Non-boronized compared with boronized operation of ASDEX Upgrade with full-tungsten plasma facing components
Non-boronized compared with boronized operation of ASDEX Upgrade with full-tungsten plasma facing components
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DOI：
10.1088/0029-5515/49/4/045007
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发表时间：
2009-04
期刊：
影响因子：
3.3
通讯作者：
A. Kallenbach;R. Dux;M. Mayer;R. Neu;T. Pütterich;V. Bobkov;J. Fuchs;T. Eich;L. Giannone
中科院分区：
文献类型：
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作者：
A. Kallenbach;R. Dux;M. Mayer;R. Neu;T. Pütterich;V. Bobkov;J. Fuchs;T. Eich;L. Giannone
在完成所有面向等离子体组件的钨涂层后，ASDEX升级版在没有硼化的情况下运行了1 1/2个实验活动。这使得燃料保留的研究条件下，相对较低的D共沉积与低Z杂质，以及操作空间的全钨设备的不利条件下，相对较高的本征杂质水平。在操作中的限制是由于钨的中心积累结合密度峰值，导致H-L的反跃迁诱导过低的分界线功率通量。已发现最重要的控制参数是主要由ECRH提供的中央加热功率，以及最容易由气体喷吹控制的ELM频率。一般来说，ELM表现出积极的影响，与杂质冲刷出的基座区超过平衡ELM诱导的W源的效果。在未硼化的W机的等离子体操作的限制主要发生在低或中等功率条件下。在中高功率条件下，实现了硼化和未硼化放电之间几乎没有差异的稳定操作。由于硼化降低了固有辐射，VPS涂层偏滤器瓦的功率处理能力有限（约10 MW m−2），只有在辐射冷却的情况下才能在高加热功率下进行硼化操作。为了实现这一点，以前开发的反馈系统使用（热）电流测量作为偏滤器功率通量的近似传感器被引入到标准AUG操作。为了避免由于核心等离子体辐射而导致ELM频率降低的问题，选择氮作为辐射物质，因为与Ne和Ar相比，氮的辐射特征峰在较低的电子温度下，有利于SOL和偏滤器辐射损失。氮播种不仅导致所需的偏滤器功率负载的降低，而且还改善了能量约束，以及在较小的ELM。
After completion of the tungsten coating of all plasma facing components, ASDEX Upgrade has been operated without boronization for 1 1/2 experimental campaigns. This has allowed the study of fuel retention under conditions of relatively low D co-deposition with low-Z impurities as well as the operational space of a full-tungsten device for the unfavourable condition of a relatively high intrinsic impurity level. Restrictions in operation were caused by the central accumulation of tungsten in combination with density peaking, resulting in H–L backtransitions induced by too low separatrix power flux. Most important control parameters have been found to be the central heating power, as delivered predominantly by ECRH, and the ELM frequency, most easily controlled by gas puffing. Generally, ELMs exhibit a positive impact, with the effect of impurity flushing out of the pedestal region overbalancing the ELM-induced W source. The restrictions of plasma operation in the unboronized W machine occurred predominantly under low or medium power conditions. Under medium-high power conditions, stable operation with virtually no difference between boronized and unboronized discharges was achieved. Due to the reduced intrinsic radiation with boronization and the limited power handling capability of VPS coated divertor tiles (≈10 MW m−2), boronized operation at high heating powers was possible only with radiative cooling. To enable this, a previously developed feedback system using (thermo-)electric current measurements as approximate sensor for the divertor power flux was introduced into the standard AUG operation. To avoid the problems with reduced ELM frequency due to core plasma radiation, nitrogen was selected as radiating species since its radiative characteristic peaks at lower electron temperatures in comparison with Ne and Ar, favouring SOL and divertor radiative losses. Nitrogen seeding resulted not only in the desired divertor power load reduction but also in improved energy confinement, as well as in smaller ELMs.