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Confinement transitions in TJ-II under Li-coated wall conditions

机译:锂涂层壁条件下TJ-II的限制转变

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This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma-wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 10~(19) m~(-3) and T_e ≈ 250-300 eV, with peaked density, rather flat T_e profiles and higher ion temperatures. Due to the achievedrndensity control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Ha emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.
机译:本文介绍了TJ-II恒星仪中限制研究的最新结果。通过真空蒸发镀锂后,已成功降低了TJ-II固有的强等离子体壁相互作用。除了保留氢和降低Z外,选择Li的原因还在于该元素对反应堆的需求,因此对其性能的研究特别重要。锂涂层导致等离子体性能发生重大变化。特别是,NBI等离子体中的有效密度极限已扩展到达到中心值8×10〜(19)m〜(-3)和T_e≈250-300 eV,具有峰值密度,相当平坦的T_e轮廓和更高的离子温度。由于实现了密度控制,第二种类型的跃迁已添加到先前在ECRH等离子体中观察到的低密度跃迁中:高密度跃迁的特征是Ha辐射的下降,陡峭的密度梯度的出现和湍流的减少;这是过渡到H模式的特征。对ECH等离子体的限制研究表明,即使在低剪切环境中,最低阶磁共振也会局部降低有效电子热扩散率,而在NBI等离子体中不稳定的Alfven本征模式会影响快速离子限制。

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