Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas
Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas
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研究类 JET ITER 壁 L 模式和 H 模式等离子体中刮掉层密度肩的形成
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
S. Wiesen
中科院分区：
文献类型：
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作者：
A. Wynn;B. Lipschultz;I. Cziegler;J. Harrison;A. Jaervinen;G. Matthews;J. Schmitz;B. Tál;M. Brix;C. Guillemaut;D. Frigione;A. Huber;E. Joffrin;U. Kruzei;F. Militello;A. Nielsen;N. Walkden;S. Wiesen
热核和周围容器之间的低温边界层等离子体（刮擦层或SOL）决定了材料表面的功率负荷、侵蚀和植入水平，从而决定了托卡马克聚变作为能量来源的可行性。本研究探讨了影响低场侧（LFS） SOL平坦密度剖面形成的机制，即所谓的“密度肩”，它改变了表面的离子和中性通量，以及随后的侵蚀。有证据反对局部增强电离诱导肩形成。我们发现SOL平行电阻率的增加Λdiv (=[L||νeiΩi]/csΩe)，假定通过SOL湍流特性的变化导致肩增长，与SOL肩振幅的增加相关，As，但仅在一部分条件下（d2燃料的L模式密度扫描与水平目标上的外部打击点）。Λdiv不能与As的情况下的N2播种或扫荡期间的打击点横跨水平目标。对于h模放电，Λdiv和As的有限相关性也被发现。因此，虽然Λdiv在肩部形成和/或生长时可能需要高于~1的阈值，但需要另一种机制。更重要的是，我们发现与平行电阻率相反，外导流器循环，由外导流器总巴尔默Dα发射量量化，I-Dα与as成比例，其中Λdiv与as成比例，甚至Λdiv与as不成比例。导流器的循环利用可以通过以下途径导致溶胶密度肩的形成：(a)减少从溶胶到导流器的离子平行于场的流动（损失）；(b)导致E × b极向流的径向电场的变化，以及可能影响SOL湍流生成特性的变化。因此，转向剂循环的变化可能是导致SOL密度肩的唯一过程，也可能是与并联电阻率串联起作用。
The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. This study explores mechanisms affecting the formation of flattened density profiles, so-called ‘density shoulders’, in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λdiv (=[L||νeiΩi]/csΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, As, but only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with As for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and As is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer Dα emission, I–Dα, does scale with As where Λdiv does and even where Λdiv does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E × B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Thus, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.