October 24, 2020

Ultra-high spatial-temporal resolution Thomson scattering diagnostic system developed by plasma

[ Instrument Network Instrument Development ] Recently, the ultra-high-temporal resolution Thomson scattering diagnostic system developed by the Diagnostics Group of Plasma has successfully passed the expert acceptance. The diagnostic system can simultaneously measure plasma electron temperature and density in a 4kHz YAG laser UHF mode (10 pulses) and 100Hz YAG laser continuous mode. Currently, the diagnostic system is the highest frequency Thomson scattering diagnostic implemented by a single laser internationally.
Electron temperature and density distribution are important basic parameters of fusion devices, and they are also the basis for many research on fusion physics. The laser Thomson scattering diagnosis obtains electron temperature and density experimental data by the shape and intensity of the scattering spectrum of electrons under the action of laser light. Because of its clear principle, it is widely recognized as the most reliable diagnostic method for electronic temperature and density distribution in fusion research. It is a diagnostic tool for the development of international fusion devices including ITER. Since Thomson scattering diagnosis requires analysis of the scattering spectrum of photons generated by lasers and electrons in nanosecond time, this system places extremely high demands on laser and weak fast signal detection technology, which is considered to be the most difficult in fusion research. One of the several diagnoses, only a few developed countries had a complete development capability.
For EAST with high parameters and long pulses, the temperature of electrons above 100 million degrees must be accurately measured by Thomson scattering, but the 100 millionth electron laser scattering spectrum is wider and weaker. The precision signal puts higher requirements on the system laser and the detector, that is, it needs to consider the rapid physical process as well as the diagnosis and stable operation time of more than 1000 seconds. In recent years, the Plasma Thomson Scattering Group of Plasma has continuously absorbed the international advanced laser and detection technology for the experimental requirements of the EAST device, and successfully developed the Thomson scattering diagnostic system with ultra-high spatial and temporal resolution. Recently, the research team pioneered a series of pulse methods and carried out technical research, and successfully developed a distinctive 4kHz/3J YAG pulsed laser. At the same time, it overcomes the key technical problems of high-performance scattered light splitting, infrared weak signal detection, high-speed acquisition, high-efficiency laser transmission and automatic collimation. The system successfully realizes space 45 measurement points, highest time resolution 250μs, and highest spatial resolution on the EAST device. Measurement of full-space electron temperature density distribution with a rate of 3 mm, electron temperature and density error of less than 10% and 15%, respectively. The system is the most frequently used YAG Thomson scattering diagnostic system realized by a single laser in the world. Its main key technical indicators have reached the world's leading edge level, especially the 4 kHz high-power laser has far surpassed the dozens of commonly used devices on the current mainstream devices. Hertz and ITER are researching 300Hz lasers.
At the same time, the research team developed a 3.5J/100Hz full-lamp pumping mode laser through a full-cavity water-cooling structure. The laser can work continuously at 100Hz for more than 10 minutes in 3.5J high-power mode. The laser comprehensive parameters have reached international standards. Frontier level. The laser cooperates with the 4 kHz laser through laser beam combining technology, which provides a reliable research method for the long-time scale study of EAST long-pulse steady-state operation. The completed EAST Thomson Scattering Diagnostic System is at the forefront of the world in key technologies such as time resolution (4 kHz), spatial resolution (3 mm) and operational stability.
The related work is in the National Magnetic Restricted Nuclear Fusion Energy Development Research Project of the Ministry of Science and Technology. "Study on the critical power distribution parameters of the EAST plasma to the external power dynamic response" "East high-constraint mode boundary transport transport fine structure research" and the National Natural Science Foundation project Supported by the support, it has provided important data support for EAST's successful implementation of 100-second H-mode and electronic temperature 100 million-degree plasma discharge.

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