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Visible array (lithium), runaway electrons & Zeff edge tang. chords, midplane filterscope

90 R-0

Lithium Beam (Visible array)

The  local  edge  current  density  j(r)  is  a  parameter  of  basic  importance  in understanding the stability of high performance tokamaks as well as the dynamics of ELM behavior. On DIII-D the lithium beam polarimetry diagnostic provides precise measurements of the local magnetic field projection along the field of view at 32 radial locations in the plasma edge. Using these measurements, the known spatial calibration and a minimal amount of information about the magnetic field shape from equilibrium reconstructions, Ampères law may be used to provide a straightforward parameterization for the edge toroidal current density in terms of the measured magnetic field and its radial derivative. This approach is relatively insensitive to errors in the reconstruction and is simple to apply.

Filterscope

The DIII-D filterscope system simultaneously monitors the intensities of the atomic emission lines D-alpha (6562 Å), D-beta (4861 Å), CIII (4650 Å), and He II (4686 Å) along multiple viewchords through the plasma. The diagnostic contains upward and downward directed sightlines in a poloidal plane, as well as tangential sightlines in the vessel midplane.Light from the tokamak is conducted to the Control Room Annex via optical fibers, split into multiple paths, and detected with compact photomultipliers, each equipped with a bandpass filter to isolate a specific spectral line.

Midplane Filterscope (tangential system)

The tangential systems consists of the eight viewchords (FS1MID - FS8MID) shown in the plan view of the vessel midplane, below. The collection optics for these chords are located in the 90R 0:B port. Each chord is outfitted with a viewing dump on the opposing wall of the 30 degree beam box. Each spatial channel detects three atomic emission lines: Da (6561 A), C III (4650 A), and He II (4686 A).