Correlation ECE for core turbulence measurements on Alcator C-Mod - PowerPoint PPT Presentation

Correlation ECE for core turbulence measurements on Alcator C-Mod C-Mod Ideas Forum 2011 A. White, J. Irby, R. Vieira, W. Peebles (UCLA) 1/6/11 A. White C-Mod C-Mod Ideas Forum 2011 1

This is a proposal to install a new, Correlation ECE diagnostic on C-Mod for measurement of core turbulence ITER relevance of C-Mod plasmas + Uncertainty in our predictive capabilities = Put more core turbulence diagnostics on C-Mod in order to collect crucial data needed to validate turbulence-transport models CECE is radiometer based diagnostic, allows for local measurement of Te-tilde: a “pill box” volume in plasma is probed ∆ R < 1 cm, from emission layer width. ∆ Z ~ 1 cm, from antenna pattern is needed for turbulence When GPC and FRCECE have core access, the CECE system would have access: this covers most C-Mod operating regimes. CECE can be calibrated. CECE correlates two signals that are 1) within L rad of turbulence and 2) disjoint in frequency space. With correlation analysis, ECE can measure broadband (0-1 MHz) T-tilde/T down to 0.3% level with Bvid = 1 MHz and Bif = 100 MHz. (Linewidth and Lrad are ~ 1-2 GHz in C-Mod) 1/6/11 A. White C-Mod C-Mod Ideas Forum 2011

Extensive GYRO modeling was used to determine upper limit of 1 cm for spot size (1/e 2 intensity diameter of Gaussian beam) 2w 0 = 1 cm spot size Question: Can in-vessel optics produce a 1 cm spot size in region 0.4 < r/a < 0.8 ? 1/6/11 A. White C-Mod C-Mod Ideas Forum 2011

IDL gaussbeam code suggests that it is possible to obtain ∆ Z < 1cm at C-Mod with 200 < 2f ECE < 300 GHz using large optics, mirror diameters < 10 cm. Options for inter-mirror distances, focal lengths can be quickly assessed Predicted spot-size ~ 3.0-3.5 cm agrees with DIII-D data and calculations IDL gaussbeam code has been verified against laboratory tests f = 48 cm f = 130 cm NEXT STEPS: OSLO mirror design CAD drawings to begin exact in-vessel planning Design of mounts for inner wall, disruption forces, effects of boron coatings….other issues to tackle? UCLA collaboration 1/6/11 A. White C-Mod C-Mod Ideas Forum 2011