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

Abstract

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 Dα 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.