Visible Doppler Spectrometer for Edge Toroidal Rotation M.J. May, A. Graf, P. Beiersdorfer The Alcator C-Mod Ideas Forum MIT Plasma Fusion Center Dec. 2-3, 2004

Edge Toroidal Rotation Measurements with Fast Time Resolution Present C-Mod Measurements Toroidal rotation velocity measurements: • 3 chords through the plasma core with ~ 20 ms temporal resolution (x-ray). • Single chord edge view ~50 ms temporal resolution (UV-visible) • Outside SOL via magnetic probes Proposed Measurement Measure the toroidal rotation velocity via Doppler shifted visible line emission at several discrete spatial locations in the outer half of the plasma with a high temporal resolution (~ 1 ms) Complement the present visible spectrometer with faster time resolution and more sensitive velocity measurements. Measurements potentially do not require a neutral beam.

Spectrometer Capabilities Toroidal Rotation Measurement Other Measurements: Constructed high throughput visible spectrometer (3500 - 6800 Å) Measurements independent of the DNB: Utilize visible emission from B V (4945 Å) and B II (4940 Å) Currently a mono-chordal device but feasibility of multichordal upgrade has been demonstrated • Rotation velocity at several radii for r/a > 0.5. Spatial resolution ~ 1 cm (existing UT in vessel collection optics) • Resolving power ~ 15000 at 5500Å (50 mm slit) (i.e. fwhm ~ 0.5 Å) Rotational velocity sensitivity: ~1 km/s (2 - 10 times greater than previous measurements) Spectrometer Speed: f/# ~ 3, Hamamatsu Detector: ~ 1 ms/frame (~ 10 times faster than present measurements) Ion temperature from emission line broadening and poloidal rotation

Spectrometer Side View To Invessel Optics Top View