Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks

doi:10.1088/1674-1056/19/11/115205

摘要/Abstract

摘要： In this paper, the effect of finite Larmor radius (FLR) on high n ballooning modes is studied on the basis of FLR magnetohydrodynamic (FLR-MHD) theory. A linear FLR ballooning mode equation is derived in an '? - α ' type equilibrium of circular-flux-surfaces, which is reduced to the ideal ballooning mode equation when the FLR effect is neglected. The present model reproduces some basic features of FLR effects on ballooning mode obtained previously by kinetic ballooning mode theories. That is, the FLR introduces a real frequency into ballooning mode and has a stabilising effect on ballooning modes (e.g., in the case of high magnetic shear ? ≥ 0.8). In particular, some new properties of FLR effects on ballooning mode are discovered in the present research. Here it is found that in a high magnetic shear region (? ≥ 0.8) the critical pressure gradient (α_c,FLR ) of ballooning mode is larger than the ideal one (α_c,IMHD ) and becomes larger and larger with the increase of FLR parameter b₀ . However, in a low magnetic shear region, the FLR ballooning mode is more unstable than the ideal one, and the α_c,FLR is much lower than the α_c,IMHD . Moreover, the present results indicate that there exist some new weaker instabilities near the second stability boundary (obtained from ideal MHD theory), which means that the second stable region becomes narrow.

Abstract: In this paper, the effect of finite Larmor radius (FLR) on high n ballooning modes is studied on the basis of FLR magnetohydrodynamic (FLR-MHD) theory. A linear FLR ballooning mode equation is derived in an '$\hat{s}$- \alpha' type equilibrium of circular-flux-surfaces, which is reduced to the ideal ballooning mode equation when the FLR effect is neglected. The present model reproduces some basic features of FLR effects on ballooning mode obtained previously by kinetic ballooning mode theories. That is, the FLR introduces a real frequency into ballooning mode and has a stabilising effect on ballooning modes (e.g., in the case of high magnetic shear $\hat{s}$ ≥ 0.8). In particular, some new properties of FLR effects on ballooning mode are discovered in the present research. Here it is found that in a high magnetic shear region ($\hat{s}$ ≥ 0.8) the critical pressure gradient (α_c,FLR ) of ballooning mode is larger than the ideal one (α_c,IMHD ) and becomes larger and larger with the increase of FLR parameter b₀ . However, in a low magnetic shear region, the FLR ballooning mode is more unstable than the ideal one, and the α_c,FLR is much lower than the α_c,IMHD . Moreover, the present results indicate that there exist some new weaker instabilities near the second stability boundary (obtained from ideal MHD theory), which means that the second stable region becomes narrow.

Key words: ballooning mode, finite Larmor radius effect

中图分类号: (Magnetohydrodynamics (including electron magnetohydrodynamics))

52.30.Cv

52.35.Py (Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)) 52.35.Vd (Magnetic reconnection) 52.55.Fa (Tokamaks, spherical tokamaks)

蒋海斌, 王爱科, 彭晓东. Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks[J]. 中国物理B, 2010, 19(11): 115205-116801.

Jiang Hai-Bin(蒋海斌), Wang Ai-Ke(王爱科), and Peng Xiao-Dong(彭晓东). Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks[J]. Chin. Phys. B, 2010, 19(11): 115205-116801.

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