Hot spots induced by LHCD in the shadow of antenna limiters in the EAST tokamak

Li, Y. L.; Xu, G. S.; Wu, Zhenwei; Zhang, B.; Zhang, Ling; Yang, Xiaodong; Chen, M. W.; Zhang, Tao; Liu, Haiqing; Wan, Baonian; Gong, Xianzu; Goniche, M.; Warrier, M.; Xiao, C.; Gao, Wei; Ou, Jing; Cao, Lei; Liu, C. L.; Wang, M.; Li, Miaohui; Li, Y. C.; Xu, Qianfan; Liang, Yun-Feng; Wang, Liang; Sun, Zhonghua; Xu, Jichan; Feng, Wei; Niu, Y.; Chen, R.

doi:10.1063/1.5019255

Cited by 15 publications

(11 citation statements)

References 36 publications

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“…Continuous growth of Z eff during the LHW ramping-up phase is most likely caused by the impurity sputtering from the interactions between ELMs and surface or the 'hotspot' often occurring in the case of high P LHW . [54] The increased C W after 6.2 s is due to tungsten droplet events. Using this droplet event, the tungsten confinement time is also evaluated to be about 68.5 ms.…”

Section: Impurity Confinement In Lhw and Ecrh Heated Small Elmy H-mod...mentioning

confidence: 98%

Reduction of impurity confinement time by combined heating of LHW and ECRH in EAST*

Xu¹,

Wu²,

Zhang³

et al. 2021

Chinese Phys. B

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The core impurity confinement properties are experimentally investigated in the Experimental Advanced Superconducting Tokamak (EAST) plasma heated by lower hybrid wave (LHW) and electron cyclotron resonance heating (ECRH) (LHW+ECRH). It is shown that the impurity confinement time (τ imp) in the L-mode plasma jointly heated by LHW and ECRH is weakly dependent on electron density but strongly dependent on the heating power, thus it is shorter than that in LHW-only heated L-mode plasma with the similar plasma parameters. The combined heating of LHW and ECRH can reduce the collisionality and indicates a more effective heating method for core τ imp reduction and normalized poloidal beta (β P) improvement. It should be emphasized that in this high β P operation window the small ELM regime can be accessed, and an L-mode level τ imp (40 ms–80 ms) and high β N (∼ 1.7) can be obtained simultaneously. It means that this typical small ELMy H-mode regime has an advantage in avoiding the serious tungsten accumulation, and will be competitive in future long-pulse steady-state and high-performance operation with high-Z material plasma-facing components.

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Section: Impurity Confinement In Lhw and Ecrh Heated Small Elmy H-mod...mentioning

confidence: 98%

Reduction of impurity confinement time by combined heating of LHW and ECRH in EAST*

Xu¹,

Wu²,

Zhang³

et al. 2021

Chinese Phys. B

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“…Severe hotspot issues were observed in the 2016 EAST campaign with higher lower hybrid input power. The experi ments indicated that plasma disruptions happened at high plasma densities [9]. Unfortunately there were no direct meas urements of plasma density and electron temperature near the antenna in the 2016 campaign.…”

Section: Simulation Model and Setupmentioning

confidence: 98%

“…For EAST, there are two lower hybrid power systems with two frequencies at 2.45 GHz and 4.6 GHz, respectively. The incident powers for 2.45 GHz and 4.6 GHz systems are typically around 1 MW and 1.5 MW, and hotspots are often observed when the input power for 4.6 GHz is above 1.8 MW [8][9][10]. In this work, we focus on hotspots induced by 4.6 GHz LHW.…”

Section: Simulation Model and Setupmentioning

confidence: 99%

“…Lower hybrid current drive (LHCD) has been proven to be one of the most promising approaches to achieving steady state operations on tokamaks [1][2][3]. As the input power increases in LHCD experiments, hotspots, which could damage the first wall components and degrade the device operations, have been widely observed on guard limiters in JET [4], Tore supra [5], TdeV [6], ASDEX [7] and EAST [8][9][10]. The exper imental observations suggested that the hotspots might be related to the power deposition caused by electron accelera tion [6].…”

