| This paper is based on the radial soft X ray diagnostic system used in International Thermonuclear Experimental Reactor.Soft X-ray diagnostic system,mainly used for the plasma system,given radiation poloidal distribution of time and spatial resolution,widely used in physics research of sawtooth,fishbone mode MHD phenomenon and imaging inversion,etc.The environment around ITER tokamak is complex and harsh,high temperature,complex electromagnetic field and vacuum environment are coexisted.The high temperature can easily causes parameters and performance change of detector,which will cause the signal interference increase of detection;the complex electromagnetic interference is also easily coupled to the diagnostic system to impact signal acquisition.In particular,electron cyclotron resonance heating(ECRH)/current driver and ion cyclotron resonance heating/current driving(ICRH/ICCD)will produce high-frequency electromagnetic interference.Therefore,a stable,reliable and electromagnetic compatibility diagnostic system should be designed to meet the needs of ITER tokamak.Based on the problems above,this paper analyzes and studies the soft X ray diagnostic system and its electromagnetic compatibility in detail.It mainly includes the analysis of static and disturbed magnetic fields in the ITER environment,the structure design of the electromagnetic shielding box and the analysis of shielding effectiveness,analysis of the detector characters and noise suppression and the electromagnetic compatibility of detector circuits,and the closed cooling circuit is designed to reduce detector temperature and ensure its stable performance.It is because of that the electromagnetic interference source produced by ITER can not be suppressed,in order to protect the soft X ray diagnosis system from electromagnetic interference,the shielding is used to cut off the propagation path of the electromagnetic interference,so the design of the shielding box of the soft X ray diagnosis system is very important.Shielding box structure,line holes,gaps and materials of shielding box have great influence on shielding effectiveness.In this paper,the magnetic analysis software Maxwell is used to analyze the static magnetic field distribution and the HFSS simulation software is used to simulate the effect of the shielding body to radiance magnetic field.Through electromagnetic simulation,the whole structure of the shielding box,the structure of the wire hole,the gap and the material influence on the electromagnetic shielding are analysized.Through structure design,the static magnetic field inside the box is reduced to 5mT from 200mT and theradiation magnetic attenuates 80dB-110dB.Secondly,the influence of the parameters of the photodiode detector on the signal acquisition is introduced,and the junction capacitance,the dark current and the reverse bias voltage of the photodiode are analyzed.Through the parameters analysis of detector,when the environment temperature changes,the thermal noise,the scattering noise and the dark current of the detector will also change,which causes strong noise to the signal.Therefore,the performance of the detector can be improved by cooling detector and adding reverse bias voltage,and the appropriate reverse bias voltage added on the photodiode is determined.Thirdly,the design of the soft X ray detection amplifying circuit and its electromagnetic compatibility(EMC)is carried out.The noise and integrity of the power supply system are analyzed.The power EMI filter is designed to reduce the noise of the power supply system.The design,layout and selection of electronic components of the circuit board are optimized by the small signal SIwave simulation software.The resonance of the PCB is suppressed;the noise of the power supply is reduced to 8mV by the optimization of the signal detection circuit and the anti-interference design,and the overall noise of the signal is reduced to 8mV,thus the performance of the detection system is improved.Finally,when DSM is in the baking stage,the temperature can reach 240(±10)?,and the temperature of DSM at the normal discharge in the D-D stage is about 140?,the detector temperature will rise for absorbing the radiation heat from DSM.With the increase of detector temperature,the dark current will increase,and the noise interference of detector will increase,which will affect the detection of weak signal.Considering the above problems,a detector cooling circuit is designed to reduce the detector temperature.Many Tokamak systems uses water to cool the detector,and water cooling is easy to activate in the D-T discharge stage of ITER tokamak system.Therefore,this paper focuses on the design of the helium cooling system.The thermal simulation of the soft X camera and its cooling system is carried out,and the baking-cooling test platform is set up to test the cooling circuit.The test results show that the temperature of the detector can be reduced to below 65? by cooling system in the ambient temperature of 250?,which proves the feasibility of the design of the gas cooling circuit.Of course,the temperature of the detector can be reduced by changing the cooling gas parameters(eg flow,pressure and temperature),thus ensuring the stability of the detection system. |
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