3月12日 The fast Thomson scattering system in LHD

报告题目：The fast Thomson scattering system in LHD

报告人：Prof. Ryo Yasuhara

报告时间：3月12日10:00-11:00

报告地点：控制大厅3楼会议室

主持人：臧庆

报告内容简介：In the field of nuclear fusion plasma diagnostics, Laser Thomson Scattering (LTS) systems have long been recognized as a highly reliable method for measuring electron temperature and density profiles. However, the high-energy pulsed lasers typically employed in such systems are restricted by thermal limitations in the laser medium, resulting in relatively low repetition rates—on the order of tens to hundreds of hertz. Consequently, it has been challenging to track electron temperature and density fluctuations on the millisecond timescale, such as those associated with hydrogen pellet ablation, plasma collapses, or rapid heating processes.

In this study, we introduce a high–time-resolution Thomson scattering system capable of operating at 20 kHz, achieved by developing a novel Q-switched Nd:YAG laser oscillator with a pulse width of approximately 20 ns and an IGBT-driven flash-lamp power supply. By integrating this laser with a dedicated analog-to-digital converter (ADC), the system can acquire Thomson scattering data at a 20 kHz repetition rate, over 100 consecutive shots, with a temporal resolution of 20 ns at 70 spatial points. Compared to conventional Thomson scattering techniques, this approach drastically enhances time resolution and makes it possible to directly observe rapid phenomena, including hydrogen pellet ablation, plasma collapses [1,2], and the effects of electron cyclotron heating (ECH) as well as transient magnetohydrodynamic (MHD) events. Moreover, our latest developments have further increased the laser’s repetition rate to 40 kHz, significantly broadening the measurement capabilities for advanced plasma physics research.

[1]. H. Funaba, R. Yasuhara, H. Uehara, I. Yamada, R. Sakamoto, M. Osakabe, D. J. Den Hartog, Electron temperature and density measurement by Thomson scattering with a high repetition rate laser of 20 kHz on LHD, Scientific Reports volume 12, Article number: 15112 (2022).

[2]. N. Kenmochi, K. Ida, T. Tokuzawa, R. Yasuhara, H. Funaba, H. Uehara, D. J. Den Hartog, I. Yamada, M. Yoshinuma, Y. Takemura and H. Igami, Preceding propagation of turbulence pulses at avalanche events in a magnetically confined plasma, Scientific Reports volume 12, 6979 (2022).

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