| International Thermonuclear Experimental Reactor is a major international cooperation project to solve the energy problem.It is the first fusion device in the world to target plasma self-sustaining combustion.The Radial X-ray Camera(RXC)is an important diagnostic system in the ITER device.By monitoring the intensity and distribution of soft X-ray radiation during the operation,the key problems of plasma operation instability,characteristics of sawtooth and impurity radiation can be studied,and the diagnostic data can be provided for plasma control.The hardware system of the RXC consists of detectors,pre-amplifiers,mid-amplifiers and data acquisition as well as the central control system of CODAC.The detector converts the soft X-ray radiation signal to a current signal of 10 n A?10?A.The signal with a gain of 10~6(V/A)is amplified by the pre-amplifier.The output signal of the pre-amplifier ranges from 10m V to 10 V and is transmitted to the mid-amplifier system.This paper studies the mid-amplifier system.The mid-amplifier system mainly consists of three parts:the shielding box with cooling system,the radiation-resistant chassis and the electronic card.The shielding box plays a protective role in the electronic diagnostic system under the environment of strong nuclear radiation and strong magnetic field in ITER.The chassis includes input/output signal transfer card,backplane,heat dissipation structure;the electronic card includes 16-channel programmable gain amplify,self-test module,communication module with host computer,temperature alarm module,etc.The mid-amplifier card needs to consider the anti-radiation,programmable gain control and remote upgrade function.The card uses Inter FPGA as the main controller.In the hardware structure,the differential voltage signal from the output of pre-amplifier is transmit to the input end of the mid-amplifier thought the backplane of chassis.The input switching between the original signal and the self-test signal is realized by the linear gate which is controlled by FPGA,and the gain can also be configured by FPGA.The 16-bit DAC is controlled by FPGA code to generate self-test signal,and the temperature of the card is monitored by temperature and humidity sensors.FPGA transfers data to the host computer through the serial port to the optical fiber module.The host computer and FPGA realize remote upgrading.The card is powered by the backplane as a whole,but the chassis itself does not contain power supply.It also needs to use programmable DC regulated power supply to power the chassis backplane remotely(100 meters).PC software based on Lab VIEW realizes data communication between computer and mid-amplifier.In the system function verification stage,in order to realize the whole signal chain verification,a set of self-test design system for RXC signal using laser diode is developed.The system controls the switch and luminous intensity of the laser diode through the host computer,and the laser is reflected to the detector through the diffuse reflection plate to provide a signal source.The detector converts the optical signal into electrical signal,which is amplified by the pre-amplifier and transmits the voltage signal to the mid-amplifier card.After programmable gain amplification,the signal is transmitted to the acquisition system for waveform acquisition,and the data is uploaded to the upper computer to complete the signal chain self-test.The electronic performance parameters of the mid-amplifier are verified by performance test and system joint debugging.The system noise,linearity,bandwidth,gain control and temperature stability can meet the design requirements of ITER.The research results provide a reference for other diagnostic design of ITER project. |
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