Reconstruction of magnetohydrodynamic equilibrium configurations with hollow current density profiles in the HL-2A tokamak

He, Huimin; Dong, J. Q.; Zheng, Guoyao; He, Zhanxiang; Lu, Gaimin; Peng, Xiaodong; Shi, Z.B.; Zhang, J H

doi:10.1088/0031-8949/85/04/045501

Phys. Scr.

2012

DOI: 10.1088/0031-8949/85/04/045501

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Reconstruction of magnetohydrodynamic equilibrium configurations with hollow current density profiles in the HL-2A tokamak

Huimin He¹,

J. Q. Dong²,

Guoyao Zheng³

et al.

Abstract: Magnetohydrodynamic equilibrium configurations with hollow current density profiles in the HL-2A tokamak are reconstructed for pellet injection discharges. The experimental data of pressure profiles, resulting from electron temperature measurements and a model density profile, analogous to that measured in the JET experiment, and Mirnov pickup coil signals are employed in the reconstructions. It is explicitly shown for the first time that configurations with hollow current density profiles may be realized by m… Show more

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“…The results show that LHCD experiment successfully suppresses magnetohydrodynamic (MHD) instability [14,15]. In addition, pellet injection is also an important method to induce the hollow toroidal current through cooling down the central part of the plasma column by deep injection, which was observed in the HL-2A tokamak in the 2000s, indicating that the hollow current profile may exist after pellet injection [16].…”

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confidence: 99%

Stability nature of ohmic discharges with hollow current profiles on the HL-2A tokamak

Shen¹,

Dong²,

He³

et al. 2020

Nucl. Fusion

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The equilibrium configurations with hollow current density profiles can effectively improve plasma confinement. The stability of the ohmic discharges with hollow current density profiles on the HL-2A tokamak was studied for various parameters, such as plasma poloidal beta β p , the axial and edge safety factors q 0 and q s , as well as the minimum safety factor q min . The results suggest that the restriction to the parameters of discharges with hollow current density profiles is stricter than that of conventional discharges with peaked current density profiles. In the case of q profile with reverse shear, the instability of the configuration is significantly improved with higher β p . As a result, the configuration with a hollow toroidal current profile is stable for high β p operations. Only if q 0 , q s and q min satisfy the specific limitations, i.e. on HL-2A, only if both q 0 ≳ 2.1 and q s ≳ 3 hold, together with q s − q 0 ≳ 0.7 and q 0 − q min ≳ 0.7, may the configurations with the reverse shears be stable for hollow-current-type Ohmic discharge. The results may give hints for the role of the discharges with hollow toroidal current densities in the coming advanced tokamak operations.

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mentioning

confidence: 99%

Stability nature of ohmic discharges with hollow current profiles on the HL-2A tokamak

Shen¹,

Dong²,

He³

et al. 2020

Nucl. Fusion

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Hollow current and reversed magnetic shear configurations in pellet injection discharges on Huanliuqi 2A tokamak

Yong¹,

Dong²,

He³

et al. 2021

Acta Phys. Sin.

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The tokamak with weak or negative magnetic shear and internal transport barrier (ITB) is considered to be the most promising approach to improving fusion performance. The hollow current density profile, as well as the reversed <i>q</i> profile (negative magnetic shear), is one of the key conditions for improving core confinement in advanced tokamak schemes. In the Huanliuqi 2A (HL-2A) experiment, a hollow current distribution with a discharge duration of about 100 ms is successfully achieved by injecting the pellets in the Ohmic discharge. The discharge is characteristic of circular equilibrium configuration and three frozen pellets are injected continuously at three different time moments. As a result, the hollow current profiles are formed in the plasma with weak hollow electron temperature in the core region. At the same time, the hollow currents are combined with the reversed magnetic shear profiles. Because the power of Ohmic heating is not so high and there is no external auxiliary heating, we can see only a trend of the formation of weak internal transport barrier in the stable hollow current discharge stage. However, the electron thermal diffusivity decreases significantly after the pellets have been injected. The deep injection of frozen pellets improves the energy confinement. The enhancement of plasma performance is due to the peaked electron density profile in the center, caused by pellet injection and the negative magnetic shear in the plasma center. It is concluded that the electron density profile peaked highly in the core plasma, caused by pellet injection, is beneficial to the improvement of particle confinement and plays an important role in enhancing the energy confinement. In addition, it is also demonstrated that, in general, during a hollow current discharge, the poloidal beta <inline-formula><tex-math id="M2">\begin{document}$ {\beta }_{\mathrm{p}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M2.png"/></alternatives></inline-formula> value and normalized beta <inline-formula><tex-math id="M3">\begin{document}$ {\beta }_{\mathrm{N}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M3.png"/></alternatives></inline-formula> value are both obviously low although the reversed magnetic shear is conducive to stabilizing ballooning modes and weakening the drift instabilities. However, comparing with the hollow current profile, the plasma with peaked current profile is very beneficial to the improvement of beta limit. In order to improve the <inline-formula><tex-math id="M4">\begin{document}$ {\beta }_{\mathrm{N}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20210641_M4.png"/></alternatives></inline-formula> limit, a conductive wall is necessary to be placed near the plasma boundary. The results of HL-2A pellet injection experiments present a possibility of obtaining high parameter discharge on a limiter tokamak.

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Reconstruction of magnetohydrodynamic equilibrium configurations with hollow current density profiles in the HL-2A tokamak

Cited by 2 publications

References 20 publications

Stability nature of ohmic discharges with hollow current profiles on the HL-2A tokamak

Stability nature of ohmic discharges with hollow current profiles on the HL-2A tokamak

Hollow current and reversed magnetic shear configurations in pellet injection discharges on Huanliuqi 2A tokamak

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