Poloidal rotation in Alcator C

Abstract

The poloidal rotation velocity in the edge region of ohmically heated Alcator C plasmas was measured using the Doppler shift of impurity emission lines. The measurements were made using a high-resolution, photon counting detector, sensitive to wavelengths from ∼1200 to ∼2000 Å, mounted in the exit plane of a 1-m Ebert–Fastie spectrometer. The transitions used were the 2s2p 1P01–2p2 1D2 at 1371.292 Å in O v and 2s 2S1/2–2p 2P01/2 at 1242.804 Å in N v, both of which exist near the limiter radius in Alcator C. The measured rotation velocity is ∼4.1×105 ±2.1×105 cm/s at n̄e∼1.7×1014 cm−3 in the direction of the electron diamagnetic drift and is ∼1.4×105 ±2.5×105 cm/s at n̄e∼2.3×1014 cm−3 in the ion diamagnetic drift direction, although the error bars associated with this last measurement do not preclude the possibility of zero rotation or rotation in the electron diamagnetic drift direction.