Experimental study on the relationship between particle flow distribution and neutral gas pressure on the target plate of the upper external diverter on EAST

doi:10.16568/j.0254-6086.202501014

Abstract

Abstract:

The baffle structure of the tokamak divertor can enhance the particle closure of the divertor, but it may also prevent part of the particle flow in the scrape-off layer from entering the divertor, which can affect the distribution of particle flow on the divertor target Studying the relationship between target particle flow distribution and neutral pressure can help optimize plasma configuration,promote divertor to be detached, and improve compatibility with main plasma.The correlation coefficient between particle flow changes on the surface of EAST divertor and neutral pressure changes was calculated,and the dependence of the correlation coefficient on the different positions of the divertor surface is studied under the typical conditions of lower hybrid wave heating and RMP modulation. The results show that the correlation coefficient has a steep change at the position of the 6th and 7th probes of the outer target plate(The 6th and 7th probes are about 149.6mm and 126.0mm away from the upper edge of the outer target plate respectively)，which reflects that the particle flow received in the divertor target area above the position is the main contributor to the neutral pressure of the divertor and can be better confined by the divertor. The particle flow received in the lower part of the position is difficult to enter the divertor, which plays the role of baffle. The spectroscopic analysis of the divertor shows that the electron and ion recombination process in the target area is an important factor affecting the neutral pressure.

Key words: Divertor, Baffle, Target particle flow, Neutral pressure, Correlation coefficient

摘要：

托卡马克偏滤器的挡板结构可以增强偏滤器的粒子封闭性，但也可能会阻挡刮削层中部分粒子流进入偏滤器，这会影响偏滤器靶板粒子流的分布。研究靶板粒子流分布与中性气压的关系，有助于优化等离子体位形，促进偏滤器脱靶，并改善与主等离子体的兼容性。计算EAST偏滤器表面的粒子流变化与中性气压变化之间的相关性系数，研究了在典型的低杂波加热和RMP调制两种条件下，这种相关性系数与偏滤器表面不同位置的依赖关系。结果显示，相关性系数在上外靶板第6号和第7号探针位置之间(第6、7号探针分别距离外靶板上边缘约149.6mm和126.0mm)存在陡变，反映了该位置以上的偏滤器靶板区域接收到的粒子流可以更好地被偏滤器约束，是偏滤器中性气压的主要贡献者；该位置以下部分接收到的粒子流则较难进入偏滤器，承担着baffle的作用。偏滤器光谱分析结果显示靶板区域的电子离子复合过程是影响中性气压的一个重要因素。

关键词: 偏滤器, 挡板, 靶板粒子流, 中性气压, 相关性系数

CLC Number:

TL65+1

ZHAO Ping-an, DING Fang, ZHANG Qing, YU Lin, MENG Ling-yi, HU Zhen-hua, WANG Liang, YU Yao-wei, DING Rui, LUO Guang-nan. Experimental study on the relationship between particle flow distribution and neutral gas pressure on the target plate of the upper external diverter on EAST[J]. Nuclear Fusion and Plasma Physics, 2025, 45(1): 84-90.

赵平安, 丁芳, 张青, 余林, 孟令义, 胡振华, 王亮, 余耀伟, 丁锐, 罗广南. EAST上外偏滤器靶板粒子流分布与中性气体压强关系的实验研究[J]. 核工业西南物理研究院, 2025, 45(1): 84-90.

References

[1] PITTS R A, BONNIN X, ESCOURBIAC F, et al. Physics basis for the first ITER tungsten divertor [J]. Nuclear Materials and Energy, 2019, 20: 100696.

[2] LOARTE A. Effects of divertor geometry on tokamak plasmas [J]. Plasma Physics and Controlled Fusion, 2001, 43(6): R183-R224.

[3] KLEPPER C C, HOGAN J T, HILL D N, et al. Divertor neutral pressure enhancement with a baffle in DIII-D [J]. Nuclear Fusion, 1993, 33(4): 533.

[4] NEU R, FUCHS J C, KALLENBACH A, et al. The ASDEX Upgrade divertor IIb-a closed divertor for strongly shaped plasmas [J]. Nuclear Fusion, 2003, 43(10): 1191.

[5] REIMERDES H, DUVAL B P, ELAIAN H, et al. Initial TCV operation with a baffled divertor [J]. Nuclear Fusion, 2021, 61(2): 024002.

[6] SAKURAI S, SHIMIZU K, MASAKI K, et al. Particle control design for modification of JT-60 with superconducting coils [J]. Plasma Physics and Controlled Fusion, 2002, 44(6): 749.

[7] FENG W, WANG L, RACK M, et al. Evidence and modeling of 3D divertor footprint induced by lower hybrid waves on EAST with tungsten divertor operations [J]. Nuclear Fusion, 2017, 57(12): 126054.

[8] LI J, GUO H Y, WAN B N, et al. A long-pulse high-confinement plasma regime in the experimental advanced superconducting tokamak [J]. Nature Physics, 2013, 9(12): 817.

[9] WAN B, LI J, GUO H, et al. Advances in H-mode physics for long-pulse operation on EAST [J]. Nuclear Fusion, 2015, 55(10): 104015.

[10] GONG X, GAROFALO A M, HUANG J, et al. Integrated operation of steady-state long-pulse H-mode in experimental advanced superconducting tokamak [J]. Nuclear Fusion, 2019, 59(8): 086030.

[11] XU J C, WANG L, XU G S, et al. Upgrade of Langmuir probe diagnostic in ITER-like tungsten mono-block divertor on experimental advanced superconducting tokamak [J]. Review of Scientific Instruments, 2016, 87(8): 083504.

[12] LIN X, YANG Q Q, XU G S, et al. Plasma performance improvement with favourable B_t relative to unfavourable B_t in RF-heated H-mode plasmas in EAST [J]. Nuclear Fusion, 2021, 61(2): 026014.

[13] MAO H M, DING F, LUO G N, et al. A multichannel visible spectroscopy system for the ITER-like W divertor on EAST [J]. Review of Scientific Instruments, 2017, 88(4): 043502.

[14] GALASSI D, REIMERDES H, THEILER C, et al. Numerical investigation of optimal divertor gas baffle closure on TCV [J]. Plasma Physics and Controlled Fusion, 2020, 62(11): 115009.

[15] LIANG Y, KOSLOWSKI H R, THOMAS P R, et al. Active control of type-I edge-localized modes with n=1 perturbation fields in the JET tokamak [J]. Physical Review Letters, 2007, 98(26): 265004.

[16] JIA M, SUN Y, ZHONG F, et al. Vacuum modeling of three-dimensional magnetic field topology under resonant magnetic perturbations on EAST [J]. Plasma Physics and Controlled Fusion, 2016, 58(5): 055010.

[17] MCCRACKEN G M, STAMP M F, MONK R D, et al. Evidence for volume recombination in jet detached divertor plasmas [J]. Nuclear Fusion, 1998, 38(4): 619.

[18] FUJIMOTO K, NAKANO T, KUBO H, et al. Spatial structure of volume recombination in JT-60U detached divertor plasmas [J]. Plasma and Fusion Research, 2009, 4: 025.