Poloidal rotation velocities in the outer half of Alcator-Cplasmas

Poloidal rotation velocities in the outer half of ohmically heated Alcator-C plasmas have been determined from 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 following transitions were used: 2s2$p^1$P${°}_1$–2$p^2$ ${}^1$ $D_2$ at 1371.292 at 1371.292 Å in O v, 2s${}^2$ $S_{1/2}$–2$p^2$P${°}_{1/2}$ at 1242.804 Å in N v (both of which exist near the limiter radius in Alcator-C), and 1s2s ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$–1s2p ${}_{}{}^3{}_{}{}^{}°_2^{}{}_{}{}^{}$ at 1623.63 Å in O v i i (which exists at r/a∼0.8). The measured rotation velocities are 4–5×${10}^5$ cm/s in the direction of the electron diamagnetic drift at the radius of the O v emission shell and ∼6×${10}^5$ cm/s at the radius of the O v i i emission shell, again in the electron diamagnetic drift direction. Therefore poloidal rotation of the outer half of the Alcator-C plasma with a velocity of several times ${10}^5$ cm/s in the direction of the electron diamagnetic drift is firmly established by these measurements.