题   目： Configuration Effects on Confinement, Transport, and MHD Instabilities in Heliotron J

报告人： Kazunobu NAGASAKI 教授， Engineering from Kyoto University

时   间： 2024年3月14日（周四）  上午 9：30 

地   点： 实验楼大会议室

摘   要： Magnetic configuration is one of the important factors in determining plasma performance in toroidal magnetic confinement systems such as tokamaks and stellarator/heliotron. The Heliotron J device, a medium-sized plasma experimental helical device (R/ap = 1.2/0.17 m, B0= 1.5 T), has a flexible and wide range of magnetic configurations by independent control of a helical coil, two types of toroidal coils, and three pairs of vertical coils. Such a high configuration flexibility of the Heliotron J provides us with a physics study on the role of magnetic configuration on plasma performance. Plasma heating schemes (ECH of 70 GHz, 0.4 MW, two tangential NBIs of 1.2 MW / 30 kV) are applied for plasma production, heating, and current drive, and high-intensity short-pulse gas-puff (HIGP) and pellet injection makes it possible to expand the accessible plasma parameters (ne < 1020 m-3, Te < 3 keV, Ti < 0.4 keV). In this paper, we show recent experimental results on the configuration effects on plasma performance, such as confinement, transport, and energetic-particle-driven MHD instabilities in Heliotron J.

The toroidal mirror ripple (bumpiness) scan shows that optimization of neoclassical transport is compatible with the reduction of turbulent transport. The available energy of trapped electrons, which relates to collisionless turbulence energy flux driven by trapped electron mode (TEM), depends on the bumpiness in the same tendency as the experimental result. The rotational transform also affects the energy confinement. In the rotational transform scan, the dependence is found to contradict with ISS04 scaling. The plasma is unstable when /2 Is slightly higher than 4/8, while the edge magnetic island chain may improve core particle and heat transport. A Doppler reflectometer measurement shows that the Er shear is formed at the inner side of the magnetic island, and a Langmuir probe measurement shows that the turbulence-driven particle flux is non-uniform inside the magnetic island. We will also present the controllability of EP-driven MHD instabilities by the magnetic configuration and ECH/ECCD.

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