Two-polarizer method for the pitch angle measurement of magnetic field in a toroidal plasma

Asymmetry of the motional Stark spectrum is caused by large angular divergence of an injected natural beam. To avoid this difficulty caused by the spectrum asymmetry, only the sigma component is used to determine the pitch angle in the case of a high magnetic field with an optical system that contains two polarizers tilted +/-45 degrees with respect to the horizontal direction. II is predicted that the pitch angle could be measured with an accuracy better than 0.2 degrees. (C) 1997 Elsevier Science S.A.