Optimization And Investigation On The Uncertainities Of Magnetic Diagnostics In J-TEXT

Magnetic diagnostics,which is one of the most basic and important diagnostics in tokamaks,play an important role in measuring and controlling Magnetohydrodynamic(MHD)instabilities.Joint Texas Experimental Tokamak(J-TEXT)has set up multiple magnetic diagnostics,which have been widely used in physical experiments.However,with the gradual deepening of experimental research,more accurate measurements on the time-frequency characteristics(magnitude,frequency,phase,etc.)of MHD instabilities are required,which led to higher requirements on magnetic diagnostics:1)Eddy current is a major kind of uncertainities in magnetic diagnostics.It is urgent to compensate and optimize the impact of eddy current response under complex electromagnetic effects on magnetic diagnostics;2)It is necessary to upgrade magnetic diagnostics on low frequency(<1 k Hz)MHD instability measurement.According to the requirements above,this thesis studied the response characteristics of the magnetic diagnostics on J-TEXT and then optimizes and upgrades them.This thesis also set up a simulation to analyze the uncertainities for the magnetic diagnostic system on International Thermonuclear Experimental Reactor(ITER)and then optimized the design.This thesis investagated the high-frequency eddy current response of Mirnov probes on J-TEXT.A test platform,which is capable of generating a uniform AC magnetic field within the frequency range of 1–300 k Hz has been designed and set up in order to simulate the complex electromagnetic environment in tokamak.The eddy current response on Mirnov probe with respect to the materials and distance of surrounding conductors,and magnetic field frequency has been investagated.The phasor expression is introduced to describe the AC magnetic field.It is found that the eddy current effect increases with the frequency increased and decreasing of the distance between the probe and conductor.When the increase of frequency leads to the skin depth is half of the conductor thickness(about 100k Hz for graphite),the amplitude of the eddy current field decreases with increasing frequency.The phase of the eddy current field will gradually be completely opposite to the original magnetic field as the frequency increases(about 50k Hz for 304 stainless steel).The study also found that the eddy current effect on graphite caused by the magnetic disturbance of lower frequency(<10 k Hz)is negligible.According to the research,larger magnetic disturbance amplitude can be obtained and the time delay of MHD instabilities can be reduced by compensating the measurement signal in J-TEXT experiments.In addition,the conductor material and distance combination with the smallest eddy current response can be considered in the magnetic diagnostics design for the specific frequency of the signal to be measured.This thesis designed and upgraded the high field side magnetic probe array on J-TEXT tokamak.For the divertor shape experiment on J-TEXT,the poloidal Mirnov probe arrays were modified.Meanwhile,a new magnetic probe array has been designed and installed behind the high field side divertor.Two groups(10)B_zprobes are set up to make up the missing of poloidal spatial resolution due to the removing of the poloidal Mirnov probe arrays;Two groups(14)B_rprobes are set up to measure the locked mode,which avoided perturbation field saddle coils to ensure the measurement is not affected by the coils when carrying out the perturbation field experiment.The n=1 locked mode and more poloidal informations caused by the penetration in the 2/1 resonance magnetic perturbations experiment can be obtain using the high field side magnetic probe array.A preliminary conceive and work on the integration of the magnetic diagnostics system has also been done.This thesis also introduces the set-up of the simulation of Fiber Optical Current Sensor(FOCS)uncertainties and the parameter sensitivity analysis of FOCS on ITER.The simulation is based on the principle of birefringence in FOCS.According to the simulation,the parameters,plasma current,polarization angle of the input light and the uncertainity of the Fafaday Mirror were analyzed.It was found that bend and twist induced birefringence will have a significant effect on the output state of polarization.A feedback approach to compenstate and optimize the uncertainities above has been designed.