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Visible Doppler Spectrometer for Edge Toroidal Rotation

This paper discusses the construction of a high throughput visible spectrometer for measuring toroidal rotation velocity with fast time resolution. The spectrometer utilizes Doppler-shifted visible line emission at discrete spatial locations in the plasma, complementing the existing visible spectrometer with faster time resolution and more sensitive velocity measurements. The measurements potentially do not require a neutral beam and have a spatial resolution of about 1 cm.

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Visible Doppler Spectrometer for Edge Toroidal Rotation

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  1. 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

  2. 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.

  3. Toroidal Rotation Measurement • 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) Other Measurements: Ion temperature from emission line broadening and poloidal rotation Spectrometer Capabilities

  4. Spectrometer Side View To Invessel Optics Top View

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