题   目：Numerically investigating incomplete-reconnection sawteeth in Tokamaks

报告人：张威特聘研究员，浙江大学

时   间：2023年03月13日（周一） 下午 13：30 

地   点：聚变所二楼大会议室

摘   要：Sawtooth oscillations are common phenomena in Tokamaks when the safety factor on the magnetic axis is below 1.0. Sawtooth oscillations can not only reduce the central plasma temperature but also induce seed islands on nearby resonant surfaces and cause Neo-classical tearing instability that could cause degradation of plasma confinement. However, It is also found that small-amplitude sawteeth sometimes exist. These small sawtooth oscillations can help to expel helium ash in fusion reactors and will not significantly reduce plasma confinement. The small sawtooth crashes are believed to be related to incomplete reconnection during sawtooth crashes. There are several theories for the incomplete reconnection sawteeth. However, none of them has been verified by self-consistently numerical simulations. As a result, it has been doubted whether incomplete-reconnection sawteeth have ever occurred. The mechanism of the incomplete-reconnection sawteeth is still in strong debate. In the present presentation, we report our recent works on sawteeth in Tokamaks, including the time scales for fast pressure crashes and the formation of non-axisymmetric equilibrium with the m/n=1/1 island. Then, we present our simulation results to validate several important incomplete-reconnection models in the literature. We find that incomplete reconnection is most likely triggered by the enhancement of the electron diamagnetic effect at the nonlinear stage. Through the self-consistent simulations from the CLT code, we first present incomplete-reconnection sawtooth oscillations and explain why the fast reconnection process caused by the two-fluids effect does not occur during incomplete reconnection. By collaborating with the EAST team, we have also found that the electron diamagnetic drift frequency is significantly increased during sawtooth crashes.

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