New cross-channel calibration for mm-wave scattering diagnostics at the DIII-D tokamak

The design and development of a new cross-channel calibration circuit for mm-wave scattering diagnostics at the DIII-D tokamak is presented. This calibration circuit is designed to measure the launch and receive power of mm-waves used by the Doppler Back Scattering (DBS) diagnostic [1]. The DBS system uses 8 simultaneous fixed-frequency channels (55-75 GHz) to make local measurements of plasma flow and density fluctuations. Reliable and frequent cross-channel calibration data simplifies comparing fluctuations at different plasma locations. The relative power between each systems' channels is recorded throughout plasma discharges using swept YIG filters and diode power-meters. The YIG filters are used to isolate the 8 channels of the DBS system. Data characterizing the performance and capabilities of the new system is presented. Plasma measurements with and without calibration are contrasted.     

Work supported by USDOE Grants DE-SC0019352, DE-FG02-08ER54984, and DE-FC02-04ER54698.

[1] Review of Scientific Instruments 80, 083507 (2009)