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

Shen, Yong; Dong, J. Q.; He, Hailong; Shi, Z.B.; Jia, Li; Han, Mingkun; Li, Jiquan; Sun, A.P.; Pan, Li

doi:10.1088/1741-4326/abad83

Cited by 3 publications

(2 citation statements)

References 25 publications

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“…径𝑎与磁场𝐵单位分别是 m 和 Tesla。可以通过优化等离子体剖面、使等离子体发生形变 [1] ，以及优化稳定性、输运和优化偏滤器运行等措施 [17] ，来提高运行𝛽，实现稳态放电 [2] 。有些放电如 HL-2A 装置弹丸注入中空电流型放电的𝛽 是低的，但存在中心负磁剪切位形和内部输运垒 [18,19] 。 Garofaro 等 [20] 讨论了通过内部输运垒和中心负磁磁切来来实现可持续的高𝛽放电。在上述问题中，人们关注的重点是改进 MHD 稳定性 [21][22][23] 。大量的研究结果还表明，如果在离等离子体中心 1.5…”

Section: 引言unclassified

Ideal conductive wall and magnetohydrodynamic instability in Tokamak

Shen¹,

Dong²,

He³

et al. 2023

Acta Phys. Sin.

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In order to explore the conductive wall effect of plasma magnetohydrodynamic (MHD) instability and the wall designing idea, the various forms of ideal conductive walls based on divertor equilibrium configurations in the HL-2A tokamak and their role in the suppression of kink modes were studied. The MHD instabilities and the ideal MHD operational β limits under free boundary or ideal wall conditions were compared. In the stability calculation,n=1 kink mode was considered, which had a decisive influence on the MHD instability of tokamak plasmas. The research focuses on verifying the effectiveness of various shapes of conductive walls in suppressing internal and external kink modes, and observing the operational β limit changes, and discussing and analyzing related physics. It is found that an ideal conducting wall placed at a suitable distance from the plasma could effectively suppress the external kink modes. Under the condition that the average distance between the wall and the plasma surface is the same and small enough, the circular cross-section wall is not necessarily the best choice. Setting an optimized polygonal conductive wall can more effectively suppress the MHD instability. It makes the ideal MHD operational β limit of the device, βN, increase to 2.73, which is about 6.5% higher than that for the device with a wall assumed to be set at infinity (~2.56). This implies that it is necessary to optimize and make a polygonal conductive wall as close as possible to the average distance from the plasma surface according to the poloidal-section shape of the elongated and shaped plasma, so as to achieve the suppression of external kink mode and increase the operational β limits. The physical mechanism of the stabilizing effect of the ideal wall on external kink modes was analyzed. With the development of the kink mode, when the plasma column is twisted close to the wall, the plasma column will squeeze the magnetic field in the vacuum area, making the magnetic field line compressed and bent. At this time, the magnetic pressure and the component force of the magnetic tension in the opposite direction of the radial direction push the plasma back, thus stabilizing the kink mode. Finally, a conclusion was given.

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Section: 引言unclassified

Ideal conductive wall and magnetohydrodynamic instability in Tokamak

Shen¹,

Dong²,

He³

et al. 2023

Acta Phys. Sin.

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“…The advanced tokamak (AT) scenario [1][2][3][4][5][6][7][8][9][10][11] with the strong reversed magnetic shear is an attractive candidate of the steady state tokamak because the strong internal transport barrier (ITB) [12] leads to the high bootstrap current fraction f BS , resulting in the reduction of the cost of the fusion reactor. On the other hand, it is well known that many kinds of MHD instabilities [1][2][3][4][5][6][7][8][9][10][11] can occur in plasmas with the strong pressure gradient of ITB and the reversed magnetic shear, such as double tearing mode [2], locked tearing mode [4], resistive interchange mode [9], and resistive wall mode (RWM) [8,13].…”

Section: Introductionmentioning

confidence: 99%

On Collapses in Strong Reversed Shear Plasmas During or Just After Plasma Current Ramp-Up in JT-60U

Bando

Tojo

Takechi

et al. 2021

Plasma and Fusion Research

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The advanced tokamak (AT) scenario with the strong reversed magnetic shear is an attractive candidate of the steady state tokamak because the strong internal transport barrier leads to the high bootstrap current fraction, resulting in the reduction of the cost of the fusion reactor. In this paper, the causes of the collapses during or just after plasma current ramp-up of the experimental campaign of the AT scenario [Y. Sakamoto et al., Nucl. Fusion 49, 095017 (2009)] in 2007 and 2008 are investigated and the initial results are reported. As the observations are consistent with characteristics of the stability on the resistive wall mode (RWM) and the results of MARG2D code, the RWM is suggested as the candidate of the cause of the collapses in the analyzed AT scenario.

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

Cited by 3 publications

References 25 publications

Ideal conductive wall and magnetohydrodynamic instability in Tokamak

Ideal conductive wall and magnetohydrodynamic instability in Tokamak

On Collapses in Strong Reversed Shear Plasmas During or Just After Plasma Current Ramp-Up in JT-60U

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

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