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 1

• A. White C-Mod C-Mod Ideas Forum 2011

This is a proposal to install a new, Correlation ECE diagnostic on C-Mod for measurement of core turbulence

1/6/11

• A. White C-Mod C-Mod Ideas Forum 2011

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 Lrad 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) 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

Extensive GYRO modeling was used to determine upper limit of 1 cm for spot size (1/e2 intensity diameter of Gaussian beam)

1/6/11

• A. White C-Mod C-Mod Ideas Forum 2011

Question: Can in-vessel optics produce a 1 cm spot size in region 0.4 < r/a < 0.8 ?

2w0 = 1 cm spot size

IDL gaussbeam code suggests that it is possible to obtain ∆Z < 1cm at C-Mod with 200 < 2fECE < 300 GHz using large optics, mirror diameters < 10 cm.

1/6/11

• A. White C-Mod C-Mod Ideas Forum 2011

Options for inter-mirror distances, focal lengths can be quickly assessed IDL gaussbeam code has been verified against laboratory tests 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

f = 48 cm f = 130 cm Predicted spot-size ~ 3.0-3.5 cm agrees with DIII-D data and calculations