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In a magnetic confinement fusion device, the plasma undergoing nuclear fusion reaction must be maintained in a high-temperature and high-density confinement state for a long enough time to release high energy, while the heat loads on the divertor target plates need to be reduced to avoid damage to wall at the same time. The latter is one of the key challenges of ITER and commercial fusion reactors in future. Divertor detachment provides an effective solution to reduce the heat load on the target plate of tokamak. However, this may result in the change of plasma states at the boundary, thus affecting the plasma confinement. In this paper, edge plasma poloidal rotation and turbulence momentum transport are studied experimentally during the divertor detachment in the L-mode discharge of HL-2A tokamak. The detachment is achieved by injecting a mixture of gas (60% nitrogen+40% deuterium) into the divertor. The gas mixture is injected by pulsed injection, with pulse length being in a range of 5–20 ms. During the divertor detached phase, both the ion saturation current density and the heat flux to the outer target plate decrease considerably. The enhanced radiation is also observed in the divertor and X-point region. It is found that in the process of attachment-to-pre-detachement, the
$ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow velocity in the near scrape-off layer (SOL) changes from ion magnetic drift direction to electron magnetic drift direction. The turbulent driving force of poloidal flow, which is characterized by the negative radial gradient of momentum transfer flux (Reynolds stress), shows the same trend. In the detached phase, both the$ \boldsymbol{E}\times \boldsymbol{B} $ flow and the Reynolds force become very small. Therefore, the dynamics of$ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow velocity in the SOL is consistent with the evolution of rotation driving effect induced by the turbulent momentum transport. Combined with the$ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow measured by the probe in the SOL and the beam emission spectrum inside the LCFS, the$ \boldsymbol{E}\times \boldsymbol{B} $ poloidal velocity shearing rate near the LCFS can be inferred. Compared with the attached state, when the divertor is detached, the edge poloidal flow shearing rate decreases significantly, leading to the obviously enhanced turbulence level. Under the influence of both enhanced turbulent transport and radiation, the global confinement degrades moderately. The energy confinement time decreases about 15% and the confinement factor$ {H}_{89-P} $ decreases about 10%. These results indicate that edge turbulent transport and plasma rotation dynamics play a role in the core-edge coupling process in which the divertor detachment affects the global confinement.-
Keywords:
- nuclear fusion power /
- divertors /
- plasma turbulence /
- plasma dynamics and flow
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图 1 偏滤器脱靶实验的主要放电参数 (a)环向磁场; (b)等离子体电流; (c)中心弦平均密度; (d)中性束加热功率; (e)偏滤器注气; (f)靶板离子饱和流密度; (g)外靶板热流密度; (h)外靶板电子温度; (i)主真空室热辐射信号; (j)氮辐射强度
Figure 1. The main discharge parameters in the divertor detachment experiment: (a) Toroidal field; (b) plasma current; (c) central line-averaged density; (d) NBI heating power; (e) gas puffing in divertor; (f) ion saturation current density onto target; (g) heat flux onto outer target; (h) electron temperature at outer target; (i) bolometer signal through the main chamber; (j) nitrogen radiation intensity.
图 2 (a)偏滤器脱靶前和(b)偏滤器脱靶后的可见光图像
Figure 2. The visible light images taken by a CCD camera (a) before the detachment and (b) after the divertor detachment.
图 3 位于HL-2A托卡马克外中平面的静电探针阵列示意图
Figure 3. Schematic diagram of Langmuir probe array on the outer mid-plane of HL-2A tokamak.
图 4 偏滤器脱靶过程 (a)电子温度; (b)电势; (c) $ \boldsymbol{E}\times \boldsymbol{B} $极向流速; (d)湍流雷诺应力的演化
Figure 4. (a) Temperature; (b) potential; (c) $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal velocity and (d) Reynolds force during the divertor detachment.
图 5 偏滤器脱靶过程 (a)等离子体边缘$ \boldsymbol{E}\times \boldsymbol{B} $极向速度剪切; (b)密度扰动的时频自功率谱; (c)能量约束时间; (d)能量约束增强因子的变化
Figure 5. (a) Edge $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal velocity shear; (b) time-frequency auto-spectrum of density fluctuations; (c) plasma energy confinement time; (d) energy confinement enhanced factor during the divertor detachment.
图 6 偏滤器脱靶过程 (a)等离子体密度; (b)电子温度; (c)压强; (d)总的$ {v}_{\theta , \boldsymbol{E}\times \boldsymbol{B}} $和逆磁速度$ {v}_{\theta , \nabla p} $
Figure 6. (a) Density, (b) temperature, (c) pressure, (d) total $ {v}_{\theta , \boldsymbol{E}\times \boldsymbol{B}} $ and diamagnetic velocity $ {v}_{\theta , \nabla p} $.
