The Establishment Of J-TEXT Polarimeter-interferometer Far-infrared Laser Feedback System

Far-infrared laser diagnostic technique is one of the major plasmas diagnostics in tokamak experiment. HCN far-infrared laser interferometer for plasma electron density and three-wave polarimeter-interferometer for both the electron density and current density profile are established on J-TEXT tokamak. As a basic diagnostic in plasma experiment, the signal quality of far-infrared interferometer is the issue that we always concern. Moreover, the three-wave polarimeter-interferometer for additional physics research on J-TEXT tokamak has achieved 0.1 degree phase resolution of Faraday rotation angle and 1?s temporal resolution with 8 chords. While the stabilization of three far-infrared laser sources plays an important role in the accuracy of measurement of polarimeter-interferometer. Therefore, two parts are included in this dissertation as far-infrared laser interferometer signal optimization and establishment of laser sources feedback system for three-wave polarimeter-interferometer.The first part of this dissertation begins with a detail view of the intermediate signal noise in far-infrared interferomete. Then the works of signal optimization are respectively presented in three aspects: the route optimization included ground reconstruction, signal isolation and shielding three aparts; the preamplifier circuit improvement for pyroelectric detector; the application of six order elliptic filter.The second part firstly make an illustration about how the intermediate frequencies fluctuation and laser power decay, both caused by laser sources instability, affect the measurement of three-wave polarimeter-interferometer. Subsequently, a laser feedback method suiting to the application of three-wave technique is detailed. This method aims to control the lasers with fixed frequency difference but not fixed frequency of each laser, and then make the three lasers approaching their radiation spectrum center by laser power feedback. The realization of above feedback method, based on the application of TMS320F2812 DSP, is presented next. For keeping the high measurement resolution of Faraday rotation angle, the establishment of feedback system will not impact the essential optical structure at all. By this feedback method, The intermediate frequencies can be controlled with a drift < ±12 kHz and optimal laser powers can be kept with drift less than±7% in long term operation, with no negative impact to the resolution of the measurement. And the measurement resolution of Faraday rotation angle and integrated density when the laser feedback works are tested in the end of dissertation.