manufactured at Communications and Power Industries (CPI) [2] has added
Summary
Recent years have seen an increase in the large variety of experiments involving injection of 110 GHz EC power into the DIII-D tokamak plasma, with operational regimes approaching or exceeding the density limits for X-mode second harmonic resonance absorption. In these high-density plasmas, the EC beam can be refracted, possibly causing damage to EC launchers or diagnostic systems located behind hightransmission windows. A new gyrotron operating at a higher frequency of 117.5 GHz has been added alongside the other operational 110 GHz, 1.0 MW class gyrotrons in the existing electron cyclotron heating and current drive (ECH/ECCD) complex on the DIII-D tokamak [1], all manufactured at Communications and Power Industries (CPI) [2] has added. O-mode second harmonic resonance electron cyclotron heating scenario was used successfully in high density plasmas
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