Divertor impurity seeding experiments at the COMPASS tokamak
Divertor impurity seeding experiments at the COMPASS tokamak
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DOI：
10.1088/1741-4326/ab34d2
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发表时间：
2019-10-01
期刊：
影响因子：
3.3
通讯作者：
Weinzettl, V
中科院分区：
文献类型：
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作者：
Komm, M.;Khodunov, I;Weinzettl, V
部分脱离是ITER和其他下一步设备中基线燃烧等离子体场景的理想状态，因为它允许通过刮除层耗散带电粒子携带的大部分能量，从而避免偏滤器区域中的局部热通量沉积。COMPASS托卡马克配备了一个开放式偏滤器，连接长度相对较短，这两个因素都不利于脱离。因此，它只允许在非常高的线平均密度（>10（20）m（-3））下自然分离操作的方法，这与保持ELMy H模式状态不相容。为了在较低密度下实现分离，必须在偏滤器区域向等离子体中注入杂质（如氮气）。在偏滤器的不同位置进行了一系列每秒1-9 x 10（20）个分子的杂质注入实验，目的是冷却等离子体，影响偏滤器靶上的粒子和热输运，并引起部分分离。之前报道的结果（Komm等人，2017年第44届EPS会议论文集，P1.118）通过在偏滤器外靶处注入氮气而得到了很大程度的扩展。为了分析种子等离子体中的偏滤器热通量足迹，引入了缓冲热通量q（B），径向分布近似为指数衰减。提出了一组新的通用参数-峰值热通量q（峰值），功率达到目标的分数f（div），偏滤器足迹扩展因子S-f-来计算分离条件下的偏滤器足迹。
Partial detachment is the desired regime for the baseline burning plasma scenario in ITER and other next-step devices, as it allows for the dissipation of the majority of the energy carried by charged particles through the scrape-off-layer and thus avoids localised heat flux deposition in the divertor region. The COMPASS tokamak is equipped with an open divertor and has a relatively short connection length, both factors being unfavourable for access to detachment. As such, it only allows for the approach to naturally detached operation at very high line-averaged densities (>10(20) m(-3)), which are incompatible with maintaining the ELMy H-mode regime. In order to achieve detachment at lower densities, impurities (such as nitrogen) must be injected into the plasma in the divertor region.A series of experiments with impurity injection in the range of 1-9 x 10(20) molecules per second at different locations in the divertor were performed with the aim being to cool the plasma and influence particle and heat transport onto the divertor targets and provoke partial detachment. Previously reported results (Komm et al 2017 Proc. of the 44th EPS Conf. P1.118) were largely extended by injection of nitrogen at the outer divertor target.In order to analyze the divertor heat flux footprint in seeded plasmas, the buffered heat flux q(B) was introduced, with the radial profile being approximated by an exponential decay. A new set of generic parameters-the peak heat flux q(peak), the fraction of power reaching the target f(div), and divertor footprint spreading factor S-f-were proposed to characterise the divertor footprint under detached conditions.