Section: Introductionmentioning

confidence: 99%

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Interactions of plasma and guard limiter in front of lower hybrid wave antenna on EAST tokamak

Xiang

Men

et al. 2019

Nucl. Fusion

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The hotspots on the guard limiters of the lower hybrid wave (LHW) antenna on EAST tokamak not only cause serious damage to the guard limiters, but also strongly degrade the plasma performance due to enhanced impurity productions. In published studies, the heat flux to the limiters is assumed to be carried to limiter walls by electrons which can absorb a small amount of the launched wave energy via interactions with the lower hybrid modes of high parallel refractive index , and the effects of the sheaths formed in front of the limiter surface are ignored. In this work, the heat fluxes to the limiter surfaces are obtained consistently by conducting one-dimension particle-in-cell (PIC) simulations. For the plasma between two guard limiters, while the ions are assumed to be Maxwellian, the electrons are described by using the Fisch model, whose velocity distribution function (VDF) has a resonant plateau in the superthermal region formed by the electron and LHW interaction. Secondary electron emission (SEE) from the limiter surfaces is taken into account by considering two kinds of wall materials, carbon and tungsten. It is found that the sheath potential drop is significantly raised due to the presence of fast electrons. As a result, both ion and electron heat fluxes to the limiters are strongly enhanced compared to those in a Maxwellian plasma, which increases the wall temperature and gives rise to hotspots. The heat flux to the guard limiters increases with the width of the resonant plateau of the electron VDF (i.e. the electron energy). With the enhancement of the sheath potential drop, the physical sputtering yield from the primary and impurity ions on limiter surfaces is found to be significant, which may affect the plasma confinement and discharges.

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“…Hot spots induced by fast particles in EAST (experimental advanced superconducting tokamak) have been found to limit the improvement of the plasma performance (Li et al. 2018). The CX losses of NBI fast ions may produce hot spots in EAST.…”

Section: Introductionmentioning

confidence: 99%

Guiding-centre orbit-following simulations of charge exchange loss of NBI ions with the finite Larmor radius effect

Xu,

Wang,

et al. 2023

J. Plasma Phys.

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Guiding-centre orbit-following simulations of the charge exchange (CX) loss of neutral beam injection (NBI) ions are presented. The finite Larmor radius (FLR) effect in the fast ion–neutral collision can be included in guiding-centre orbit-following simulations by using the gyroaverage method. It is proved that the neutralization probability of fast ions computed by using the gyroaverage method in the guiding-centre orbit simulation is roughly the same as that computed in the full-orbit simulation when the time step in the guiding-centre simulation is the order of the gyroperiod. The CX losses of NBI fast ions for two NBIs in the EAST tokamak have been simulated by the guiding-centre orbit-following code GYCAVA, and the FLR effect in the fast ion–neutral collision on CX losses has been numerically studied. The CX effect of the fast ion–neutral collision can significantly enhance NBI ion losses on EAST. The FLR effect in the fast ion–neutral collision can enhance the CX loss. Vertical asymmetry of localized heat loads induced by CX losses is found, which is related to the FLR effect of fast ions and the strong radial gradient of the neutral density near the plasma edge. Heat loads induced by CX losses are localized in the regions near the poloidal angle $\theta =-60^\circ$ , because the likelihood of exchanging charge is the largest at gyrophase $\xi ={\rm \pi}$ , and this leads to fast downwards moving neutrals. Fast ion loss fractions induced by CX increase with the neutral density increasing.

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Hot spots induced by LHCD in the shadow of antenna limiters in the EAST tokamak

Cited by 15 publications

References 36 publications

Reduction of impurity confinement time by combined heating of LHW and ECRH in EAST*

Reduction of impurity confinement time by combined heating of LHW and ECRH in EAST*

Interactions of plasma and guard limiter in front of lower hybrid wave antenna on EAST tokamak

Guiding-centre orbit-following simulations of charge exchange loss of NBI ions with the finite Larmor radius effect

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