| In the magnetic confined fusion plasma,the safety factor(q)is one of the basic physical parameters,which has an important influence on the investigation of plasma transport and magnetic fluid instability.Motion Stark Effect(MSE)diagnosis can directly give the distribution of safety factors by directly measuring the information of the magnetic field pitch angle,and combine with EFIT's equilibrium reconstruction code to give the distribution of safety factors.In order to support the design and hardware implementation of multi-channel MSE diagnostic system,the simulation of the EAST multi-channel MSE system is completed by using the neutral beam radiation spectrum simulation programs ALCBEAM and NBASS.The assembly and testing of the multi-channel MSE system,which has developed on EAST,are completed and the measured pitch angle has been obtained.With the experimentally measured spectrum,a preliminary spectrum analysis is performed.The multi-channel MSE diagnostic system is based on an active measurement of the Neutral Beam Injection(NBI),which measures the polarization of the characteristic spectral line Da radiated after the neutral beam interacts with the plasma,to obtain the pitch angle information.With the ALCBEAM and NBASS programs,starting from the basic principles,taking into account the impact of complex factors such as the neutral beam,light collection system and acquisition system on the measurement results,we perform the simulation of multi-channel MSE system on EAST,the attenuation distribution of the neutral beam in spatial and MSE spectrum.The simulation results give a spatial resolution of 0.9 cm?2.3 cm(boundary to core),which verifies the rationality of the design.In polarization measurement,the center wavelength and half-height width of the filter will affect the polarization of the signal light passing through the filter and directly affect the signal-to-noise ratio of the output signal.Through the simulation of the multi-channel MSE diagnostic system,the relationship between filter bandwidth selection and light transmittance is obtained,which provides a reference for filter parameter design.The high-voltage change of the neutral beam allows the center wavelength of the filter to shift.In this paper,the shift value of the center wavelength of the filter under different high voltage is obtained by simulation.In the EAST experiment,it is found that the interaction between the plasma and the neutral beam of the multi-ion source will cause serious spectral line overlap,which increases the difficulty of data analysis.ALCBEAM and NBASS codes are used to simulate the interaction process between the neutral beam and the plasma,and the threshold of spectral line overlap and the combination of neutral beam energy at a high signal-to-noise ratio are obtained,which provides a reference for the experiment.Based on the above simulation results,the multi-channel MSE diagnostic system has been constructed and tested.The system has 10 spatial observation channels,the measuring range is in the large radius R=1.8?2.33 m,the spatial resolution is less than 3 cm,the time resolution is 10 ms and the observed wavelength range is 651 ? 661 nm.The low vander ZF7 glass used in the front collection lens can effectively reduce the influence on the degree of polarization of the collected polarized light by placing a dielectric film on the reflector.The focal length of the lens is 130 mm and the F-number of the lens is 2.6.The baking temperature of the lens is 1500 as it is inside the vacuum chamber.The polarization information of the polarized light is modulated into intensity information using PEM(photo-elastic modulator)with an angle of 450 between the two fast axes.A linear polarizer of 22.50 after PEM is installed to eliminate light polarized in other directions.The modulated signal is transmitted to the laboratory through optical fiber,and the target spectral line is selected through a 4 nm narrow band filter.The photoelectric acquisition system is used for rapid acquisition,and then the amplitude of the specific double frequency component is extracted through the lock-in amplifier to obtain the polarization angle.In addition,the optical path system with double coupling design has been used to transmit the light signal conducted by the optical fiber to the spectrometer for acquisition to obtain the MSE spectrum.The split value between the a and ? components of the MSE spectral line is closely related to the magnetic field value.Using the experimental spectral line split value,the magnetic field value distribution is obtained.The measured value of the spectrum is basically consistent with the total magnetic field generated by the coil current,which verifies the feasibility of the spectral method to analyze the magnetic field on the EAST device,thus providing a reference for plasma control. |
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