Magnetic field pitch-angle measurments in the PBX-M tokamak using the motional Stark effect

Polarimetry measurements of the Doppler-shifted ${\mathrm{H}}_{\mathrm{\ensuremath{\alpha}}}$ emission from a neutral hydrogen beam on the PBX-M tokamak have been employed in a novel technique for obtaining q(r) and magnetic field pitch-angle profiles using the Stark effect. The resulting q(r) profile is very broad and its central value, q(0), is significantly below 1, which has important implications for theoretical models of sawteeth.