The Establishment Of J-TEXT Three-wave Far-infrared Laser Polarimeter-interferometer

Current density profile is a fundamental element in tokamak plasma, which is closely relevant to processes of confinement, transport, and MHD activities. Measurement of current density profile is inevitable for advanced tokamak operation, while determination of current density profile also offers great help for MHD relevant study. As one of those parameters that are most difficult to measure, current density profile could only be obtained by limited means, in which polarimetry towards measurement of Faraday Effect is now considered as one of the most reliable methods.Motivated by the needs of plasma physics research and diagnostic technique study, a polarimeter-interferometer diagnostic was proposed for J-TEXT tokamak in2010and established at the end of2012. The establishment of the system, including systematic design, system integration, tests, coding, and system operation and optimization, are the main contents of the dissertation.In the thesis, diagnostic principle of polarimeter-interferometer is briefly reviewed firstly. Techniques used to determine Faraday angle are introduced. Precision of the measurement and sources of errors are discussed. Design of J-TEXT polarimeter-interferometer is given secondly, including conceptual design, optical design and mechanical design. Three-wave technique is adopted and unique beam-expanded optics is used, which allow the system be able to perform measurement with high phase resolution, spatial resolution and temporal resolution. Integration and tests of the system are shown. Capabilities of sub-systems and optical components are checked, and performance of the system is preliminarily confirmed. Design and test of J-TEXT profile inversion code based on equilibrium magnetic surface geometry are presented. Inversed error of the code is estimated, and capability of the code for inversion of data from J-TEXT polarimeter-interferometer is validated. Finally the experimental operation of the system is described. Simultaneous measurements of Faraday rotation angle and line-integrated density are achieved. Optimizations of mechanical vibration and colinearity are done to improve the performance of the system. J-TEXT polarimeter-interferometer has achieved0.1degree phase resolution and1μs temporal resolution with8chords. Benefited from these capabilities, small amplitude perturbations on Faraday rotation angle and line-integrated density are observed. Reasonable inversion results are obtained from experimental data.