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[1] Loarte A, Lipschultz B, Kukushkin A S, et al. 2007 Nucl. Fusion 47 S203
Google Scholar
[2] Shimada M, Campbell D J, Mukhovatov V, et al. 2007 Nucl. Fusion 47 S1
Google Scholar
[3] Wang L, Wang H Q, Ding S, et al. 2021 Nat. Commun. 12 1365
Google Scholar
[4] Leonard A W, Mahdavi M A, Allen S L, et al. 1997 Phys. Rev. Lett. 78 4769
Google Scholar
[5] ITER-EDA 1999 Nucl. Fusion 39 2391
Google Scholar
[6] Vianello N, Carralero D, Tsui C K, et al. 2020 Nucl. Fusion 60 016001
Google Scholar
[7] Kallenbach A, Bernert M, Beurskens M, et al. 2015 Nucl. Fusion 55 053026
Google Scholar
[8] Huber A, Brezinsek S, Groth M, et al. 2013 J. Nucl. Mater. 438 S139
Google Scholar
[9] Diamond P H, Itoh S I, Itoh K, Hahm T S 2005 Plasma Phys. Control. Fusion 47 R35
Google Scholar
[10] Liang A S, Zhong W L, Zou X L, et al. 2018 Phys. Plasmas 25 022501
Google Scholar
[11] Long T, Diamond P H, Xu M, Ke R, Nie L, Li B, Wang Z H, Xu J Q, Duan X R 2019 Nucl. Fusion 59 106010
Google Scholar
[12] Long T, Diamond P H, et al. 2021 Nucl. Fusion 61 126066
Google Scholar
[13] 龙婷, Diamond P H, 柯锐, 洪荣杰, 许敏, 聂林, 王占辉, 李波, 高金明, HL-2A团队 2022 核聚变与等离子体物理 42 152
Long T, Diamond P H, Ke R, Hong R J, Xu M, Nie L, Wang Z H, Li B, Gao J M, HL-2A Team 2022 Nucl. Fusion Plasma Phys. 42 152
[14] Gao J M, Cai L Z, Zou X L, et al. 2021 Nucl. Fusion 61 066024
Google Scholar
[15] Duan X R, Xu M, Zhong W L, et al. 2022 Nucl. Fusion 62 042020
Google Scholar
[16] Huang Z H, Cheng J, Wu N, Yan L W, Xu H B, Wang W, Miao X G, Yi K Y, Xu J Q, Cai L Z, Shi Z B, Dong J Q, Liu Y, Zhong W L, Yang Q W, Xu M, Duan X R 2022 Plasma Sci. Technol. 24 054002
Google Scholar
[17] Gao J M, Li W, Xia Z W, Pan Y D, Lu J, Yi P, Liu Y 2013 Chin. Phys. B 22 015202
Google Scholar
[18] 高金明, 程钧, 严龙文, 李伟, 聂林, 冯北滨, 陈程远, 卢杰, 易萍, 季小全 2015 核聚变与等离子体物理 35 1
Google Scholar
Gao J M, Cheng J, Yan L W, Li W, Nie L, Feng B B, Chen C Y, Lu J, Yi P, Ji X Q 2015 Nucl. Fusion Plasma Phys. 35 1
Google Scholar
[19] Zheng D L, Zhang K, Cui Z Y, Sun P, Dong C F, Lu P, Fu B Z, Liu Z T, Shi Z B, Yang Q W 2018 Plasma Sci. Technol. 20 105103
Google Scholar
[20] Meng L Y, Liu J B, Xu J C, et al. 2020 Plasma Phys. Control. Fusion 62 065008
Google Scholar
[21] Wu N, Yi K, Wang W, Huang Z, Yan L, Cheng J, Du H, Shi Z, Zhong W, Xu M 2022 Proceedings of the 6th Asia-Pacific Conference on Plasma Physics, Remote October 9-14, 2022 p1
[22] Wu T, Nie L, Yu Y, Gao J M, Li J Y, Ma H C, Wen J, Ke R, Wu N, Huang Z H, Liu L, Zheng D L, Yi K Y, Gao X Y, Wang W, Cheng J, Yan L W, Cai L Z, Wang Z H, Xu M 2023 Plasma Sci. Technol. 25 015102
Google Scholar
[23] Stangeby P C 2000 The Plasma Boundary of Magnetic Fusion Devices (Philadelphia: Institute of Physics Publishing) p84
[24] Nie L, Xu M, Ke R, Yuan B D, Wu Y F, Cheng J, Lan T, Yu Y, Hong R J, Guo D, Ting L, Dong Y B, Zhang Y P, Song X M, Zhong W L, Wang Z H, Sun A P, Xu J Q, Chen W, Yan L W, Zou X L, Duan X R, team H-A 2018 Nucl. Fusion 58 036021
Google Scholar
[25] Schmid B, Manz P, Ramisch M, Stroth U 2017 Phys. Rev. Lett. 118 055001
Google Scholar
[26] Diamond P H, Kim Y B 1991 Phys. Fluids B 3 1626
Google Scholar
[27] Manz P, Xu M, Fedorczak N, Thakur S C, Tynan G R 2012 Phys. Plasmas 19 012309
Google Scholar
[28] Shaing K C, Crume E C 1989 Phys. Rev. Lett. 63 2369
Google Scholar
[29] Connor J W, Wilson H R 2000 Plasma Phys. Control. Fusion 42 R1
Google Scholar
[30] Xu M, Tynan G R, Diamond P H, Manz P, Holland C, Fedorczak N, Thakur S C, Yu J H, Zhao K J, Dong J Q, Cheng J, Hong W Y, Yan L W, Yang Q W, Song X M, Huang Y, Cai L Z, Zhong W L, Shi Z B, Ding X T, Duan X R, Liu Y 2012 Phys. Rev. Lett. 108 245001
Google Scholar
[31] Ke R, Wu Y F, McKee G R, Yan Z, Jaehnig K, Xu M, Kriete M, Lu P, Wu T, Morton L A, Qin X, Song X M, Cao J Y, Ding X T, Duan X R 2018 Rev. Sci. Instrum. 89 10D122
Google Scholar
[32] Wesson J 2011 Tokamaks (Fourth edition) (Oxford: Oxford University Press) p177
[33] Greenwald M 2002 Plasma Phys. Control. Fusion 44 R27
Google Scholar
[34] Simmet E, Team A 1996 Plasma Phys. Control. Fusion 38 689
Google Scholar
[35] Zhong W L, Shi Z B, Yang Z J, et al. 2016 Phys. Plasmas 23 060702
Google Scholar
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