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. Spectrometer Capabilities
Toroidal Rotation Measurement
Other Measurements:
Constructed high throughput visible spectrometer ( 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 ~ at 5500Å (50 mm slit) (i.e. fwhm ~ 0.5 Å)
Rotational velocity sensitivity: ~1 km/s ( 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

4. Spectrometer
Side View
To Invessel Optics
Top View