The Geometric Phase Of Faraday Rotation Effect Measured By Polarimetry In EAST Tokamak

The magnitude of geometric phase in the signal of Faraday rotation angle is evaluated theoretically under the parameter conditions of EAST Tokamak. The optimum schemes for geometric phase measurement in EAST Tokamak are proposed. Meanwhile, relevant experimental studies are conducted for realizing geometric phase measurement.The three-wave Polarimeter-Interferometer (POINT) system is one of the most important diagnostics in EAST Tokamak to provide simultaneous line-integrated electron density and line-integrated poloidal magnetic field. The conventional three-wave polarimeter-interferometer technique only takes into account the dynamical phase, which is calculated using the dispersion relations, the geometric effect resulting from the deviation of wave trajectories and non-uniformity of the magnetized plasmas is ignored. The experimental observation of geometric phase in plasma systems is a fundamental physical problem. Meanwhile, by introducing the influence of geometric phase on the measurement of Faraday rotation angle, the system error of existing signal processing technology for diagnostics can be reduced.To estimate the realistic geometric phase in POINT system, the beam trajectories in non-uniform magnetized plasma is calculated using the ray-tracing simulations. The geometric phase can be obtained by computing the integrals along the wave trajectory in the parameter space. According to the simulation results, the geometric phase in the signals of present EAST POINT system is smaller than the resolution of POINT system. At the present stage, the geometric phase cannot be observed directly in signal.Two schemes for geometric phase measurement in EAST Tokamak have been designed. Scheme A: geometric phase measurement can be realized by further improvement of the diagnostic accuracy; Scheme B:the geometric phase can be increased to a measurable level by increasing the toroidal angle.In order to attain the experimental conditions in the schemes for geometric phase measurement, the reflecting properties of retro reflector have been investigated systematically. These results are the basis of geometric phase measurement in EAST Tokamak in near future.