High resolution transmission grating spectrometer for edge toroidal rotation measurements of tokamak plasmas.

We present a high throughput (f/3) visible (3500–7000 Å) Doppler spectrometer for toroidal rotation velocity measurements of the Alcator C-Mod tokamak plasma. The spectrometer has a temporal response of 1 ms and a rotation velocity sensitivity of ∼10⁵ cm/s. This diagnostic will have a tangential view and map out the plasma rotation at several locations along the outer half of the minor radius (r/a>0.5). The plasma rotation will be determined from the Doppler shifted wavelengths of D_α and magnetic and electric dipole transitions of highly ionized impurities in the plasma. The fast time resolution and high spectral resolving power are possible due to a 6 in. diam circular transmission grating that is capable of λ/Δλ∼15 500 at 5769 Å in conjunction with a 50 μm slit. [ABSTRACT FROM AUTHOR]